gdb/doc/annotate.texinfo

\input texinfo   @c -*-texinfo-*-
@c %**start of header
@setfilename annotate.info

@c This is a dir.info fragment to support semi-automated addition of
@c manuals to an info tree.
@dircategory Software development
@direntry
* Annotate: (annotate).                 The obsolete annotation interface.
@end direntry

@c
@include gdb-cfg.texi
@c
@settitle @value{GDBN}'s Obsolete Annotations
@setchapternewpage off
@c %**end of header

@set EDITION 1.0
@set DATE July 2003

@c NOTE: cagney/2003-07-28:
@c Don't make this migration document an appendix of GDB's user guide.
@c By keeping this separate, the size of the user guide is contained. If
@c the user guide to get much bigger it would need to switch to a larger,
@c more expensive, form factor and would drive up the manuals publication
@c cost.  Having a smaller cheaper manual helps the GNU Press with its sales.

@copying
Copyright @copyright{} 1994--2021 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@end copying

@ifnottex
This file documents @value{GDBN}'s obsolete annotations.

@insertcopying
@end ifnottex

@titlepage
@title @value{GDBN}'s Obsolete Annotations
@subtitle Edition @value{EDITION}
@subtitle @value{DATE}
@author Free Software Foundation
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@ifnottex
@node Top
@top GDB Annotations

This document describes the obsolete level two annotation interface
implemented in older @value{GDBN} versions.

@ignore
This is Edition @value{EDITION}, @value{DATE}.
@end ignore
@end ifnottex

@menu
* Annotations Overview::  What annotations are; the general syntax.
* Limitations::           Limitations of the annotation interface.
* Migrating to GDB/MI::   Migrating to GDB/MI
* Server Prefix::       Issuing a command without affecting user state.
* Value Annotations::   Values are marked as such.
* Frame Annotations::   Stack frames are annotated.
* Displays::            @value{GDBN} can be told to display something periodically.
* Prompting::           Annotations marking @value{GDBN}'s need for input.
* Errors::              Annotations for error messages.
* Breakpoint Info::     Information on breakpoints.
* 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.
* Multi-threaded Apps:: An annotation that reports multi-threadedness.

* GNU Free Documentation License::
@end menu

@contents

@node Annotations Overview
@chapter What is an Annotation?
@cindex annotations

To produce obsolete level two annotations, start @value{GDBN} with the
@code{--annotate=2} option.

Annotations start with a newline character, two @samp{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 @samp{control-z}
characters denotes literal output from @value{GDBN}.  Currently there is
no need for @value{GDBN} to output a newline followed by two
@samp{control-z} characters, but if there was such a need, the
annotations could be extended with an @samp{escape} annotation which
means those three characters as output.

A simple example of starting up @value{GDBN} with annotations is:

@smallexample
$ gdb --annotate=2
GNU GDB 5.0
Copyright 2000 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 "sparc-sun-sunos4.1.3"

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

^Z^Zpost-prompt
$ 
@end smallexample

Here @samp{quit} is input to @value{GDBN}; the rest is output from
@value{GDBN}.  The three lines beginning @samp{^Z^Z} (where @samp{^Z}
denotes a @samp{control-z} character) are annotations; the rest is
output from @value{GDBN}.

@node Limitations
@chapter Limitations of the Annotation Interface

The level two annotations mechanism is known to have a number of
technical and architectural limitations.  As a consequence, in 2001,
with the release of @value{GDBN} 5.1 and the addition of @sc{gdb/mi},
the annotation interface was marked as deprecated.

This chapter discusses the known problems.

@section Dependant on @sc{cli} output

The annotation interface works by interspersing markups with
@value{GDBN} normal command-line interpreter output.  Unfortunately, this
makes the annotation client dependant on not just the annotations, but
also the @sc{cli} output.  This is because the client is forced to
assume that specific @value{GDBN} commands provide specific information.
Any change to @value{GDBN}'s @sc{cli} output modifies or removes that
information and, consequently, likely breaks the client.

Since the @sc{gdb/mi} output is independent of the @sc{cli}, it does not
have this problem.

@section Scalability

The annotation interface relies on value annotations (@pxref{Value
Annotations}) and the display mechanism as a way of obtaining up-to-date
value information.  These mechanisms are not scalable.

In a graphical environment, where many values can be displayed
simultaneously, a serious performance problem occurs when the client
tries to first extract from @value{GDBN}, and then re-display, all those
values.  The client should instead only request and update the values
that changed.

