| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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 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." --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Debugging with GDB: Hooks</title> |
| |
| <meta name="description" content="Debugging with GDB: Hooks"> |
| <meta name="keywords" content="Debugging with GDB: Hooks"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Sequences.html#Sequences" rel="up" title="Sequences"> |
| <link href="Command-Files.html#Command-Files" rel="next" title="Command Files"> |
| <link href="Define.html#Define" rel="prev" title="Define"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Hooks"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Command-Files.html#Command-Files" accesskey="n" rel="next">Command Files</a>, Previous: <a href="Define.html#Define" accesskey="p" rel="prev">Define</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="User_002ddefined-Command-Hooks"></a> |
| <h4 class="subsection">23.1.2 User-defined Command Hooks</h4> |
| <a name="index-command-hooks"></a> |
| <a name="index-hooks_002c-for-commands"></a> |
| <a name="index-hooks_002c-pre_002dcommand"></a> |
| |
| <a name="index-hook"></a> |
| <p>You may define <em>hooks</em>, which are a special kind of user-defined |
| command. Whenever you run the command ‘<samp>foo</samp>’, if the user-defined |
| command ‘<samp>hook-foo</samp>’ exists, it is executed (with no arguments) |
| before that command. |
| </p> |
| <a name="index-hooks_002c-post_002dcommand"></a> |
| <a name="index-hookpost"></a> |
| <p>A hook may also be defined which is run after the command you executed. |
| Whenever you run the command ‘<samp>foo</samp>’, if the user-defined command |
| ‘<samp>hookpost-foo</samp>’ exists, it is executed (with no arguments) after |
| that command. Post-execution hooks may exist simultaneously with |
| pre-execution hooks, for the same command. |
| </p> |
| <p>It is valid for a hook to call the command which it hooks. If this |
| occurs, the hook is not re-executed, thereby avoiding infinite recursion. |
| </p> |
| |
| <a name="index-stop_002c-a-pseudo_002dcommand"></a> |
| <p>In addition, a pseudo-command, ‘<samp>stop</samp>’ exists. Defining |
| (‘<samp>hook-stop</samp>’) makes the associated commands execute every time |
| execution stops in your program: before breakpoint commands are run, |
| displays are printed, or the stack frame is printed. |
| </p> |
| <p>For example, to ignore <code>SIGALRM</code> signals while |
| single-stepping, but treat them normally during normal execution, |
| you could define: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">define hook-stop |
| handle SIGALRM nopass |
| end |
| |
| define hook-run |
| handle SIGALRM pass |
| end |
| |
| define hook-continue |
| handle SIGALRM pass |
| end |
| </pre></div> |
| |
| <p>As a further example, to hook at the beginning and end of the <code>echo</code> |
| command, and to add extra text to the beginning and end of the message, |
| you could define: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">define hook-echo |
| echo <<<--- |
| end |
| |
| define hookpost-echo |
| echo --->>>\n |
| end |
| |
| (gdb) echo Hello World |
| <<<---Hello World--->>> |
| (gdb) |
| |
| </pre></div> |
| |
| <p>You can define a hook for any single-word command in <small>GDB</small>, but |
| not for command aliases; you should define a hook for the basic command |
| name, e.g. <code>backtrace</code> rather than <code>bt</code>. |
| You can hook a multi-word command by adding <code>hook-</code> or |
| <code>hookpost-</code> to the last word of the command, e.g. |
| ‘<samp>define target hook-remote</samp>’ to add a hook to ‘<samp>target remote</samp>’. |
| </p> |
| <p>If an error occurs during the execution of your hook, execution of |
| <small>GDB</small> commands stops and <small>GDB</small> issues a prompt |
| (before the command that you actually typed had a chance to run). |
| </p> |
| <p>If you try to define a hook which does not match any known command, you |
| get a warning from the <code>define</code> command. |
| </p> |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Command-Files.html#Command-Files" accesskey="n" rel="next">Command Files</a>, Previous: <a href="Define.html#Define" accesskey="p" rel="prev">Define</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
