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INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb: (gdb).                     The GNU debugger.
* gdbserver: (gdb) Server.        The GNU debugging server.
END-INFO-DIR-ENTRY

   This file documents the GNU debugger GDB.

   This is the Tenth Edition, of 'Debugging with GDB: the GNU
Source-Level Debugger' for GDB (GDB) Version 8.2.50.20190219-git.

   Copyright (C) 1988-2018 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
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any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."


File: gdb.info,  Node: Annotations,  Next: JIT Interface,  Prev: GDB/MI,  Up: Top

28 GDB Annotations
******************

This chapter describes annotations in GDB.  Annotations were designed to
interface GDB to graphical user interfaces or other similar programs
which want to interact with GDB at a relatively high level.

   The annotation mechanism has largely been superseded by GDB/MI (*note
GDB/MI::).

* Menu:

* Annotations Overview::  What annotations are; the general syntax.
* Server Prefix::       Issuing a command without affecting user state.
* Prompting::           Annotations marking GDB's need for input.
* Errors::              Annotations for error messages.
* Invalidation::        Some annotations describe things now invalid.
* Annotations for Running::
                        Whether the program is running, how it stopped, etc.
* Source Annotations::  Annotations describing source code.


File: gdb.info,  Node: Annotations Overview,  Next: Server Prefix,  Up: Annotations

28.1 What is an Annotation?
===========================

Annotations start with a newline character, two 'control-z' characters,
and the name of the annotation.  If there is no additional information
associated with this annotation, the name of the annotation is followed
immediately by a newline.  If there is additional information, the name
of the annotation is followed by a space, the additional information,
and a newline.  The additional information cannot contain newline
characters.

   Any output not beginning with a newline and two 'control-z'
characters denotes literal output from GDB.  Currently there is no need
for GDB to output a newline followed by two 'control-z' characters, but
if there was such a need, the annotations could be extended with an
'escape' annotation which means those three characters as output.

   The annotation LEVEL, which is specified using the '--annotate'
command line option (*note Mode Options::), controls how much
information GDB prints together with its prompt, values of expressions,
source lines, and other types of output.  Level 0 is for no annotations,
level 1 is for use when GDB is run as a subprocess of GNU Emacs, level 3
is the maximum annotation suitable for programs that control GDB, and
level 2 annotations have been made obsolete (*note Limitations of the
Annotation Interface: (annotate)Limitations.).

'set annotate LEVEL'
     The GDB command 'set annotate' sets the level of annotations to the
     specified LEVEL.

'show annotate'
     Show the current annotation level.

   This chapter describes level 3 annotations.

   A simple example of starting up GDB with annotations is:

     $ gdb --annotate=3
     GNU gdb 6.0
     Copyright 2003 Free Software Foundation, Inc.
     GDB is free software, covered by the GNU General Public License,
     and you are welcome to change it and/or distribute copies of it
     under certain conditions.
     Type "show copying" to see the conditions.
     There is absolutely no warranty for GDB.  Type "show warranty"
     for details.
     This GDB was configured as "i386-pc-linux-gnu"

     ^Z^Zpre-prompt
     (gdb)
     ^Z^Zprompt
     quit

     ^Z^Zpost-prompt
     $

   Here 'quit' is input to GDB; the rest is output from GDB.  The three
lines beginning '^Z^Z' (where '^Z' denotes a 'control-z' character) are
annotations; the rest is output from GDB.


File: gdb.info,  Node: Server Prefix,  Next: Prompting,  Prev: Annotations Overview,  Up: Annotations

28.2 The Server Prefix
======================

If you prefix a command with 'server ' then it will not affect the
command history, nor will it affect GDB's notion of which command to
repeat if <RET> is pressed on a line by itself.  This means that
commands can be run behind a user's back by a front-end in a transparent
manner.

   The 'server ' prefix does not affect the recording of values into the
value history; to print a value without recording it into the value
history, use the 'output' command instead of the 'print' command.

   Using this prefix also disables confirmation requests (*note
confirmation requests::).


File: gdb.info,  Node: Prompting,  Next: Errors,  Prev: Server Prefix,  Up: Annotations

28.3 Annotation for GDB Input
=============================

When GDB prompts for input, it annotates this fact so it is possible to
know when to send output, when the output from a given command is over,
etc.

   Different kinds of input each have a different "input type".  Each
input type has three annotations: a 'pre-' annotation, which denotes the
beginning of any prompt which is being output, a plain annotation, which
denotes the end of the prompt, and then a 'post-' annotation which
denotes the end of any echo which may (or may not) be associated with
the input.  For example, the 'prompt' input type features the following
annotations:

     ^Z^Zpre-prompt
     ^Z^Zprompt
     ^Z^Zpost-prompt

   The input types are

'prompt'
     When GDB is prompting for a command (the main GDB prompt).

'commands'
     When GDB prompts for a set of commands, like in the 'commands'
     command.  The annotations are repeated for each command which is
     input.

'overload-choice'
     When GDB wants the user to select between various overloaded
     functions.

'query'
     When GDB wants the user to confirm a potentially dangerous
     operation.

'prompt-for-continue'
     When GDB is asking the user to press return to continue.  Note:
     Don't expect this to work well; instead use 'set height 0' to
     disable prompting.  This is because the counting of lines is buggy
     in the presence of annotations.


File: gdb.info,  Node: Errors,  Next: Invalidation,  Prev: Prompting,  Up: Annotations

28.4 Errors
===========

     ^Z^Zquit

   This annotation occurs right before GDB responds to an interrupt.

     ^Z^Zerror

   This annotation occurs right before GDB responds to an error.

   Quit and error annotations indicate that any annotations which GDB
was in the middle of may end abruptly.  For example, if a
'value-history-begin' annotation is followed by a 'error', one cannot
expect to receive the matching 'value-history-end'.  One cannot expect
not to receive it either, however; an error annotation does not
necessarily mean that GDB is immediately returning all the way to the
top level.

   A quit or error annotation may be preceded by

     ^Z^Zerror-begin

   Any output between that and the quit or error annotation is the error
message.

   Warning messages are not yet annotated.


File: gdb.info,  Node: Invalidation,  Next: Annotations for Running,  Prev: Errors,  Up: Annotations

28.5 Invalidation Notices
=========================

The following annotations say that certain pieces of state may have
changed.

'^Z^Zframes-invalid'

     The frames (for example, output from the 'backtrace' command) may
     have changed.

'^Z^Zbreakpoints-invalid'

     The breakpoints may have changed.  For example, the user just added
     or deleted a breakpoint.


File: gdb.info,  Node: Annotations for Running,  Next: Source Annotations,  Prev: Invalidation,  Up: Annotations

28.6 Running the Program
========================

When the program starts executing due to a GDB command such as 'step' or
'continue',

     ^Z^Zstarting

   is output.  When the program stops,

     ^Z^Zstopped

   is output.  Before the 'stopped' annotation, a variety of annotations
describe how the program stopped.

'^Z^Zexited EXIT-STATUS'
     The program exited, and EXIT-STATUS is the exit status (zero for
     successful exit, otherwise nonzero).

'^Z^Zsignalled'
     The program exited with a signal.  After the '^Z^Zsignalled', the
     annotation continues:

          INTRO-TEXT
          ^Z^Zsignal-name
          NAME
          ^Z^Zsignal-name-end
          MIDDLE-TEXT
          ^Z^Zsignal-string
          STRING
          ^Z^Zsignal-string-end
          END-TEXT

     where NAME is the name of the signal, such as 'SIGILL' or
     'SIGSEGV', and STRING is the explanation of the signal, such as
     'Illegal Instruction' or 'Segmentation fault'.  The arguments
     INTRO-TEXT, MIDDLE-TEXT, and END-TEXT are for the user's benefit
     and have no particular format.

'^Z^Zsignal'
     The syntax of this annotation is just like 'signalled', but GDB is
     just saying that the program received the signal, not that it was
     terminated with it.

'^Z^Zbreakpoint NUMBER'
     The program hit breakpoint number NUMBER.

'^Z^Zwatchpoint NUMBER'
     The program hit watchpoint number NUMBER.


File: gdb.info,  Node: Source Annotations,  Prev: Annotations for Running,  Up: Annotations

28.7 Displaying Source
======================

The following annotation is used instead of displaying source code:

     ^Z^Zsource FILENAME:LINE:CHARACTER:MIDDLE:ADDR

   where FILENAME is an absolute file name indicating which source file,
LINE is the line number within that file (where 1 is the first line in
the file), CHARACTER is the character position within the file (where 0
is the first character in the file) (for most debug formats this will
necessarily point to the beginning of a line), MIDDLE is 'middle' if
ADDR is in the middle of the line, or 'beg' if ADDR is at the beginning
of the line, and ADDR is the address in the target program associated
with the source which is being displayed.  The ADDR is in the form '0x'
followed by one or more lowercase hex digits (note that this does not
depend on the language).


File: gdb.info,  Node: JIT Interface,  Next: In-Process Agent,  Prev: Annotations,  Up: Top

29 JIT Compilation Interface
****************************

This chapter documents GDB's "just-in-time" (JIT) compilation interface.
A JIT compiler is a program or library that generates native executable
code at runtime and executes it, usually in order to achieve good
performance while maintaining platform independence.

   Programs that use JIT compilation are normally difficult to debug
because portions of their code are generated at runtime, instead of
being loaded from object files, which is where GDB normally finds the
program's symbols and debug information.  In order to debug programs
that use JIT compilation, GDB has an interface that allows the program
to register in-memory symbol files with GDB at runtime.

   If you are using GDB to debug a program that uses this interface,
then it should work transparently so long as you have not stripped the
binary.  If you are developing a JIT compiler, then the interface is
documented in the rest of this chapter.  At this time, the only known
client of this interface is the LLVM JIT.

   Broadly speaking, the JIT interface mirrors the dynamic loader
interface.  The JIT compiler communicates with GDB by writing data into
a global variable and calling a fuction at a well-known symbol.  When
GDB attaches, it reads a linked list of symbol files from the global
variable to find existing code, and puts a breakpoint in the function so
that it can find out about additional code.

* Menu:

* Declarations::                Relevant C struct declarations
* Registering Code::            Steps to register code
* Unregistering Code::          Steps to unregister code
* Custom Debug Info::           Emit debug information in a custom format


File: gdb.info,  Node: Declarations,  Next: Registering Code,  Up: JIT Interface

29.1 JIT Declarations
=====================

These are the relevant struct declarations that a C program should
include to implement the interface:

     typedef enum
     {
       JIT_NOACTION = 0,
       JIT_REGISTER_FN,
       JIT_UNREGISTER_FN
     } jit_actions_t;

     struct jit_code_entry
     {
       struct jit_code_entry *next_entry;
       struct jit_code_entry *prev_entry;
       const char *symfile_addr;
       uint64_t symfile_size;
     };

     struct jit_descriptor
     {
       uint32_t version;
       /* This type should be jit_actions_t, but we use uint32_t
          to be explicit about the bitwidth.  */
       uint32_t action_flag;
       struct jit_code_entry *relevant_entry;
       struct jit_code_entry *first_entry;
     };

     /* GDB puts a breakpoint in this function.  */
     void __attribute__((noinline)) __jit_debug_register_code() { };

     /* Make sure to specify the version statically, because the
        debugger may check the version before we can set it.  */
     struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

   If the JIT is multi-threaded, then it is important that the JIT
synchronize any modifications to this global data properly, which can
easily be done by putting a global mutex around modifications to these
structures.


File: gdb.info,  Node: Registering Code,  Next: Unregistering Code,  Prev: Declarations,  Up: JIT Interface

29.2 Registering Code
=====================

To register code with GDB, the JIT should follow this protocol:

   * Generate an object file in memory with symbols and other desired
     debug information.  The file must include the virtual addresses of
     the sections.

   * Create a code entry for the file, which gives the start and size of
     the symbol file.

   * Add it to the linked list in the JIT descriptor.

   * Point the relevant_entry field of the descriptor at the entry.

   * Set 'action_flag' to 'JIT_REGISTER' and call
     '__jit_debug_register_code'.

   When GDB is attached and the breakpoint fires, GDB uses the
'relevant_entry' pointer so it doesn't have to walk the list looking for
new code.  However, the linked list must still be maintained in order to
allow GDB to attach to a running process and still find the symbol
files.


File: gdb.info,  Node: Unregistering Code,  Next: Custom Debug Info,  Prev: Registering Code,  Up: JIT Interface

29.3 Unregistering Code
=======================

If code is freed, then the JIT should use the following protocol:

   * Remove the code entry corresponding to the code from the linked
     list.

   * Point the 'relevant_entry' field of the descriptor at the code
     entry.

   * Set 'action_flag' to 'JIT_UNREGISTER' and call
     '__jit_debug_register_code'.

   If the JIT frees or recompiles code without unregistering it, then
GDB and the JIT will leak the memory used for the associated symbol
files.


File: gdb.info,  Node: Custom Debug Info,  Prev: Unregistering Code,  Up: JIT Interface

29.4 Custom Debug Info
======================

Generating debug information in platform-native file formats (like ELF
or COFF) may be an overkill for JIT compilers; especially if all the
debug info is used for is displaying a meaningful backtrace.  The issue
can be resolved by having the JIT writers decide on a debug info format
and also provide a reader that parses the debug info generated by the
JIT compiler.  This section gives a brief overview on writing such a
parser.  More specific details can be found in the source file
'gdb/jit-reader.in', which is also installed as a header at
'INCLUDEDIR/gdb/jit-reader.h' for easy inclusion.

   The reader is implemented as a shared object (so this functionality
is not available on platforms which don't allow loading shared objects
at runtime).  Two GDB commands, 'jit-reader-load' and
'jit-reader-unload' are provided, to be used to load and unload the
readers from a preconfigured directory.  Once loaded, the shared object
is used the parse the debug information emitted by the JIT compiler.

* Menu:

* Using JIT Debug Info Readers::       How to use supplied readers correctly
* Writing JIT Debug Info Readers::     Creating a debug-info reader


File: gdb.info,  Node: Using JIT Debug Info Readers,  Next: Writing JIT Debug Info Readers,  Up: Custom Debug Info

29.4.1 Using JIT Debug Info Readers
-----------------------------------

Readers can be loaded and unloaded using the 'jit-reader-load' and
'jit-reader-unload' commands.

'jit-reader-load READER'
     Load the JIT reader named READER, which is a shared object
     specified as either an absolute or a relative file name.  In the
     latter case, GDB will try to load the reader from a pre-configured
     directory, usually 'LIBDIR/gdb/' on a UNIX system (here LIBDIR is
     the system library directory, often '/usr/local/lib').

     Only one reader can be active at a time; trying to load a second
     reader when one is already loaded will result in GDB reporting an
     error.  A new JIT reader can be loaded by first unloading the
     current one using 'jit-reader-unload' and then invoking
     'jit-reader-load'.

'jit-reader-unload'
     Unload the currently loaded JIT reader.


File: gdb.info,  Node: Writing JIT Debug Info Readers,  Prev: Using JIT Debug Info Readers,  Up: Custom Debug Info

29.4.2 Writing JIT Debug Info Readers
-------------------------------------

As mentioned, a reader is essentially a shared object conforming to a
certain ABI. This ABI is described in 'jit-reader.h'.

   'jit-reader.h' defines the structures, macros and functions required
to write a reader.  It is installed (along with GDB), in
'INCLUDEDIR/gdb' where INCLUDEDIR is the system include directory.

   Readers need to be released under a GPL compatible license.  A reader
can be declared as released under such a license by placing the macro
'GDB_DECLARE_GPL_COMPATIBLE_READER' in a source file.

   The entry point for readers is the symbol 'gdb_init_reader', which is
expected to be a function with the prototype

     extern struct gdb_reader_funcs *gdb_init_reader (void);

   'struct gdb_reader_funcs' contains a set of pointers to callback
functions.  These functions are executed to read the debug info
generated by the JIT compiler ('read'), to unwind stack frames
('unwind') and to create canonical frame IDs ('get_Frame_id').  It also
has a callback that is called when the reader is being unloaded
('destroy').  The struct looks like this

     struct gdb_reader_funcs
     {
       /* Must be set to GDB_READER_INTERFACE_VERSION.  */
       int reader_version;

       /* For use by the reader.  */
       void *priv_data;

       gdb_read_debug_info *read;
       gdb_unwind_frame *unwind;
       gdb_get_frame_id *get_frame_id;
       gdb_destroy_reader *destroy;
     };

   The callbacks are provided with another set of callbacks by GDB to do
their job.  For 'read', these callbacks are passed in a 'struct
gdb_symbol_callbacks' and for 'unwind' and 'get_frame_id', in a 'struct
gdb_unwind_callbacks'.  'struct gdb_symbol_callbacks' has callbacks to
create new object files and new symbol tables inside those object files.
'struct gdb_unwind_callbacks' has callbacks to read registers off the
current frame and to write out the values of the registers in the
previous frame.  Both have a callback ('target_read') to read bytes off
the target's address space.


File: gdb.info,  Node: In-Process Agent,  Next: GDB Bugs,  Prev: JIT Interface,  Up: Top

30 In-Process Agent
*******************

The traditional debugging model is conceptually low-speed, but works
fine, because most bugs can be reproduced in debugging-mode execution.
However, as multi-core or many-core processors are becoming mainstream,
and multi-threaded programs become more and more popular, there should
be more and more bugs that only manifest themselves at normal-mode
execution, for example, thread races, because debugger's interference
with the program's timing may conceal the bugs.  On the other hand, in
some applications, it is not feasible for the debugger to interrupt the
program's execution long enough for the developer to learn anything
helpful about its behavior.  If the program's correctness depends on its
real-time behavior, delays introduced by a debugger might cause the
program to fail, even when the code itself is correct.  It is useful to
be able to observe the program's behavior without interrupting it.

   Therefore, traditional debugging model is too intrusive to reproduce
some bugs.  In order to reduce the interference with the program, we can
reduce the number of operations performed by debugger.  The "In-Process
Agent", a shared library, is running within the same process with
inferior, and is able to perform some debugging operations itself.  As a
result, debugger is only involved when necessary, and performance of
debugging can be improved accordingly.  Note that interference with
program can be reduced but can't be removed completely, because the
in-process agent will still stop or slow down the program.

   The in-process agent can interpret and execute Agent Expressions
(*note Agent Expressions::) during performing debugging operations.  The
agent expressions can be used for different purposes, such as collecting
data in tracepoints, and condition evaluation in breakpoints.

   You can control whether the in-process agent is used as an aid for
debugging with the following commands:

'set agent on'
     Causes the in-process agent to perform some operations on behalf of
     the debugger.  Just which operations requested by the user will be
     done by the in-process agent depends on the its capabilities.  For
     example, if you request to evaluate breakpoint conditions in the
     in-process agent, and the in-process agent has such capability as
     well, then breakpoint conditions will be evaluated in the
     in-process agent.

'set agent off'
     Disables execution of debugging operations by the in-process agent.
     All of the operations will be performed by GDB.

'show agent'
     Display the current setting of execution of debugging operations by
     the in-process agent.

* Menu:

* In-Process Agent Protocol::


File: gdb.info,  Node: In-Process Agent Protocol,  Up: In-Process Agent

30.1 In-Process Agent Protocol
==============================

The in-process agent is able to communicate with both GDB and GDBserver
(*note In-Process Agent::).  This section documents the protocol used
for communications between GDB or GDBserver and the IPA. In general, GDB
or GDBserver sends commands (*note IPA Protocol Commands::) and data to
in-process agent, and then in-process agent replies back with the return
result of the command, or some other information.  The data sent to
in-process agent is composed of primitive data types, such as 4-byte or
8-byte type, and composite types, which are called objects (*note IPA
Protocol Objects::).

* Menu:

* IPA Protocol Objects::
* IPA Protocol Commands::


File: gdb.info,  Node: IPA Protocol Objects,  Next: IPA Protocol Commands,  Up: In-Process Agent Protocol

30.1.1 IPA Protocol Objects
---------------------------

The commands sent to and results received from agent may contain some
complex data types called "objects".

   The in-process agent is running on the same machine with GDB or
GDBserver, so it doesn't have to handle as much differences between two
ends as remote protocol (*note Remote Protocol::) tries to handle.
However, there are still some differences of two ends in two processes:

  1. word size.  On some 64-bit machines, GDB or GDBserver can be
     compiled as a 64-bit executable, while in-process agent is a 32-bit
     one.
  2. ABI. Some machines may have multiple types of ABI, GDB or GDBserver
     is compiled with one, and in-process agent is compiled with the
     other one.

   Here are the IPA Protocol Objects:

  1. agent expression object.  It represents an agent expression (*note
     Agent Expressions::).
  2. tracepoint action object.  It represents a tracepoint action (*note
     Tracepoint Action Lists: Tracepoint Actions.) to collect registers,
     memory, static trace data and to evaluate expression.
  3. tracepoint object.  It represents a tracepoint (*note
     Tracepoints::).

   The following table describes important attributes of each IPA
protocol object:

Name                   Size           Description
---------------------------------------------------------------------------
_agent expression
object_
length                 4              length of bytes code
byte code              LENGTH         contents of byte code
_tracepoint action
for collecting
memory_
'M'                    1              type of tracepoint action
addr                   8              if BASEREG is '-1', ADDR is the
                                      address of the lowest byte to
                                      collect, otherwise ADDR is the
                                      offset of BASEREG for memory
                                      collecting.
len                    8              length of memory for collecting
basereg                4              the register number containing the
                                      starting memory address for
                                      collecting.
_tracepoint action
for collecting
registers_
'R'                    1              type of tracepoint action
_tracepoint action
for collecting
static trace data_
'L'                    1              type of tracepoint action
_tracepoint action
for expression
evaluation_
'X'                    1              type of tracepoint action
agent expression       length of      *note agent expression object::
_tracepoint object_
number                 4              number of tracepoint
address                8              address of tracepoint inserted on
type                   4              type of tracepoint
enabled                1              enable or disable of tracepoint
step_count             8              step
pass_count             8              pass
numactions             4              number of tracepoint actions
hit count              8              hit count
trace frame usage      8              trace frame usage
compiled_cond          8              compiled condition
orig_size              8              orig size
condition              4 if           zero if condition is NULL,
                       condition is   otherwise is
                       NULL           *note agent expression object::
                       otherwise
                       length of
                       *note agent expression object::
actions                variable       numactions number of
                                      *note tracepoint action object::


File: gdb.info,  Node: IPA Protocol Commands,  Prev: IPA Protocol Objects,  Up: In-Process Agent Protocol

30.1.2 IPA Protocol Commands
----------------------------

The spaces in each command are delimiters to ease reading this commands
specification.  They don't exist in real commands.

'FastTrace:TRACEPOINT_OBJECT GDB_JUMP_PAD_HEAD'
     Installs a new fast tracepoint described by TRACEPOINT_OBJECT
     (*note tracepoint object::).  The GDB_JUMP_PAD_HEAD, 8-byte long,
     is the head of "jumppad", which is used to jump to data collection
     routine in IPA finally.

     Replies:
     'OK TARGET_ADDRESS GDB_JUMP_PAD_HEAD FJUMP_SIZE FJUMP'
          TARGET_ADDRESS is address of tracepoint in the inferior.  The
          GDB_JUMP_PAD_HEAD is updated head of jumppad.  Both of
          TARGET_ADDRESS and GDB_JUMP_PAD_HEAD are 8-byte long.  The
          FJUMP contains a sequence of instructions jump to jumppad
          entry.  The FJUMP_SIZE, 4-byte long, is the size of FJUMP.
     'E NN'
          for an error

'close'
     Closes the in-process agent.  This command is sent when GDB or
     GDBserver is about to kill inferiors.

'qTfSTM'
     *Note qTfSTM::.
'qTsSTM'
     *Note qTsSTM::.
'qTSTMat'
     *Note qTSTMat::.
'probe_marker_at:ADDRESS'
     Asks in-process agent to probe the marker at ADDRESS.

     Replies:
     'E NN'
          for an error
'unprobe_marker_at:ADDRESS'
     Asks in-process agent to unprobe the marker at ADDRESS.


File: gdb.info,  Node: GDB Bugs,  Next: Command Line Editing,  Prev: In-Process Agent,  Up: Top

31 Reporting Bugs in GDB
************************

Your bug reports play an essential role in making GDB reliable.

   Reporting a bug may help you by bringing a solution to your problem,
or it may not.  But in any case the principal function of a bug report
is to help the entire community by making the next version of GDB work
better.  Bug reports are your contribution to the maintenance of GDB.

   In order for a bug report to serve its purpose, you must include the
information that enables us to fix the bug.

* Menu:

* Bug Criteria::                Have you found a bug?
* Bug Reporting::               How to report bugs


File: gdb.info,  Node: Bug Criteria,  Next: Bug Reporting,  Up: GDB Bugs

31.1 Have You Found a Bug?
==========================

If you are not sure whether you have found a bug, here are some
guidelines:

   * If the debugger gets a fatal signal, for any input whatever, that
     is a GDB bug.  Reliable debuggers never crash.

   * If GDB produces an error message for valid input, that is a bug.
     (Note that if you're cross debugging, the problem may also be
     somewhere in the connection to the target.)

   * If GDB does not produce an error message for invalid input, that is
     a bug.  However, you should note that your idea of "invalid input"
     might be our idea of "an extension" or "support for traditional
     practice".

   * If you are an experienced user of debugging tools, your suggestions
     for improvement of GDB are welcome in any case.


File: gdb.info,  Node: Bug Reporting,  Prev: Bug Criteria,  Up: GDB Bugs

31.2 How to Report Bugs
=======================

A number of companies and individuals offer support for GNU products.
If you obtained GDB from a support organization, we recommend you
contact that organization first.

   You can find contact information for many support companies and
individuals in the file 'etc/SERVICE' in the GNU Emacs distribution.

   In any event, we also recommend that you submit bug reports for GDB.
The preferred method is to submit them directly using GDB's Bugs web
page (http://www.gnu.org/software/gdb/bugs/).  Alternatively, the e-mail
gateway <bug-gdb@gnu.org> can be used.

   *Do not send bug reports to 'info-gdb', or to 'help-gdb', or to any
newsgroups.*  Most users of GDB do not want to receive bug reports.
Those that do have arranged to receive 'bug-gdb'.

   The mailing list 'bug-gdb' has a newsgroup 'gnu.gdb.bug' which serves
as a repeater.  The mailing list and the newsgroup carry exactly the
same messages.  Often people think of posting bug reports to the
newsgroup instead of mailing them.  This appears to work, but it has one
problem which can be crucial: a newsgroup posting often lacks a mail
path back to the sender.  Thus, if we need to ask for more information,
we may be unable to reach you.  For this reason, it is better to send
bug reports to the mailing list.

   The fundamental principle of reporting bugs usefully is this: *report
all the facts*.  If you are not sure whether to state a fact or leave it
out, state it!

   Often people omit facts because they think they know what causes the
problem and assume that some details do not matter.  Thus, you might
assume that the name of the variable you use in an example does not
matter.  Well, probably it does not, but one cannot be sure.  Perhaps
the bug is a stray memory reference which happens to fetch from the
location where that name is stored in memory; perhaps, if the name were
different, the contents of that location would fool the debugger into
doing the right thing despite the bug.  Play it safe and give a
specific, complete example.  That is the easiest thing for you to do,
and the most helpful.

   Keep in mind that the purpose of a bug report is to enable us to fix
the bug.  It may be that the bug has been reported previously, but
neither you nor we can know that unless your bug report is complete and
self-contained.

   Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?"  Those bug reports are useless, and we urge everyone to _refuse
to respond to them_ except to chide the sender to report bugs properly.

   To enable us to fix the bug, you should include all these things:

   * The version of GDB.  GDB announces it if you start with no
     arguments; you can also print it at any time using 'show version'.

     Without this, we will not know whether there is any point in
     looking for the bug in the current version of GDB.

   * The type of machine you are using, and the operating system name
     and version number.

   * The details of the GDB build-time configuration.  GDB shows these
     details if you invoke it with the '--configuration' command-line
     option, or if you type 'show configuration' at GDB's prompt.

   * What compiler (and its version) was used to compile GDB--e.g.
     "gcc-2.8.1".

   * What compiler (and its version) was used to compile the program you
     are debugging--e.g. "gcc-2.8.1", or "HP92453-01 A.10.32.03 HP C
     Compiler".  For GCC, you can say 'gcc --version' to get this
     information; for other compilers, see the documentation for those
     compilers.

   * The command arguments you gave the compiler to compile your example
     and observe the bug.  For example, did you use '-O'?  To guarantee
     you will not omit something important, list them all.  A copy of
     the Makefile (or the output from make) is sufficient.

     If we were to try to guess the arguments, we would probably guess
     wrong and then we might not encounter the bug.

   * A complete input script, and all necessary source files, that will
     reproduce the bug.

   * A description of what behavior you observe that you believe is
     incorrect.  For example, "It gets a fatal signal."

     Of course, if the bug is that GDB gets a fatal signal, then we will
     certainly notice it.  But if the bug is incorrect output, we might
     not notice unless it is glaringly wrong.  You might as well not
     give us a chance to make a mistake.

     Even if the problem you experience is a fatal signal, you should
     still say so explicitly.  Suppose something strange is going on,
     such as, your copy of GDB is out of synch, or you have encountered
     a bug in the C library on your system.  (This has happened!)  Your
     copy might crash and ours would not.  If you told us to expect a
     crash, then when ours fails to crash, we would know that the bug
     was not happening for us.  If you had not told us to expect a
     crash, then we would not be able to draw any conclusion from our
     observations.

     To collect all this information, you can use a session recording
     program such as 'script', which is available on many Unix systems.
     Just run your GDB session inside 'script' and then include the
     'typescript' file with your bug report.

     Another way to record a GDB session is to run GDB inside Emacs and
     then save the entire buffer to a file.

   * If you wish to suggest changes to the GDB source, send us context
     diffs.  If you even discuss something in the GDB source, refer to
     it by context, not by line number.

     The line numbers in our development sources will not match those in
     your sources.  Your line numbers would convey no useful information
     to us.

   Here are some things that are not necessary:

   * A description of the envelope of the bug.