The @sc{gdb/mi} Variable Objects provide just that mechanism.

@section Correctness

The annotation interface assumes that a variable's value can only be
changed when the target is running.  This assumption is not correct.  A
single assignment to a single variable can result in the entire target,
and all displayed values, needing an update.

The @sc{gdb/mi} Variable Objects include a mechanism for efficiently
reporting such changes.

@section Reliability

The @sc{gdb/mi} interface includes a dedicated test directory
(@file{gdb/gdb.mi}), and any addition or fix to @sc{gdb/mi} must include
testsuite changes.

@section Maintainability

The annotation mechanism was implemented by interspersing @sc{cli} print
statements with various annotations.  As a consequence, any @sc{cli}
output change can alter the annotation output.

Since the @sc{gdb/mi} output is independent of the @sc{cli}, and the
@sc{gdb/mi} is increasingly implemented independent of the @sc{cli}
code, its long term maintenance is much easier.

@node Migrating to GDB/MI
@chapter Migrating to @sc{gdb/mi}

By using the @samp{interp mi} command, it is possible for annotation
clients to invoke @sc{gdb/mi} commands, and hence access the
@sc{gdb/mi}.  By doing this, existing annotation clients have a
migration path from this obsolete interface to @sc{gdb/mi}.

@node Server Prefix
@chapter The Server Prefix
@cindex server prefix for annotations

To issue a command to @value{GDBN} without affecting certain aspects of
the state which is seen by users, prefix it with @samp{server }.  This
means that this command will not affect the command history, nor will it
affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
pressed on a line by itself.

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 @code{output} command instead of the @code{print} command.

@node Value Annotations
@chapter Values

@emph{Value Annotations have been removed.  @sc{gdb/mi} instead provides
Variable Objects.}

@cindex annotations for values
When a value is printed in various contexts, @value{GDBN} uses
annotations to delimit the value from the surrounding text.

@findex value-history-begin
@findex value-history-value
@findex value-history-end
If a value is printed using @code{print} and added to the value history,
the annotation looks like

@smallexample
^Z^Zvalue-history-begin @var{history-number} @var{value-flags}
@var{history-string}
^Z^Zvalue-history-value
@var{the-value}
^Z^Zvalue-history-end
@end smallexample

@noindent
where @var{history-number} is the number it is getting in the value
history, @var{history-string} is a string, such as @samp{$5 = }, which
introduces the value to the user, @var{the-value} is the output
corresponding to the value itself, and @var{value-flags} is @samp{*} for
a value which can be dereferenced and @samp{-} for a value which cannot.

@findex value-begin
@findex value-end
If the value is not added to the value history (it is an invalid float
or it is printed with the @code{output} command), the annotation is similar:

@smallexample
^Z^Zvalue-begin @var{value-flags}
@var{the-value}
^Z^Zvalue-end
@end smallexample

@findex arg-begin
@findex arg-name-end
@findex arg-value
@findex arg-end
When @value{GDBN} prints an argument to a function (for example, in the output
from the @code{backtrace} command), it annotates it as follows:

@smallexample
^Z^Zarg-begin
@var{argument-name}
^Z^Zarg-name-end
@var{separator-string}
^Z^Zarg-value @var{value-flags}
@var{the-value}
^Z^Zarg-end
@end smallexample

@noindent
where @var{argument-name} is the name of the argument,
@var{separator-string} is text which separates the name from the value
for the user's benefit (such as @samp{=}), and @var{value-flags} and
@var{the-value} have the same meanings as in a
@code{value-history-begin} annotation.

@findex field-begin
@findex field-name-end
@findex field-value
@findex field-end
When printing a structure, @value{GDBN} annotates it as follows:

@smallexample
^Z^Zfield-begin @var{value-flags}
@var{field-name}
^Z^Zfield-name-end
@var{separator-string}
^Z^Zfield-value
@var{the-value}
^Z^Zfield-end
@end smallexample

@noindent
where @var{field-name} is the name of the field, @var{separator-string}
is text which separates the name from the value for the user's benefit
(such as @samp{=}), and @var{value-flags} and @var{the-value} have the
same meanings as in a @code{value-history-begin} annotation.

