diff options
Diffstat (limited to 'share/doc/gdb/Forks.html')
| -rw-r--r-- | share/doc/gdb/Forks.html | 276 |
1 files changed, 276 insertions, 0 deletions
diff --git a/share/doc/gdb/Forks.html b/share/doc/gdb/Forks.html new file mode 100644 index 0000000..77dd6f1 --- /dev/null +++ b/share/doc/gdb/Forks.html @@ -0,0 +1,276 @@ +<!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: Forks</title> + +<meta name="description" content="Debugging with GDB: Forks"> +<meta name="keywords" content="Debugging with GDB: Forks"> +<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="Running.html#Running" rel="up" title="Running"> +<link href="Checkpoint_002fRestart.html#Checkpoint_002fRestart" rel="next" title="Checkpoint/Restart"> +<link href="Threads.html#Threads" rel="previous" title="Threads"> +<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="Forks"></a> +<div class="header"> +<p> +Next: <a href="Checkpoint_002fRestart.html#Checkpoint_002fRestart" accesskey="n" rel="next">Checkpoint/Restart</a>, Previous: <a href="Threads.html#Threads" accesskey="p" rel="previous">Threads</a>, Up: <a href="Running.html#Running" accesskey="u" rel="up">Running</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="Debugging-Forks"></a> +<h3 class="section">4.11 Debugging Forks</h3> + +<a name="index-fork_002c-debugging-programs-which-call"></a> +<a name="index-multiple-processes"></a> +<a name="index-processes_002c-multiple"></a> +<p>On most systems, <small>GDB</small> has no special support for debugging +programs which create additional processes using the <code>fork</code> +function. When a program forks, <small>GDB</small> will continue to debug the +parent process and the child process will run unimpeded. If you have +set a breakpoint in any code which the child then executes, the child +will get a <code>SIGTRAP</code> signal which (unless it catches the signal) +will cause it to terminate. +</p> +<p>However, if you want to debug the child process there is a workaround +which isn’t too painful. Put a call to <code>sleep</code> in the code which +the child process executes after the fork. It may be useful to sleep +only if a certain environment variable is set, or a certain file exists, +so that the delay need not occur when you don’t want to run <small>GDB</small> +on the child. While the child is sleeping, use the <code>ps</code> program to +get its process ID. Then tell <small>GDB</small> (a new invocation of +<small>GDB</small> if you are also debugging the parent process) to attach to +the child process (see <a href="Attach.html#Attach">Attach</a>). From that point on you can debug +the child process just like any other process which you attached to. +</p> +<p>On some systems, <small>GDB</small> provides support for debugging programs +that create additional processes using the <code>fork</code> or <code>vfork</code> +functions. On <small>GNU</small>/Linux platforms, this feature is supported +with kernel version 2.5.46 and later. +</p> +<p>The fork debugging commands are supported in native mode and when +connected to <code>gdbserver</code> in either <code>target remote</code> mode or +<code>target extended-remote</code> mode. +</p> +<p>By default, when a program forks, <small>GDB</small> will continue to debug +the parent process and the child process will run unimpeded. +</p> +<p>If you want to follow the child process instead of the parent process, +use the command <code>set <span class="nolinebreak">follow-fork-mode</span></code><!-- /@w -->. +</p> +<dl compact="compact"> +<dd><a name="index-set-follow_002dfork_002dmode"></a> +</dd> +<dt><code>set follow-fork-mode <var>mode</var></code></dt> +<dd><p>Set the debugger response to a program call of <code>fork</code> or +<code>vfork</code>. A call to <code>fork</code> or <code>vfork</code> creates a new +process. The <var>mode</var> argument can be: +</p> +<dl compact="compact"> +<dt><code>parent</code></dt> +<dd><p>The original process is debugged after a fork. The child process runs +unimpeded. This is the default. +</p> +</dd> +<dt><code>child</code></dt> +<dd><p>The new process is debugged after a fork. The parent process runs +unimpeded. +</p> +</dd> +</dl> + +<a name="index-show-follow_002dfork_002dmode"></a> +</dd> +<dt><code>show follow-fork-mode</code></dt> +<dd><p>Display the current debugger response to a <code>fork</code> or <code>vfork</code> call. +</p></dd> +</dl> + +<a name="index-debugging-multiple-processes"></a> +<p>On Linux, if you want to debug both the parent and child processes, use the +command <code>set <span class="nolinebreak">detach-on-fork</span></code><!