     Often people who encounter a bug spend a lot of time investigating
     which changes to the input file will make the bug go away and which
     changes will not affect it.

     This is often time consuming and not very useful, because the way
     we will find the bug is by running a single example under the
     debugger with breakpoints, not by pure deduction from a series of
     examples.  We recommend that you save your time for something else.

     Of course, if you can find a simpler example to report _instead_ of
     the original one, that is a convenience for us.  Errors in the
     output will be easier to spot, running under the debugger will take
     less time, and so on.

     However, simplification is not vital; if you do not want to do
     this, report the bug anyway and send us the entire test case you
     used.

   * A patch for the bug.

     A patch for the bug does help us if it is a good one.  But do not
     omit the necessary information, such as the test case, on the
     assumption that a patch is all we need.  We might see problems with
     your patch and decide to fix the problem another way, or we might
     not understand it at all.

     Sometimes with a program as complicated as GDB it is very hard to
     construct an example that will make the program follow a certain
     path through the code.  If you do not send us the example, we will
     not be able to construct one, so we will not be able to verify that
     the bug is fixed.

     And if we cannot understand what bug you are trying to fix, or why
     your patch should be an improvement, we will not install it.  A
     test case will help us to understand.

   * A guess about what the bug is or what it depends on.

     Such guesses are usually wrong.  Even we cannot guess right about
     such things without first using the debugger to find the facts.


File: gdb.info,  Node: Command Line Editing,  Next: Using History Interactively,  Prev: GDB Bugs,  Up: Top

32 Command Line Editing
***********************

This chapter describes the basic features of the GNU command line
editing interface.

* Menu:

* Introduction and Notation::	Notation used in this text.
* Readline Interaction::	The minimum set of commands for editing a line.
* Readline Init File::		Customizing Readline from a user's view.
* Bindable Readline Commands::	A description of most of the Readline commands
				available for binding
* Readline vi Mode::		A short description of how to make Readline
				behave like the vi editor.


File: gdb.info,  Node: Introduction and Notation,  Next: Readline Interaction,  Up: Command Line Editing

32.1 Introduction to Line Editing
=================================

The following paragraphs describe the notation used to represent
keystrokes.

   The text 'C-k' is read as 'Control-K' and describes the character
produced when the <k> key is pressed while the Control key is depressed.

   The text 'M-k' is read as 'Meta-K' and describes the character
produced when the Meta key (if you have one) is depressed, and the <k>
key is pressed.  The Meta key is labeled <ALT> on many keyboards.  On
keyboards with two keys labeled <ALT> (usually to either side of the
space bar), the <ALT> on the left side is generally set to work as a
Meta key.  The <ALT> key on the right may also be configured to work as
a Meta key or may be configured as some other modifier, such as a
Compose key for typing accented characters.

   If you do not have a Meta or <ALT> key, or another key working as a
Meta key, the identical keystroke can be generated by typing <ESC>
_first_, and then typing <k>.  Either process is known as "metafying"
the <k> key.

   The text 'M-C-k' is read as 'Meta-Control-k' and describes the
character produced by "metafying" 'C-k'.

   In addition, several keys have their own names.  Specifically, <DEL>,
<ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves when seen
in this text, or in an init file (*note Readline Init File::).  If your
keyboard lacks a <LFD> key, typing <C-j> will produce the desired
character.  The <RET> key may be labeled <Return> or <Enter> on some
keyboards.


File: gdb.info,  Node: Readline Interaction,  Next: Readline Init File,  Prev: Introduction and Notation,  Up: Command Line Editing

32.2 Readline Interaction
=========================

Often during an interactive session you type in a long line of text,
only to notice that the first word on the line is misspelled.  The
Readline library gives you a set of commands for manipulating the text
as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line.  Using these editing commands,
you move the cursor to the place that needs correction, and delete or
insert the text of the corrections.  Then, when you are satisfied with
the line, you simply press <RET>.  You do not have to be at the end of
the line to press <RET>; the entire line is accepted regardless of the
location of the cursor within the line.

* Menu:

* Readline Bare Essentials::	The least you need to know about Readline.
* Readline Movement Commands::	Moving about the input line.
* Readline Killing Commands::	How to delete text, and how to get it back!
* Readline Arguments::		Giving numeric arguments to commands.
* Searching::			Searching through previous lines.


File: gdb.info,  Node: Readline Bare Essentials,  Next: Readline Movement Commands,  Up: Readline Interaction

32.2.1 Readline Bare Essentials
-------------------------------

In order to enter characters into the line, simply type them.  The typed
character appears where the cursor was, and then the cursor moves one
space to the right.  If you mistype a character, you can use your erase
character to back up and delete the mistyped character.

   Sometimes you may mistype a character, and not notice the error until
you have typed several other characters.  In that case, you can type
'C-b' to move the cursor to the left, and then correct your mistake.
Afterwards, you can move the cursor to the right with 'C-f'.

   When you add text in the middle of a line, you will notice that
characters to the right of the cursor are 'pushed over' to make room for
the text that you have inserted.  Likewise, when you delete text behind
the cursor, characters to the right of the cursor are 'pulled back' to
fill in the blank space created by the removal of the text.  A list of
the bare essentials for editing the text of an input line follows.

'C-b'
     Move back one character.
'C-f'
     Move forward one character.
<DEL> or <Backspace>
     Delete the character to the left of the cursor.
'C-d'
     Delete the character underneath the cursor.
Printing characters
     Insert the character into the line at the cursor.
'C-_' or 'C-x C-u'
     Undo the last editing command.  You can undo all the way back to an
     empty line.

(Depending on your configuration, the <Backspace> key be set to delete
the character to the left of the cursor and the <DEL> key set to delete
the character underneath the cursor, like 'C-d', rather than the
character to the left of the cursor.)


File: gdb.info,  Node: Readline Movement Commands,  Next: Readline Killing Commands,  Prev: Readline Bare Essentials,  Up: Readline Interaction

32.2.2 Readline Movement Commands
---------------------------------

The above table describes the most basic keystrokes that you need in
order to do editing of the input line.  For your convenience, many other
commands have been added in addition to 'C-b', 'C-f', 'C-d', and <DEL>.
Here are some commands for moving more rapidly about the line.

'C-a'
     Move to the start of the line.
'C-e'
     Move to the end of the line.
'M-f'
     Move forward a word, where a word is composed of letters and
     digits.
'M-b'
     Move backward a word.
'C-l'
     Clear the screen, reprinting the current line at the top.

   Notice how 'C-f' moves forward a character, while 'M-f' moves forward
a word.  It is a loose convention that control keystrokes operate on
characters while meta keystrokes operate on words.


File: gdb.info,  Node: Readline Killing Commands,  Next: Readline Arguments,  Prev: Readline Movement Commands,  Up: Readline Interaction

32.2.3 Readline Killing Commands
--------------------------------

"Killing" text means to delete the text from the line, but to save it
away for later use, usually by "yanking" (re-inserting) it back into the
line.  ('Cut' and 'paste' are more recent jargon for 'kill' and 'yank'.)

   If the description for a command says that it 'kills' text, then you
can be sure that you can get the text back in a different (or the same)
place later.

   When you use a kill command, the text is saved in a "kill-ring".  Any
number of consecutive kills save all of the killed text together, so
that when you yank it back, you get it all.  The kill ring is not line
specific; the text that you killed on a previously typed line is
available to be yanked back later, when you are typing another line.

   Here is the list of commands for killing text.

'C-k'
     Kill the text from the current cursor position to the end of the
     line.

'M-d'
     Kill from the cursor to the end of the current word, or, if between
     words, to the end of the next word.  Word boundaries are the same
     as those used by 'M-f'.

'M-<DEL>'
     Kill from the cursor the start of the current word, or, if between
     words, to the start of the previous word.  Word boundaries are the
     same as those used by 'M-b'.

'C-w'
     Kill from the cursor to the previous whitespace.  This is different
     than 'M-<DEL>' because the word boundaries differ.

   Here is how to "yank" the text back into the line.  Yanking means to
copy the most-recently-killed text from the kill buffer.

'C-y'
     Yank the most recently killed text back into the buffer at the
     cursor.

'M-y'
     Rotate the kill-ring, and yank the new top.  You can only do this
     if the prior command is 'C-y' or 'M-y'.


File: gdb.info,  Node: Readline Arguments,  Next: Searching,  Prev: Readline Killing Commands,  Up: Readline Interaction

32.2.4 Readline Arguments
-------------------------

You can pass numeric arguments to Readline commands.  Sometimes the
argument acts as a repeat count, other times it is the sign of the
argument that is significant.  If you pass a negative argument to a
command which normally acts in a forward direction, that command will
act in a backward direction.  For example, to kill text back to the
start of the line, you might type 'M-- C-k'.

   The general way to pass numeric arguments to a command is to type
meta digits before the command.  If the first 'digit' typed is a minus
sign ('-'), then the sign of the argument will be negative.  Once you
have typed one meta digit to get the argument started, you can type the
remainder of the digits, and then the command.  For example, to give the
'C-d' command an argument of 10, you could type 'M-1 0 C-d', which will
delete the next ten characters on the input line.


File: gdb.info,  Node: Searching,  Prev: Readline Arguments,  Up: Readline Interaction

32.2.5 Searching for Commands in the History
--------------------------------------------

Readline provides commands for searching through the command history for
lines containing a specified string.  There are two search modes:
"incremental" and "non-incremental".

   Incremental searches begin before the user has finished typing the
search string.  As each character of the search string is typed,
Readline displays the next entry from the history matching the string
typed so far.  An incremental search requires only as many characters as
needed to find the desired history entry.  To search backward in the
history for a particular string, type 'C-r'.  Typing 'C-s' searches
forward through the history.  The characters present in the value of the
'isearch-terminators' variable are used to terminate an incremental
search.  If that variable has not been assigned a value, the <ESC> and
'C-J' characters will terminate an incremental search.  'C-g' will abort
an incremental search and restore the original line.  When the search is
terminated, the history entry containing the search string becomes the
current line.

   To find other matching entries in the history list, type 'C-r' or
'C-s' as appropriate.  This will search backward or forward in the
history for the next entry matching the search string typed so far.  Any
other key sequence bound to a Readline command will terminate the search
and execute that command.  For instance, a <RET> will terminate the
search and accept the line, thereby executing the command from the
history list.  A movement command will terminate the search, make the
last line found the current line, and begin editing.

   Readline remembers the last incremental search string.  If two 'C-r's
are typed without any intervening characters defining a new search
string, any remembered search string is used.

   Non-incremental searches read the entire search string before
starting to search for matching history lines.  The search string may be
typed by the user or be part of the contents of the current line.


File: gdb.info,  Node: Readline Init File,  Next: Bindable Readline Commands,  Prev: Readline Interaction,  Up: Command Line Editing

32.3 Readline Init File
=======================

Although the Readline library comes with a set of Emacs-like keybindings
installed by default, it is possible to use a different set of
keybindings.  Any user can customize programs that use Readline by
putting commands in an "inputrc" file, conventionally in his home
directory.  The name of this file is taken from the value of the
environment variable 'INPUTRC'.  If that variable is unset, the default
is '~/.inputrc'.  If that file does not exist or cannot be read, the
ultimate default is '/etc/inputrc'.

   When a program which uses the Readline library starts up, the init
file is read, and the key bindings are set.

   In addition, the 'C-x C-r' command re-reads this init file, thus
incorporating any changes that you might have made to it.

* Menu:

* Readline Init File Syntax::	Syntax for the commands in the inputrc file.

* Conditional Init Constructs::	Conditional key bindings in the inputrc file.

* Sample Init File::		An example inputrc file.


File: gdb.info,  Node: Readline Init File Syntax,  Next: Conditional Init Constructs,  Up: Readline Init File

32.3.1 Readline Init File Syntax
--------------------------------

There are only a few basic constructs allowed in the Readline init file.
Blank lines are ignored.  Lines beginning with a '#' are comments.
Lines beginning with a '$' indicate conditional constructs (*note
Conditional Init Constructs::).  Other lines denote variable settings
and key bindings.

Variable Settings
     You can modify the run-time behavior of Readline by altering the
     values of variables in Readline using the 'set' command within the
     init file.  The syntax is simple:

          set VARIABLE VALUE

     Here, for example, is how to change from the default Emacs-like key
     binding to use 'vi' line editing commands:

          set editing-mode vi

     Variable names and values, where appropriate, are recognized
     without regard to case.  Unrecognized variable names are ignored.

     Boolean variables (those that can be set to on or off) are set to
     on if the value is null or empty, ON (case-insensitive), or 1.  Any
     other value results in the variable being set to off.

     A great deal of run-time behavior is changeable with the following
     variables.

     'bell-style'
          Controls what happens when Readline wants to ring the terminal
          bell.  If set to 'none', Readline never rings the bell.  If
          set to 'visible', Readline uses a visible bell if one is
          available.  If set to 'audible' (the default), Readline
          attempts to ring the terminal's bell.

     'bind-tty-special-chars'
          If set to 'on', Readline attempts to bind the control
          characters treated specially by the kernel's terminal driver
          to their Readline equivalents.

     'comment-begin'
          The string to insert at the beginning of the line when the
          'insert-comment' command is executed.  The default value is
          '"#"'.

     'completion-display-width'
          The number of screen columns used to display possible matches
          when performing completion.  The value is ignored if it is
          less than 0 or greater than the terminal screen width.  A
          value of 0 will cause matches to be displayed one per line.
          The default value is -1.

     'completion-ignore-case'
          If set to 'on', Readline performs filename matching and
          completion in a case-insensitive fashion.  The default value
          is 'off'.

     'completion-map-case'
          If set to 'on', and COMPLETION-IGNORE-CASE is enabled,
          Readline treats hyphens ('-') and underscores ('_') as
          equivalent when performing case-insensitive filename matching
          and completion.

     'completion-prefix-display-length'
          The length in characters of the common prefix of a list of
          possible completions that is displayed without modification.
          When set to a value greater than zero, common prefixes longer
          than this value are replaced with an ellipsis when displaying
          possible completions.

     'completion-query-items'
          The number of possible completions that determines when the
          user is asked whether the list of possibilities should be
          displayed.  If the number of possible completions is greater
          than this value, Readline will ask the user whether or not he
          wishes to view them; otherwise, they are simply listed.  This
          variable must be set to an integer value greater than or equal
          to 0.  A negative value means Readline should never ask.  The
          default limit is '100'.

     'convert-meta'
          If set to 'on', Readline will convert characters with the
          eighth bit set to an ASCII key sequence by stripping the
          eighth bit and prefixing an <ESC> character, converting them
          to a meta-prefixed key sequence.  The default value is 'on'.

     'disable-completion'
          If set to 'On', Readline will inhibit word completion.
          Completion characters will be inserted into the line as if
          they had been mapped to 'self-insert'.  The default is 'off'.

     'editing-mode'
          The 'editing-mode' variable controls which default set of key
          bindings is used.  By default, Readline starts up in Emacs
          editing mode, where the keystrokes are most similar to Emacs.
          This variable can be set to either 'emacs' or 'vi'.

     'echo-control-characters'
          When set to 'on', on operating systems that indicate they
          support it, readline echoes a character corresponding to a
          signal generated from the keyboard.  The default is 'on'.

     'enable-keypad'
          When set to 'on', Readline will try to enable the application
          keypad when it is called.  Some systems need this to enable
          the arrow keys.  The default is 'off'.

     'enable-meta-key'
          When set to 'on', Readline will try to enable any meta
          modifier key the terminal claims to support when it is called.
          On many terminals, the meta key is used to send eight-bit
          characters.  The default is 'on'.

     'expand-tilde'
          If set to 'on', tilde expansion is performed when Readline
          attempts word completion.  The default is 'off'.

     'history-preserve-point'
          If set to 'on', the history code attempts to place the point
          (the current cursor position) at the same location on each
          history line retrieved with 'previous-history' or
          'next-history'.  The default is 'off'.

     'history-size'
          Set the maximum number of history entries saved in the history
          list.  If set to zero, the number of entries in the history
          list is not limited.

     'horizontal-scroll-mode'
          This variable can be set to either 'on' or 'off'.  Setting it
          to 'on' means that the text of the lines being edited will
          scroll horizontally on a single screen line when they are
          longer than the width of the screen, instead of wrapping onto
          a new screen line.  By default, this variable is set to 'off'.

     'input-meta'
          If set to 'on', Readline will enable eight-bit input (it will
          not clear the eighth bit in the characters it reads),
          regardless of what the terminal claims it can support.  The
          default value is 'off'.  The name 'meta-flag' is a synonym for
          this variable.

     'isearch-terminators'
          The string of characters that should terminate an incremental
          search without subsequently executing the character as a
          command (*note Searching::).  If this variable has not been
          given a value, the characters <ESC> and 'C-J' will terminate
          an incremental search.

     'keymap'
          Sets Readline's idea of the current keymap for key binding
          commands.  Acceptable 'keymap' names are 'emacs',
          'emacs-standard', 'emacs-meta', 'emacs-ctlx', 'vi', 'vi-move',
          'vi-command', and 'vi-insert'.  'vi' is equivalent to
          'vi-command'; 'emacs' is equivalent to 'emacs-standard'.  The
          default value is 'emacs'.  The value of the 'editing-mode'
          variable also affects the default keymap.

     'mark-directories'
          If set to 'on', completed directory names have a slash
          appended.  The default is 'on'.

     'mark-modified-lines'
          This variable, when set to 'on', causes Readline to display an
          asterisk ('*') at the start of history lines which have been
          modified.  This variable is 'off' by default.

     'mark-symlinked-directories'
          If set to 'on', completed names which are symbolic links to
          directories have a slash appended (subject to the value of
          'mark-directories').  The default is 'off'.

     'match-hidden-files'
          This variable, when set to 'on', causes Readline to match
          files whose names begin with a '.' (hidden files) when
          performing filename completion.  If set to 'off', the leading
          '.' must be supplied by the user in the filename to be
          completed.  This variable is 'on' by default.

     'menu-complete-display-prefix'
          If set to 'on', menu completion displays the common prefix of
          the list of possible completions (which may be empty) before
          cycling through the list.  The default is 'off'.

     'output-meta'
          If set to 'on', Readline will display characters with the
          eighth bit set directly rather than as a meta-prefixed escape
          sequence.  The default is 'off'.

     'page-completions'
          If set to 'on', Readline uses an internal 'more'-like pager to
          display a screenful of possible completions at a time.  This
          variable is 'on' by default.

     'print-completions-horizontally'
          If set to 'on', Readline will display completions with matches
          sorted horizontally in alphabetical order, rather than down
          the screen.  The default is 'off'.

     'revert-all-at-newline'
          If set to 'on', Readline will undo all changes to history
          lines before returning when 'accept-line' is executed.  By
          default, history lines may be modified and retain individual
          undo lists across calls to 'readline'.  The default is 'off'.

     'show-all-if-ambiguous'
          This alters the default behavior of the completion functions.
          If set to 'on', words which have more than one possible
          completion cause the matches to be listed immediately instead
          of ringing the bell.  The default value is 'off'.

     'show-all-if-unmodified'
          This alters the default behavior of the completion functions
          in a fashion similar to SHOW-ALL-IF-AMBIGUOUS.  If set to
          'on', words which have more than one possible completion
          without any possible partial completion (the possible
          completions don't share a common prefix) cause the matches to
          be listed immediately instead of ringing the bell.  The
          default value is 'off'.

     'skip-completed-text'
          If set to 'on', this alters the default completion behavior
          when inserting a single match into the line.  It's only active
          when performing completion in the middle of a word.  If
          enabled, readline does not insert characters from the
          completion that match characters after point in the word being
          completed, so portions of the word following the cursor are
          not duplicated.  For instance, if this is enabled, attempting
          completion when the cursor is after the 'e' in 'Makefile' will
          result in 'Makefile' rather than 'Makefilefile', assuming
          there is a single possible completion.  The default value is
          'off'.

     'visible-stats'
          If set to 'on', a character denoting a file's type is appended
          to the filename when listing possible completions.  The
          default is 'off'.

Key Bindings
     The syntax for controlling key bindings in the init file is simple.
     First you need to find the name of the command that you want to
     change.  The following sections contain tables of the command name,
     the default keybinding, if any, and a short description of what the
     command does.

     Once you know the name of the command, simply place on a line in
     the init file the name of the key you wish to bind the command to,
     a colon, and then the name of the command.  There can be no space
     between the key name and the colon - that will be interpreted as
     part of the key name.  The name of the key can be expressed in
     different ways, depending on what you find most comfortable.

     In addition to command names, readline allows keys to be bound to a
     string that is inserted when the key is pressed (a MACRO).

     KEYNAME: FUNCTION-NAME or MACRO
          KEYNAME is the name of a key spelled out in English.  For
          example:
               Control-u: universal-argument
               Meta-Rubout: backward-kill-word
               Control-o: "> output"

          In the above example, 'C-u' is bound to the function
          'universal-argument', 'M-DEL' is bound to the function
          'backward-kill-word', and 'C-o' is bound to run the macro
          expressed on the right hand side (that is, to insert the text
          '> output' into the line).

          A number of symbolic character names are recognized while
          processing this key binding syntax: DEL, ESC, ESCAPE, LFD,
          NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.

     "KEYSEQ": FUNCTION-NAME or MACRO
          KEYSEQ differs from KEYNAME above in that strings denoting an
          entire key sequence can be specified, by placing the key
          sequence in double quotes.  Some GNU Emacs style key escapes
          can be used, as in the following example, but the special
          character names are not recognized.

               "\C-u": universal-argument
               "\C-x\C-r": re-read-init-file
               "\e[11~": "Function Key 1"

          In the above example, 'C-u' is again bound to the function
          'universal-argument' (just as it was in the first example),
          ''C-x' 'C-r'' is bound to the function 're-read-init-file',
          and '<ESC> <[> <1> <1> <~>' is bound to insert the text
          'Function Key 1'.

     The following GNU Emacs style escape sequences are available when
     specifying key sequences:

     '\C-'
          control prefix
     '\M-'
          meta prefix
     '\e'
          an escape character
     '\\'
          backslash
     '\"'
          <">, a double quotation mark
     '\''
          <'>, a single quote or apostrophe

     In addition to the GNU Emacs style escape sequences, a second set
     of backslash escapes is available:

     '\a'
          alert (bell)
     '\b'
          backspace
     '\d'
          delete
     '\f'
          form feed
     '\n'
          newline
     '\r'
          carriage return
     '\t'
          horizontal tab
     '\v'
          vertical tab
     '\NNN'
          the eight-bit character whose value is the octal value NNN
          (one to three digits)
     '\xHH'
          the eight-bit character whose value is the hexadecimal value
          HH (one or two hex digits)

     When entering the text of a macro, single or double quotes must be
     used to indicate a macro definition.  Unquoted text is assumed to
     be a function name.  In the macro body, the backslash escapes
     described above are expanded.  Backslash will quote any other
     character in the macro text, including '"' and '''.  For example,
     the following binding will make ''C-x' \' insert a single '\' into
     the line:
          "\C-x\\": "\\"


File: gdb.info,  Node: Conditional Init Constructs,  Next: Sample Init File,  Prev: Readline Init File Syntax,  Up: Readline Init File

32.3.2 Conditional Init Constructs
----------------------------------

Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key bindings and
variable settings to be performed as the result of tests.  There are
four parser directives used.

'$if'
     The '$if' construct allows bindings to be made based on the editing
     mode, the terminal being used, or the application using Readline.
     The text of the test extends to the end of the line; no characters
     are required to isolate it.

     'mode'
          The 'mode=' form of the '$if' directive is used to test
          whether Readline is in 'emacs' or 'vi' mode.  This may be used
          in conjunction with the 'set keymap' command, for instance, to
          set bindings in the 'emacs-standard' and 'emacs-ctlx' keymaps
          only if Readline is starting out in 'emacs' mode.

     'term'
          The 'term=' form may be used to include terminal-specific key
          bindings, perhaps to bind the key sequences output by the
          terminal's function keys.  The word on the right side of the
          '=' is tested against both the full name of the terminal and
          the portion of the terminal name before the first '-'.  This
          allows 'sun' to match both 'sun' and 'sun-cmd', for instance.

     'application'
          The APPLICATION construct is used to include
          application-specific settings.  Each program using the
          Readline library sets the APPLICATION NAME, and you can test
          for a particular value.  This could be used to bind key
          sequences to functions useful for a specific program.  For
          instance, the following command adds a key sequence that
          quotes the current or previous word in Bash:
               $if Bash
               # Quote the current or previous word
               "\C-xq": "\eb\"\ef\""
               $endif

'$endif'
     This command, as seen in the previous example, terminates an '$if'
     command.

'$else'
     Commands in this branch of the '$if' directive are executed if the
     test fails.

'$include'
     This directive takes a single filename as an argument and reads
     commands and bindings from that file.  For example, the following
     directive reads from '/etc/inputrc':
          $include /etc/inputrc


File: gdb.info,  Node: Sample Init File,  Prev: Conditional Init Constructs,  Up: Readline Init File

32.3.3 Sample Init File
-----------------------

Here is an example of an INPUTRC file.  This illustrates key binding,
variable assignment, and conditional syntax.

     # This file controls the behaviour of line input editing for
     # programs that use the GNU Readline library.  Existing
     # programs include FTP, Bash, and GDB.
     #
     # You can re-read the inputrc file with C-x C-r.
     # Lines beginning with '#' are comments.
     #
     # First, include any systemwide bindings and variable
     # assignments from /etc/Inputrc
     $include /etc/Inputrc

     #
     # Set various bindings for emacs mode.

     set editing-mode emacs

     $if mode=emacs

     Meta-Control-h:	backward-kill-word	Text after the function name is ignored

     #
     # Arrow keys in keypad mode
     #
     #"\M-OD":        backward-char
     #"\M-OC":        forward-char
     #"\M-OA":        previous-history
     #"\M-OB":        next-history
     #
     # Arrow keys in ANSI mode
     #
     "\M-[D":        backward-char
     "\M-[C":        forward-char
     "\M-[A":        previous-history
     "\M-[B":        next-history
     #
     # Arrow keys in 8 bit keypad mode
     #
     #"\M-\C-OD":       backward-char
     #"\M-\C-OC":       forward-char
     #"\M-\C-OA":       previous-history
     #"\M-\C-OB":       next-history
     #
     # Arrow keys in 8 bit ANSI mode
     #
     #"\M-\C-[D":       backward-char
     #"\M-\C-[C":       forward-char
     #"\M-\C-[A":       previous-history
     #"\M-\C-[B":       next-history

     C-q: quoted-insert

     $endif

     # An old-style binding.  This happens to be the default.
     TAB: complete

     # Macros that are convenient for shell interaction
     $if Bash
     # edit the path
     "\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
     # prepare to type a quoted word --
     # insert open and close double quotes
     # and move to just after the open quote
     "\C-x\"": "\"\"\C-b"
     # insert a backslash (testing backslash escapes
     # in sequences and macros)
     "\C-x\\": "\\"
     # Quote the current or previous word
     "\C-xq": "\eb\"\ef\""
     # Add a binding to refresh the line, which is unbound
     "\C-xr": redraw-current-line
     # Edit variable on current line.
     "\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
     $endif

     # use a visible bell if one is available
     set bell-style visible

     # don't strip characters to 7 bits when reading
     set input-meta on

     # allow iso-latin1 characters to be inserted rather
     # than converted to prefix-meta sequences
     set convert-meta off

     # display characters with the eighth bit set directly
     # rather than as meta-prefixed characters
     set output-meta on

     # if there are more than 150 possible completions for
     # a word, ask the user if he wants to see all of them
     set completion-query-items 150

     # For FTP
     $if Ftp
     "\C-xg": "get \M-?"
     "\C-xt": "put \M-?"
     "\M-.": yank-last-arg
     $endif


File: gdb.info,  Node: Bindable Readline Commands,  Next: Readline vi Mode,  Prev: Readline Init File,  Up: Command Line Editing

32.4 Bindable Readline Commands
===============================

* Menu:

* Commands For Moving::		Moving about the line.
* Commands For History::	Getting at previous lines.
* Commands For Text::		Commands for changing text.
* Commands For Killing::	Commands for killing and yanking.
* Numeric Arguments::		Specifying numeric arguments, repeat counts.
* Commands For Completion::	Getting Readline to do the typing for you.
* Keyboard Macros::		Saving and re-executing typed characters
* Miscellaneous Commands::	Other miscellaneous commands.

This section describes Readline commands that may be bound to key
sequences.  Command names without an accompanying key sequence are
unbound by default.

   In the following descriptions, "point" refers to the current cursor
position, and "mark" refers to a cursor position saved by the 'set-mark'
command.  The text between the point and mark is referred to as the
"region".


File: gdb.info,  Node: Commands For Moving,  Next: Commands For History,  Up: Bindable Readline Commands

32.4.1 Commands For Moving
--------------------------

'beginning-of-line (C-a)'
     Move to the start of the current line.

'end-of-line (C-e)'
     Move to the end of the line.

'forward-char (C-f)'
     Move forward a character.

'backward-char (C-b)'
     Move back a character.

'forward-word (M-f)'
     Move forward to the end of the next word.  Words are composed of
     letters and digits.

'backward-word (M-b)'
     Move back to the start of the current or previous word.  Words are
     composed of letters and digits.

'clear-screen (C-l)'
     Clear the screen and redraw the current line, leaving the current
     line at the top of the screen.

'redraw-current-line ()'
     Refresh the current line.  By default, this is unbound.


File: gdb.info,  Node: Commands For History,  Next: Commands For Text,  Prev: Commands For Moving,  Up: Bindable Readline Commands

32.4.2 Commands For Manipulating The History
--------------------------------------------

'accept-line (Newline or Return)'
     Accept the line regardless of where the cursor is.  If this line is
     non-empty, it may be added to the history list for future recall
     with 'add_history()'.  If this line is a modified history line, the
     history line is restored to its original state.

'previous-history (C-p)'
     Move 'back' through the history list, fetching the previous
     command.

'next-history (C-n)'
     Move 'forward' through the history list, fetching the next command.