When printing an array, @value{GDBN} annotates it as follows:

@smallexample
^Z^Zarray-section-begin @var{array-index} @var{value-flags}
@end smallexample

@noindent
where @var{array-index} is the index of the first element being
annotated and @var{value-flags} has the same meaning as in a
@code{value-history-begin} annotation.  This is followed by any number
of elements, where is element can be either a single element:

@findex elt
@smallexample
@samp{,} @var{whitespace}         ; @r{omitted for the first element}
@var{the-value}
^Z^Zelt
@end smallexample

or a repeated element

@findex elt-rep
@findex elt-rep-end
@smallexample
@samp{,} @var{whitespace}         ; @r{omitted for the first element}
@var{the-value}
^Z^Zelt-rep @var{number-of-repetitions}
@var{repetition-string}
^Z^Zelt-rep-end
@end smallexample

In both cases, @var{the-value} is the output for the value of the
element and @var{whitespace} can contain spaces, tabs, and newlines.  In
the repeated case, @var{number-of-repetitions} is the number of
consecutive array elements which contain that value, and
@var{repetition-string} is a string which is designed to convey to the
user that repetition is being depicted.

@findex array-section-end
Once all the array elements have been output, the array annotation is
ended with

@smallexample
^Z^Zarray-section-end
@end smallexample

@node Frame Annotations
@chapter Frames

@emph{Value Annotations have been removed.  @sc{gdb/mi} instead provides
a number of frame commands.}

@emph{Frame annotations are no longer available.  The @sc{gdb/mi}
provides @samp{-stack-list-arguments}, @samp{-stack-list-locals}, and
@samp{-stack-list-frames} commands.}

@cindex annotations for frames
Whenever @value{GDBN} prints a frame, it annotates it.  For example, this applies
to frames printed when @value{GDBN} stops, output from commands such as
@code{backtrace} or @code{up}, etc.

@findex frame-begin
The frame annotation begins with

@smallexample
^Z^Zframe-begin @var{level} @var{address}
@var{level-string}
@end smallexample

@noindent
where @var{level} is the number of the frame (0 is the innermost frame,
and other frames have positive numbers), @var{address} is the address of
the code executing in that frame, and @var{level-string} is a string
designed to convey the level to the user.  @var{address} is in the form
@samp{0x} followed by one or more lowercase hex digits (note that this
does not depend on the language).  The frame ends with

@findex frame-end
@smallexample
^Z^Zframe-end
@end smallexample

Between these annotations is the main body of the frame, which can
consist of

@itemize @bullet
@item
@findex function-call
@smallexample
^Z^Zfunction-call
@var{function-call-string}
@end smallexample

where @var{function-call-string} is text designed to convey to the user
that this frame is associated with a function call made by @value{GDBN} to a
function in the program being debugged.

@item
@findex signal-handler-caller
@smallexample
^Z^Zsignal-handler-caller
@var{signal-handler-caller-string}
@end smallexample

where @var{signal-handler-caller-string} is text designed to convey to
the user that this frame is associated with whatever mechanism is used
by this operating system to call a signal handler (it is the frame which
calls the signal handler, not the frame for the signal handler itself).

@item
A normal frame.

@findex frame-address
@findex frame-address-end
This can optionally (depending on whether this is thought of as
interesting information for the user to see) begin with

@smallexample
^Z^Zframe-address
@var{address}
^Z^Zframe-address-end
@var{separator-string}
@end smallexample

where @var{address} is the address executing in the frame (the same
address as in the @code{frame-begin} annotation, but printed in a form
which is intended for user consumption---in particular, the syntax varies
depending on the language), and @var{separator-string} is a string
intended to separate this address from what follows for the user's
benefit.

@findex frame-function-name
@findex frame-args
Then comes

@smallexample
^Z^Zframe-function-name
@var{function-name}
^Z^Zframe-args
@var{arguments}
@end smallexample

where @var{function-name} is the name of the function executing in the
frame, or @samp{??} if not known, and @var{arguments} are the arguments
to the frame, with parentheses around them (each argument is annotated
individually as well, @pxref{Value Annotations}).

@findex frame-source-begin
@findex frame-source-file
@findex frame-source-file-end
@findex frame-source-line
@findex frame-source-end
If source information is available, a reference to it is then printed:

@smallexample
^Z^Zframe-source-begin
@var{source-intro-string}
^Z^Zframe-source-file
@var{filename}
^Z^Zframe-source-file-end
:
^Z^Zframe-source-line
@var{line-number}
^Z^Zframe-source-end
@end smallexample

where @var{source-intro-string} separates for the user's benefit the
reference from the text which precedes it, @var{filename} is the name of
the source file, and @var{line-number} is the line number within that
file (the first line is line 1).

