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diff --git a/share/doc/gdb/Conditions.html b/share/doc/gdb/Conditions.html new file mode 100644 index 0000000..dee6359 --- /dev/null +++ b/share/doc/gdb/Conditions.html @@ -0,0 +1,216 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Conditions</title> + +<meta name="description" content="Debugging with GDB: Conditions"> +<meta name="keywords" content="Debugging with GDB: Conditions"> +<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="Breakpoints.html#Breakpoints" rel="up" title="Breakpoints"> +<link href="Break-Commands.html#Break-Commands" rel="next" title="Break Commands"> +<link href="Disabling.html#Disabling" rel="previous" title="Disabling"> +<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="Conditions"></a> +<div class="header"> +<p> +Next: <a href="Break-Commands.html#Break-Commands" accesskey="n" rel="next">Break Commands</a>, Previous: <a href="Disabling.html#Disabling" accesskey="p" rel="previous">Disabling</a>, Up: <a href="Breakpoints.html#Breakpoints" accesskey="u" rel="up">Breakpoints</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="Break-Conditions"></a> +<h4 class="subsection">5.1.6 Break Conditions</h4> +<a name="index-conditional-breakpoints"></a> +<a name="index-breakpoint-conditions"></a> + +<p>The simplest sort of breakpoint breaks every time your program reaches a +specified place. You can also specify a <em>condition</em> for a +breakpoint. A condition is just a Boolean expression in your +programming language (see <a href="Expressions.html#Expressions">Expressions</a>). A breakpoint with +a condition evaluates the expression each time your program reaches it, +and your program stops only if the condition is <em>true</em>. +</p> +<p>This is the converse of using assertions for program validation; in that +situation, you want to stop when the assertion is violated—that is, +when the condition is false. In C, if you want to test an assertion expressed +by the condition <var>assert</var>, you should set the condition +‘<samp>! <var>assert</var></samp>’ on the appropriate breakpoint. +</p> +<p>Conditions are also accepted for watchpoints; you may not need them, +since a watchpoint is inspecting the value of an expression anyhow—but +it might be simpler, say, to just set a watchpoint on a variable name, +and specify a condition that tests whether the new value is an interesting +one. +</p> +<p>Break conditions can have side effects, and may even call functions in +your program. This can be useful, for example, to activate functions +that log program progress, or to use your own print functions to +format special data structures. The effects are completely predictable +unless there is another enabled breakpoint at the same address. (In +that case, <small>GDB</small> might see the other breakpoint first and stop your +program without checking the condition of this one.) Note that +breakpoint commands are usually more convenient and flexible than break +conditions for the +purpose of performing side effects when a breakpoint is reached +(see <a href="Break-Commands.html#Break-Commands">Breakpoint Command Lists</a>). +</p> +<p>Breakpoint conditions can also be evaluated on the target’s side if +the target supports it. Instead of evaluating the conditions locally, +<small>GDB</small> encodes the expression into an agent expression +(see <a href="Agent-Expressions.html#Agent-Expressions">Agent Expressions</a>) suitable for execution on the target, +independently of <small>GDB</small>. Global variables become raw memory +locations, locals become stack accesses, and so forth. +</p> +<p>In this case, <small>GDB</small> will only be notified of a breakpoint trigger +when its condition evaluates to true. This mechanism may provide faster +response times depending on the performance characteristics of the target +since it does not need to keep <small>GDB</small> informed about +every breakpoint trigger, even those with false conditions. +</p> +<p>Break conditions can be specified when a breakpoint is set, by using +‘<samp>if</samp>’ in the arguments to the <code>break</code> command. See <a href="Set-Breaks.html#Set-Breaks">Setting Breakpoints</a>. They can also be changed at any time +with the <code>condition</code> command. +</p> +<p>You can also use the <code>if</code> keyword with the <code>watch</code> command. +The <code>catch</code> command does not recognize the <code>if</code> keyword; +<code>condition</code> is the only way to impose a further condition on a +catchpoint. +</p> +<dl compact="compact"> +<dd><a name="index-condition"></a> +</dd> +<dt><code>condition <var>bnum</var> <var>expression</var></code></dt> +<dd><p>Specify <var>expression</var> as the break condition for breakpoint, +watchpoint, or catchpoint number <var>bnum</var>. After you set a condition, +breakpoint <var>bnum</var> stops your program only if the value of +<var>expression</var> is true (nonzero, in C). When you use +<code>condition</code>, <small>GDB</small> checks <var>expression</var> immediately for +syntactic correctness, and to determine whether symbols in it have +referents in the context of your breakpoint. If <var>expression</var> uses +symbols not referenced in the context of the breakpoint, <small>GDB</small> +prints an error message: +</p> +<div class="smallexample"> +<pre class="smallexample">No symbol "foo" in current context. +</pre></div> + +<p><small>GDB</small> does +not actually evaluate <var>expression</var> at the time the <code>condition</code> +command (or a command that sets a breakpoint with a condition, like +<code>break if …</code>) is given, however. See <a href="Expressions.html#Expressions">Expressions</a>. +</p> +</dd> +<dt><code>condition -force <var>bnum</var> <var>expression</var></code></dt> +<dd><p>When the <code>-force</code> flag is used, define the condition even if +<var>expression</var> is invalid at all the current locations of breakpoint +<var>bnum</var>. This is similar to the <code>-force-condition</code> option +of the <code>break</code> command. +</p> +</dd> +<dt><code>condition <var>bnum</var></code></dt> +<dd><p>Remove the condition from breakpoint number <var>bnum</var>. It becomes +an ordinary unconditional breakpoint. +</p></dd> +</dl> + +<a name="index-ignore-count-_0028of-breakpoint_0029"></a> +<p>A special case of a breakpoint condition is to stop only when the +breakpoint has been reached a certain number of times. This is so +useful that there is a special way to do it, using the <em>ignore +count</em> of the breakpoint. Every breakpoint has an ignore count, which +is an integer. Most of the time, the ignore count is zero, and +therefore has no effect. But if your program reaches a breakpoint whose +ignore count is positive, then instead of stopping, it just decrements +the ignore count by one and continues. As a result, if the ignore count +value is <var>n</var>, the breakpoint does not stop the next <var>n</var> times +your program reaches it. +</p> +<dl compact="compact"> +<dd><a name="index-ignore"></a> +</dd> +<dt><code>ignore <var>bnum</var> <var>count</var></code></dt> +<dd><p>Set the ignore count of breakpoint number <var>bnum</var> to <var>count</var>. +The next <var>count</var> times the breakpoint is reached, your program’s +execution does not stop; other than to decrement the ignore count, <small>GDB</small> +takes no action. +</p> +<p>To make the breakpoint stop the next time it is reached, specify +a count of zero. +</p> +<p>When you use <code>continue</code> to resume execution of your program from a +breakpoint, you can specify an ignore count directly as an argument to +<code>continue</code>, rather than using <code>ignore</code>. See <a href="Continuing-and-Stepping.html#Continuing-and-Stepping">Continuing and Stepping</a>. +</p> +<p>If a breakpoint has a positive ignore count and a condition, the +condition is not checked. Once the ignore count reaches zero, +<small>GDB</small> resumes checking the condition. +</p> +<p>You could achieve the effect of the ignore count with a condition such +as ‘<samp><span class="nolinebreak">$foo--</span> <= 0</samp>’<!-- /@w --> using a debugger convenience variable that +is decremented each time. See <a href="Convenience-Vars.html#Convenience-Vars">Convenience +Variables</a>. +</p></dd> +</dl> + +<p>Ignore counts apply to breakpoints, watchpoints, and catchpoints. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Break-Commands.html#Break-Commands" accesskey="n" rel="next">Break Commands</a>, Previous: <a href="Disabling.html#Disabling" accesskey="p" rel="previous">Disabling</a>, Up: <a href="Breakpoints.html#Breakpoints" accesskey="u" rel="up">Breakpoints</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> |