'beginning-of-history (M-<)'
     Move to the first line in the history.

'end-of-history (M->)'
     Move to the end of the input history, i.e., the line currently
     being entered.

'reverse-search-history (C-r)'
     Search backward starting at the current line and moving 'up'
     through the history as necessary.  This is an incremental search.

'forward-search-history (C-s)'
     Search forward starting at the current line and moving 'down'
     through the the history as necessary.  This is an incremental
     search.

'non-incremental-reverse-search-history (M-p)'
     Search backward starting at the current line and moving 'up'
     through the history as necessary using a non-incremental search for
     a string supplied by the user.

'non-incremental-forward-search-history (M-n)'
     Search forward starting at the current line and moving 'down'
     through the the history as necessary using a non-incremental search
     for a string supplied by the user.

'history-search-forward ()'
     Search forward through the history for the string of characters
     between the start of the current line and the point.  This is a
     non-incremental search.  By default, this command is unbound.

'history-search-backward ()'
     Search backward through the history for the string of characters
     between the start of the current line and the point.  This is a
     non-incremental search.  By default, this command is unbound.

'yank-nth-arg (M-C-y)'
     Insert the first argument to the previous command (usually the
     second word on the previous line) at point.  With an argument N,
     insert the Nth word from the previous command (the words in the
     previous command begin with word 0).  A negative argument inserts
     the Nth word from the end of the previous command.  Once the
     argument N is computed, the argument is extracted as if the '!N'
     history expansion had been specified.

'yank-last-arg (M-. or M-_)'
     Insert last argument to the previous command (the last word of the
     previous history entry).  With a numeric argument, behave exactly
     like 'yank-nth-arg'.  Successive calls to 'yank-last-arg' move back
     through the history list, inserting the last word (or the word
     specified by the argument to the first call) of each line in turn.
     Any numeric argument supplied to these successive calls determines
     the direction to move through the history.  A negative argument
     switches the direction through the history (back or forward).  The
     history expansion facilities are used to extract the last argument,
     as if the '!$' history expansion had been specified.


File: gdb.info,  Node: Commands For Text,  Next: Commands For Killing,  Prev: Commands For History,  Up: Bindable Readline Commands

32.4.3 Commands For Changing Text
---------------------------------

'delete-char (C-d)'
     Delete the character at point.  If point is at the beginning of the
     line, there are no characters in the line, and the last character
     typed was not bound to 'delete-char', then return EOF.

'backward-delete-char (Rubout)'
     Delete the character behind the cursor.  A numeric argument means
     to kill the characters instead of deleting them.

'forward-backward-delete-char ()'
     Delete the character under the cursor, unless the cursor is at the
     end of the line, in which case the character behind the cursor is
     deleted.  By default, this is not bound to a key.

'quoted-insert (C-q or C-v)'
     Add the next character typed to the line verbatim.  This is how to
     insert key sequences like 'C-q', for example.

'tab-insert (M-<TAB>)'
     Insert a tab character.

'self-insert (a, b, A, 1, !, ...)'
     Insert yourself.

'transpose-chars (C-t)'
     Drag the character before the cursor forward over the character at
     the cursor, moving the cursor forward as well.  If the insertion
     point is at the end of the line, then this transposes the last two
     characters of the line.  Negative arguments have no effect.

'transpose-words (M-t)'
     Drag the word before point past the word after point, moving point
     past that word as well.  If the insertion point is at the end of
     the line, this transposes the last two words on the line.

'upcase-word (M-u)'
     Uppercase the current (or following) word.  With a negative
     argument, uppercase the previous word, but do not move the cursor.

'downcase-word (M-l)'
     Lowercase the current (or following) word.  With a negative
     argument, lowercase the previous word, but do not move the cursor.

'capitalize-word (M-c)'
     Capitalize the current (or following) word.  With a negative
     argument, capitalize the previous word, but do not move the cursor.

'overwrite-mode ()'
     Toggle overwrite mode.  With an explicit positive numeric argument,
     switches to overwrite mode.  With an explicit non-positive numeric
     argument, switches to insert mode.  This command affects only
     'emacs' mode; 'vi' mode does overwrite differently.  Each call to
     'readline()' starts in insert mode.

     In overwrite mode, characters bound to 'self-insert' replace the
     text at point rather than pushing the text to the right.
     Characters bound to 'backward-delete-char' replace the character
     before point with a space.

     By default, this command is unbound.


File: gdb.info,  Node: Commands For Killing,  Next: Numeric Arguments,  Prev: Commands For Text,  Up: Bindable Readline Commands

32.4.4 Killing And Yanking
--------------------------

'kill-line (C-k)'
     Kill the text from point to the end of the line.

'backward-kill-line (C-x Rubout)'
     Kill backward to the beginning of the line.

'unix-line-discard (C-u)'
     Kill backward from the cursor to the beginning of the current line.

'kill-whole-line ()'
     Kill all characters on the current line, no matter where point is.
     By default, this is unbound.

'kill-word (M-d)'
     Kill from point to the end of the current word, or if between
     words, to the end of the next word.  Word boundaries are the same
     as 'forward-word'.

'backward-kill-word (M-<DEL>)'
     Kill the word behind point.  Word boundaries are the same as
     'backward-word'.

'unix-word-rubout (C-w)'
     Kill the word behind point, using white space as a word boundary.
     The killed text is saved on the kill-ring.

'unix-filename-rubout ()'
     Kill the word behind point, using white space and the slash
     character as the word boundaries.  The killed text is saved on the
     kill-ring.

'delete-horizontal-space ()'
     Delete all spaces and tabs around point.  By default, this is
     unbound.

'kill-region ()'
     Kill the text in the current region.  By default, this command is
     unbound.

'copy-region-as-kill ()'
     Copy the text in the region to the kill buffer, so it can be yanked
     right away.  By default, this command is unbound.

'copy-backward-word ()'
     Copy the word before point to the kill buffer.  The word boundaries
     are the same as 'backward-word'.  By default, this command is
     unbound.

'copy-forward-word ()'
     Copy the word following point to the kill buffer.  The word
     boundaries are the same as 'forward-word'.  By default, this
     command is unbound.

'yank (C-y)'
     Yank the top of the kill ring into the buffer at point.

'yank-pop (M-y)'
     Rotate the kill-ring, and yank the new top.  You can only do this
     if the prior command is 'yank' or 'yank-pop'.


File: gdb.info,  Node: Numeric Arguments,  Next: Commands For Completion,  Prev: Commands For Killing,  Up: Bindable Readline Commands

32.4.5 Specifying Numeric Arguments
-----------------------------------

'digit-argument (M-0, M-1, ... M--)'
     Add this digit to the argument already accumulating, or start a new
     argument.  'M--' starts a negative argument.

'universal-argument ()'
     This is another way to specify an argument.  If this command is
     followed by one or more digits, optionally with a leading minus
     sign, those digits define the argument.  If the command is followed
     by digits, executing 'universal-argument' again ends the numeric
     argument, but is otherwise ignored.  As a special case, if this
     command is immediately followed by a character that is neither a
     digit or minus sign, the argument count for the next command is
     multiplied by four.  The argument count is initially one, so
     executing this function the first time makes the argument count
     four, a second time makes the argument count sixteen, and so on.
     By default, this is not bound to a key.


File: gdb.info,  Node: Commands For Completion,  Next: Keyboard Macros,  Prev: Numeric Arguments,  Up: Bindable Readline Commands

32.4.6 Letting Readline Type For You
------------------------------------

'complete (<TAB>)'
     Attempt to perform completion on the text before point.  The actual
     completion performed is application-specific.  The default is
     filename completion.

'possible-completions (M-?)'
     List the possible completions of the text before point.  When
     displaying completions, Readline sets the number of columns used
     for display to the value of 'completion-display-width', the value
     of the environment variable 'COLUMNS', or the screen width, in that
     order.

'insert-completions (M-*)'
     Insert all completions of the text before point that would have
     been generated by 'possible-completions'.

'menu-complete ()'
     Similar to 'complete', but replaces the word to be completed with a
     single match from the list of possible completions.  Repeated
     execution of 'menu-complete' steps through the list of possible
     completions, inserting each match in turn.  At the end of the list
     of completions, the bell is rung (subject to the setting of
     'bell-style') and the original text is restored.  An argument of N
     moves N positions forward in the list of matches; a negative
     argument may be used to move backward through the list.  This
     command is intended to be bound to <TAB>, but is unbound by
     default.

'menu-complete-backward ()'
     Identical to 'menu-complete', but moves backward through the list
     of possible completions, as if 'menu-complete' had been given a
     negative argument.

'delete-char-or-list ()'
     Deletes the character under the cursor if not at the beginning or
     end of the line (like 'delete-char').  If at the end of the line,
     behaves identically to 'possible-completions'.  This command is
     unbound by default.


File: gdb.info,  Node: Keyboard Macros,  Next: Miscellaneous Commands,  Prev: Commands For Completion,  Up: Bindable Readline Commands

32.4.7 Keyboard Macros
----------------------

'start-kbd-macro (C-x ()'
     Begin saving the characters typed into the current keyboard macro.

'end-kbd-macro (C-x ))'
     Stop saving the characters typed into the current keyboard macro
     and save the definition.

'call-last-kbd-macro (C-x e)'
     Re-execute the last keyboard macro defined, by making the
     characters in the macro appear as if typed at the keyboard.


File: gdb.info,  Node: Miscellaneous Commands,  Prev: Keyboard Macros,  Up: Bindable Readline Commands

32.4.8 Some Miscellaneous Commands
----------------------------------

're-read-init-file (C-x C-r)'
     Read in the contents of the INPUTRC file, and incorporate any
     bindings or variable assignments found there.

'abort (C-g)'
     Abort the current editing command and ring the terminal's bell
     (subject to the setting of 'bell-style').

'do-uppercase-version (M-a, M-b, M-X, ...)'
     If the metafied character X is lowercase, run the command that is
     bound to the corresponding uppercase character.

'prefix-meta (<ESC>)'
     Metafy the next character typed.  This is for keyboards without a
     meta key.  Typing '<ESC> f' is equivalent to typing 'M-f'.

'undo (C-_ or C-x C-u)'
     Incremental undo, separately remembered for each line.

'revert-line (M-r)'
     Undo all changes made to this line.  This is like executing the
     'undo' command enough times to get back to the beginning.

'tilde-expand (M-~)'
     Perform tilde expansion on the current word.

'set-mark (C-@)'
     Set the mark to the point.  If a numeric argument is supplied, the
     mark is set to that position.

'exchange-point-and-mark (C-x C-x)'
     Swap the point with the mark.  The current cursor position is set
     to the saved position, and the old cursor position is saved as the
     mark.

'character-search (C-])'
     A character is read and point is moved to the next occurrence of
     that character.  A negative count searches for previous
     occurrences.

'character-search-backward (M-C-])'
     A character is read and point is moved to the previous occurrence
     of that character.  A negative count searches for subsequent
     occurrences.

'skip-csi-sequence ()'
     Read enough characters to consume a multi-key sequence such as
     those defined for keys like Home and End.  Such sequences begin
     with a Control Sequence Indicator (CSI), usually ESC-[.  If this
     sequence is bound to "\e[", keys producing such sequences will have
     no effect unless explicitly bound to a readline command, instead of
     inserting stray characters into the editing buffer.  This is
     unbound by default, but usually bound to ESC-[.

'insert-comment (M-#)'
     Without a numeric argument, the value of the 'comment-begin'
     variable is inserted at the beginning of the current line.  If a
     numeric argument is supplied, this command acts as a toggle: if the
     characters at the beginning of the line do not match the value of
     'comment-begin', the value is inserted, otherwise the characters in
     'comment-begin' are deleted from the beginning of the line.  In
     either case, the line is accepted as if a newline had been typed.

'dump-functions ()'
     Print all of the functions and their key bindings to the Readline
     output stream.  If a numeric argument is supplied, the output is
     formatted in such a way that it can be made part of an INPUTRC
     file.  This command is unbound by default.

'dump-variables ()'
     Print all of the settable variables and their values to the
     Readline output stream.  If a numeric argument is supplied, the
     output is formatted in such a way that it can be made part of an
     INPUTRC file.  This command is unbound by default.

'dump-macros ()'
     Print all of the Readline key sequences bound to macros and the
     strings they output.  If a numeric argument is supplied, the output
     is formatted in such a way that it can be made part of an INPUTRC
     file.  This command is unbound by default.

'emacs-editing-mode (C-e)'
     When in 'vi' command mode, this causes a switch to 'emacs' editing
     mode.

'vi-editing-mode (M-C-j)'
     When in 'emacs' editing mode, this causes a switch to 'vi' editing
     mode.


File: gdb.info,  Node: Readline vi Mode,  Prev: Bindable Readline Commands,  Up: Command Line Editing

32.5 Readline vi Mode
=====================

While the Readline library does not have a full set of 'vi' editing
functions, it does contain enough to allow simple editing of the line.
The Readline 'vi' mode behaves as specified in the POSIX standard.

   In order to switch interactively between 'emacs' and 'vi' editing
modes, use the command 'M-C-j' (bound to emacs-editing-mode when in 'vi'
mode and to vi-editing-mode in 'emacs' mode).  The Readline default is
'emacs' mode.

   When you enter a line in 'vi' mode, you are already placed in
'insertion' mode, as if you had typed an 'i'.  Pressing <ESC> switches
you into 'command' mode, where you can edit the text of the line with
the standard 'vi' movement keys, move to previous history lines with 'k'
and subsequent lines with 'j', and so forth.


File: gdb.info,  Node: Using History Interactively,  Next: In Memoriam,  Prev: Command Line Editing,  Up: Top

33 Using History Interactively
******************************

This chapter describes how to use the GNU History Library interactively,
from a user's standpoint.  It should be considered a user's guide.  For
information on using the GNU History Library in your own programs, *note
(history)Programming with GNU History::.

* Menu:

* History Interaction::		What it feels like using History as a user.


File: gdb.info,  Node: History Interaction,  Up: Using History Interactively

33.1 History Expansion
======================

The History library provides a history expansion feature that is similar
to the history expansion provided by 'csh'.  This section describes the
syntax used to manipulate the history information.

   History expansions introduce words from the history list into the
input stream, making it easy to repeat commands, insert the arguments to
a previous command into the current input line, or fix errors in
previous commands quickly.

   History expansion takes place in two parts.  The first is to
determine which line from the history list should be used during
substitution.  The second is to select portions of that line for
inclusion into the current one.  The line selected from the history is
called the "event", and the portions of that line that are acted upon
are called "words".  Various "modifiers" are available to manipulate the
selected words.  The line is broken into words in the same fashion that
Bash does, so that several words surrounded by quotes are considered one
word.  History expansions are introduced by the appearance of the
history expansion character, which is '!' by default.

* Menu:

* Event Designators::	How to specify which history line to use.
* Word Designators::	Specifying which words are of interest.
* Modifiers::		Modifying the results of substitution.


File: gdb.info,  Node: Event Designators,  Next: Word Designators,  Up: History Interaction

33.1.1 Event Designators
------------------------

An event designator is a reference to a command line entry in the
history list.  Unless the reference is absolute, events are relative to
the current position in the history list.

'!'
     Start a history substitution, except when followed by a space, tab,
     the end of the line, or '='.

'!N'
     Refer to command line N.

'!-N'
     Refer to the command N lines back.

'!!'
     Refer to the previous command.  This is a synonym for '!-1'.

'!STRING'
     Refer to the most recent command preceding the current position in
     the history list starting with STRING.

'!?STRING[?]'
     Refer to the most recent command preceding the current position in
     the history list containing STRING.  The trailing '?' may be
     omitted if the STRING is followed immediately by a newline.

'^STRING1^STRING2^'
     Quick Substitution.  Repeat the last command, replacing STRING1
     with STRING2.  Equivalent to '!!:s/STRING1/STRING2/'.

'!#'
     The entire command line typed so far.


File: gdb.info,  Node: Word Designators,  Next: Modifiers,  Prev: Event Designators,  Up: History Interaction

33.1.2 Word Designators
-----------------------

Word designators are used to select desired words from the event.  A ':'
separates the event specification from the word designator.  It may be
omitted if the word designator begins with a '^', '$', '*', '-', or '%'.
Words are numbered from the beginning of the line, with the first word
being denoted by 0 (zero).  Words are inserted into the current line
separated by single spaces.

   For example,

'!!'
     designates the preceding command.  When you type this, the
     preceding command is repeated in toto.

'!!:$'
     designates the last argument of the preceding command.  This may be
     shortened to '!$'.

'!fi:2'
     designates the second argument of the most recent command starting
     with the letters 'fi'.

   Here are the word designators:

'0 (zero)'
     The '0'th word.  For many applications, this is the command word.

'N'
     The Nth word.

'^'
     The first argument; that is, word 1.

'$'
     The last argument.

'%'
     The word matched by the most recent '?STRING?' search.

'X-Y'
     A range of words; '-Y' abbreviates '0-Y'.

'*'
     All of the words, except the '0'th.  This is a synonym for '1-$'.
     It is not an error to use '*' if there is just one word in the
     event; the empty string is returned in that case.

'X*'
     Abbreviates 'X-$'

'X-'
     Abbreviates 'X-$' like 'X*', but omits the last word.

   If a word designator is supplied without an event specification, the
previous command is used as the event.


File: gdb.info,  Node: Modifiers,  Prev: Word Designators,  Up: History Interaction

33.1.3 Modifiers
----------------

After the optional word designator, you can add a sequence of one or
more of the following modifiers, each preceded by a ':'.

'h'
     Remove a trailing pathname component, leaving only the head.

't'
     Remove all leading pathname components, leaving the tail.

'r'
     Remove a trailing suffix of the form '.SUFFIX', leaving the
     basename.

'e'
     Remove all but the trailing suffix.

'p'
     Print the new command but do not execute it.

's/OLD/NEW/'
     Substitute NEW for the first occurrence of OLD in the event line.
     Any delimiter may be used in place of '/'.  The delimiter may be
     quoted in OLD and NEW with a single backslash.  If '&' appears in
     NEW, it is replaced by OLD.  A single backslash will quote the '&'.
     The final delimiter is optional if it is the last character on the
     input line.

'&'
     Repeat the previous substitution.

'g'
'a'
     Cause changes to be applied over the entire event line.  Used in
     conjunction with 's', as in 'gs/OLD/NEW/', or with '&'.

'G'
     Apply the following 's' modifier once to each word in the event.


File: gdb.info,  Node: In Memoriam,  Next: Formatting Documentation,  Prev: Using History Interactively,  Up: Top

Appendix A In Memoriam
**********************

The GDB project mourns the loss of the following long-time contributors:

'Fred Fish'
     Fred was a long-standing contributor to GDB (1991-2006), and to
     Free Software in general.  Outside of GDB, he was known in the
     Amiga world for his series of Fish Disks, and the GeekGadget
     project.

'Michael Snyder'
     Michael was one of the Global Maintainers of the GDB project, with
     contributions recorded as early as 1996, until 2011.  In addition
     to his day to day participation, he was a large driving force
     behind adding Reverse Debugging to GDB.

   Beyond their technical contributions to the project, they were also
enjoyable members of the Free Software Community.  We will miss them.


File: gdb.info,  Node: Formatting Documentation,  Next: Installing GDB,  Prev: In Memoriam,  Up: Top

Appendix B Formatting Documentation
***********************************

The GDB 4 release includes an already-formatted reference card, ready
for printing with PostScript or Ghostscript, in the 'gdb' subdirectory
of the main source directory(1).  If you can use PostScript or
Ghostscript with your printer, you can print the reference card
immediately with 'refcard.ps'.

   The release also includes the source for the reference card.  You can
format it, using TeX, by typing:

     make refcard.dvi

   The GDB reference card is designed to print in "landscape" mode on US
"letter" size paper; that is, on a sheet 11 inches wide by 8.5 inches
high.  You will need to specify this form of printing as an option to
your DVI output program.

   All the documentation for GDB comes as part of the machine-readable
distribution.  The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual.  You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or 'texi2roff') to typeset the printed version.

   GDB includes an already formatted copy of the on-line Info version of
this manual in the 'gdb' subdirectory.  The main Info file is
'gdb-8.2.50.20190219-git/gdb/gdb.info', and it refers to subordinate
files matching 'gdb.info*' in the same directory.  If necessary, you can
print out these files, or read them with any editor; but they are easier
to read using the 'info' subsystem in GNU Emacs or the standalone 'info'
program, available as part of the GNU Texinfo distribution.

   If you want to format these Info files yourself, you need one of the
Info formatting programs, such as 'texinfo-format-buffer' or 'makeinfo'.

   If you have 'makeinfo' installed, and are in the top level GDB source
directory ('gdb-8.2.50.20190219-git', in the case of version
8.2.50.20190219-git), you can make the Info file by typing:

     cd gdb
     make gdb.info

   If you want to typeset and print copies of this manual, you need TeX,
a program to print its DVI output files, and 'texinfo.tex', the Texinfo
definitions file.

   TeX is a typesetting program; it does not print files directly, but
produces output files called DVI files.  To print a typeset document,
you need a program to print DVI files.  If your system has TeX
installed, chances are it has such a program.  The precise command to
use depends on your system; 'lpr -d' is common; another (for PostScript
devices) is 'dvips'.  The DVI print command may require a file name
without any extension or a '.dvi' extension.

   TeX also requires a macro definitions file called 'texinfo.tex'.
This file tells TeX how to typeset a document written in Texinfo format.
On its own, TeX cannot either read or typeset a Texinfo file.
'texinfo.tex' is distributed with GDB and is located in the
'gdb-VERSION-NUMBER/texinfo' directory.

   If you have TeX and a DVI printer program installed, you can typeset
and print this manual.  First switch to the 'gdb' subdirectory of the
main source directory (for example, to 'gdb-8.2.50.20190219-git/gdb')
and type:

     make gdb.dvi

   Then give 'gdb.dvi' to your DVI printing program.

   ---------- Footnotes ----------

   (1) In 'gdb-8.2.50.20190219-git/gdb/refcard.ps' of the version
8.2.50.20190219-git release.


File: gdb.info,  Node: Installing GDB,  Next: Maintenance Commands,  Prev: Formatting Documentation,  Up: Top

Appendix C Installing GDB
*************************

* Menu:

* Requirements::                Requirements for building GDB
* Running Configure::           Invoking the GDB 'configure' script
* Separate Objdir::             Compiling GDB in another directory
* Config Names::                Specifying names for hosts and targets
* Configure Options::           Summary of options for configure
* System-wide configuration::   Having a system-wide init file


File: gdb.info,  Node: Requirements,  Next: Running Configure,  Up: Installing GDB

C.1 Requirements for Building GDB
=================================

Building GDB requires various tools and packages to be available.  Other
packages will be used only if they are found.

Tools/Packages Necessary for Building GDB
=========================================

C++11 compiler
     GDB is written in C++11.  It should be buildable with any recent
     C++11 compiler, e.g. GCC.

GNU make
     GDB's build system relies on features only found in the GNU make
     program.  Other variants of 'make' will not work.

Tools/Packages Optional for Building GDB
========================================

Expat
     GDB can use the Expat XML parsing library.  This library may be
     included with your operating system distribution; if it is not, you
     can get the latest version from <http://expat.sourceforge.net>.
     The 'configure' script will search for this library in several
     standard locations; if it is installed in an unusual path, you can
     use the '--with-libexpat-prefix' option to specify its location.

     Expat is used for:

        * Remote protocol memory maps (*note Memory Map Format::)
        * Target descriptions (*note Target Descriptions::)
        * Remote shared library lists (*Note Library List Format::, or
          alternatively *note Library List Format for SVR4 Targets::)
        * MS-Windows shared libraries (*note Shared Libraries::)
        * Traceframe info (*note Traceframe Info Format::)
        * Branch trace (*note Branch Trace Format::, *note Branch Trace
          Configuration Format::)

Guile
     GDB can be scripted using GNU Guile.  *Note Guile::.  By default,
     GDB will be compiled if the Guile libraries are installed and are
     found by 'configure'.  You can use the '--with-guile' option to
     request Guile, and pass either the Guile version number or the file
     name of the relevant 'pkg-config' program to choose a particular
     version of Guile.

iconv
     GDB's features related to character sets (*note Character Sets::)
     require a functioning 'iconv' implementation.  If you are on a GNU
     system, then this is provided by the GNU C Library.  Some other
     systems also provide a working 'iconv'.

     If GDB is using the 'iconv' program which is installed in a
     non-standard place, you will need to tell GDB where to find it.
     This is done with '--with-iconv-bin' which specifies the directory
     that contains the 'iconv' program.  This program is run in order to
     make a list of the available character sets.

     On systems without 'iconv', you can install GNU Libiconv.  If
     Libiconv is installed in a standard place, GDB will automatically
     use it if it is needed.  If you have previously installed Libiconv
     in a non-standard place, you can use the '--with-libiconv-prefix'
     option to 'configure'.

     GDB's top-level 'configure' and 'Makefile' will arrange to build
     Libiconv if a directory named 'libiconv' appears in the top-most
     source directory.  If Libiconv is built this way, and if the
     operating system does not provide a suitable 'iconv'
     implementation, then the just-built library will automatically be
     used by GDB.  One easy way to set this up is to download GNU
     Libiconv, unpack it inside the top-level directory of the GDB
     source tree, and then rename the directory holding the Libiconv
     source code to 'libiconv'.

lzma
     GDB can support debugging sections that are compressed with the
     LZMA library.  *Note MiniDebugInfo::.  If this library is not
     included with your operating system, you can find it in the xz
     package at <http://tukaani.org/xz/>.  If the LZMA library is
     available in the usual place, then the 'configure' script will use
     it automatically.  If it is installed in an unusual path, you can
     use the '--with-lzma-prefix' option to specify its location.

MPFR
     GDB can use the GNU MPFR multiple-precision floating-point library.
     This library may be included with your operating system
     distribution; if it is not, you can get the latest version from
     <http://www.mpfr.org>.  The 'configure' script will search for this
     library in several standard locations; if it is installed in an
     unusual path, you can use the '--with-libmpfr-prefix' option to
     specify its location.

     GNU MPFR is used to emulate target floating-point arithmetic during
     expression evaluation when the target uses different floating-point
     formats than the host.  If GNU MPFR it is not available, GDB will
     fall back to using host floating-point arithmetic.

Python
     GDB can be scripted using Python language.  *Note Python::.  By
     default, GDB will be compiled if the Python libraries are installed
     and are found by 'configure'.  You can use the '--with-python'
     option to request Python, and pass either the file name of the
     relevant 'python' executable, or the name of the directory in which
     Python is installed, to choose a particular installation of Python.

zlib
     GDB will use the 'zlib' library, if available, to read compressed
     debug sections.  Some linkers, such as GNU gold, are capable of
     producing binaries with compressed debug sections.  If GDB is
     compiled with 'zlib', it will be able to read the debug information
     in such binaries.

     The 'zlib' library is likely included with your operating system
     distribution; if it is not, you can get the latest version from
     <http://zlib.net>.


File: gdb.info,  Node: Running Configure,  Next: Separate Objdir,  Prev: Requirements,  Up: Installing GDB

C.2 Invoking the GDB 'configure' Script
=======================================

GDB comes with a 'configure' script that automates the process of
preparing GDB for installation; you can then use 'make' to build the
'gdb' program.

   The GDB distribution includes all the source code you need for GDB in
a single directory, whose name is usually composed by appending the
version number to 'gdb'.

   For example, the GDB version 8.2.50.20190219-git distribution is in
the 'gdb-8.2.50.20190219-git' directory.  That directory contains:

'gdb-8.2.50.20190219-git/configure (and supporting files)'
     script for configuring GDB and all its supporting libraries

'gdb-8.2.50.20190219-git/gdb'
     the source specific to GDB itself

'gdb-8.2.50.20190219-git/bfd'
     source for the Binary File Descriptor library

'gdb-8.2.50.20190219-git/include'
     GNU include files

'gdb-8.2.50.20190219-git/libiberty'
     source for the '-liberty' free software library

'gdb-8.2.50.20190219-git/opcodes'
     source for the library of opcode tables and disassemblers

'gdb-8.2.50.20190219-git/readline'
     source for the GNU command-line interface

   There may be other subdirectories as well.

   The simplest way to configure and build GDB is to run 'configure'
from the 'gdb-VERSION-NUMBER' source directory, which in this example is
the 'gdb-8.2.50.20190219-git' directory.

   First switch to the 'gdb-VERSION-NUMBER' source directory if you are
not already in it; then run 'configure'.  Pass the identifier for the
platform on which GDB will run as an argument.

   For example:

     cd gdb-8.2.50.20190219-git
     ./configure
     make

   Running 'configure' and then running 'make' builds the included
supporting libraries, then 'gdb' itself.  The configured source files,
and the binaries, are left in the corresponding source directories.

   'configure' is a Bourne-shell ('/bin/sh') script; if your system does
not recognize this automatically when you run a different shell, you may
need to run 'sh' on it explicitly:

     sh configure

   You should run the 'configure' script from the top directory in the
source tree, the 'gdb-VERSION-NUMBER' directory.  If you run 'configure'
from one of the subdirectories, you will configure only that
subdirectory.  That is usually not what you want.  In particular, if you
run the first 'configure' from the 'gdb' subdirectory of the
'gdb-VERSION-NUMBER' directory, you will omit the configuration of
'bfd', 'readline', and other sibling directories of the 'gdb'
subdirectory.  This leads to build errors about missing include files
such as 'bfd/bfd.h'.

   You can install 'GDB' anywhere.  The best way to do this is to pass
the '--prefix' option to 'configure', and then install it with 'make
install'.


File: gdb.info,  Node: Separate Objdir,  Next: Config Names,  Prev: Running Configure,  Up: Installing GDB

C.3 Compiling GDB in Another Directory
======================================

If you want to run GDB versions for several host or target machines, you
need a different 'gdb' compiled for each combination of host and target.
'configure' is designed to make this easy by allowing you to generate
each configuration in a separate subdirectory, rather than in the source
directory.  If your 'make' program handles the 'VPATH' feature (GNU
'make' does), running 'make' in each of these directories builds the
'gdb' program specified there.