@findex frame-where
If @value{GDBN} prints some information about where the frame is from (which
library, which load segment, etc.; currently only done on the RS/6000),
it is annotated with

@smallexample
^Z^Zframe-where
@var{information}
@end smallexample

Then, if source is to actually be displayed for this frame (for example,
this is not true for output from the @code{backtrace} command), then a
@code{source} annotation (@pxref{Source Annotations}) is displayed.  Unlike
most annotations, this is output instead of the normal text which would be
output, not in addition.
@end itemize

@node Displays
@chapter Displays

@emph{Display Annotations have been removed.  @sc{gdb/mi} instead
provides Variable Objects.}

@findex display-begin
@findex display-number-end
@findex display-format
@findex display-expression
@findex display-expression-end
@findex display-value
@findex display-end
@cindex annotations for display
When @value{GDBN} is told to display something using the @code{display} command,
the results of the display are annotated:

@smallexample
^Z^Zdisplay-begin
@var{number}
^Z^Zdisplay-number-end
@var{number-separator}
^Z^Zdisplay-format
@var{format}
^Z^Zdisplay-expression
@var{expression}
^Z^Zdisplay-expression-end
@var{expression-separator}
^Z^Zdisplay-value
@var{value}
^Z^Zdisplay-end
@end smallexample

@noindent
where @var{number} is the number of the display, @var{number-separator}
is intended to separate the number from what follows for the user,
@var{format} includes information such as the size, format, or other
information about how the value is being displayed, @var{expression} is
the expression being displayed, @var{expression-separator} is intended
to separate the expression from the text that follows for the user,
and @var{value} is the actual value being displayed.

@node Prompting
@chapter Annotation for @value{GDBN} Input

@cindex annotations for prompts
When @value{GDBN} 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 @dfn{input type}.  Each
input type has three annotations: a @code{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 @code{post-}
annotation which denotes the end of any echo which may (or may not) be
associated with the input.  For example, the @code{prompt} input type
features the following annotations:

@smallexample
^Z^Zpre-prompt
^Z^Zprompt
^Z^Zpost-prompt
@end smallexample

The input types are

@table @code
@findex pre-prompt
@findex prompt
@findex post-prompt
@item prompt
When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).

@findex pre-commands
@findex commands
@findex post-commands
@item commands
When @value{GDBN} prompts for a set of commands, like in the @code{commands}
command.  The annotations are repeated for each command which is input.

@findex pre-overload-choice
@findex overload-choice
@findex post-overload-choice
@item overload-choice
When @value{GDBN} wants the user to select between various overloaded functions.

@findex pre-query
@findex query
@findex post-query
@item query
When @value{GDBN} wants the user to confirm a potentially dangerous operation.

@findex pre-prompt-for-continue
@findex prompt-for-continue
@findex post-prompt-for-continue
@item prompt-for-continue
When @value{GDBN} is asking the user to press return to continue.  Note: Don't
expect this to work well; instead use @code{set height 0} to disable
prompting.  This is because the counting of lines is buggy in the
presence of annotations.
@end table

@node Errors
@chapter Errors
@cindex annotations for errors, warnings and interrupts

@findex quit
@smallexample
^Z^Zquit
@end smallexample

This annotation occurs right before @value{GDBN} responds to an interrupt.

@findex error
@smallexample
^Z^Zerror
@end smallexample

This annotation occurs right before @value{GDBN} responds to an error.

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

@findex error-begin
A quit or error annotation may be preceded by

@smallexample
^Z^Zerror-begin
@end smallexample

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

Warning messages are not yet annotated.
@c If we want to change that, need to fix warning(), type_error(),
@c range_error(), and possibly other places.

@node Breakpoint Info
@chapter Information on Breakpoints

@emph{Breakpoint Annotations have been removed.  @sc{gdb/mi} instead
provides breakpoint commands.}

@cindex annotations for breakpoints
The output from the @code{info breakpoints} command is annotated as follows:

@findex breakpoints-headers
@findex breakpoints-table
@smallexample
^Z^Zbreakpoints-headers
@var{header-entry}
^Z^Zbreakpoints-table
@end smallexample

@noindent
where @var{header-entry} has the same syntax as an entry (see below) but
instead of containing data, it contains strings which are intended to
convey the meaning of each field to the user.  This is followed by any
number of entries.  If a field does not apply for this entry, it is
omitted.  Fields may contain trailing whitespace.  Each entry consists
of:

@findex record
@findex field
@smallexample
^Z^Zrecord
^Z^Zfield 0
@var{number}
^Z^Zfield 1
@var{type}
^Z^Zfield 2
@var{disposition}
^Z^Zfield 3
@var{enable}
^Z^Zfield 4
@var{address}
^Z^Zfield 5
@var{what}
^Z^Zfield 6
@var{frame}
^Z^Zfield 7
@var{condition}
^Z^Zfield 8
@var{ignore-count}
^Z^Zfield 9
@var{commands}
@end smallexample

Note that @var{address} is intended for user consumption---the syntax
varies depending on the language.