   To build 'gdb' in a separate directory, run 'configure' with the
'--srcdir' option to specify where to find the source.  (You also need
to specify a path to find 'configure' itself from your working
directory.  If the path to 'configure' would be the same as the argument
to '--srcdir', you can leave out the '--srcdir' option; it is assumed.)

   For example, with version 8.2.50.20190219-git, you can build GDB in a
separate directory for a Sun 4 like this:

     cd gdb-8.2.50.20190219-git
     mkdir ../gdb-sun4
     cd ../gdb-sun4
     ../gdb-8.2.50.20190219-git/configure
     make

   When 'configure' builds a configuration using a remote source
directory, it creates a tree for the binaries with the same structure
(and using the same names) as the tree under the source directory.  In
the example, you'd find the Sun 4 library 'libiberty.a' in the directory
'gdb-sun4/libiberty', and GDB itself in 'gdb-sun4/gdb'.

   Make sure that your path to the 'configure' script has just one
instance of 'gdb' in it.  If your path to 'configure' looks like
'../gdb-8.2.50.20190219-git/gdb/configure', you are configuring only one
subdirectory of GDB, not the whole package.  This leads to build errors
about missing include files such as 'bfd/bfd.h'.

   One popular reason to build several GDB configurations in separate
directories is to configure GDB for cross-compiling (where GDB runs on
one machine--the "host"--while debugging programs that run on another
machine--the "target").  You specify a cross-debugging target by giving
the '--target=TARGET' option to 'configure'.

   When you run 'make' to build a program or library, you must run it in
a configured directory--whatever directory you were in when you called
'configure' (or one of its subdirectories).

   The 'Makefile' that 'configure' generates in each source directory
also runs recursively.  If you type 'make' in a source directory such as
'gdb-8.2.50.20190219-git' (or in a separate configured directory
configured with '--srcdir=DIRNAME/gdb-8.2.50.20190219-git'), you will
build all the required libraries, and then build GDB.

   When you have multiple hosts or targets configured in separate
directories, you can run 'make' on them in parallel (for example, if
they are NFS-mounted on each of the hosts); they will not interfere with
each other.


File: gdb.info,  Node: Config Names,  Next: Configure Options,  Prev: Separate Objdir,  Up: Installing GDB

C.4 Specifying Names for Hosts and Targets
==========================================

The specifications used for hosts and targets in the 'configure' script
are based on a three-part naming scheme, but some short predefined
aliases are also supported.  The full naming scheme encodes three pieces
of information in the following pattern:

     ARCHITECTURE-VENDOR-OS

   For example, you can use the alias 'sun4' as a HOST argument, or as
the value for TARGET in a '--target=TARGET' option.  The equivalent full
name is 'sparc-sun-sunos4'.

   The 'configure' script accompanying GDB does not provide any query
facility to list all supported host and target names or aliases.
'configure' calls the Bourne shell script 'config.sub' to map
abbreviations to full names; you can read the script, if you wish, or
you can use it to test your guesses on abbreviations--for example:

     % sh config.sub i386-linux
     i386-pc-linux-gnu
     % sh config.sub alpha-linux
     alpha-unknown-linux-gnu
     % sh config.sub hp9k700
     hppa1.1-hp-hpux
     % sh config.sub sun4
     sparc-sun-sunos4.1.1
     % sh config.sub sun3
     m68k-sun-sunos4.1.1
     % sh config.sub i986v
     Invalid configuration `i986v': machine `i986v' not recognized

'config.sub' is also distributed in the GDB source directory
('gdb-8.2.50.20190219-git', for version 8.2.50.20190219-git).


File: gdb.info,  Node: Configure Options,  Next: System-wide configuration,  Prev: Config Names,  Up: Installing GDB

C.5 'configure' Options
=======================

Here is a summary of the 'configure' options and arguments that are most
often useful for building GDB.  'configure' also has several other
options not listed here.  *note (autoconf.info)Running configure
scripts::, for a full explanation of 'configure'.

     configure [--help]
               [--prefix=DIR]
               [--exec-prefix=DIR]
               [--srcdir=DIRNAME]
               [--target=TARGET]

You may introduce options with a single '-' rather than '--' if you
prefer; but you may abbreviate option names if you use '--'.

'--help'
     Display a quick summary of how to invoke 'configure'.

'--prefix=DIR'
     Configure the source to install programs and files under directory
     'DIR'.

'--exec-prefix=DIR'
     Configure the source to install programs under directory 'DIR'.

'--srcdir=DIRNAME'
     Use this option to make configurations in directories separate from
     the GDB source directories.  Among other things, you can use this
     to build (or maintain) several configurations simultaneously, in
     separate directories.  'configure' writes configuration-specific
     files in the current directory, but arranges for them to use the
     source in the directory DIRNAME.  'configure' creates directories
     under the working directory in parallel to the source directories
     below DIRNAME.

'--target=TARGET'
     Configure GDB for cross-debugging programs running on the specified
     TARGET.  Without this option, GDB is configured to debug programs
     that run on the same machine (HOST) as GDB itself.

     There is no convenient way to generate a list of all available
     targets.  Also see the '--enable-targets' option, below.

   There are many other options that are specific to GDB.  This lists
just the most common ones; there are some very specialized options not
described here.

'--enable-targets=[TARGET]...'
'--enable-targets=all'
     Configure GDB for cross-debugging programs running on the specified
     list of targets.  The special value 'all' configures GDB for
     debugging programs running on any target it supports.

'--with-gdb-datadir=PATH'
     Set the GDB-specific data directory.  GDB will look here for
     certain supporting files or scripts.  This defaults to the 'gdb'
     subdirectory of 'datadi' (which can be set using '--datadir').

'--with-relocated-sources=DIR'
     Sets up the default source path substitution rule so that directory
     names recorded in debug information will be automatically adjusted
     for any directory under DIR.  DIR should be a subdirectory of GDB's
     configured prefix, the one mentioned in the '--prefix' or
     '--exec-prefix' options to configure.  This option is useful if GDB
     is supposed to be moved to a different place after it is built.

'--enable-64-bit-bfd'
     Enable 64-bit support in BFD on 32-bit hosts.

'--disable-gdbmi'
     Build GDB without the GDB/MI machine interface (*note GDB/MI::).

'--enable-tui'
     Build GDB with the text-mode full-screen user interface (TUI).
     Requires a curses library (ncurses and cursesX are also supported).

'--with-curses'
     Use the curses library instead of the termcap library, for
     text-mode terminal operations.

'--with-libunwind-ia64'
     Use the libunwind library for unwinding function call stack on ia64
     target platforms.  See http://www.nongnu.org/libunwind/index.html
     for details.

'--with-system-readline'
     Use the readline library installed on the host, rather than the
     library supplied as part of GDB.

'--with-system-zlib'
     Use the zlib library installed on the host, rather than the library
     supplied as part of GDB.

'--with-expat'
     Build GDB with Expat, a library for XML parsing.  (Done by default
     if libexpat is installed and found at configure time.)  This
     library is used to read XML files supplied with GDB.  If it is
     unavailable, some features, such as remote protocol memory maps,
     target descriptions, and shared library lists, that are based on
     XML files, will not be available in GDB.  If your host does not
     have libexpat installed, you can get the latest version from
     'http://expat.sourceforge.net'.

'--with-libiconv-prefix[=DIR]'

     Build GDB with GNU libiconv, a character set encoding conversion
     library.  This is not done by default, as on GNU systems the
     'iconv' that is built in to the C library is sufficient.  If your
     host does not have a working 'iconv', you can get the latest
     version of GNU iconv from 'https://www.gnu.org/software/libiconv/'.

     GDB's build system also supports building GNU libiconv as part of
     the overall build.  *Note Requirements::.

'--with-lzma'
     Build GDB with LZMA, a compression library.  (Done by default if
     liblzma is installed and found at configure time.)  LZMA is used by
     GDB's "mini debuginfo" feature, which is only useful on platforms
     using the ELF object file format.  If your host does not have
     liblzma installed, you can get the latest version from
     'https://tukaani.org/xz/'.

'--with-mpfr'
     Build GDB with GNU MPFR, a library for multiple-precision
     floating-point computation with correct rounding.  (Done by default
     if GNU MPFR is installed and found at configure time.)  This
     library is used to emulate target floating-point arithmetic during
     expression evaluation when the target uses different floating-point
     formats than the host.  If GNU MPFR is not available, GDB will fall
     back to using host floating-point arithmetic.  If your host does
     not have GNU MPFR installed, you can get the latest version from
     'http://www.mpfr.org'.

'--with-python[=PYTHON]'
     Build GDB with Python scripting support.  (Done by default if
     libpython is present and found at configure time.)  Python makes
     GDB scripting much more powerful than the restricted CLI scripting
     language.  If your host does not have Python installed, you can
     find it on 'http://www.python.org/download/'.  The oldest version
     of Python supported by GDB is 2.4.  The optional argument PYTHON is
     used to find the Python headers and libraries.  It can be either
     the name of a Python executable, or the name of the directory in
     which Python is installed.

'--with-guile[=GUILE]''
     Build GDB with GNU Guile scripting support.  (Done by default if
     libguile is present and found at configure time.)  If your host
     does not have Guile installed, you can find it at
     'https://www.gnu.org/software/guile/'.  The optional argument GUILE
     can be a version number, which will cause 'configure' to try to use
     that version of Guile; or the file name of a 'pkg-config'
     executable, which will be queried to find the information needed to
     compile and link against Guile.

'--without-included-regex'
     Don't use the regex library included with GDB (as part of the
     libiberty library).  This is the default on hosts with version 2 of
     the GNU C library.

'--with-sysroot=DIR'
     Use DIR as the default system root directory for libraries whose
     file names begin with '/lib'' or '/usr/lib''.  (The value of DIR
     can be modified at run time by using the 'set sysroot' command.)
     If DIR is under the GDB configured prefix (set with '--prefix' or
     '--exec-prefix options', the default system root will be
     automatically adjusted if and when GDB is moved to a different
     location.

'--with-system-gdbinit=FILE'
     Configure GDB to automatically load a system-wide init file.  FILE
     should be an absolute file name.  If FILE is in a directory under
     the configured prefix, and GDB is moved to another location after
     being built, the location of the system-wide init file will be
     adjusted accordingly.

'--enable-build-warnings'
     When building the GDB sources, ask the compiler to warn about any
     code which looks even vaguely suspicious.  It passes many different
     warning flags, depending on the exact version of the compiler you
     are using.

'--enable-werror'
     Treat compiler warnings as werrors.  It adds the '-Werror' flag to
     the compiler, which will fail the compilation if the compiler
     outputs any warning messages.

'--enable-ubsan'
     Enable the GCC undefined behavior sanitizer.  This is disabled by
     default, but passing '--enable-ubsan=yes' or '--enable-ubsan=auto'
     to 'configure' will enable it.  The undefined behavior sanitizer
     checks for C++ undefined behavior.  It has a performance cost, so
     if you are looking at GDB's performance, you should disable it.
     The undefined behavior sanitizer was first introduced in GCC 4.9.


File: gdb.info,  Node: System-wide configuration,  Prev: Configure Options,  Up: Installing GDB

C.6 System-wide configuration and settings
==========================================

GDB can be configured to have a system-wide init file; this file will be
read and executed at startup (*note What GDB does during startup:
Startup.).

   Here is the corresponding configure option:

'--with-system-gdbinit=FILE'
     Specify that the default location of the system-wide init file is
     FILE.

   If GDB has been configured with the option '--prefix=$prefix', it may
be subject to relocation.  Two possible cases:

   * If the default location of this init file contains '$prefix', it
     will be subject to relocation.  Suppose that the configure options
     are '--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit';
     if GDB is moved from '$prefix' to '$install', the system init file
     is looked for as '$install/etc/gdbinit' instead of
     '$prefix/etc/gdbinit'.

   * By contrast, if the default location does not contain the prefix,
     it will not be relocated.  E.g. if GDB has been configured with
     '--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit',
     then GDB will always look for '/usr/share/gdb/gdbinit', wherever
     GDB is installed.

   If the configured location of the system-wide init file (as given by
the '--with-system-gdbinit' option at configure time) is in the
data-directory (as specified by '--with-gdb-datadir' at configure time)
or in one of its subdirectories, then GDB will look for the system-wide
init file in the directory specified by the '--data-directory'
command-line option.  Note that the system-wide init file is only read
once, during GDB initialization.  If the data-directory is changed after
GDB has started with the 'set data-directory' command, the file will not
be reread.

* Menu:

* System-wide Configuration Scripts::  Installed System-wide Configuration Scripts


File: gdb.info,  Node: System-wide Configuration Scripts,  Up: System-wide configuration

C.6.1 Installed System-wide Configuration Scripts
-------------------------------------------------

The 'system-gdbinit' directory, located inside the data-directory (as
specified by '--with-gdb-datadir' at configure time) contains a number
of scripts which can be used as system-wide init files.  To
automatically source those scripts at startup, GDB should be configured
with '--with-system-gdbinit'.  Otherwise, any user should be able to
source them by hand as needed.

   The following scripts are currently available:

   * 'elinos.py' This script is useful when debugging a program on an
     ELinOS target.  It takes advantage of the environment variables
     defined in a standard ELinOS environment in order to determine the
     location of the system shared libraries, and then sets the
     'solib-absolute-prefix' and 'solib-search-path' variables
     appropriately.

   * 'wrs-linux.py' This script is useful when debugging a program on a
     target running Wind River Linux.  It expects the 'ENV_PREFIX' to be
     set to the host-side sysroot used by the target system.


File: gdb.info,  Node: Maintenance Commands,  Next: Remote Protocol,  Prev: Installing GDB,  Up: Top

Appendix D Maintenance Commands
*******************************

In addition to commands intended for GDB users, GDB includes a number of
commands intended for GDB developers, that are not documented elsewhere
in this manual.  These commands are provided here for reference.  (For
commands that turn on debugging messages, see *note Debugging Output::.)

'maint agent [-at LOCATION,] EXPRESSION'
'maint agent-eval [-at LOCATION,] EXPRESSION'
     Translate the given EXPRESSION into remote agent bytecodes.  This
     command is useful for debugging the Agent Expression mechanism
     (*note Agent Expressions::).  The 'agent' version produces an
     expression useful for data collection, such as by tracepoints,
     while 'maint agent-eval' produces an expression that evaluates
     directly to a result.  For instance, a collection expression for
     'globa + globb' will include bytecodes to record four bytes of
     memory at each of the addresses of 'globa' and 'globb', while
     discarding the result of the addition, while an evaluation
     expression will do the addition and return the sum.  If '-at' is
     given, generate remote agent bytecode for LOCATION.  If not,
     generate remote agent bytecode for current frame PC address.

'maint agent-printf FORMAT,EXPR,...'
     Translate the given format string and list of argument expressions
     into remote agent bytecodes and display them as a disassembled
     list.  This command is useful for debugging the agent version of
     dynamic printf (*note Dynamic Printf::).

'maint info breakpoints'
     Using the same format as 'info breakpoints', display both the
     breakpoints you've set explicitly, and those GDB is using for
     internal purposes.  Internal breakpoints are shown with negative
     breakpoint numbers.  The type column identifies what kind of
     breakpoint is shown:

     'breakpoint'
          Normal, explicitly set breakpoint.

     'watchpoint'
          Normal, explicitly set watchpoint.

     'longjmp'
          Internal breakpoint, used to handle correctly stepping through
          'longjmp' calls.

     'longjmp resume'
          Internal breakpoint at the target of a 'longjmp'.

     'until'
          Temporary internal breakpoint used by the GDB 'until' command.

     'finish'
          Temporary internal breakpoint used by the GDB 'finish'
          command.

     'shlib events'
          Shared library events.

'maint info btrace'
     Pint information about raw branch tracing data.

'maint btrace packet-history'
     Print the raw branch trace packets that are used to compute the
     execution history for the 'record btrace' command.  Both the
     information and the format in which it is printed depend on the
     btrace recording format.

     'bts'
          For the BTS recording format, print a list of blocks of
          sequential code.  For each block, the following information is
          printed:

          Block number
               Newer blocks have higher numbers.  The oldest block has
               number zero.
          Lowest 'PC'
          Highest 'PC'

     'pt'
          For the Intel Processor Trace recording format, print a list
          of Intel Processor Trace packets.  For each packet, the
          following information is printed:

          Packet number
               Newer packets have higher numbers.  The oldest packet has
               number zero.
          Trace offset
               The packet's offset in the trace stream.
          Packet opcode and payload

'maint btrace clear-packet-history'
     Discards the cached packet history printed by the 'maint btrace
     packet-history' command.  The history will be computed again when
     needed.

'maint btrace clear'
     Discard the branch trace data.  The data will be fetched anew and
     the branch trace will be recomputed when needed.

     This implicitly truncates the branch trace to a single branch trace
     buffer.  When updating branch trace incrementally, the branch trace
     available to GDB may be bigger than a single branch trace buffer.

'maint set btrace pt skip-pad'
'maint show btrace pt skip-pad'
     Control whether GDB will skip PAD packets when computing the packet
     history.

'set displaced-stepping'
'show displaced-stepping'
     Control whether or not GDB will do "displaced stepping" if the
     target supports it.  Displaced stepping is a way to single-step
     over breakpoints without removing them from the inferior, by
     executing an out-of-line copy of the instruction that was
     originally at the breakpoint location.  It is also known as
     out-of-line single-stepping.

     'set displaced-stepping on'
          If the target architecture supports it, GDB will use displaced
          stepping to step over breakpoints.

     'set displaced-stepping off'
          GDB will not use displaced stepping to step over breakpoints,
          even if such is supported by the target architecture.

     'set displaced-stepping auto'
          This is the default mode.  GDB will use displaced stepping
          only if non-stop mode is active (*note Non-Stop Mode::) and
          the target architecture supports displaced stepping.

'maint check-psymtabs'
     Check the consistency of currently expanded psymtabs versus
     symtabs.  Use this to check, for example, whether a symbol is in
     one but not the other.

'maint check-symtabs'
     Check the consistency of currently expanded symtabs.

'maint expand-symtabs [REGEXP]'
     Expand symbol tables.  If REGEXP is specified, only expand symbol
     tables for file names matching REGEXP.

'maint set catch-demangler-crashes [on|off]'
'maint show catch-demangler-crashes'
     Control whether GDB should attempt to catch crashes in the symbol
     name demangler.  The default is to attempt to catch crashes.  If
     enabled, the first time a crash is caught, a core file is created,
     the offending symbol is displayed and the user is presented with
     the option to terminate the current session.

'maint cplus first_component NAME'
     Print the first C++ class/namespace component of NAME.

'maint cplus namespace'
     Print the list of possible C++ namespaces.

'maint deprecate COMMAND [REPLACEMENT]'
'maint undeprecate COMMAND'
     Deprecate or undeprecate the named COMMAND.  Deprecated commands
     cause GDB to issue a warning when you use them.  The optional
     argument REPLACEMENT says which newer command should be used in
     favor of the deprecated one; if it is given, GDB will mention the
     replacement as part of the warning.

'maint dump-me'
     Cause a fatal signal in the debugger and force it to dump its core.
     This is supported only on systems which support aborting a program
     with the 'SIGQUIT' signal.

'maint internal-error [MESSAGE-TEXT]'
'maint internal-warning [MESSAGE-TEXT]'
'maint demangler-warning [MESSAGE-TEXT]'

     Cause GDB to call the internal function 'internal_error',
     'internal_warning' or 'demangler_warning' and hence behave as
     though an internal problem has been detected.  In addition to
     reporting the internal problem, these functions give the user the
     opportunity to either quit GDB or (for 'internal_error' and
     'internal_warning') create a core file of the current GDB session.

     These commands take an optional parameter MESSAGE-TEXT that is used
     as the text of the error or warning message.

     Here's an example of using 'internal-error':

          (gdb) maint internal-error testing, 1, 2
          .../maint.c:121: internal-error: testing, 1, 2
          A problem internal to GDB has been detected.  Further
          debugging may prove unreliable.
          Quit this debugging session? (y or n) n
          Create a core file? (y or n) n
          (gdb)

'maint set internal-error ACTION [ask|yes|no]'
'maint show internal-error ACTION'
'maint set internal-warning ACTION [ask|yes|no]'
'maint show internal-warning ACTION'
'maint set demangler-warning ACTION [ask|yes|no]'
'maint show demangler-warning ACTION'
     When GDB reports an internal problem (error or warning) it gives
     the user the opportunity to both quit GDB and create a core file of
     the current GDB session.  These commands let you override the
     default behaviour for each particular ACTION, described in the
     table below.

     'quit'
          You can specify that GDB should always (yes) or never (no)
          quit.  The default is to ask the user what to do.

     'corefile'
          You can specify that GDB should always (yes) or never (no)
          create a core file.  The default is to ask the user what to
          do.  Note that there is no 'corefile' option for
          'demangler-warning': demangler warnings always create a core
          file and this cannot be disabled.

'maint packet TEXT'
     If GDB is talking to an inferior via the serial protocol, then this
     command sends the string TEXT to the inferior, and displays the
     response packet.  GDB supplies the initial '$' character, the
     terminating '#' character, and the checksum.

'maint print architecture [FILE]'
     Print the entire architecture configuration.  The optional argument
     FILE names the file where the output goes.

'maint print c-tdesc'
     Print the target description (*note Target Descriptions::) as a C
     source file.  By default, the target description is for the current
     target, but if the optional argument FILE is provided, that file is
     used to produce the description.  The FILE should be an XML
     document, of the form described in *note Target Description
     Format::.  The created source file is built into GDB when GDB is
     built again.  This command is used by developers after they add or
     modify XML target descriptions.

'maint check xml-descriptions DIR'
     Check that the target descriptions dynamically created by GDB equal
     the descriptions created from XML files found in DIR.

'maint check libthread-db'
     Run integrity checks on the current inferior's thread debugging
     library.  This exercises all 'libthread_db' functionality used by
     GDB on GNU/Linux systems, and by extension also exercises the
     'proc_service' functions provided by GDB that 'libthread_db' uses.
     Note that parts of the test may be skipped on some platforms when
     debugging core files.

'maint print dummy-frames'
     Prints the contents of GDB's internal dummy-frame stack.

          (gdb) b add
          ...
          (gdb) print add(2,3)
          Breakpoint 2, add (a=2, b=3) at ...
          58	  return (a + b);
          The program being debugged stopped while in a function called from GDB.
          ...
          (gdb) maint print dummy-frames
          0xa8206d8: id={stack=0xbfffe734,code=0xbfffe73f,!special}, ptid=process 9353
          (gdb)

     Takes an optional file parameter.

'maint print registers [FILE]'
'maint print raw-registers [FILE]'
'maint print cooked-registers [FILE]'
'maint print register-groups [FILE]'
'maint print remote-registers [FILE]'
     Print GDB's internal register data structures.

     The command 'maint print raw-registers' includes the contents of
     the raw register cache; the command 'maint print cooked-registers'
     includes the (cooked) value of all registers, including registers
     which aren't available on the target nor visible to user; the
     command 'maint print register-groups' includes the groups that each
     register is a member of; and the command 'maint print
     remote-registers' includes the remote target's register numbers and
     offsets in the 'G' packets.

     These commands take an optional parameter, a file name to which to
     write the information.

'maint print reggroups [FILE]'
     Print GDB's internal register group data structures.  The optional
     argument FILE tells to what file to write the information.

     The register groups info looks like this:

          (gdb) maint print reggroups
           Group      Type
           general    user
           float      user
           all        user
           vector     user
           system     user
           save       internal
           restore    internal

'flushregs'
     This command forces GDB to flush its internal register cache.

'maint print objfiles [REGEXP]'
     Print a dump of all known object files.  If REGEXP is specified,
     only print object files whose names match REGEXP.  For each object
     file, this command prints its name, address in memory, and all of
     its psymtabs and symtabs.

'maint print user-registers'
     List all currently available "user registers".  User registers
     typically provide alternate names for actual hardware registers.
     They include the four "standard" registers '$fp', '$pc', '$sp', and
     '$ps'.  *Note standard registers::.  User registers can be used in
     expressions in the same way as the canonical register names, but
     only the latter are listed by the 'info registers' and 'maint print
     registers' commands.

'maint print section-scripts [REGEXP]'
     Print a dump of scripts specified in the '.debug_gdb_section'
     section.  If REGEXP is specified, only print scripts loaded by
     object files matching REGEXP.  For each script, this command prints
     its name as specified in the objfile, and the full path if known.
     *Note dotdebug_gdb_scripts section::.

'maint print statistics'
     This command prints, for each object file in the program, various
     data about that object file followed by the byte cache ("bcache")
     statistics for the object file.  The objfile data includes the
     number of minimal, partial, full, and stabs symbols, the number of
     types defined by the objfile, the number of as yet unexpanded psym
     tables, the number of line tables and string tables, and the amount
     of memory used by the various tables.  The bcache statistics
     include the counts, sizes, and counts of duplicates of all and
     unique objects, max, average, and median entry size, total memory
     used and its overhead and savings, and various measures of the hash
     table size and chain lengths.

'maint print target-stack'
     A "target" is an interface between the debugger and a particular
     kind of file or process.  Targets can be stacked in "strata", so
     that more than one target can potentially respond to a request.  In
     particular, memory accesses will walk down the stack of targets
     until they find a target that is interested in handling that
     particular address.

     This command prints a short description of each layer that was
     pushed on the "target stack", starting from the top layer down to
     the bottom one.

'maint print type EXPR'
     Print the type chain for a type specified by EXPR.  The argument
     can be either a type name or a symbol.  If it is a symbol, the type
     of that symbol is described.  The type chain produced by this
     command is a recursive definition of the data type as stored in
     GDB's data structures, including its flags and contained types.

'maint selftest [FILTER]'
     Run any self tests that were compiled in to GDB.  This will print a
     message showing how many tests were run, and how many failed.  If a
     FILTER is passed, only the tests with FILTER in their name will by
     ran.

'maint info selftests'
     List the selftests compiled in to GDB.

'maint set dwarf always-disassemble'
'maint show dwarf always-disassemble'
     Control the behavior of 'info address' when using DWARF debugging
     information.

     The default is 'off', which means that GDB should try to describe a
     variable's location in an easily readable format.  When 'on', GDB
     will instead display the DWARF location expression in an
     assembly-like format.  Note that some locations are too complex for
     GDB to describe simply; in this case you will always see the
     disassembly form.

     Here is an example of the resulting disassembly:

          (gdb) info addr argc
          Symbol "argc" is a complex DWARF expression:
               1: DW_OP_fbreg 0

     For more information on these expressions, see the DWARF standard
     (http://www.dwarfstd.org/).

'maint set dwarf max-cache-age'
'maint show dwarf max-cache-age'
     Control the DWARF compilation unit cache.

     In object files with inter-compilation-unit references, such as
     those produced by the GCC option '-feliminate-dwarf2-dups', the
     DWARF reader needs to frequently refer to previously read
     compilation units.  This setting controls how long a compilation
     unit will remain in the cache if it is not referenced.  A higher
     limit means that cached compilation units will be stored in memory
     longer, and more total memory will be used.  Setting it to zero
     disables caching, which will slow down GDB startup, but reduce
     memory consumption.

'maint set dwarf unwinders'
'maint show dwarf unwinders'
     Control use of the DWARF frame unwinders.

     Many targets that support DWARF debugging use GDB's DWARF frame
     unwinders to build the backtrace.  Many of these targets will also
     have a second mechanism for building the backtrace for use in cases
     where DWARF information is not available, this second mechanism is
     often an analysis of a function's prologue.

     In order to extend testing coverage of the second level stack
     unwinding mechanisms it is helpful to be able to disable the DWARF
     stack unwinders, this can be done with this switch.

     In normal use of GDB disabling the DWARF unwinders is not
     advisable, there are cases that are better handled through DWARF
     than prologue analysis, and the debug experience is likely to be
     better with the DWARF frame unwinders enabled.

     If DWARF frame unwinders are not supported for a particular target
     architecture, then enabling this flag does not cause them to be
     used.
'maint set profile'
'maint show profile'
     Control profiling of GDB.

     Profiling will be disabled until you use the 'maint set profile'
     command to enable it.  When you enable profiling, the system will
     begin collecting timing and execution count data; when you disable
     profiling or exit GDB, the results will be written to a log file.
     Remember that if you use profiling, GDB will overwrite the
     profiling log file (often called 'gmon.out').  If you have a record
     of important profiling data in a 'gmon.out' file, be sure to move
     it to a safe location.

     Configuring with '--enable-profiling' arranges for GDB to be
     compiled with the '-pg' compiler option.

'maint set show-debug-regs'
'maint show show-debug-regs'
     Control whether to show variables that mirror the hardware debug
     registers.  Use 'on' to enable, 'off' to disable.  If enabled, the
     debug registers values are shown when GDB inserts or removes a
     hardware breakpoint or watchpoint, and when the inferior triggers a
     hardware-assisted breakpoint or watchpoint.

'maint set show-all-tib'
'maint show show-all-tib'
     Control whether to show all non zero areas within a 1k block
     starting at thread local base, when using the 'info w32
     thread-information-block' command.

'maint set target-async'
'maint show target-async'
     This controls whether GDB targets operate in synchronous or
     asynchronous mode (*note Background Execution::).  Normally the
     default is asynchronous, if it is available; but this can be
     changed to more easily debug problems occurring only in synchronous
     mode.

'maint set target-non-stop'
'maint show target-non-stop'

     This controls whether GDB targets always operate in non-stop mode
     even if 'set non-stop' is 'off' (*note Non-Stop Mode::).  The
     default is 'auto', meaning non-stop mode is enabled if supported by
     the target.

     'maint set target-non-stop auto'
          This is the default mode.  GDB controls the target in non-stop
          mode if the target supports it.

     'maint set target-non-stop on'
          GDB controls the target in non-stop mode even if the target
          does not indicate support.

     'maint set target-non-stop off'
          GDB does not control the target in non-stop mode even if the
          target supports it.

'maint set per-command'
'maint show per-command'

     GDB can display the resources used by each command.  This is useful
     in debugging performance problems.

     'maint set per-command space [on|off]'
     'maint show per-command space'
          Enable or disable the printing of the memory used by GDB for
          each command.  If enabled, GDB will display how much memory
          each command took, following the command's own output.  This
          can also be requested by invoking GDB with the '--statistics'
          command-line switch (*note Mode Options::).

     'maint set per-command time [on|off]'
     'maint show per-command time'
          Enable or disable the printing of the execution time of GDB
          for each command.  If enabled, GDB will display how much time
          it took to execute each command, following the command's own
          output.  Both CPU time and wallclock time are printed.
          Printing both is useful when trying to determine whether the
          cost is CPU or, e.g., disk/network latency.  Note that the CPU
          time printed is for GDB only, it does not include the
          execution time of the inferior because there's no mechanism
          currently to compute how much time was spent by GDB and how
          much time was spent by the program been debugged.  This can
          also be requested by invoking GDB with the '--statistics'
          command-line switch (*note Mode Options::).

     'maint set per-command symtab [on|off]'
     'maint show per-command symtab'
          Enable or disable the printing of basic symbol table
          statistics for each command.  If enabled, GDB will display the
          following information:

            a. number of symbol tables
            b. number of primary symbol tables
            c. number of blocks in the blockvector

'maint set check-libthread-db [on|off]'
'maint show check-libthread-db'
     Control whether GDB should run integrity checks on inferior
     specific thread debugging libraries as they are loaded.  The
     default is not to perform such checks.  If any check fails GDB will
     unload the library and continue searching for a suitable candidate
     as described in *note set libthread-db-search-path::.  For more
     information about the tests, see *note maint check libthread-db::.

'maint space VALUE'
     An alias for 'maint set per-command space'.  A non-zero value
     enables it, zero disables it.

'maint time VALUE'
     An alias for 'maint set per-command time'.  A non-zero value
     enables it, zero disables it.

'maint translate-address [SECTION] ADDR'
     Find the symbol stored at the location specified by the address
     ADDR and an optional section name SECTION.  If found, GDB prints
     the name of the closest symbol and an offset from the symbol's
     location to the specified address.  This is similar to the 'info
     address' command (*note Symbols::), except that this command also
     allows to find symbols in other sections.

     If section was not specified, the section in which the symbol was
     found is also printed.  For dynamically linked executables, the
     name of executable or shared library containing the symbol is
     printed as well.

   The following command is useful for non-interactive invocations of
GDB, such as in the test suite.

'set watchdog NSEC'
     Set the maximum number of seconds GDB will wait for the target
     operation to finish.  If this time expires, GDB reports and error
     and the command is aborted.

'show watchdog'
     Show the current setting of the target wait timeout.


File: gdb.info,  Node: Remote Protocol,  Next: Agent Expressions,  Prev: Maintenance Commands,  Up: Top

Appendix E GDB Remote Serial Protocol
*************************************

* Menu:

* Overview::
* Packets::
* Stop Reply Packets::
* General Query Packets::
* Architecture-Specific Protocol Details::
* Tracepoint Packets::
* Host I/O Packets::
* Interrupts::
* Notification Packets::
* Remote Non-Stop::
* Packet Acknowledgment::
* Examples::
* File-I/O Remote Protocol Extension::
* Library List Format::
* Library List Format for SVR4 Targets::
* Memory Map Format::
* Thread List Format::
* Traceframe Info Format::
* Branch Trace Format::
* Branch Trace Configuration Format::


File: gdb.info,  Node: Overview,  Next: Packets,  Up: Remote Protocol

E.1 Overview
============

There may be occasions when you need to know something about the
protocol--for example, if there is only one serial port to your target
machine, you might want your program to do something special if it
recognizes a packet meant for GDB.

   In the examples below, '->' and '<-' are used to indicate transmitted
and received data, respectively.

   All GDB commands and responses (other than acknowledgments and
notifications, see *note Notification Packets::) are sent as a PACKET.
A PACKET is introduced with the character '$', the actual PACKET-DATA,
and the terminating character '#' followed by a two-digit CHECKSUM:

     $PACKET-DATA#CHECKSUM

The two-digit CHECKSUM is computed as the modulo 256 sum of all
characters between the leading '$' and the trailing '#' (an eight bit
unsigned checksum).

   Implementors should note that prior to GDB 5.0 the protocol
specification also included an optional two-digit SEQUENCE-ID:

     $SEQUENCE-ID:PACKET-DATA#CHECKSUM

That SEQUENCE-ID was appended to the acknowledgment.  GDB has never
output SEQUENCE-IDs.  Stubs that handle packets added since GDB 5.0 must
not accept SEQUENCE-ID.

   When either the host or the target machine receives a packet, the
first response expected is an acknowledgment: either '+' (to indicate
the package was received correctly) or '-' (to request retransmission):

     -> $PACKET-DATA#CHECKSUM
     <- +

   The '+'/'-' acknowledgments can be disabled once a connection is
established.  *Note Packet Acknowledgment::, for details.

   The host (GDB) sends COMMANDs, and the target (the debugging stub
incorporated in your program) sends a RESPONSE.  In the case of step and
continue COMMANDs, the response is only sent when the operation has
completed, and the target has again stopped all threads in all attached
processes.  This is the default all-stop mode behavior, but the remote
protocol also supports GDB's non-stop execution mode; see *note Remote
Non-Stop::, for details.

   PACKET-DATA consists of a sequence of characters with the exception
of '#' and '$' (see 'X' packet for additional exceptions).

   Fields within the packet should be separated using ',' ';' or ':'.
Except where otherwise noted all numbers are represented in HEX with
leading zeros suppressed.

   Implementors should note that prior to GDB 5.0, the character ':'
could not appear as the third character in a packet (as it would
potentially conflict with the SEQUENCE-ID).

   Binary data in most packets is encoded either as two hexadecimal
digits per byte of binary data.  This allowed the traditional remote
protocol to work over connections which were only seven-bit clean.  Some
packets designed more recently assume an eight-bit clean connection, and
use a more efficient encoding to send and receive binary data.

   The binary data representation uses '7d' (ASCII '}') as an escape
character.  Any escaped byte is transmitted as the escape character
followed by the original character XORed with '0x20'.  For example, the
byte '0x7d' would be transmitted as the two bytes '0x7d 0x5d'.  The
bytes '0x23' (ASCII '#'), '0x24' (ASCII '$'), and '0x7d' (ASCII '}')
must always be escaped.  Responses sent by the stub must also escape
'0x2a' (ASCII '*'), so that it is not interpreted as the start of a
run-length encoded sequence (described next).

   Response DATA can be run-length encoded to save space.  Run-length
encoding replaces runs of identical characters with one instance of the
repeated character, followed by a '*' and a repeat count.  The repeat
count is itself sent encoded, to avoid binary characters in DATA: a
value of N is sent as 'N+29'.  For a repeat count greater or equal to 3,
this produces a printable ASCII character, e.g. a space (ASCII code 32)
for a repeat count of 3.  (This is because run-length encoding starts to
win for counts 3 or more.)  Thus, for example, '0* ' is a run-length
encoding of "0000": the space character after '*' means repeat the
leading '0' '32 - 29 = 3' more times.

   The printable characters '#' and '$' or with a numeric value greater
than 126 must not be used.  Runs of six repeats ('#') or seven repeats
('$') can be expanded using a repeat count of only five ('"').  For
example, '00000000' can be encoded as '0*"00'.

   The error response returned for some packets includes a two character
error number.  That number is not well defined.

   For any COMMAND not supported by the stub, an empty response ('$#00')
should be returned.  That way it is possible to extend the protocol.  A
newer GDB can tell if a packet is supported based on that response.

   At a minimum, a stub is required to support the 'g' and 'G' commands
for register access, and the 'm' and 'M' commands for memory access.
Stubs that only control single-threaded targets can implement run
control with the 'c' (continue), and 's' (step) commands.  Stubs that
support multi-threading targets should support the 'vCont' command.  All
other commands are optional.


File: gdb.info,  Node: Packets,  Next: Stop Reply Packets,  Prev: Overview,  Up: Remote Protocol

E.2 Packets
===========

The following table provides a complete list of all currently defined
COMMANDs and their corresponding response DATA.  *Note File-I/O Remote
Protocol Extension::, for details about the File I/O extension of the
remote protocol.

   Each packet's description has a template showing the packet's overall
syntax, followed by an explanation of the packet's meaning.  We include
spaces in some of the templates for clarity; these are not part of the
packet's syntax.  No GDB packet uses spaces to separate its components.
For example, a template like 'foo BAR BAZ' describes a packet beginning
with the three ASCII bytes 'foo', followed by a BAR, followed directly
by a BAZ.  GDB does not transmit a space character between the 'foo' and
the BAR, or between the BAR and the BAZ.

   Several packets and replies include a THREAD-ID field to identify a
thread.  Normally these are positive numbers with a target-specific
interpretation, formatted as big-endian hex strings.  A THREAD-ID can
also be a literal '-1' to indicate all threads, or '0' to pick any
thread.

   In addition, the remote protocol supports a multiprocess feature in
which the THREAD-ID syntax is extended to optionally include both
process and thread ID fields, as 'pPID.TID'.  The PID (process) and TID
(thread) components each have the format described above: a positive
number with target-specific interpretation formatted as a big-endian hex
string, literal '-1' to indicate all processes or threads
(respectively), or '0' to indicate an arbitrary process or thread.
Specifying just a process, as 'pPID', is equivalent to 'pPID.-1'.  It is
an error to specify all processes but a specific thread, such as
'p-1.TID'.  Note that the 'p' prefix is _not_ used for those packets and
replies explicitly documented to include a process ID, rather than a
THREAD-ID.

   The multiprocess THREAD-ID syntax extensions are only used if both
GDB and the stub report support for the 'multiprocess' feature using
'qSupported'.  *Note multiprocess extensions::, for more information.

   Note that all packet forms beginning with an upper- or lower-case
letter, other than those described here, are reserved for future use.

   Here are the packet descriptions.

'!'
     Enable extended mode.  In extended mode, the remote server is made
     persistent.  The 'R' packet is used to restart the program being
     debugged.

     Reply:
     'OK'
          The remote target both supports and has enabled extended mode.

'?'
     Indicate the reason the target halted.  The reply is the same as
     for step and continue.  This packet has a special interpretation
     when the target is in non-stop mode; see *note Remote Non-Stop::.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'A ARGLEN,ARGNUM,ARG,...'
     Initialized 'argv[]' array passed into program.  ARGLEN specifies
     the number of bytes in the hex encoded byte stream ARG.  See
     'gdbserver' for more details.

     Reply:
     'OK'
          The arguments were set.
     'E NN'
          An error occurred.

'b BAUD'
     (Don't use this packet; its behavior is not well-defined.)  Change
     the serial line speed to BAUD.

     JTC: _When does the transport layer state change?  When it's
     received, or after the ACK is transmitted.  In either case, there
     are problems if the command or the acknowledgment packet is
     dropped._

     Stan: _If people really wanted to add something like this, and get
     it working for the first time, they ought to modify ser-unix.c to
     send some kind of out-of-band message to a specially-setup stub and
     have the switch happen "in between" packets, so that from remote
     protocol's point of view, nothing actually happened._

'B ADDR,MODE'
     Set (MODE is 'S') or clear (MODE is 'C') a breakpoint at ADDR.

     Don't use this packet.  Use the 'Z' and 'z' packets instead (*note
     insert breakpoint or watchpoint packet::).

'bc'
     Backward continue.  Execute the target system in reverse.  No
     parameter.  *Note Reverse Execution::, for more information.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'bs'
     Backward single step.  Execute one instruction in reverse.  No
     parameter.  *Note Reverse Execution::, for more information.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'c [ADDR]'
     Continue at ADDR, which is the address to resume.  If ADDR is
     omitted, resume at current address.

     This packet is deprecated for multi-threading support.  *Note vCont
     packet::.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'C SIG[;ADDR]'
     Continue with signal SIG (hex signal number).  If ';ADDR' is
     omitted, resume at same address.

     This packet is deprecated for multi-threading support.  *Note vCont
     packet::.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'd'
     Toggle debug flag.

     Don't use this packet; instead, define a general set packet (*note
     General Query Packets::).

'D'
'D;PID'
     The first form of the packet is used to detach GDB from the remote
     system.  It is sent to the remote target before GDB disconnects via
     the 'detach' command.

     The second form, including a process ID, is used when multiprocess
     protocol extensions are enabled (*note multiprocess extensions::),
     to detach only a specific process.  The PID is specified as a
     big-endian hex string.

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'F RC,EE,CF;XX'
     A reply from GDB to an 'F' packet sent by the target.  This is part
     of the File-I/O protocol extension.  *Note File-I/O Remote Protocol
     Extension::, for the specification.

'g'
     Read general registers.

     Reply:
     'XX...'
          Each byte of register data is described by two hex digits.
          The bytes with the register are transmitted in target byte
          order.  The size of each register and their position within
          the 'g' packet are determined by the GDB internal gdbarch
          functions 'DEPRECATED_REGISTER_RAW_SIZE' and
          'gdbarch_register_name'.

          When reading registers from a trace frame (*note Using the
          Collected Data: Analyze Collected Data.), the stub may also
          return a string of literal 'x''s in place of the register data
          digits, to indicate that the corresponding register has not
          been collected, thus its value is unavailable.  For example,
          for an architecture with 4 registers of 4 bytes each, the
          following reply indicates to GDB that registers 0 and 2 have
          not been collected, while registers 1 and 3 have been
          collected, and both have zero value:

               -> g
               <- xxxxxxxx00000000xxxxxxxx00000000

     'E NN'
          for an error.

'G XX...'
     Write general registers.  *Note read registers packet::, for a
     description of the XX... data.

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'H OP THREAD-ID'
     Set thread for subsequent operations ('m', 'M', 'g', 'G', et.al.).
     Depending on the operation to be performed, OP should be 'c' for
     step and continue operations (note that this is deprecated,
     supporting the 'vCont' command is a better option), and 'g' for
     other operations.  The thread designator THREAD-ID has the format
     and interpretation described in *note thread-id syntax::.

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'i [ADDR[,NNN]]'
     Step the remote target by a single clock cycle.  If ',NNN' is
     present, cycle step NNN cycles.  If ADDR is present, cycle step
     starting at that address.

'I'
     Signal, then cycle step.  *Note step with signal packet::.  *Note
     cycle step packet::.

'k'
     Kill request.

     The exact effect of this packet is not specified.

     For a bare-metal target, it may power cycle or reset the target
     system.  For that reason, the 'k' packet has no reply.

     For a single-process target, it may kill that process if possible.

     A multiple-process target may choose to kill just one process, or
     all that are under GDB's control.  For more precise control, use
     the vKill packet (*note vKill packet::).

     If the target system immediately closes the connection in response
     to 'k', GDB does not consider the lack of packet acknowledgment to
     be an error, and assumes the kill was successful.

     If connected using 'target extended-remote', and the target does
     not close the connection in response to a kill request, GDB probes
     the target state as if a new connection was opened (*note ?
     packet::).

'm ADDR,LENGTH'
     Read LENGTH addressable memory units starting at address ADDR
     (*note addressable memory unit::).  Note that ADDR may not be
     aligned to any particular boundary.

     The stub need not use any particular size or alignment when
     gathering data from memory for the response; even if ADDR is
     word-aligned and LENGTH is a multiple of the word size, the stub is
     free to use byte accesses, or not.  For this reason, this packet
     may not be suitable for accessing memory-mapped I/O devices.

     Reply:
     'XX...'
          Memory contents; each byte is transmitted as a two-digit
          hexadecimal number.  The reply may contain fewer addressable
          memory units than requested if the server was able to read
          only part of the region of memory.
     'E NN'
          NN is errno

'M ADDR,LENGTH:XX...'
     Write LENGTH addressable memory units starting at address ADDR
     (*note addressable memory unit::).  The data is given by XX...;
     each byte is transmitted as a two-digit hexadecimal number.

     Reply:
     'OK'
          for success
     'E NN'
          for an error (this includes the case where only part of the
          data was written).

'p N'
     Read the value of register N; N is in hex.  *Note read registers
     packet::, for a description of how the returned register value is
     encoded.

     Reply:
     'XX...'
          the register's value
     'E NN'
          for an error
     ''
          Indicating an unrecognized QUERY.

'P N...=R...'
     Write register N... with value R....  The register number N is in
     hexadecimal, and R... contains two hex digits for each byte in the
     register (target byte order).

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'q NAME PARAMS...'
'Q NAME PARAMS...'
     General query ('q') and set ('Q').  These packets are described
     fully in *note General Query Packets::.

'r'
     Reset the entire system.

     Don't use this packet; use the 'R' packet instead.

'R XX'
     Restart the program being debugged.  The XX, while needed, is
     ignored.  This packet is only available in extended mode (*note
     extended mode::).

     The 'R' packet has no reply.

's [ADDR]'
     Single step, resuming at ADDR.  If ADDR is omitted, resume at same
     address.

     This packet is deprecated for multi-threading support.  *Note vCont
     packet::.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'S SIG[;ADDR]'
     Step with signal.  This is analogous to the 'C' packet, but
     requests a single-step, rather than a normal resumption of
     execution.

     This packet is deprecated for multi-threading support.  *Note vCont
     packet::.

     Reply: *Note Stop Reply Packets::, for the reply specifications.

't ADDR:PP,MM'
     Search backwards starting at address ADDR for a match with pattern
     PP and mask MM, both of which are are 4 byte long.  There must be
     at least 3 digits in ADDR.

'T THREAD-ID'
     Find out if the thread THREAD-ID is alive.  *Note thread-id
     syntax::.

     Reply:
     'OK'
          thread is still alive
     'E NN'
          thread is dead

'v'
     Packets starting with 'v' are identified by a multi-letter name, up
     to the first ';' or '?' (or the end of the packet).

'vAttach;PID'
     Attach to a new process with the specified process ID PID.  The
     process ID is a hexadecimal integer identifying the process.  In
     all-stop mode, all threads in the attached process are stopped; in
     non-stop mode, it may be attached without being stopped if that is
     supported by the target.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'E NN'
          for an error
     'Any stop packet'
          for success in all-stop mode (*note Stop Reply Packets::)
     'OK'
          for success in non-stop mode (*note Remote Non-Stop::)

'vCont[;ACTION[:THREAD-ID]]...'
     Resume the inferior, specifying different actions for each thread.

     For each inferior thread, the leftmost action with a matching
     THREAD-ID is applied.  Threads that don't match any action remain
     in their current state.  Thread IDs are specified using the syntax
     described in *note thread-id syntax::.  If multiprocess extensions
     (*note multiprocess extensions::) are supported, actions can be
     specified to match all threads in a process by using the 'pPID.-1'
     form of the THREAD-ID.  An action with no THREAD-ID matches all
     threads.  Specifying no actions is an error.

     Currently supported actions are:

     'c'
          Continue.
     'C SIG'
          Continue with signal SIG.  The signal SIG should be two hex
          digits.
     's'
          Step.
     'S SIG'
          Step with signal SIG.  The signal SIG should be two hex
          digits.
     't'
          Stop.
     'r START,END'
          Step once, and then keep stepping as long as the thread stops
          at addresses between START (inclusive) and END (exclusive).
          The remote stub reports a stop reply when either the thread
          goes out of the range or is stopped due to an unrelated
          reason, such as hitting a breakpoint.  *Note range stepping::.

          If the range is empty (START == END), then the action becomes
          equivalent to the 's' action.  In other words, single-step
          once, and report the stop (even if the stepped instruction
          jumps to START).

          (A stop reply may be sent at any point even if the PC is still
          within the stepping range; for example, it is valid to
          implement this packet in a degenerate way as a single
          instruction step operation.)

     The optional argument ADDR normally associated with the 'c', 'C',
     's', and 'S' packets is not supported in 'vCont'.

     The 't' action is only relevant in non-stop mode (*note Remote
     Non-Stop::) and may be ignored by the stub otherwise.  A stop reply
     should be generated for any affected thread not already stopped.
     When a thread is stopped by means of a 't' action, the
     corresponding stop reply should indicate that the thread has
     stopped with signal '0', regardless of whether the target uses some
     other signal as an implementation detail.

     The server must ignore 'c', 'C', 's', 'S', and 'r' actions for
     threads that are already running.  Conversely, the server must
     ignore 't' actions for threads that are already stopped.

     _Note:_ In non-stop mode, a thread is considered running until GDB
     acknowleges an asynchronous stop notification for it with the
     'vStopped' packet (*note Remote Non-Stop::).

     The stub must support 'vCont' if it reports support for
     multiprocess extensions (*note multiprocess extensions::).

     Reply: *Note Stop Reply Packets::, for the reply specifications.

'vCont?'
     Request a list of actions supported by the 'vCont' packet.

     Reply:
     'vCont[;ACTION...]'
          The 'vCont' packet is supported.  Each ACTION is a supported
          command in the 'vCont' packet.
     ''
          The 'vCont' packet is not supported.

'vCtrlC'
     Interrupt remote target as if a control-C was pressed on the remote
     terminal.  This is the equivalent to reacting to the '^C' ('\003',
     the control-C character) character in all-stop mode while the
     target is running, except this works in non-stop mode.  *Note
     interrupting remote targets::, for more info on the all-stop
     variant.

     Reply:
     'E NN'
          for an error
     'OK'
          for success

'vFile:OPERATION:PARAMETER...'
     Perform a file operation on the target system.  For details, see
     *note Host I/O Packets::.

'vFlashErase:ADDR,LENGTH'
     Direct the stub to erase LENGTH bytes of flash starting at ADDR.
     The region may enclose any number of flash blocks, but its start
     and end must fall on block boundaries, as indicated by the flash
     block size appearing in the memory map (*note Memory Map Format::).
     GDB groups flash memory programming operations together, and sends
     a 'vFlashDone' request after each group; the stub is allowed to
     delay erase operation until the 'vFlashDone' packet is received.

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'vFlashWrite:ADDR:XX...'
     Direct the stub to write data to flash address ADDR.  The data is
     passed in binary form using the same encoding as for the 'X' packet
     (*note Binary Data::).  The memory ranges specified by
     'vFlashWrite' packets preceding a 'vFlashDone' packet must not
     overlap, and must appear in order of increasing addresses (although
     'vFlashErase' packets for higher addresses may already have been
     received; the ordering is guaranteed only between 'vFlashWrite'
     packets).  If a packet writes to an address that was neither erased
     by a preceding 'vFlashErase' packet nor by some other
     target-specific method, the results are unpredictable.

     Reply:
     'OK'
          for success
     'E.memtype'
          for vFlashWrite addressing non-flash memory
     'E NN'
          for an error

'vFlashDone'
     Indicate to the stub that flash programming operation is finished.
     The stub is permitted to delay or batch the effects of a group of
     'vFlashErase' and 'vFlashWrite' packets until a 'vFlashDone' packet
     is received.  The contents of the affected regions of flash memory
     are unpredictable until the 'vFlashDone' request is completed.

'vKill;PID'
     Kill the process with the specified process ID PID, which is a
     hexadecimal integer identifying the process.  This packet is used
     in preference to 'k' when multiprocess protocol extensions are
     supported; see *note multiprocess extensions::.

     Reply:
     'E NN'
          for an error
     'OK'
          for success

'vMustReplyEmpty'
     The correct reply to an unknown 'v' packet is to return the empty
     string, however, some older versions of 'gdbserver' would
     incorrectly return 'OK' for unknown 'v' packets.

     The 'vMustReplyEmpty' is used as a feature test to check how
     'gdbserver' handles unknown packets, it is important that this
     packet be handled in the same way as other unknown 'v' packets.  If
     this packet is handled differently to other unknown 'v' packets
     then it is possile that GDB may run into problems in other areas,
     specifically around use of 'vFile:setfs:'.

'vRun;FILENAME[;ARGUMENT]...'
     Run the program FILENAME, passing it each ARGUMENT on its command
     line.  The file and arguments are hex-encoded strings.  If FILENAME
     is an empty string, the stub may use a default program (e.g. the
     last program run).  The program is created in the stopped state.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'E NN'
          for an error
     'Any stop packet'
          for success (*note Stop Reply Packets::)

'vStopped'
     *Note Notification Packets::.

'X ADDR,LENGTH:XX...'
     Write data to memory, where the data is transmitted in binary.
     Memory is specified by its address ADDR and number of addressable
     memory units LENGTH (*note addressable memory unit::); 'XX...' is
     binary data (*note Binary Data::).

     Reply:
     'OK'
          for success
     'E NN'
          for an error

'z TYPE,ADDR,KIND'
'Z TYPE,ADDR,KIND'
     Insert ('Z') or remove ('z') a TYPE breakpoint or watchpoint
     starting at address ADDRESS of kind KIND.

     Each breakpoint and watchpoint packet TYPE is documented
     separately.

     _Implementation notes: A remote target shall return an empty string
     for an unrecognized breakpoint or watchpoint packet TYPE.  A remote
     target shall support either both or neither of a given 'ZTYPE...'
     and 'zTYPE...' packet pair.  To avoid potential problems with
     duplicate packets, the operations should be implemented in an
     idempotent way._

'z0,ADDR,KIND'
'Z0,ADDR,KIND[;COND_LIST...][;cmds:PERSIST,CMD_LIST...]'
     Insert ('Z0') or remove ('z0') a software breakpoint at address
     ADDR of type KIND.

     A software breakpoint is implemented by replacing the instruction
     at ADDR with a software breakpoint or trap instruction.  The KIND
     is target-specific and typically indicates the size of the
     breakpoint in bytes that should be inserted.  E.g., the ARM and
     MIPS can insert either a 2 or 4 byte breakpoint.  Some
     architectures have additional meanings for KIND (*note
     Architecture-Specific Protocol Details::); if no
     architecture-specific value is being used, it should be '0'.  KIND
     is hex-encoded.  COND_LIST is an optional list of conditional
     expressions in bytecode form that should be evaluated on the
     target's side.  These are the conditions that should be taken into
     consideration when deciding if the breakpoint trigger should be
     reported back to GDB.

     See also the 'swbreak' stop reason (*note swbreak stop reason::)
     for how to best report a software breakpoint event to GDB.

     The COND_LIST parameter is comprised of a series of expressions,
     concatenated without separators.  Each expression has the following
     form:

     'X LEN,EXPR'
          LEN is the length of the bytecode expression and EXPR is the
          actual conditional expression in bytecode form.

     The optional CMD_LIST parameter introduces commands that may be run
     on the target, rather than being reported back to GDB.  The
     parameter starts with a numeric flag PERSIST; if the flag is
     nonzero, then the breakpoint may remain active and the commands
     continue to be run even when GDB disconnects from the target.
     Following this flag is a series of expressions concatenated with no
     separators.  Each expression has the following form:

     'X LEN,EXPR'
          LEN is the length of the bytecode expression and EXPR is the
          actual commands expression in bytecode form.

     _Implementation note: It is possible for a target to copy or move
     code that contains software breakpoints (e.g., when implementing
     overlays).  The behavior of this packet, in the presence of such a
     target, is not defined._

     Reply:
     'OK'
          success
     ''
          not supported
     'E NN'
          for an error

'z1,ADDR,KIND'
'Z1,ADDR,KIND[;COND_LIST...][;cmds:PERSIST,CMD_LIST...]'
     Insert ('Z1') or remove ('z1') a hardware breakpoint at address
     ADDR.

     A hardware breakpoint is implemented using a mechanism that is not
     dependent on being able to modify the target's memory.  The KIND,
     COND_LIST, and CMD_LIST arguments have the same meaning as in 'Z0'
     packets.

     _Implementation note: A hardware breakpoint is not affected by code
     movement._

     Reply:
     'OK'
          success
     ''
          not supported
     'E NN'
          for an error

'z2,ADDR,KIND'
'Z2,ADDR,KIND'
     Insert ('Z2') or remove ('z2') a write watchpoint at ADDR.  The
     number of bytes to watch is specified by KIND.

     Reply:
     'OK'
          success
     ''
          not supported
     'E NN'
          for an error

'z3,ADDR,KIND'
'Z3,ADDR,KIND'
     Insert ('Z3') or remove ('z3') a read watchpoint at ADDR.  The
     number of bytes to watch is specified by KIND.

     Reply:
     'OK'
          success
     ''
          not supported
     'E NN'
          for an error

'z4,ADDR,KIND'
'Z4,ADDR,KIND'
     Insert ('Z4') or remove ('z4') an access watchpoint at ADDR.  The
     number of bytes to watch is specified by KIND.

     Reply:
     'OK'
          success
     ''
          not supported
     'E NN'
          for an error


File: gdb.info,  Node: Stop Reply Packets,  Next: General Query Packets,  Prev: Packets,  Up: Remote Protocol

E.3 Stop Reply Packets
======================

The 'C', 'c', 'S', 's', 'vCont', 'vAttach', 'vRun', 'vStopped', and '?'
packets can receive any of the below as a reply.  Except for '?' and
'vStopped', that reply is only returned when the target halts.  In the
below the exact meaning of "signal number" is defined by the header
'include/gdb/signals.h' in the GDB source code.

   In non-stop mode, the server will simply reply 'OK' to commands such
as 'vCont'; any stop will be the subject of a future notification.
*Note Remote Non-Stop::.

   As in the description of request packets, we include spaces in the
reply templates for clarity; these are not part of the reply packet's
syntax.  No GDB stop reply packet uses spaces to separate its
components.

'S AA'
     The program received signal number AA (a two-digit hexadecimal
     number).  This is equivalent to a 'T' response with no N:R pairs.

'T AA N1:R1;N2:R2;...'
     The program received signal number AA (a two-digit hexadecimal
     number).  This is equivalent to an 'S' response, except that the
     'N:R' pairs can carry values of important registers and other
     information directly in the stop reply packet, reducing round-trip
     latency.  Single-step and breakpoint traps are reported this way.
     Each 'N:R' pair is interpreted as follows:

        * If N is a hexadecimal number, it is a register number, and the
          corresponding R gives that register's value.  The data R is a
          series of bytes in target byte order, with each byte given by
          a two-digit hex number.

        * If N is 'thread', then R is the THREAD-ID of the stopped
          thread, as specified in *note thread-id syntax::.