The output ends with

@findex breakpoints-table-end
@smallexample
^Z^Zbreakpoints-table-end
@end smallexample

@node Invalidation
@chapter Invalidation Notices

@cindex annotations for invalidation messages
The following annotations say that certain pieces of state may have
changed.

@table @code
@findex frames-invalid
@item ^Z^Zframes-invalid

The frames (for example, output from the @code{backtrace} command) may
have changed.

@findex breakpoints-invalid
@item ^Z^Zbreakpoints-invalid

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

@node Annotations for Running
@chapter Running the Program
@cindex annotations for running programs

@findex starting
@findex stopping
When the program starts executing due to a @value{GDBN} command such as
@code{step} or @code{continue}, 

@smallexample
^Z^Zstarting
@end smallexample

is output.  When the program stops, 

@smallexample
^Z^Zstopped
@end smallexample

is output.  Before the @code{stopped} annotation, a variety of
annotations describe how the program stopped.

@table @code
@findex exited
@item ^Z^Zexited @var{exit-status}
The program exited, and @var{exit-status} is the exit status (zero for
successful exit, otherwise nonzero).

@findex signalled
@findex signal-name
@findex signal-name-end
@findex signal-string
@findex signal-string-end
@item ^Z^Zsignalled
The program exited with a signal.  After the @code{^Z^Zsignalled}, the
annotation continues:

@smallexample
@var{intro-text}
^Z^Zsignal-name
@var{name}
^Z^Zsignal-name-end
@var{middle-text}
^Z^Zsignal-string
@var{string}
^Z^Zsignal-string-end
@var{end-text}
@end smallexample

@noindent
where @var{name} is the name of the signal, such as @code{SIGILL} or
@code{SIGSEGV}, and @var{string} is the explanation of the signal, such
as @code{Illegal Instruction} or @code{Segmentation fault}.
@var{intro-text}, @var{middle-text}, and @var{end-text} are for the
user's benefit and have no particular format.

@findex signal
@item ^Z^Zsignal
The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
just saying that the program received the signal, not that it was
terminated with it.

@findex breakpoint
@item ^Z^Zbreakpoint @var{number}
The program hit breakpoint number @var{number}.

@findex watchpoint
@item ^Z^Zwatchpoint @var{number}
The program hit watchpoint number @var{number}.
@end table

@node Source Annotations
@chapter Displaying Source
@cindex annotations for source display

@findex source
The following annotation is used instead of displaying source code:

@smallexample
^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
@end smallexample

where @var{filename} is an absolute file name indicating which source
file, @var{line} is the line number within that file (where 1 is the
first line in the file), @var{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),
@var{middle} is @samp{middle} if @var{addr} is in the middle of the
line, or @samp{beg} if @var{addr} is at the beginning of the line, and
@var{addr} is the address in the target program associated with the
source which is being displayed.  @var{addr} is in the form @samp{0x}
followed by one or more lowercase hex digits (note that this does not
depend on the language).

@node Multi-threaded Apps
@chapter Multi-threaded Applications
@cindex annotations for multi-threaded apps

The following annotations report thread related changes of state.

@table @code
@findex new-thread@r{, annotation}
@item ^Z^Znew-thread

This annotation is issued once for each thread that is created apart from
the main thread, which is not reported.

@findex thread-changed@r{, annotation}
@item ^Z^Zthread-changed

The selected thread has changed.  This may occur at the request of the
user with the @code{thread} command, or as a result of execution,
e.g., another thread hits a breakpoint.

@findex thread-exited@r{, annotation}
@item ^Z^Zthread-exited,id="@var{id}",group-id="@var{gid}"

This annotation is issued once for each thread that exits.  The @var{id}
field contains the global @value{GDBN} identifier of the thread.  The
@var{gid} field identifies the thread group this thread belongs to.

@end table

@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include fdl.texi

@ignore
@node Index
@unnumbered Index

@printindex fn
@end ignore

@bye