        * If N is 'core', then R is the hexadecimal number of the core
          on which the stop event was detected.

        * If N is a recognized "stop reason", it describes a more
          specific event that stopped the target.  The currently defined
          stop reasons are listed below.  The AA should be '05', the
          trap signal.  At most one stop reason should be present.

        * Otherwise, GDB should ignore this 'N:R' pair and go on to the
          next; this allows us to extend the protocol in the future.

     The currently defined stop reasons are:

     'watch'
     'rwatch'
     'awatch'
          The packet indicates a watchpoint hit, and R is the data
          address, in hex.

     'syscall_entry'
     'syscall_return'
          The packet indicates a syscall entry or return, and R is the
          syscall number, in hex.

     'library'
          The packet indicates that the loaded libraries have changed.
          GDB should use 'qXfer:libraries:read' to fetch a new list of
          loaded libraries.  The R part is ignored.

     'replaylog'
          The packet indicates that the target cannot continue replaying
          logged execution events, because it has reached the end (or
          the beginning when executing backward) of the log.  The value
          of R will be either 'begin' or 'end'.  *Note Reverse
          Execution::, for more information.

     'swbreak'
          The packet indicates a software breakpoint instruction was
          executed, irrespective of whether it was GDB that planted the
          breakpoint or the breakpoint is hardcoded in the program.  The
          R part must be left empty.

          On some architectures, such as x86, at the architecture level,
          when a breakpoint instruction executes the program counter
          points at the breakpoint address plus an offset.  On such
          targets, the stub is responsible for adjusting the PC to point
          back at the breakpoint address.

          This packet should not be sent by default; older GDB versions
          did not support it.  GDB requests it, by supplying an
          appropriate 'qSupported' feature (*note qSupported::).  The
          remote stub must also supply the appropriate 'qSupported'
          feature indicating support.

          This packet is required for correct non-stop mode operation.

     'hwbreak'
          The packet indicates the target stopped for a hardware
          breakpoint.  The R part must be left empty.

          The same remarks about 'qSupported' and non-stop mode above
          apply.

     'fork'
          The packet indicates that 'fork' was called, and R is the
          thread ID of the new child process.  Refer to *note thread-id
          syntax:: for the format of the THREAD-ID field.  This packet
          is only applicable to targets that support fork events.

          This packet should not be sent by default; older GDB versions
          did not support it.  GDB requests it, by supplying an
          appropriate 'qSupported' feature (*note qSupported::).  The
          remote stub must also supply the appropriate 'qSupported'
          feature indicating support.

     'vfork'
          The packet indicates that 'vfork' was called, and R is the
          thread ID of the new child process.  Refer to *note thread-id
          syntax:: for the format of the THREAD-ID field.  This packet
          is only applicable to targets that support vfork events.

          This packet should not be sent by default; older GDB versions
          did not support it.  GDB requests it, by supplying an
          appropriate 'qSupported' feature (*note qSupported::).  The
          remote stub must also supply the appropriate 'qSupported'
          feature indicating support.

     'vforkdone'
          The packet indicates that a child process created by a vfork
          has either called 'exec' or terminated, so that the address
          spaces of the parent and child process are no longer shared.
          The R part is ignored.  This packet is only applicable to
          targets that support vforkdone events.

          This packet should not be sent by default; older GDB versions
          did not support it.  GDB requests it, by supplying an
          appropriate 'qSupported' feature (*note qSupported::).  The
          remote stub must also supply the appropriate 'qSupported'
          feature indicating support.

     'exec'
          The packet indicates that 'execve' was called, and R is the
          absolute pathname of the file that was executed, in hex.  This
          packet is only applicable to targets that support exec events.

          This packet should not be sent by default; older GDB versions
          did not support it.  GDB requests it, by supplying an
          appropriate 'qSupported' feature (*note qSupported::).  The
          remote stub must also supply the appropriate 'qSupported'
          feature indicating support.

     'create'
          The packet indicates that the thread was just created.  The
          new thread is stopped until GDB sets it running with a
          resumption packet (*note vCont packet::).  This packet should
          not be sent by default; GDB requests it with the *note
          QThreadEvents:: packet.  See also the 'w' (*note thread exit
          event::) remote reply below.  The R part is ignored.

'W AA'
'W AA ; process:PID'
     The process exited, and AA is the exit status.  This is only
     applicable to certain targets.

     The second form of the response, including the process ID of the
     exited process, can be used only when GDB has reported support for
     multiprocess protocol extensions; see *note multiprocess
     extensions::.  Both AA and PID are formatted as big-endian hex
     strings.

'X AA'
'X AA ; process:PID'
     The process terminated with signal AA.

     The second form of the response, including the process ID of the
     terminated process, can be used only when GDB has reported support
     for multiprocess protocol extensions; see *note multiprocess
     extensions::.  Both AA and PID are formatted as big-endian hex
     strings.

'w AA ; TID'

     The thread exited, and AA is the exit status.  This response should
     not be sent by default; GDB requests it with the *note
     QThreadEvents:: packet.  See also *note thread create event::
     above.  AA is formatted as a big-endian hex string.

'N'
     There are no resumed threads left in the target.  In other words,
     even though the process is alive, the last resumed thread has
     exited.  For example, say the target process has two threads:
     thread 1 and thread 2.  The client leaves thread 1 stopped, and
     resumes thread 2, which subsequently exits.  At this point, even
     though the process is still alive, and thus no 'W' stop reply is
     sent, no thread is actually executing either.  The 'N' stop reply
     thus informs the client that it can stop waiting for stop replies.
     This packet should not be sent by default; older GDB versions did
     not support it.  GDB requests it, by supplying an appropriate
     'qSupported' feature (*note qSupported::).  The remote stub must
     also supply the appropriate 'qSupported' feature indicating
     support.

'O XX...'
     'XX...' is hex encoding of ASCII data, to be written as the
     program's console output.  This can happen at any time while the
     program is running and the debugger should continue to wait for
     'W', 'T', etc.  This reply is not permitted in non-stop mode.

'F CALL-ID,PARAMETER...'
     CALL-ID is the identifier which says which host system call should
     be called.  This is just the name of the function.  Translation
     into the correct system call is only applicable as it's defined in
     GDB.  *Note File-I/O Remote Protocol Extension::, for a list of
     implemented system calls.

     'PARAMETER...' is a list of parameters as defined for this very
     system call.

     The target replies with this packet when it expects GDB to call a
     host system call on behalf of the target.  GDB replies with an
     appropriate 'F' packet and keeps up waiting for the next reply
     packet from the target.  The latest 'C', 'c', 'S' or 's' action is
     expected to be continued.  *Note File-I/O Remote Protocol
     Extension::, for more details.


File: gdb.info,  Node: General Query Packets,  Next: Architecture-Specific Protocol Details,  Prev: Stop Reply Packets,  Up: Remote Protocol

E.4 General Query Packets
=========================

Packets starting with 'q' are "general query packets"; packets starting
with 'Q' are "general set packets".  General query and set packets are a
semi-unified form for retrieving and sending information to and from the
stub.

   The initial letter of a query or set packet is followed by a name
indicating what sort of thing the packet applies to.  For example, GDB
may use a 'qSymbol' packet to exchange symbol definitions with the stub.
These packet names follow some conventions:

   * The name must not contain commas, colons or semicolons.
   * Most GDB query and set packets have a leading upper case letter.
   * The names of custom vendor packets should use a company prefix, in
     lower case, followed by a period.  For example, packets designed at
     the Acme Corporation might begin with 'qacme.foo' (for querying
     foos) or 'Qacme.bar' (for setting bars).

   The name of a query or set packet should be separated from any
parameters by a ':'; the parameters themselves should be separated by
',' or ';'.  Stubs must be careful to match the full packet name, and
check for a separator or the end of the packet, in case two packet names
share a common prefix.  New packets should not begin with 'qC', 'qP', or
'qL'(1).

   Like the descriptions of the other packets, each description here has
a template showing the packet's overall syntax, followed by an
explanation of the packet's meaning.  We include spaces in some of the
templates for clarity; these are not part of the packet's syntax.  No
GDB packet uses spaces to separate its components.

   Here are the currently defined query and set packets:

'QAgent:1'
'QAgent:0'
     Turn on or off the agent as a helper to perform some debugging
     operations delegated from GDB (*note Control Agent::).

'QAllow:OP:VAL...'
     Specify which operations GDB expects to request of the target, as a
     semicolon-separated list of operation name and value pairs.
     Possible values for OP include 'WriteReg', 'WriteMem',
     'InsertBreak', 'InsertTrace', 'InsertFastTrace', and 'Stop'.  VAL
     is either 0, indicating that GDB will not request the operation, or
     1, indicating that it may.  (The target can then use this to set up
     its own internals optimally, for instance if the debugger never
     expects to insert breakpoints, it may not need to install its own
     trap handler.)

'qC'
     Return the current thread ID.

     Reply:
     'QC THREAD-ID'
          Where THREAD-ID is a thread ID as documented in *note
          thread-id syntax::.
     '(anything else)'
          Any other reply implies the old thread ID.

'qCRC:ADDR,LENGTH'
     Compute the CRC checksum of a block of memory using CRC-32 defined
     in IEEE 802.3.  The CRC is computed byte at a time, taking the most
     significant bit of each byte first.  The initial pattern code
     '0xffffffff' is used to ensure leading zeros affect the CRC.

     _Note:_ This is the same CRC used in validating separate debug
     files (*note Debugging Information in Separate Files: Separate
     Debug Files.).  However the algorithm is slightly different.  When
     validating separate debug files, the CRC is computed taking the
     _least_ significant bit of each byte first, and the final result is
     inverted to detect trailing zeros.

     Reply:
     'E NN'
          An error (such as memory fault)
     'C CRC32'
          The specified memory region's checksum is CRC32.

'QDisableRandomization:VALUE'
     Some target operating systems will randomize the virtual address
     space of the inferior process as a security feature, but provide a
     feature to disable such randomization, e.g. to allow for a more
     deterministic debugging experience.  On such systems, this packet
     with a VALUE of 1 directs the target to disable address space
     randomization for processes subsequently started via 'vRun'
     packets, while a packet with a VALUE of 0 tells the target to
     enable address space randomization.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QDisableRandomization' is not
          supported by the stub.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support disabling address space randomization.

'QStartupWithShell:VALUE'
     On UNIX-like targets, it is possible to start the inferior using a
     shell program.  This is the default behavior on both GDB and
     'gdbserver' (*note set startup-with-shell::).  This packet is used
     to inform 'gdbserver' whether it should start the inferior using a
     shell or not.

     If VALUE is '0', 'gdbserver' will not use a shell to start the
     inferior.  If VALUE is '1', 'gdbserver' will use a shell to start
     the inferior.  All other values are considered an error.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support starting the inferior using a shell.

     Use of this packet is controlled by the 'set startup-with-shell'
     command; *note set startup-with-shell::.

'QEnvironmentHexEncoded:HEX-VALUE'
     On UNIX-like targets, it is possible to set environment variables
     that will be passed to the inferior during the startup process.
     This packet is used to inform 'gdbserver' of an environment
     variable that has been defined by the user on GDB (*note set
     environment::).

     The packet is composed by HEX-VALUE, an hex encoded representation
     of the NAME=VALUE format representing an environment variable.  The
     name of the environment variable is represented by NAME, and the
     value to be assigned to the environment variable is represented by
     VALUE.  If the variable has no value (i.e., the value is 'null'),
     then VALUE will not be present.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support passing environment variables to the starting inferior.

     This packet is related to the 'set environment' command; *note set
     environment::.

'QEnvironmentUnset:HEX-VALUE'
     On UNIX-like targets, it is possible to unset environment variables
     before starting the inferior in the remote target.  This packet is
     used to inform 'gdbserver' of an environment variable that has been
     unset by the user on GDB (*note unset environment::).

     The packet is composed by HEX-VALUE, an hex encoded representation
     of the name of the environment variable to be unset.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support passing environment variables to the starting inferior.

     This packet is related to the 'unset environment' command; *note
     unset environment::.

'QEnvironmentReset'
     On UNIX-like targets, this packet is used to reset the state of
     environment variables in the remote target before starting the
     inferior.  In this context, reset means unsetting all environment
     variables that were previously set by the user (i.e., were not
     initially present in the environment).  It is sent to 'gdbserver'
     before the 'QEnvironmentHexEncoded' (*note
     QEnvironmentHexEncoded::) and the 'QEnvironmentUnset' (*note
     QEnvironmentUnset::) packets.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support passing environment variables to the starting inferior.

'QSetWorkingDir:[DIRECTORY]'
     This packet is used to inform the remote server of the intended
     current working directory for programs that are going to be
     executed.

     The packet is composed by DIRECTORY, an hex encoded representation
     of the directory that the remote inferior will use as its current
     working directory.  If DIRECTORY is an empty string, the remote
     server should reset the inferior's current working directory to its
     original, empty value.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

'qfThreadInfo'
'qsThreadInfo'
     Obtain a list of all active thread IDs from the target (OS). Since
     there may be too many active threads to fit into one reply packet,
     this query works iteratively: it may require more than one
     query/reply sequence to obtain the entire list of threads.  The
     first query of the sequence will be the 'qfThreadInfo' query;
     subsequent queries in the sequence will be the 'qsThreadInfo'
     query.

     NOTE: This packet replaces the 'qL' query (see below).

     Reply:
     'm THREAD-ID'
          A single thread ID
     'm THREAD-ID,THREAD-ID...'
          a comma-separated list of thread IDs
     'l'
          (lower case letter 'L') denotes end of list.

     In response to each query, the target will reply with a list of one
     or more thread IDs, separated by commas.  GDB will respond to each
     reply with a request for more thread ids (using the 'qs' form of
     the query), until the target responds with 'l' (lower-case ell, for
     "last").  Refer to *note thread-id syntax::, for the format of the
     THREAD-ID fields.

     _Note: GDB will send the 'qfThreadInfo' query during the initial
     connection with the remote target, and the very first thread ID
     mentioned in the reply will be stopped by GDB in a subsequent
     message.  Therefore, the stub should ensure that the first thread
     ID in the 'qfThreadInfo' reply is suitable for being stopped by
     GDB._

'qGetTLSAddr:THREAD-ID,OFFSET,LM'
     Fetch the address associated with thread local storage specified by
     THREAD-ID, OFFSET, and LM.

     THREAD-ID is the thread ID associated with the thread for which to
     fetch the TLS address.  *Note thread-id syntax::.

     OFFSET is the (big endian, hex encoded) offset associated with the
     thread local variable.  (This offset is obtained from the debug
     information associated with the variable.)

     LM is the (big endian, hex encoded) OS/ABI-specific encoding of the
     load module associated with the thread local storage.  For example,
     a GNU/Linux system will pass the link map address of the shared
     object associated with the thread local storage under
     consideration.  Other operating environments may choose to
     represent the load module differently, so the precise meaning of
     this parameter will vary.

     Reply:
     'XX...'
          Hex encoded (big endian) bytes representing the address of the
          thread local storage requested.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'qGetTLSAddr' is not supported
          by the stub.

'qGetTIBAddr:THREAD-ID'
     Fetch address of the Windows OS specific Thread Information Block.

     THREAD-ID is the thread ID associated with the thread.

     Reply:
     'XX...'
          Hex encoded (big endian) bytes representing the linear address
          of the thread information block.

     'E NN'
          An error occured.  This means that either the thread was not
          found, or the address could not be retrieved.

     ''
          An empty reply indicates that 'qGetTIBAddr' is not supported
          by the stub.

'qL STARTFLAG THREADCOUNT NEXTTHREAD'
     Obtain thread information from RTOS. Where: STARTFLAG (one hex
     digit) is one to indicate the first query and zero to indicate a
     subsequent query; THREADCOUNT (two hex digits) is the maximum
     number of threads the response packet can contain; and NEXTTHREAD
     (eight hex digits), for subsequent queries (STARTFLAG is zero), is
     returned in the response as ARGTHREAD.

     Don't use this packet; use the 'qfThreadInfo' query instead (see
     above).

     Reply:
     'qM COUNT DONE ARGTHREAD THREAD...'
          Where: COUNT (two hex digits) is the number of threads being
          returned; DONE (one hex digit) is zero to indicate more
          threads and one indicates no further threads; ARGTHREADID
          (eight hex digits) is NEXTTHREAD from the request packet;
          THREAD... is a sequence of thread IDs, THREADID (eight hex
          digits), from the target.  See
          'remote.c:parse_threadlist_response()'.

'qOffsets'
     Get section offsets that the target used when relocating the
     downloaded image.

     Reply:
     'Text=XXX;Data=YYY[;Bss=ZZZ]'
          Relocate the 'Text' section by XXX from its original address.
          Relocate the 'Data' section by YYY from its original address.
          If the object file format provides segment information (e.g.
          ELF 'PT_LOAD' program headers), GDB will relocate entire
          segments by the supplied offsets.

          _Note: while a 'Bss' offset may be included in the response,
          GDB ignores this and instead applies the 'Data' offset to the
          'Bss' section._

     'TextSeg=XXX[;DataSeg=YYY]'
          Relocate the first segment of the object file, which
          conventionally contains program code, to a starting address of
          XXX.  If 'DataSeg' is specified, relocate the second segment,
          which conventionally contains modifiable data, to a starting
          address of YYY.  GDB will report an error if the object file
          does not contain segment information, or does not contain at
          least as many segments as mentioned in the reply.  Extra
          segments are kept at fixed offsets relative to the last
          relocated segment.

'qP MODE THREAD-ID'
     Returns information on THREAD-ID.  Where: MODE is a hex encoded 32
     bit mode; THREAD-ID is a thread ID (*note thread-id syntax::).

     Don't use this packet; use the 'qThreadExtraInfo' query instead
     (see below).

     Reply: see 'remote.c:remote_unpack_thread_info_response()'.

'QNonStop:1'
'QNonStop:0'
     Enter non-stop ('QNonStop:1') or all-stop ('QNonStop:0') mode.
     *Note Remote Non-Stop::, for more information.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QNonStop' is not supported by
          the stub.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  Use of this packet is controlled by the 'set
     non-stop' command; *note Non-Stop Mode::.

'QCatchSyscalls:1 [;SYSNO]...'
'QCatchSyscalls:0'
     Enable ('QCatchSyscalls:1') or disable ('QCatchSyscalls:0')
     catching syscalls from the inferior process.

     For 'QCatchSyscalls:1', each listed syscall SYSNO (encoded in hex)
     should be reported to GDB.  If no syscall SYSNO is listed, every
     system call should be reported.

     Note that if a syscall not in the list is reported, GDB will still
     filter the event according to its own list from all corresponding
     'catch syscall' commands.  However, it is more efficient to only
     report the requested syscalls.

     Multiple 'QCatchSyscalls:1' packets do not combine; any earlier
     'QCatchSyscalls:1' list is completely replaced by the new list.

     If the inferior process execs, the state of 'QCatchSyscalls' is
     kept for the new process too.  On targets where exec may affect
     syscall numbers, for example with exec between 32 and 64-bit
     processes, the client should send a new packet with the new syscall
     list.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  NN are hex digits.

     ''
          An empty reply indicates that 'QCatchSyscalls' is not
          supported by the stub.

     Use of this packet is controlled by the 'set remote catch-syscalls'
     command (*note set remote catch-syscalls: Remote Configuration.).
     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).

'QPassSignals: SIGNAL [;SIGNAL]...'
     Each listed SIGNAL should be passed directly to the inferior
     process.  Signals are numbered identically to continue packets and
     stop replies (*note Stop Reply Packets::).  Each SIGNAL list item
     should be strictly greater than the previous item.  These signals
     do not need to stop the inferior, or be reported to GDB.  All other
     signals should be reported to GDB.  Multiple 'QPassSignals' packets
     do not combine; any earlier 'QPassSignals' list is completely
     replaced by the new list.  This packet improves performance when
     using 'handle SIGNAL nostop noprint pass'.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QPassSignals' is not supported
          by the stub.

     Use of this packet is controlled by the 'set remote pass-signals'
     command (*note set remote pass-signals: Remote Configuration.).
     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).

'QProgramSignals: SIGNAL [;SIGNAL]...'
     Each listed SIGNAL may be delivered to the inferior process.
     Others should be silently discarded.

     In some cases, the remote stub may need to decide whether to
     deliver a signal to the program or not without GDB involvement.
     One example of that is while detaching -- the program's threads may
     have stopped for signals that haven't yet had a chance of being
     reported to GDB, and so the remote stub can use the signal list
     specified by this packet to know whether to deliver or ignore those
     pending signals.

     This does not influence whether to deliver a signal as requested by
     a resumption packet (*note vCont packet::).

     Signals are numbered identically to continue packets and stop
     replies (*note Stop Reply Packets::).  Each SIGNAL list item should
     be strictly greater than the previous item.  Multiple
     'QProgramSignals' packets do not combine; any earlier
     'QProgramSignals' list is completely replaced by the new list.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QProgramSignals' is not
          supported by the stub.

     Use of this packet is controlled by the 'set remote
     program-signals' command (*note set remote program-signals: Remote
     Configuration.).  This packet is not probed by default; the remote
     stub must request it, by supplying an appropriate 'qSupported'
     response (*note qSupported::).

'QThreadEvents:1'
'QThreadEvents:0'

     Enable ('QThreadEvents:1') or disable ('QThreadEvents:0') reporting
     of thread create and exit events.  *Note thread create event::, for
     the reply specifications.  For example, this is used in non-stop
     mode when GDB stops a set of threads and synchronously waits for
     the their corresponding stop replies.  Without exit events, if one
     of the threads exits, GDB would hang forever not knowing that it
     should no longer expect a stop for that same thread.  GDB does not
     enable this feature unless the stub reports that it supports it by
     including 'QThreadEvents+' in its 'qSupported' reply.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QThreadEvents' is not supported
          by the stub.

     Use of this packet is controlled by the 'set remote thread-events'
     command (*note set remote thread-events: Remote Configuration.).

'qRcmd,COMMAND'
     COMMAND (hex encoded) is passed to the local interpreter for
     execution.  Invalid commands should be reported using the output
     string.  Before the final result packet, the target may also
     respond with a number of intermediate 'OOUTPUT' console output
     packets.  _Implementors should note that providing access to a
     stubs's interpreter may have security implications_.

     Reply:
     'OK'
          A command response with no output.
     'OUTPUT'
          A command response with the hex encoded output string OUTPUT.
     'E NN'
          Indicate a badly formed request.
     ''
          An empty reply indicates that 'qRcmd' is not recognized.

     (Note that the 'qRcmd' packet's name is separated from the command
     by a ',', not a ':', contrary to the naming conventions above.
     Please don't use this packet as a model for new packets.)

'qSearch:memory:ADDRESS;LENGTH;SEARCH-PATTERN'
     Search LENGTH bytes at ADDRESS for SEARCH-PATTERN.  Both ADDRESS
     and LENGTH are encoded in hex; SEARCH-PATTERN is a sequence of
     bytes, also hex encoded.

     Reply:
     '0'
          The pattern was not found.
     '1,address'
          The pattern was found at ADDRESS.
     'E NN'
          A badly formed request or an error was encountered while
          searching memory.
     ''
          An empty reply indicates that 'qSearch:memory' is not
          recognized.

'QStartNoAckMode'
     Request that the remote stub disable the normal '+'/'-' protocol
     acknowledgments (*note Packet Acknowledgment::).

     Reply:
     'OK'
          The stub has switched to no-acknowledgment mode.  GDB
          acknowledges this reponse, but neither the stub nor GDB shall
          send or expect further '+'/'-' acknowledgments in the current
          connection.
     ''
          An empty reply indicates that the stub does not support
          no-acknowledgment mode.

'qSupported [:GDBFEATURE [;GDBFEATURE]... ]'
     Tell the remote stub about features supported by GDB, and query the
     stub for features it supports.  This packet allows GDB and the
     remote stub to take advantage of each others' features.
     'qSupported' also consolidates multiple feature probes at startup,
     to improve GDB performance--a single larger packet performs better
     than multiple smaller probe packets on high-latency links.  Some
     features may enable behavior which must not be on by default, e.g.
     because it would confuse older clients or stubs.  Other features
     may describe packets which could be automatically probed for, but
     are not.  These features must be reported before GDB will use them.
     This "default unsupported" behavior is not appropriate for all
     packets, but it helps to keep the initial connection time under
     control with new versions of GDB which support increasing numbers
     of packets.

     Reply:
     'STUBFEATURE [;STUBFEATURE]...'
          The stub supports or does not support each returned
          STUBFEATURE, depending on the form of each STUBFEATURE (see
          below for the possible forms).
     ''
          An empty reply indicates that 'qSupported' is not recognized,
          or that no features needed to be reported to GDB.

     The allowed forms for each feature (either a GDBFEATURE in the
     'qSupported' packet, or a STUBFEATURE in the response) are:

     'NAME=VALUE'
          The remote protocol feature NAME is supported, and associated
          with the specified VALUE.  The format of VALUE depends on the
          feature, but it must not include a semicolon.
     'NAME+'
          The remote protocol feature NAME is supported, and does not
          need an associated value.
     'NAME-'
          The remote protocol feature NAME is not supported.
     'NAME?'
          The remote protocol feature NAME may be supported, and GDB
          should auto-detect support in some other way when it is
          needed.  This form will not be used for GDBFEATURE
          notifications, but may be used for STUBFEATURE responses.

     Whenever the stub receives a 'qSupported' request, the supplied set
     of GDB features should override any previous request.  This allows
     GDB to put the stub in a known state, even if the stub had
     previously been communicating with a different version of GDB.

     The following values of GDBFEATURE (for the packet sent by GDB) are
     defined:

     'multiprocess'
          This feature indicates whether GDB supports multiprocess
          extensions to the remote protocol.  GDB does not use such
          extensions unless the stub also reports that it supports them
          by including 'multiprocess+' in its 'qSupported' reply.  *Note
          multiprocess extensions::, for details.

     'xmlRegisters'
          This feature indicates that GDB supports the XML target
          description.  If the stub sees 'xmlRegisters=' with target
          specific strings separated by a comma, it will report register
          description.

     'qRelocInsn'
          This feature indicates whether GDB supports the 'qRelocInsn'
          packet (*note Relocate instruction reply packet: Tracepoint
          Packets.).

     'swbreak'
          This feature indicates whether GDB supports the swbreak stop
          reason in stop replies.  *Note swbreak stop reason::, for
          details.

     'hwbreak'
          This feature indicates whether GDB supports the hwbreak stop
          reason in stop replies.  *Note swbreak stop reason::, for
          details.

     'fork-events'
          This feature indicates whether GDB supports fork event
          extensions to the remote protocol.  GDB does not use such
          extensions unless the stub also reports that it supports them
          by including 'fork-events+' in its 'qSupported' reply.

     'vfork-events'
          This feature indicates whether GDB supports vfork event
          extensions to the remote protocol.  GDB does not use such
          extensions unless the stub also reports that it supports them
          by including 'vfork-events+' in its 'qSupported' reply.

     'exec-events'
          This feature indicates whether GDB supports exec event
          extensions to the remote protocol.  GDB does not use such
          extensions unless the stub also reports that it supports them
          by including 'exec-events+' in its 'qSupported' reply.

     'vContSupported'
          This feature indicates whether GDB wants to know the supported
          actions in the reply to 'vCont?' packet.

     Stubs should ignore any unknown values for GDBFEATURE.  Any GDB
     which sends a 'qSupported' packet supports receiving packets of
     unlimited length (earlier versions of GDB may reject overly long
     responses).  Additional values for GDBFEATURE may be defined in the
     future to let the stub take advantage of new features in GDB, e.g.
     incompatible improvements in the remote protocol--the
     'multiprocess' feature is an example of such a feature.  The stub's
     reply should be independent of the GDBFEATURE entries sent by GDB;
     first GDB describes all the features it supports, and then the stub
     replies with all the features it supports.

     Similarly, GDB will silently ignore unrecognized stub feature
     responses, as long as each response uses one of the standard forms.

     Some features are flags.  A stub which supports a flag feature
     should respond with a '+' form response.  Other features require
     values, and the stub should respond with an '=' form response.

     Each feature has a default value, which GDB will use if
     'qSupported' is not available or if the feature is not mentioned in
     the 'qSupported' response.  The default values are fixed; a stub is
     free to omit any feature responses that match the defaults.

     Not all features can be probed, but for those which can, the
     probing mechanism is useful: in some cases, a stub's internal
     architecture may not allow the protocol layer to know some
     information about the underlying target in advance.  This is
     especially common in stubs which may be configured for multiple
     targets.

     These are the currently defined stub features and their properties:

     Feature Name              Value          Default   Probe
                               Required                 Allowed
                                                        
     'PacketSize'              Yes            '-'       No
                                                        
     'qXfer:auxv:read'         No             '-'       Yes
                                                        
     'qXfer:btrace:read'       No             '-'       Yes
                                                        
     'qXfer:btrace-conf:read'  No             '-'       Yes
                                                        
     'qXfer:exec-file:read'    No             '-'       Yes
                                                        
     'qXfer:features:read'     No             '-'       Yes
                                                        
     'qXfer:libraries:read'    No             '-'       Yes
                                                        
     'qXfer:libraries-svr4:read'No            '-'       Yes
                                                        
     'augmented-libraries-svr4-read'No        '-'       No
                                                        
     'qXfer:memory-map:read'   No             '-'       Yes
                                                        
     'qXfer:sdata:read'        No             '-'       Yes
                                                        
     'qXfer:spu:read'          No             '-'       Yes
                                                        
     'qXfer:spu:write'         No             '-'       Yes
                                                        
     'qXfer:siginfo:read'      No             '-'       Yes
                                                        
     'qXfer:siginfo:write'     No             '-'       Yes
                                                        
     'qXfer:threads:read'      No             '-'       Yes
                                                        
     'qXfer:traceframe-info:read'No           '-'       Yes
                                                        
     'qXfer:uib:read'          No             '-'       Yes
                                                        
     'qXfer:fdpic:read'        No             '-'       Yes
                                                        
     'Qbtrace:off'             Yes            '-'       Yes
                                                        
     'Qbtrace:bts'             Yes            '-'       Yes
                                                        
     'Qbtrace:pt'              Yes            '-'       Yes
                                                        
     'Qbtrace-conf:bts:size'   Yes            '-'       Yes
                                                        
     'Qbtrace-conf:pt:size'    Yes            '-'       Yes
                                                        
     'QNonStop'                No             '-'       Yes
                                                        
     'QCatchSyscalls'          No             '-'       Yes
                                                        
     'QPassSignals'            No             '-'       Yes
                                                        
     'QStartNoAckMode'         No             '-'       Yes
                                                        
     'multiprocess'            No             '-'       No
                                                        
     'ConditionalBreakpoints'  No             '-'       No
                                                        
     'ConditionalTracepoints'  No             '-'       No
                                                        
     'ReverseContinue'         No             '-'       No
                                                        
     'ReverseStep'             No             '-'       No
                                                        
     'TracepointSource'        No             '-'       No
                                                        
     'QAgent'                  No             '-'       No
                                                        
     'QAllow'                  No             '-'       No
                                                        
     'QDisableRandomization'   No             '-'       No
                                                        
     'EnableDisableTracepoints'No             '-'       No
                                                        
     'QTBuffer:size'           No             '-'       No
                                                        
     'tracenz'                 No             '-'       No
                                                        
     'BreakpointCommands'      No             '-'       No
                                                        
     'swbreak'                 No             '-'       No
                                                        
     'hwbreak'                 No             '-'       No
                                                        
     'fork-events'             No             '-'       No
                                                        
     'vfork-events'            No             '-'       No
                                                        
     'exec-events'             No             '-'       No
                                                        
     'QThreadEvents'           No             '-'       No
                                                        
     'no-resumed'              No             '-'       No
                                                        

     These are the currently defined stub features, in more detail:

     'PacketSize=BYTES'
          The remote stub can accept packets up to at least BYTES in
          length.  GDB will send packets up to this size for bulk
          transfers, and will never send larger packets.  This is a
          limit on the data characters in the packet, including the
          frame and checksum.  There is no trailing NUL byte in a remote
          protocol packet; if the stub stores packets in a
          NUL-terminated format, it should allow an extra byte in its
          buffer for the NUL. If this stub feature is not supported, GDB
          guesses based on the size of the 'g' packet response.

     'qXfer:auxv:read'
          The remote stub understands the 'qXfer:auxv:read' packet
          (*note qXfer auxiliary vector read::).

     'qXfer:btrace:read'
          The remote stub understands the 'qXfer:btrace:read' packet
          (*note qXfer btrace read::).

     'qXfer:btrace-conf:read'
          The remote stub understands the 'qXfer:btrace-conf:read'
          packet (*note qXfer btrace-conf read::).

     'qXfer:exec-file:read'
          The remote stub understands the 'qXfer:exec-file:read' packet
          (*note qXfer executable filename read::).

     'qXfer:features:read'
          The remote stub understands the 'qXfer:features:read' packet
          (*note qXfer target description read::).

     'qXfer:libraries:read'
          The remote stub understands the 'qXfer:libraries:read' packet
          (*note qXfer library list read::).

     'qXfer:libraries-svr4:read'
          The remote stub understands the 'qXfer:libraries-svr4:read'
          packet (*note qXfer svr4 library list read::).

     'augmented-libraries-svr4-read'
          The remote stub understands the augmented form of the
          'qXfer:libraries-svr4:read' packet (*note qXfer svr4 library
          list read::).

     'qXfer:memory-map:read'
          The remote stub understands the 'qXfer:memory-map:read' packet
          (*note qXfer memory map read::).

     'qXfer:sdata:read'
          The remote stub understands the 'qXfer:sdata:read' packet
          (*note qXfer sdata read::).

     'qXfer:spu:read'
          The remote stub understands the 'qXfer:spu:read' packet (*note
          qXfer spu read::).

     'qXfer:spu:write'
          The remote stub understands the 'qXfer:spu:write' packet
          (*note qXfer spu write::).

     'qXfer:siginfo:read'
          The remote stub understands the 'qXfer:siginfo:read' packet
          (*note qXfer siginfo read::).

     'qXfer:siginfo:write'
          The remote stub understands the 'qXfer:siginfo:write' packet
          (*note qXfer siginfo write::).

     'qXfer:threads:read'
          The remote stub understands the 'qXfer:threads:read' packet
          (*note qXfer threads read::).

     'qXfer:traceframe-info:read'
          The remote stub understands the 'qXfer:traceframe-info:read'
          packet (*note qXfer traceframe info read::).

     'qXfer:uib:read'
          The remote stub understands the 'qXfer:uib:read' packet (*note
          qXfer unwind info block::).

     'qXfer:fdpic:read'
          The remote stub understands the 'qXfer:fdpic:read' packet
          (*note qXfer fdpic loadmap read::).

     'QNonStop'
          The remote stub understands the 'QNonStop' packet (*note
          QNonStop::).

     'QCatchSyscalls'
          The remote stub understands the 'QCatchSyscalls' packet (*note
          QCatchSyscalls::).

     'QPassSignals'
          The remote stub understands the 'QPassSignals' packet (*note
          QPassSignals::).

     'QStartNoAckMode'
          The remote stub understands the 'QStartNoAckMode' packet and
          prefers to operate in no-acknowledgment mode.  *Note Packet
          Acknowledgment::.

     'multiprocess'
          The remote stub understands the multiprocess extensions to the
          remote protocol syntax.  The multiprocess extensions affect
          the syntax of thread IDs in both packets and replies (*note
          thread-id syntax::), and add process IDs to the 'D' packet and
          'W' and 'X' replies.  Note that reporting this feature
          indicates support for the syntactic extensions only, not that
          the stub necessarily supports debugging of more than one
          process at a time.  The stub must not use multiprocess
          extensions in packet replies unless GDB has also indicated it
          supports them in its 'qSupported' request.

     'qXfer:osdata:read'
          The remote stub understands the 'qXfer:osdata:read' packet
          ((*note qXfer osdata read::).

     'ConditionalBreakpoints'
          The target accepts and implements evaluation of conditional
          expressions defined for breakpoints.  The target will only
          report breakpoint triggers when such conditions are true
          (*note Break Conditions: Conditions.).

     'ConditionalTracepoints'
          The remote stub accepts and implements conditional expressions
          defined for tracepoints (*note Tracepoint Conditions::).

     'ReverseContinue'
          The remote stub accepts and implements the reverse continue
          packet (*note bc::).

     'ReverseStep'
          The remote stub accepts and implements the reverse step packet
          (*note bs::).

     'TracepointSource'
          The remote stub understands the 'QTDPsrc' packet that supplies
          the source form of tracepoint definitions.

     'QAgent'
          The remote stub understands the 'QAgent' packet.

     'QAllow'
          The remote stub understands the 'QAllow' packet.

     'QDisableRandomization'
          The remote stub understands the 'QDisableRandomization'
          packet.

     'StaticTracepoint'
          The remote stub supports static tracepoints.

     'InstallInTrace'
          The remote stub supports installing tracepoint in tracing.

     'EnableDisableTracepoints'
          The remote stub supports the 'QTEnable' (*note QTEnable::) and
          'QTDisable' (*note QTDisable::) packets that allow tracepoints
          to be enabled and disabled while a trace experiment is
          running.

     'QTBuffer:size'
          The remote stub supports the 'QTBuffer:size' (*note
          QTBuffer-size::) packet that allows to change the size of the
          trace buffer.

     'tracenz'
          The remote stub supports the 'tracenz' bytecode for collecting
          strings.  See *note Bytecode Descriptions:: for details about
          the bytecode.

     'BreakpointCommands'
          The remote stub supports running a breakpoint's command list
          itself, rather than reporting the hit to GDB.

     'Qbtrace:off'
          The remote stub understands the 'Qbtrace:off' packet.

     'Qbtrace:bts'
          The remote stub understands the 'Qbtrace:bts' packet.

     'Qbtrace:pt'
          The remote stub understands the 'Qbtrace:pt' packet.

     'Qbtrace-conf:bts:size'
          The remote stub understands the 'Qbtrace-conf:bts:size'
          packet.

     'Qbtrace-conf:pt:size'
          The remote stub understands the 'Qbtrace-conf:pt:size' packet.

     'swbreak'
          The remote stub reports the 'swbreak' stop reason for memory
          breakpoints.

     'hwbreak'
          The remote stub reports the 'hwbreak' stop reason for hardware
          breakpoints.

     'fork-events'
          The remote stub reports the 'fork' stop reason for fork
          events.

     'vfork-events'
          The remote stub reports the 'vfork' stop reason for vfork
          events and vforkdone events.

     'exec-events'
          The remote stub reports the 'exec' stop reason for exec
          events.

     'vContSupported'
          The remote stub reports the supported actions in the reply to
          'vCont?' packet.

     'QThreadEvents'
          The remote stub understands the 'QThreadEvents' packet.

     'no-resumed'
          The remote stub reports the 'N' stop reply.

'qSymbol::'
     Notify the target that GDB is prepared to serve symbol lookup
     requests.  Accept requests from the target for the values of
     symbols.

     Reply:
     'OK'
          The target does not need to look up any (more) symbols.
     'qSymbol:SYM_NAME'
          The target requests the value of symbol SYM_NAME (hex
          encoded).  GDB may provide the value by using the
          'qSymbol:SYM_VALUE:SYM_NAME' message, described below.

'qSymbol:SYM_VALUE:SYM_NAME'
     Set the value of SYM_NAME to SYM_VALUE.

     SYM_NAME (hex encoded) is the name of a symbol whose value the
     target has previously requested.

     SYM_VALUE (hex) is the value for symbol SYM_NAME.  If GDB cannot
     supply a value for SYM_NAME, then this field will be empty.

     Reply:
     'OK'
          The target does not need to look up any (more) symbols.
     'qSymbol:SYM_NAME'
          The target requests the value of a new symbol SYM_NAME (hex
          encoded).  GDB will continue to supply the values of symbols
          (if available), until the target ceases to request them.

'qTBuffer'
'QTBuffer'
'QTDisconnected'
'QTDP'
'QTDPsrc'
'QTDV'
'qTfP'
'qTfV'
'QTFrame'
'qTMinFTPILen'

     *Note Tracepoint Packets::.

'qThreadExtraInfo,THREAD-ID'
     Obtain from the target OS a printable string description of thread
     attributes for the thread THREAD-ID; see *note thread-id syntax::,
     for the forms of THREAD-ID.  This string may contain anything that
     the target OS thinks is interesting for GDB to tell the user about
     the thread.  The string is displayed in GDB's 'info threads'
     display.  Some examples of possible thread extra info strings are
     'Runnable', or 'Blocked on Mutex'.

     Reply:
     'XX...'
          Where 'XX...' is a hex encoding of ASCII data, comprising the
          printable string containing the extra information about the
          thread's attributes.

     (Note that the 'qThreadExtraInfo' packet's name is separated from
     the command by a ',', not a ':', contrary to the naming conventions
     above.  Please don't use this packet as a model for new packets.)

'QTNotes'
'qTP'
'QTSave'
'qTsP'
'qTsV'
'QTStart'
'QTStop'
'QTEnable'
'QTDisable'
'QTinit'
'QTro'
'qTStatus'
'qTV'
'qTfSTM'
'qTsSTM'
'qTSTMat'
     *Note Tracepoint Packets::.

'qXfer:OBJECT:read:ANNEX:OFFSET,LENGTH'
     Read uninterpreted bytes from the target's special data area
     identified by the keyword OBJECT.  Request LENGTH bytes starting at
     OFFSET bytes into the data.  The content and encoding of ANNEX is
     specific to OBJECT; it can supply additional details about what
     data to access.

     Reply:
     'm DATA'
          Data DATA (*note Binary Data::) has been read from the target.
          There may be more data at a higher address (although it is
          permitted to return 'm' even for the last valid block of data,
          as long as at least one byte of data was read).  It is
          possible for DATA to have fewer bytes than the LENGTH in the
          request.

     'l DATA'
          Data DATA (*note Binary Data::) has been read from the target.
          There is no more data to be read.  It is possible for DATA to
          have fewer bytes than the LENGTH in the request.

     'l'
          The OFFSET in the request is at the end of the data.  There is
          no more data to be read.

     'E00'
          The request was malformed, or ANNEX was invalid.

     'E NN'
          The offset was invalid, or there was an error encountered
          reading the data.  The NN part is a hex-encoded 'errno' value.

     ''
          An empty reply indicates the OBJECT string was not recognized
          by the stub, or that the object does not support reading.

     Here are the specific requests of this form defined so far.  All
     the 'qXfer:OBJECT:read:...' requests use the same reply formats,
     listed above.

     'qXfer:auxv:read::OFFSET,LENGTH'
          Access the target's "auxiliary vector".  *Note auxiliary
          vector: OS Information.  Note ANNEX must be empty.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:btrace:read:ANNEX:OFFSET,LENGTH'

          Return a description of the current branch trace.  *Note
          Branch Trace Format::.  The annex part of the generic 'qXfer'
          packet may have one of the following values:

          'all'
               Returns all available branch trace.

          'new'
               Returns all available branch trace if the branch trace
               changed since the last read request.

          'delta'
               Returns the new branch trace since the last read request.
               Adds a new block to the end of the trace that begins at
               zero and ends at the source location of the first branch
               in the trace buffer.  This extra block is used to stitch
               traces together.

               If the trace buffer overflowed, returns an error
               indicating the overflow.

          This packet is not probed by default; the remote stub must
          request it by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:btrace-conf:read::OFFSET,LENGTH'

          Return a description of the current branch trace
          configuration.  *Note Branch Trace Configuration Format::.

          This packet is not probed by default; the remote stub must
          request it by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:exec-file:read:ANNEX:OFFSET,LENGTH'
          Return the full absolute name of the file that was executed to
          create a process running on the remote system.  The annex
          specifies the numeric process ID of the process to query,
          encoded as a hexadecimal number.  If the annex part is empty
          the remote stub should return the filename corresponding to
          the currently executing process.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:features:read:ANNEX:OFFSET,LENGTH'
          Access the "target description".  *Note Target Descriptions::.
          The annex specifies which XML document to access.  The main
          description is always loaded from the 'target.xml' annex.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:libraries:read:ANNEX:OFFSET,LENGTH'
          Access the target's list of loaded libraries.  *Note Library
          List Format::.  The annex part of the generic 'qXfer' packet
          must be empty (*note qXfer read::).

          Targets which maintain a list of libraries in the program's
          memory do not need to implement this packet; it is designed
          for platforms where the operating system manages the list of
          loaded libraries.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:libraries-svr4:read:ANNEX:OFFSET,LENGTH'
          Access the target's list of loaded libraries when the target
          is an SVR4 platform.  *Note Library List Format for SVR4
          Targets::.  The annex part of the generic 'qXfer' packet must
          be empty unless the remote stub indicated it supports the
          augmented form of this packet by supplying an appropriate
          'qSupported' response (*note qXfer read::, *note
          qSupported::).

          This packet is optional for better performance on SVR4
          targets.  GDB uses memory read packets to read the SVR4
          library list otherwise.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

          If the remote stub indicates it supports the augmented form of
          this packet then the annex part of the generic 'qXfer' packet
          may contain a semicolon-separated list of 'NAME=VALUE'
          arguments.  The currently supported arguments are:

          'start=ADDRESS'
               A hexadecimal number specifying the address of the
               'struct link_map' to start reading the library list from.
               If unset or zero then the first 'struct link_map' in the
               library list will be chosen as the starting point.

          'prev=ADDRESS'
               A hexadecimal number specifying the address of the
               'struct link_map' immediately preceding the 'struct
               link_map' specified by the 'start' argument.  If unset or
               zero then the remote stub will expect that no 'struct
               link_map' exists prior to the starting point.

          Arguments that are not understood by the remote stub will be
          silently ignored.

     'qXfer:memory-map:read::OFFSET,LENGTH'
          Access the target's "memory-map".  *Note Memory Map Format::.
          The annex part of the generic 'qXfer' packet must be empty
          (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:sdata:read::OFFSET,LENGTH'

          Read contents of the extra collected static tracepoint marker
          information.  The annex part of the generic 'qXfer' packet
          must be empty (*note qXfer read::).  *Note Tracepoint Action
          Lists: Tracepoint Actions.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:siginfo:read::OFFSET,LENGTH'
          Read contents of the extra signal information on the target
          system.  The annex part of the generic 'qXfer' packet must be
          empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:spu:read:ANNEX:OFFSET,LENGTH'
          Read contents of an 'spufs' file on the target system.  The
          annex specifies which file to read; it must be of the form
          'ID/NAME', where ID specifies an SPU context ID in the target
          process, and NAME identifes the 'spufs' file in that context
          to be accessed.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:threads:read::OFFSET,LENGTH'
          Access the list of threads on target.  *Note Thread List
          Format::.  The annex part of the generic 'qXfer' packet must
          be empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:traceframe-info:read::OFFSET,LENGTH'

          Return a description of the current traceframe's contents.
          *Note Traceframe Info Format::.  The annex part of the generic
          'qXfer' packet must be empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:uib:read:PC:OFFSET,LENGTH'

          Return the unwind information block for PC.  This packet is
          used on OpenVMS/ia64 to ask the kernel unwind information.

          This packet is not probed by default.

     'qXfer:fdpic:read:ANNEX:OFFSET,LENGTH'
          Read contents of 'loadmap's on the target system.  The annex,
          either 'exec' or 'interp', specifies which 'loadmap',
          executable 'loadmap' or interpreter 'loadmap' to read.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:osdata:read::OFFSET,LENGTH'
          Access the target's "operating system information".  *Note
          Operating System Information::.

'qXfer:OBJECT:write:ANNEX:OFFSET:DATA...'
     Write uninterpreted bytes into the target's special data area
     identified by the keyword OBJECT, starting at OFFSET bytes into the
     data.  The binary-encoded data (*note Binary Data::) to be written
     is given by DATA....  The content and encoding of ANNEX is specific
     to OBJECT; it can supply additional details about what data to
     access.

     Reply:
     'NN'
          NN (hex encoded) is the number of bytes written.  This may be
          fewer bytes than supplied in the request.

     'E00'
          The request was malformed, or ANNEX was invalid.

     'E NN'
          The offset was invalid, or there was an error encountered
          writing the data.  The NN part is a hex-encoded 'errno' value.

     ''
          An empty reply indicates the OBJECT string was not recognized
          by the stub, or that the object does not support writing.

     Here are the specific requests of this form defined so far.  All
     the 'qXfer:OBJECT:write:...' requests use the same reply formats,
     listed above.

     'qXfer:siginfo:write::OFFSET:DATA...'
          Write DATA to the extra signal information on the target
          system.  The annex part of the generic 'qXfer' packet must be
          empty (*note qXfer write::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:spu:write:ANNEX:OFFSET:DATA...'
          Write DATA to an 'spufs' file on the target system.  The annex
          specifies which file to write; it must be of the form
          'ID/NAME', where ID specifies an SPU context ID in the target
          process, and NAME identifes the 'spufs' file in that context
          to be accessed.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

'qXfer:OBJECT:OPERATION:...'
     Requests of this form may be added in the future.  When a stub does
     not recognize the OBJECT keyword, or its support for OBJECT does
     not recognize the OPERATION keyword, the stub must respond with an
     empty packet.

'qAttached:PID'
     Return an indication of whether the remote server attached to an
     existing process or created a new process.  When the multiprocess
     protocol extensions are supported (*note multiprocess
     extensions::), PID is an integer in hexadecimal format identifying
     the target process.  Otherwise, GDB will omit the PID field and the
     query packet will be simplified as 'qAttached'.

     This query is used, for example, to know whether the remote process
     should be detached or killed when a GDB session is ended with the
     'quit' command.

     Reply:
     '1'
          The remote server attached to an existing process.
     '0'
          The remote server created a new process.
     'E NN'
          A badly formed request or an error was encountered.

'Qbtrace:bts'
     Enable branch tracing for the current thread using Branch Trace
     Store.

     Reply:
     'OK'
          Branch tracing has been enabled.
     'E.errtext'
          A badly formed request or an error was encountered.

'Qbtrace:pt'
     Enable branch tracing for the current thread using Intel Processor
     Trace.

     Reply:
     'OK'
          Branch tracing has been enabled.
     'E.errtext'
          A badly formed request or an error was encountered.

'Qbtrace:off'
     Disable branch tracing for the current thread.

     Reply:
     'OK'
          Branch tracing has been disabled.
     'E.errtext'
          A badly formed request or an error was encountered.

'Qbtrace-conf:bts:size=VALUE'
     Set the requested ring buffer size for new threads that use the
     btrace recording method in bts format.

     Reply:
     'OK'
          The ring buffer size has been set.
     'E.errtext'
          A badly formed request or an error was encountered.

'Qbtrace-conf:pt:size=VALUE'
     Set the requested ring buffer size for new threads that use the
     btrace recording method in pt format.

     Reply:
     'OK'
          The ring buffer size has been set.
     'E.errtext'
          A badly formed request or an error was encountered.

   ---------- Footnotes ----------

   (1) The 'qP' and 'qL' packets predate these conventions, and have
arguments without any terminator for the packet name; we suspect they
are in widespread use in places that are difficult to upgrade.  The 'qC'
packet has no arguments, but some existing stubs (e.g. RedBoot) are
known to not check for the end of the packet.


File: gdb.info,  Node: Architecture-Specific Protocol Details,  Next: Tracepoint Packets,  Prev: General Query Packets,  Up: Remote Protocol

E.5 Architecture-Specific Protocol Details
==========================================

This section describes how the remote protocol is applied to specific
target architectures.  Also see *note Standard Target Features::, for
details of XML target descriptions for each architecture.

* Menu:

* ARM-Specific Protocol Details::
* MIPS-Specific Protocol Details::


File: gdb.info,  Node: ARM-Specific Protocol Details,  Next: MIPS-Specific Protocol Details,  Up: Architecture-Specific Protocol Details

E.5.1 ARM-specific Protocol Details
-----------------------------------

* Menu:

* ARM Breakpoint Kinds::


File: gdb.info,  Node: ARM Breakpoint Kinds,  Up: ARM-Specific Protocol Details

E.5.1.1 ARM Breakpoint Kinds
............................

These breakpoint kinds are defined for the 'Z0' and 'Z1' packets.

2
     16-bit Thumb mode breakpoint.

3
     32-bit Thumb mode (Thumb-2) breakpoint.

4
     32-bit ARM mode breakpoint.


File: gdb.info,  Node: MIPS-Specific Protocol Details,  Prev: ARM-Specific Protocol Details,  Up: Architecture-Specific Protocol Details

E.5.2 MIPS-specific Protocol Details
------------------------------------

* Menu:

* MIPS Register packet Format::
* MIPS Breakpoint Kinds::


File: gdb.info,  Node: MIPS Register packet Format,  Next: MIPS Breakpoint Kinds,  Up: MIPS-Specific Protocol Details

E.5.2.1 MIPS Register Packet Format
...................................

The following 'g'/'G' packets have previously been defined.  In the
below, some thirty-two bit registers are transferred as sixty-four bits.
Those registers should be zero/sign extended (which?)  to fill the space
allocated.  Register bytes are transferred in target byte order.  The
two nibbles within a register byte are transferred most-significant -
least-significant.

MIPS32
     All registers are transferred as thirty-two bit quantities in the
     order: 32 general-purpose; sr; lo; hi; bad; cause; pc; 32
     floating-point registers; fsr; fir; fp.

MIPS64
     All registers are transferred as sixty-four bit quantities
     (including thirty-two bit registers such as 'sr').  The ordering is
     the same as 'MIPS32'.


File: gdb.info,  Node: MIPS Breakpoint Kinds,  Prev: MIPS Register packet Format,  Up: MIPS-Specific Protocol Details

E.5.2.2 MIPS Breakpoint Kinds
.............................

These breakpoint kinds are defined for the 'Z0' and 'Z1' packets.

2
     16-bit MIPS16 mode breakpoint.

3
     16-bit microMIPS mode breakpoint.

4
     32-bit standard MIPS mode breakpoint.

5
     32-bit microMIPS mode breakpoint.


File: gdb.info,  Node: Tracepoint Packets,  Next: Host I/O Packets,  Prev: Architecture-Specific Protocol Details,  Up: Remote Protocol

E.6 Tracepoint Packets
======================

Here we describe the packets GDB uses to implement tracepoints (*note
Tracepoints::).

'QTDP:N:ADDR:ENA:STEP:PASS[:FFLEN][:XLEN,BYTES][-]'
     Create a new tracepoint, number N, at ADDR.  If ENA is 'E', then
     the tracepoint is enabled; if it is 'D', then the tracepoint is
     disabled.  The STEP gives the tracepoint's step count, and PASS
     gives its pass count.  If an 'F' is present, then the tracepoint is
     to be a fast tracepoint, and the FLEN is the number of bytes that
     the target should copy elsewhere to make room for the tracepoint.
     If an 'X' is present, it introduces a tracepoint condition, which
     consists of a hexadecimal length, followed by a comma and
     hex-encoded bytes, in a manner similar to action encodings as
     described below.  If the trailing '-' is present, further 'QTDP'
     packets will follow to specify this tracepoint's actions.

     Replies:
     'OK'
          The packet was understood and carried out.
     'qRelocInsn'
          *Note Relocate instruction reply packet: Tracepoint Packets.
     ''
          The packet was not recognized.

'QTDP:-N:ADDR:[S]ACTION...[-]'
     Define actions to be taken when a tracepoint is hit.  The N and
     ADDR must be the same as in the initial 'QTDP' packet for this
     tracepoint.  This packet may only be sent immediately after another
     'QTDP' packet that ended with a '-'.  If the trailing '-' is
     present, further 'QTDP' packets will follow, specifying more
     actions for this tracepoint.

     In the series of action packets for a given tracepoint, at most one
     can have an 'S' before its first ACTION.  If such a packet is sent,
     it and the following packets define "while-stepping" actions.  Any
     prior packets define ordinary actions -- that is, those taken when
     the tracepoint is first hit.  If no action packet has an 'S', then
     all the packets in the series specify ordinary tracepoint actions.

     The 'ACTION...' portion of the packet is a series of actions,
     concatenated without separators.  Each action has one of the
     following forms:

     'R MASK'
          Collect the registers whose bits are set in MASK, a
          hexadecimal number whose I'th bit is set if register number I
          should be collected.  (The least significant bit is numbered
          zero.)  Note that MASK may be any number of digits long; it
          may not fit in a 32-bit word.

     'M BASEREG,OFFSET,LEN'
          Collect LEN bytes of memory starting at the address in
          register number BASEREG, plus OFFSET.  If BASEREG is '-1',
          then the range has a fixed address: OFFSET is the address of
          the lowest byte to collect.  The BASEREG, OFFSET, and LEN
          parameters are all unsigned hexadecimal values (the '-1' value
          for BASEREG is a special case).

     'X LEN,EXPR'
          Evaluate EXPR, whose length is LEN, and collect memory as it
          directs.  The agent expression EXPR is as described in *note
          Agent Expressions::.  Each byte of the expression is encoded
          as a two-digit hex number in the packet; LEN is the number of
          bytes in the expression (and thus one-half the number of hex
          digits in the packet).

     Any number of actions may be packed together in a single 'QTDP'
     packet, as long as the packet does not exceed the maximum packet
     length (400 bytes, for many stubs).  There may be only one 'R'
     action per tracepoint, and it must precede any 'M' or 'X' actions.
     Any registers referred to by 'M' and 'X' actions must be collected
     by a preceding 'R' action.  (The "while-stepping" actions are
     treated as if they were attached to a separate tracepoint, as far
     as these restrictions are concerned.)

     Replies:
     'OK'
          The packet was understood and carried out.
     'qRelocInsn'
          *Note Relocate instruction reply packet: Tracepoint Packets.
     ''
          The packet was not recognized.

'QTDPsrc:N:ADDR:TYPE:START:SLEN:BYTES'
     Specify a source string of tracepoint N at address ADDR.  This is
     useful to get accurate reproduction of the tracepoints originally
     downloaded at the beginning of the trace run.  The TYPE is the name
     of the tracepoint part, such as 'cond' for the tracepoint's
     conditional expression (see below for a list of types), while BYTES
     is the string, encoded in hexadecimal.

     START is the offset of the BYTES within the overall source string,
     while SLEN is the total length of the source string.  This is
     intended for handling source strings that are longer than will fit
     in a single packet.

     The available string types are 'at' for the location, 'cond' for
     the conditional, and 'cmd' for an action command.  GDB sends a
     separate packet for each command in the action list, in the same
     order in which the commands are stored in the list.

     The target does not need to do anything with source strings except
     report them back as part of the replies to the 'qTfP'/'qTsP' query
     packets.

     Although this packet is optional, and GDB will only send it if the
     target replies with 'TracepointSource' *Note General Query
     Packets::, it makes both disconnected tracing and trace files much
     easier to use.  Otherwise the user must be careful that the
     tracepoints in effect while looking at trace frames are identical
     to the ones in effect during the trace run; even a small
     discrepancy could cause 'tdump' not to work, or a particular trace
     frame not be found.

'QTDV:N:VALUE:BUILTIN:NAME'
     Create a new trace state variable, number N, with an initial value
     of VALUE, which is a 64-bit signed integer.  Both N and VALUE are
     encoded as hexadecimal values.  GDB has the option of not using
     this packet for initial values of zero; the target should simply
     create the trace state variables as they are mentioned in
     expressions.  The value BUILTIN should be 1 (one) if the trace
     state variable is builtin and 0 (zero) if it is not builtin.  GDB
     only sets BUILTIN to 1 if a previous 'qTfV' or 'qTsV' packet had it
     set.  The contents of NAME is the hex-encoded name (without the
     leading '$') of the trace state variable.

'QTFrame:N'
     Select the N'th tracepoint frame from the buffer, and use the
     register and memory contents recorded there to answer subsequent
     request packets from GDB.

     A successful reply from the stub indicates that the stub has found
     the requested frame.  The response is a series of parts,
     concatenated without separators, describing the frame we selected.
     Each part has one of the following forms:

     'F F'
          The selected frame is number N in the trace frame buffer; F is
          a hexadecimal number.  If F is '-1', then there was no frame
          matching the criteria in the request packet.

     'T T'
          The selected trace frame records a hit of tracepoint number T;
          T is a hexadecimal number.

'QTFrame:pc:ADDR'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame whose PC is ADDR; ADDR is a hexadecimal
     number.

'QTFrame:tdp:T'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame that is a hit of tracepoint T; T is a
     hexadecimal number.

'QTFrame:range:START:END'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame whose PC is between START (inclusive) and
     END (inclusive); START and END are hexadecimal numbers.

'QTFrame:outside:START:END'
     Like 'QTFrame:range:START:END', but select the first frame
     _outside_ the given range of addresses (exclusive).

'qTMinFTPILen'
     This packet requests the minimum length of instruction at which a
     fast tracepoint (*note Set Tracepoints::) may be placed.  For
     instance, on the 32-bit x86 architecture, it is possible to use a
     4-byte jump, but it depends on the target system being able to
     create trampolines in the first 64K of memory, which might or might
     not be possible for that system.  So the reply to this packet will
     be 4 if it is able to arrange for that.

     Replies:

     '0'
          The minimum instruction length is currently unknown.
     'LENGTH'
          The minimum instruction length is LENGTH, where LENGTH is a
          hexadecimal number greater or equal to 1.  A reply of 1 means
          that a fast tracepoint may be placed on any instruction
          regardless of size.
     'E'
          An error has occurred.
     ''
          An empty reply indicates that the request is not supported by
          the stub.

'QTStart'
     Begin the tracepoint experiment.  Begin collecting data from
     tracepoint hits in the trace frame buffer.  This packet supports
     the 'qRelocInsn' reply (*note Relocate instruction reply packet:
     Tracepoint Packets.).

'QTStop'
     End the tracepoint experiment.  Stop collecting trace frames.

'QTEnable:N:ADDR'
     Enable tracepoint N at address ADDR in a started tracepoint
     experiment.  If the tracepoint was previously disabled, then
     collection of data from it will resume.

'QTDisable:N:ADDR'
     Disable tracepoint N at address ADDR in a started tracepoint
     experiment.  No more data will be collected from the tracepoint
     unless 'QTEnable:N:ADDR' is subsequently issued.

'QTinit'
     Clear the table of tracepoints, and empty the trace frame buffer.

'QTro:START1,END1:START2,END2:...'
     Establish the given ranges of memory as "transparent".  The stub
     will answer requests for these ranges from memory's current
     contents, if they were not collected as part of the tracepoint hit.

     GDB uses this to mark read-only regions of memory, like those
     containing program code.  Since these areas never change, they
     should still have the same contents they did when the tracepoint
     was hit, so there's no reason for the stub to refuse to provide
     their contents.

'QTDisconnected:VALUE'
     Set the choice to what to do with the tracing run when GDB
     disconnects from the target.  A VALUE of 1 directs the target to
     continue the tracing run, while 0 tells the target to stop tracing
     if GDB is no longer in the picture.

'qTStatus'
     Ask the stub if there is a trace experiment running right now.

     The reply has the form:

     'TRUNNING[;FIELD]...'
          RUNNING is a single digit '1' if the trace is presently
          running, or '0' if not.  It is followed by semicolon-separated
          optional fields that an agent may use to report additional
          status.

     If the trace is not running, the agent may report any of several
     explanations as one of the optional fields:

     'tnotrun:0'
          No trace has been run yet.

     'tstop[:TEXT]:0'
          The trace was stopped by a user-originated stop command.  The
          optional TEXT field is a user-supplied string supplied as part
          of the stop command (for instance, an explanation of why the
          trace was stopped manually).  It is hex-encoded.

     'tfull:0'
          The trace stopped because the trace buffer filled up.

     'tdisconnected:0'
          The trace stopped because GDB disconnected from the target.

     'tpasscount:TPNUM'
          The trace stopped because tracepoint TPNUM exceeded its pass
          count.

     'terror:TEXT:TPNUM'
          The trace stopped because tracepoint TPNUM had an error.  The
          string TEXT is available to describe the nature of the error
          (for instance, a divide by zero in the condition expression);
          it is hex encoded.

     'tunknown:0'
          The trace stopped for some other reason.

     Additional optional fields supply statistical and other
     information.  Although not required, they are extremely useful for
     users monitoring the progress of a trace run.  If a trace has
     stopped, and these numbers are reported, they must reflect the
     state of the just-stopped trace.

     'tframes:N'
          The number of trace frames in the buffer.

     'tcreated:N'
          The total number of trace frames created during the run.  This
          may be larger than the trace frame count, if the buffer is
          circular.

     'tsize:N'
          The total size of the trace buffer, in bytes.

     'tfree:N'
          The number of bytes still unused in the buffer.

     'circular:N'
          The value of the circular trace buffer flag.  '1' means that
          the trace buffer is circular and old trace frames will be
          discarded if necessary to make room, '0' means that the trace
          buffer is linear and may fill up.

     'disconn:N'
          The value of the disconnected tracing flag.  '1' means that
          tracing will continue after GDB disconnects, '0' means that
          the trace run will stop.

'qTP:TP:ADDR'
     Ask the stub for the current state of tracepoint number TP at
     address ADDR.

     Replies:
     'VHITS:USAGE'
          The tracepoint has been hit HITS times so far during the trace
          run, and accounts for USAGE in the trace buffer.  Note that
          'while-stepping' steps are not counted as separate hits, but
          the steps' space consumption is added into the usage number.

'qTV:VAR'
     Ask the stub for the value of the trace state variable number VAR.

     Replies:
     'VVALUE'
          The value of the variable is VALUE.  This will be the current
          value of the variable if the user is examining a running
          target, or a saved value if the variable was collected in the
          trace frame that the user is looking at.  Note that multiple
          requests may result in different reply values, such as when
          requesting values while the program is running.

     'U'
          The value of the variable is unknown.  This would occur, for
          example, if the user is examining a trace frame in which the
          requested variable was not collected.

'qTfP'
'qTsP'
     These packets request data about tracepoints that are being used by
     the target.  GDB sends 'qTfP' to get the first piece of data, and
     multiple 'qTsP' to get additional pieces.  Replies to these packets
     generally take the form of the 'QTDP' packets that define
     tracepoints.  (FIXME add detailed syntax)

'qTfV'
'qTsV'
     These packets request data about trace state variables that are on
     the target.  GDB sends 'qTfV' to get the first vari of data, and
     multiple 'qTsV' to get additional variables.  Replies to these
     packets follow the syntax of the 'QTDV' packets that define trace
     state variables.

'qTfSTM'
'qTsSTM'
     These packets request data about static tracepoint markers that
     exist in the target program.  GDB sends 'qTfSTM' to get the first
     piece of data, and multiple 'qTsSTM' to get additional pieces.
     Replies to these packets take the following form:

     Reply:
     'm ADDRESS:ID:EXTRA'
          A single marker
     'm ADDRESS:ID:EXTRA,ADDRESS:ID:EXTRA...'
          a comma-separated list of markers
     'l'
          (lower case letter 'L') denotes end of list.
     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.
     ''
          An empty reply indicates that the request is not supported by
          the stub.

     The ADDRESS is encoded in hex; ID and EXTRA are strings encoded in
     hex.

     In response to each query, the target will reply with a list of one
     or more markers, separated by commas.  GDB will respond to each
     reply with a request for more markers (using the 'qs' form of the
     query), until the target responds with 'l' (lower-case ell, for
     "last").

'qTSTMat:ADDRESS'
     This packets requests data about static tracepoint markers in the
     target program at ADDRESS.  Replies to this packet follow the
     syntax of the 'qTfSTM' and 'qTsSTM' packets that list static
     tracepoint markers.

'QTSave:FILENAME'
     This packet directs the target to save trace data to the file name
     FILENAME in the target's filesystem.  The FILENAME is encoded as a
     hex string; the interpretation of the file name (relative vs
     absolute, wild cards, etc) is up to the target.

'qTBuffer:OFFSET,LEN'
     Return up to LEN bytes of the current contents of trace buffer,
     starting at OFFSET.  The trace buffer is treated as if it were a
     contiguous collection of traceframes, as per the trace file format.
     The reply consists as many hex-encoded bytes as the target can
     deliver in a packet; it is not an error to return fewer than were
     asked for.  A reply consisting of just 'l' indicates that no bytes
     are available.

'QTBuffer:circular:VALUE'
     This packet directs the target to use a circular trace buffer if
     VALUE is 1, or a linear buffer if the value is 0.

'QTBuffer:size:SIZE'
     This packet directs the target to make the trace buffer be of size
     SIZE if possible.  A value of '-1' tells the target to use whatever
     size it prefers.

'QTNotes:[TYPE:TEXT][;TYPE:TEXT]...'
     This packet adds optional textual notes to the trace run.
     Allowable types include 'user', 'notes', and 'tstop', the TEXT
     fields are arbitrary strings, hex-encoded.

E.6.1 Relocate instruction reply packet
---------------------------------------

When installing fast tracepoints in memory, the target may need to
relocate the instruction currently at the tracepoint address to a
different address in memory.  For most instructions, a simple copy is
enough, but, for example, call instructions that implicitly push the
return address on the stack, and relative branches or other PC-relative
instructions require offset adjustment, so that the effect of executing
the instruction at a different address is the same as if it had executed
in the original location.

   In response to several of the tracepoint packets, the target may also
respond with a number of intermediate 'qRelocInsn' request packets
before the final result packet, to have GDB handle this relocation
operation.  If a packet supports this mechanism, its documentation will
explicitly say so.  See for example the above descriptions for the
'QTStart' and 'QTDP' packets.  The format of the request is:

'qRelocInsn:FROM;TO'

     This requests GDB to copy instruction at address FROM to address
     TO, possibly adjusted so that executing the instruction at TO has
     the same effect as executing it at FROM.  GDB writes the adjusted
     instruction to target memory starting at TO.

   Replies:
'qRelocInsn:ADJUSTED_SIZE'
     Informs the stub the relocation is complete.  The ADJUSTED_SIZE is
     the length in bytes of resulting relocated instruction sequence.
'E NN'
     A badly formed request was detected, or an error was encountered
     while relocating the instruction.


File: gdb.info,  Node: Host I/O Packets,  Next: Interrupts,  Prev: Tracepoint Packets,  Up: Remote Protocol

E.7 Host I/O Packets
====================

The "Host I/O" packets allow GDB to perform I/O operations on the far
side of a remote link.  For example, Host I/O is used to upload and
download files to a remote target with its own filesystem.  Host I/O
uses the same constant values and data structure layout as the
target-initiated File-I/O protocol.  However, the Host I/O packets are
structured differently.  The target-initiated protocol relies on target
memory to store parameters and buffers.  Host I/O requests are initiated
by GDB, and the target's memory is not involved.  *Note File-I/O Remote
Protocol Extension::, for more details on the target-initiated protocol.

   The Host I/O request packets all encode a single operation along with
its arguments.  They have this format:

'vFile:OPERATION: PARAMETER...'
     OPERATION is the name of the particular request; the target should
     compare the entire packet name up to the second colon when checking
     for a supported operation.  The format of PARAMETER depends on the
     operation.  Numbers are always passed in hexadecimal.  Negative
     numbers have an explicit minus sign (i.e. two's complement is not
     used).  Strings (e.g. filenames) are encoded as a series of
     hexadecimal bytes.  The last argument to a system call may be a
     buffer of escaped binary data (*note Binary Data::).

   The valid responses to Host I/O packets are:

'F RESULT [, ERRNO] [; ATTACHMENT]'
     RESULT is the integer value returned by this operation, usually
     non-negative for success and -1 for errors.  If an error has
     occured, ERRNO will be included in the result specifying a value
     defined by the File-I/O protocol (*note Errno Values::).  For
     operations which return data, ATTACHMENT supplies the data as a
     binary buffer.  Binary buffers in response packets are escaped in
     the normal way (*note Binary Data::).  See the individual packet
     documentation for the interpretation of RESULT and ATTACHMENT.

''
     An empty response indicates that this operation is not recognized.

   These are the supported Host I/O operations:

'vFile:open: FILENAME, FLAGS, MODE'
     Open a file at FILENAME and return a file descriptor for it, or
     return -1 if an error occurs.  The FILENAME is a string, FLAGS is
     an integer indicating a mask of open flags (*note Open Flags::),
     and MODE is an integer indicating a mask of mode bits to use if the
     file is created (*note mode_t Values::).  *Note open::, for details
     of the open flags and mode values.

'vFile:close: FD'
     Close the open file corresponding to FD and return 0, or -1 if an
     error occurs.

'vFile:pread: FD, COUNT, OFFSET'
     Read data from the open file corresponding to FD.  Up to COUNT
     bytes will be read from the file, starting at OFFSET relative to
     the start of the file.  The target may read fewer bytes; common
     reasons include packet size limits and an end-of-file condition.
     The number of bytes read is returned.  Zero should only be returned
     for a successful read at the end of the file, or if COUNT was zero.

     The data read should be returned as a binary attachment on success.
     If zero bytes were read, the response should include an empty
     binary attachment (i.e. a trailing semicolon).  The return value is
     the number of target bytes read; the binary attachment may be
     longer if some characters were escaped.

'vFile:pwrite: FD, OFFSET, DATA'
     Write DATA (a binary buffer) to the open file corresponding to FD.
     Start the write at OFFSET from the start of the file.  Unlike many
     'write' system calls, there is no separate COUNT argument; the
     length of DATA in the packet is used.  'vFile:write' returns the
     number of bytes written, which may be shorter than the length of
     DATA, or -1 if an error occurred.

'vFile:fstat: FD'
     Get information about the open file corresponding to FD.  On
     success the information is returned as a binary attachment and the
     return value is the size of this attachment in bytes.  If an error
     occurs the return value is -1.  The format of the returned binary
     attachment is as described in *note struct stat::.

'vFile:unlink: FILENAME'
     Delete the file at FILENAME on the target.  Return 0, or -1 if an
     error occurs.  The FILENAME is a string.

'vFile:readlink: FILENAME'
     Read value of symbolic link FILENAME on the target.  Return the
     number of bytes read, or -1 if an error occurs.

     The data read should be returned as a binary attachment on success.
     If zero bytes were read, the response should include an empty
     binary attachment (i.e. a trailing semicolon).  The return value is
     the number of target bytes read; the binary attachment may be
     longer if some characters were escaped.

'vFile:setfs: PID'
     Select the filesystem on which 'vFile' operations with FILENAME
     arguments will operate.  This is required for GDB to be able to
     access files on remote targets where the remote stub does not share
     a common filesystem with the inferior(s).

     If PID is nonzero, select the filesystem as seen by process PID.
     If PID is zero, select the filesystem as seen by the remote stub.
     Return 0 on success, or -1 if an error occurs.  If 'vFile:setfs:'
     indicates success, the selected filesystem remains selected until
     the next successful 'vFile:setfs:' operation.


File: gdb.info,  Node: Interrupts,  Next: Notification Packets,  Prev: Host I/O Packets,  Up: Remote Protocol

E.8 Interrupts
==============

In all-stop mode, when a program on the remote target is running, GDB
may attempt to interrupt it by sending a 'Ctrl-C', 'BREAK' or a 'BREAK'
followed by 'g', control of which is specified via GDB's
'interrupt-sequence'.

   The precise meaning of 'BREAK' is defined by the transport mechanism
and may, in fact, be undefined.  GDB does not currently define a 'BREAK'
mechanism for any of the network interfaces except for TCP, in which
case GDB sends the 'telnet' BREAK sequence.

   'Ctrl-C', on the other hand, is defined and implemented for all
transport mechanisms.  It is represented by sending the single byte
'0x03' without any of the usual packet overhead described in the
Overview section (*note Overview::).  When a '0x03' byte is transmitted
as part of a packet, it is considered to be packet data and does _not_
represent an interrupt.  E.g., an 'X' packet (*note X packet::), used
for binary downloads, may include an unescaped '0x03' as part of its
packet.

   'BREAK' followed by 'g' is also known as Magic SysRq g.  When Linux
kernel receives this sequence from serial port, it stops execution and
connects to gdb.

   In non-stop mode, because packet resumptions are asynchronous (*note
vCont packet::), GDB is always free to send a remote command to the
remote stub, even when the target is running.  For that reason, GDB
instead sends a regular packet (*note vCtrlC packet::) with the usual
packet framing instead of the single byte '0x03'.

   Stubs are not required to recognize these interrupt mechanisms and
the precise meaning associated with receipt of the interrupt is
implementation defined.  If the target supports debugging of multiple
threads and/or processes, it should attempt to interrupt all
currently-executing threads and processes.  If the stub is successful at
interrupting the running program, it should send one of the stop reply
packets (*note Stop Reply Packets::) to GDB as a result of successfully
stopping the program in all-stop mode, and a stop reply for each stopped
thread in non-stop mode.  Interrupts received while the program is
stopped are queued and the program will be interrupted when it is
resumed next time.


File: gdb.info,  Node: Notification Packets,  Next: Remote Non-Stop,  Prev: Interrupts,  Up: Remote Protocol

E.9 Notification Packets
========================

The GDB remote serial protocol includes "notifications", packets that
require no acknowledgment.  Both the GDB and the stub may send
notifications (although the only notifications defined at present are
sent by the stub).  Notifications carry information without incurring
the round-trip latency of an acknowledgment, and so are useful for
low-impact communications where occasional packet loss is not a problem.

   A notification packet has the form '% DATA # CHECKSUM', where DATA is
the content of the notification, and CHECKSUM is a checksum of DATA,
computed and formatted as for ordinary GDB packets.  A notification's
DATA never contains '$', '%' or '#' characters.  Upon receiving a
notification, the recipient sends no '+' or '-' to acknowledge the
notification's receipt or to report its corruption.

   Every notification's DATA begins with a name, which contains no colon
characters, followed by a colon character.

   Recipients should silently ignore corrupted notifications and
notifications they do not understand.  Recipients should restart timeout
periods on receipt of a well-formed notification, whether or not they
understand it.

   Senders should only send the notifications described here when this
protocol description specifies that they are permitted.  In the future,
we may extend the protocol to permit existing notifications in new
contexts; this rule helps older senders avoid confusing newer
recipients.

   (Older versions of GDB ignore bytes received until they see the '$'
byte that begins an ordinary packet, so new stubs may transmit
notifications without fear of confusing older clients.  There are no
notifications defined for GDB to send at the moment, but we assume that
most older stubs would ignore them, as well.)

   Each notification is comprised of three parts:
'NAME:EVENT'
     The notification packet is sent by the side that initiates the
     exchange (currently, only the stub does that), with EVENT carrying
     the specific information about the notification, and NAME
     specifying the name of the notification.
'ACK'
     The acknowledge sent by the other side, usually GDB, to acknowledge
     the exchange and request the event.

   The purpose of an asynchronous notification mechanism is to report to
GDB that something interesting happened in the remote stub.

   The remote stub may send notification NAME:EVENT at any time, but GDB
acknowledges the notification when appropriate.  The notification event
is pending before GDB acknowledges.  Only one notification at a time may
be pending; if additional events occur before GDB has acknowledged the
previous notification, they must be queued by the stub for later
synchronous transmission in response to ACK packets from GDB.  Because
the notification mechanism is unreliable, the stub is permitted to
resend a notification if it believes GDB may not have received it.

   Specifically, notifications may appear when GDB is not otherwise
reading input from the stub, or when GDB is expecting to read a normal
synchronous response or a '+'/'-' acknowledgment to a packet it has
sent.  Notification packets are distinct from any other communication
from the stub so there is no ambiguity.

   After receiving a notification, GDB shall acknowledge it by sending a
ACK packet as a regular, synchronous request to the stub.  Such
acknowledgment is not required to happen immediately, as GDB is
permitted to send other, unrelated packets to the stub first, which the
stub should process normally.

   Upon receiving a ACK packet, if the stub has other queued events to
report to GDB, it shall respond by sending a normal EVENT.  GDB shall
then send another ACK packet to solicit further responses; again, it is
permitted to send other, unrelated packets as well which the stub should
process normally.

   If the stub receives a ACK packet and there are no additional EVENT
to report, the stub shall return an 'OK' response.  At this point, GDB
has finished processing a notification and the stub has completed
sending any queued events.  GDB won't accept any new notifications until
the final 'OK' is received .  If further notification events occur, the
stub shall send a new notification, GDB shall accept the notification,
and the process shall be repeated.

   The process of asynchronous notification can be illustrated by the
following example:
     <- %Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;
     ...
     -> vStopped
     <- T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;
     -> vStopped
     <- T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;
     -> vStopped
     <- OK

   The following notifications are defined:

NotificationAck     Event                       Description
                                                
Stop      vStopped  REPLY.  The REPLY has the   Report an asynchronous
                    form of a stop reply, as    stop event in non-stop
                    described in                mode.
                    *note Stop Reply Packets::. 
                    Refer to
                    *note Remote Non-Stop::,
                    for information on how
                    these notifications are
                    acknowledged by GDB.


File: gdb.info,  Node: Remote Non-Stop,  Next: Packet Acknowledgment,  Prev: Notification Packets,  Up: Remote Protocol

E.10 Remote Protocol Support for Non-Stop Mode
==============================================

GDB's remote protocol supports non-stop debugging of multi-threaded
programs, as described in *note Non-Stop Mode::.  If the stub supports
non-stop mode, it should report that to GDB by including 'QNonStop+' in
its 'qSupported' response (*note qSupported::).

   GDB typically sends a 'QNonStop' packet only when establishing a new
connection with the stub.  Entering non-stop mode does not alter the
state of any currently-running threads, but targets must stop all
threads in any already-attached processes when entering all-stop mode.
GDB uses the '?' packet as necessary to probe the target state after a
mode change.

   In non-stop mode, when an attached process encounters an event that
would otherwise be reported with a stop reply, it uses the asynchronous
notification mechanism (*note Notification Packets::) to inform GDB.  In
contrast to all-stop mode, where all threads in all processes are
stopped when a stop reply is sent, in non-stop mode only the thread
reporting the stop event is stopped.  That is, when reporting a 'S' or
'T' response to indicate completion of a step operation, hitting a
breakpoint, or a fault, only the affected thread is stopped; any other
still-running threads continue to run.  When reporting a 'W' or 'X'
response, all running threads belonging to other attached processes
continue to run.

   In non-stop mode, the target shall respond to the '?' packet as
follows.  First, any incomplete stop reply notification/'vStopped'
sequence in progress is abandoned.  The target must begin a new sequence
reporting stop events for all stopped threads, whether or not it has
previously reported those events to GDB.  The first stop reply is sent
as a synchronous reply to the '?' packet, and subsequent stop replies
are sent as responses to 'vStopped' packets using the mechanism
described above.  The target must not send asynchronous stop reply
notifications until the sequence is complete.  If all threads are
running when the target receives the '?' packet, or if the target is not
attached to any process, it shall respond 'OK'.

   If the stub supports non-stop mode, it should also support the
'swbreak' stop reason if software breakpoints are supported, and the
'hwbreak' stop reason if hardware breakpoints are supported (*note
swbreak stop reason::).  This is because given the asynchronous nature
of non-stop mode, between the time a thread hits a breakpoint and the
time the event is finally processed by GDB, the breakpoint may have
already been removed from the target.  Due to this, GDB needs to be able
to tell whether a trap stop was caused by a delayed breakpoint event,
which should be ignored, as opposed to a random trap signal, which
should be reported to the user.  Note the 'swbreak' feature implies that
the target is responsible for adjusting the PC when a software
breakpoint triggers, if necessary, such as on the x86 architecture.


File: gdb.info,  Node: Packet Acknowledgment,  Next: Examples,  Prev: Remote Non-Stop,  Up: Remote Protocol

E.11 Packet Acknowledgment
==========================

By default, when either the host or the target machine receives a
packet, the first response expected is an acknowledgment: either '+' (to
indicate the package was received correctly) or '-' (to request
retransmission).  This mechanism allows the GDB remote protocol to
operate over unreliable transport mechanisms, such as a serial line.

   In cases where the transport mechanism is itself reliable (such as a
pipe or TCP connection), the '+'/'-' acknowledgments are redundant.  It
may be desirable to disable them in that case to reduce communication
overhead, or for other reasons.  This can be accomplished by means of
the 'QStartNoAckMode' packet; *note QStartNoAckMode::.

   When in no-acknowledgment mode, neither the stub nor GDB shall send
or expect '+'/'-' protocol acknowledgments.  The packet and response
format still includes the normal checksum, as described in *note
Overview::, but the checksum may be ignored by the receiver.

   If the stub supports 'QStartNoAckMode' and prefers to operate in
no-acknowledgment mode, it should report that to GDB by including
'QStartNoAckMode+' in its response to 'qSupported'; *note qSupported::.
If GDB also supports 'QStartNoAckMode' and it has not been disabled via
the 'set remote noack-packet off' command (*note Remote
Configuration::), GDB may then send a 'QStartNoAckMode' packet to the
stub.  Only then may the stub actually turn off packet acknowledgments.
GDB sends a final '+' acknowledgment of the stub's 'OK' response, which
can be safely ignored by the stub.

   Note that 'set remote noack-packet' command only affects negotiation
between GDB and the stub when subsequent connections are made; it does
not affect the protocol acknowledgment state for any current connection.
Since '+'/'-' acknowledgments are enabled by default when a new
connection is established, there is also no protocol request to
re-enable the acknowledgments for the current connection, once disabled.


File: gdb.info,  Node: Examples,  Next: File-I/O Remote Protocol Extension,  Prev: Packet Acknowledgment,  Up: Remote Protocol

E.12 Examples
=============

Example sequence of a target being re-started.  Notice how the restart
does not get any direct output:

     -> R00
     <- +
     _target restarts_
     -> ?
     <- +
     <- T001:1234123412341234
     -> +

   Example sequence of a target being stepped by a single instruction:

     -> G1445...
     <- +
     -> s
     <- +
     _time passes_
     <- T001:1234123412341234
     -> +
     -> g
     <- +
     <- 1455...
     -> +


File: gdb.info,  Node: File-I/O Remote Protocol Extension,  Next: Library List Format,  Prev: Examples,  Up: Remote Protocol

E.13 File-I/O Remote Protocol Extension
=======================================

* Menu:

* File-I/O Overview::
* Protocol Basics::
* The F Request Packet::
* The F Reply Packet::
* The Ctrl-C Message::
* Console I/O::
* List of Supported Calls::
* Protocol-specific Representation of Datatypes::
* Constants::
* File-I/O Examples::


File: gdb.info,  Node: File-I/O Overview,  Next: Protocol Basics,  Up: File-I/O Remote Protocol Extension

E.13.1 File-I/O Overview
------------------------

The "File I/O remote protocol extension" (short: File-I/O) allows the
target to use the host's file system and console I/O to perform various
system calls.  System calls on the target system are translated into a
remote protocol packet to the host system, which then performs the
needed actions and returns a response packet to the target system.  This
simulates file system operations even on targets that lack file systems.

   The protocol is defined to be independent of both the host and target
systems.  It uses its own internal representation of datatypes and
values.  Both GDB and the target's GDB stub are responsible for
translating the system-dependent value representations into the internal
protocol representations when data is transmitted.

   The communication is synchronous.  A system call is possible only
when GDB is waiting for a response from the 'C', 'c', 'S' or 's'
packets.  While GDB handles the request for a system call, the target is
stopped to allow deterministic access to the target's memory.  Therefore
File-I/O is not interruptible by target signals.  On the other hand, it
is possible to interrupt File-I/O by a user interrupt ('Ctrl-C') within
GDB.

   The target's request to perform a host system call does not finish
the latest 'C', 'c', 'S' or 's' action.  That means, after finishing the
system call, the target returns to continuing the previous activity
(continue, step).  No additional continue or step request from GDB is
required.

     (gdb) continue
       <- target requests 'system call X'
       target is stopped, GDB executes system call
       -> GDB returns result
       ... target continues, GDB returns to wait for the target
       <- target hits breakpoint and sends a Txx packet

   The protocol only supports I/O on the console and to regular files on
the host file system.  Character or block special devices, pipes, named
pipes, sockets or any other communication method on the host system are
not supported by this protocol.

   File I/O is not supported in non-stop mode.


File: gdb.info,  Node: Protocol Basics,  Next: The F Request Packet,  Prev: File-I/O Overview,  Up: File-I/O Remote Protocol Extension

E.13.2 Protocol Basics
----------------------

The File-I/O protocol uses the 'F' packet as the request as well as
reply packet.  Since a File-I/O system call can only occur when GDB is
waiting for a response from the continuing or stepping target, the
File-I/O request is a reply that GDB has to expect as a result of a
previous 'C', 'c', 'S' or 's' packet.  This 'F' packet contains all
information needed to allow GDB to call the appropriate host system
call:

   * A unique identifier for the requested system call.

   * All parameters to the system call.  Pointers are given as addresses
     in the target memory address space.  Pointers to strings are given
     as pointer/length pair.  Numerical values are given as they are.
     Numerical control flags are given in a protocol-specific
     representation.

   At this point, GDB has to perform the following actions.

   * If the parameters include pointer values to data needed as input to
     a system call, GDB requests this data from the target with a
     standard 'm' packet request.  This additional communication has to
     be expected by the target implementation and is handled as any
     other 'm' packet.

   * GDB translates all value from protocol representation to host
     representation as needed.  Datatypes are coerced into the host
     types.

   * GDB calls the system call.

   * It then coerces datatypes back to protocol representation.

   * If the system call is expected to return data in buffer space
     specified by pointer parameters to the call, the data is
     transmitted to the target using a 'M' or 'X' packet.  This packet
     has to be expected by the target implementation and is handled as
     any other 'M' or 'X' packet.

   Eventually GDB replies with another 'F' packet which contains all
necessary information for the target to continue.  This at least
contains

   * Return value.

   * 'errno', if has been changed by the system call.

   * "Ctrl-C" flag.

   After having done the needed type and value coercion, the target
continues the latest continue or step action.