-- /@w -->. +</p> +<dl compact="compact"> +<dd><a name="index-set-detach_002don_002dfork"></a> +</dd> +<dt><code>set detach-on-fork <var>mode</var></code></dt> +<dd><p>Tells gdb whether to detach one of the processes after a fork, or +retain debugger control over them both. +</p> +<dl compact="compact"> +<dt><code>on</code></dt> +<dd><p>The child process (or parent process, depending on the value of +<code>follow-fork-mode</code>) will be detached and allowed to run +independently. This is the default. +</p> +</dd> +<dt><code>off</code></dt> +<dd><p>Both processes will be held under the control of <small>GDB</small>. +One process (child or parent, depending on the value of +<code>follow-fork-mode</code>) is debugged as usual, while the other +is held suspended. +</p> +</dd> +</dl> + +<a name="index-show-detach_002don_002dfork"></a> +</dd> +<dt><code>show detach-on-fork</code></dt> +<dd><p>Show whether detach-on-fork mode is on/off. +</p></dd> +</dl> + +<p>If you choose to set ‘<samp>detach-on-fork</samp>’ mode off, then <small>GDB</small> +will retain control of all forked processes (including nested forks). +You can list the forked processes under the control of <small>GDB</small> by +using the <code>info inferiors</code><!-- /@w --> command, and switch from one fork +to another by using the <code>inferior</code> command (see <a href="Inferiors-Connections-and-Programs.html#Inferiors-Connections-and-Programs">Debugging Multiple Inferiors Connections and Programs</a>). +</p> +<p>To quit debugging one of the forked processes, you can either detach +from it by using the <code>detach inferiors</code><!-- /@w --> command (allowing it +to run independently), or kill it using the <code>kill inferiors</code><!-- /@w --> +command. See <a href="Inferiors-Connections-and-Programs.html#Inferiors-Connections-and-Programs">Debugging +Multiple Inferiors Connections and Programs</a>. +</p> +<p>If you ask to debug a child process and a <code>vfork</code> is followed by an +<code>exec</code>, <small>GDB</small> executes the new target up to the first +breakpoint in the new target. If you have a breakpoint set on +<code>main</code> in your original program, the breakpoint will also be set on +the child process’s <code>main</code>. +</p> +<p>On some systems, when a child process is spawned by <code>vfork</code>, you +cannot debug the child or parent until an <code>exec</code> call completes. +</p> +<p>If you issue a <code>run</code> command to <small>GDB</small> after an <code>exec</code> +call executes, the new target restarts. To restart the parent +process, use the <code>file</code> command with the parent executable name +as its argument. By default, after an <code>exec</code> call executes, +<small>GDB</small> discards the symbols of the previous executable image. +You can change this behaviour with the <code>set <span class="nolinebreak">follow-exec-mode</span></code><!-- /@w --> +command. +</p> +<dl compact="compact"> +<dd><a name="index-set-follow_002dexec_002dmode"></a> +</dd> +<dt><code>set follow-exec-mode <var>mode</var></code></dt> +<dd> +<p>Set debugger response to a program call of <code>exec</code>. An +<code>exec</code> call replaces the program image of a process. +</p> +<p><code>follow-exec-mode</code> can be: +</p> +<dl compact="compact"> +<dt><code>new</code></dt> +<dd><p><small>GDB</small> creates a new inferior and rebinds the process to this +new inferior. The program the process was running before the +<code>exec</code> call can be restarted afterwards by restarting the +original inferior. +</p> +<p>For example: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) info inferiors +(gdb) info inferior + Id Description Executable +* 1 <null> prog1 +(gdb) run +process 12020 is executing new program: prog2 +Program exited normally. +(gdb) info inferiors + Id Description Executable + 1 <null> prog1 +* 2 <null> prog2 +</pre></div> + +</dd> +<dt><code>same</code></dt> +<dd><p><small>GDB</small> keeps the process bound to the same inferior. The new +executable image replaces the previous executable loaded in the +inferior. Restarting the inferior after the <code>exec</code> call, with +e.g., the <code>run</code> command, restarts the executable the process was +running after the <code>exec</code> call. This is the default mode. +</p> +<p>For example: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) info inferiors + Id Description Executable +* 1 <null> prog1 +(gdb) run +process 12020 is executing new program: prog2 +Program exited normally. +(gdb) info inferiors + Id Description Executable +* 1 <null> prog2 +</pre></div> + +</dd> +</dl> +</dd> +</dl> + +<p><code>follow-exec-mode</code> is supported in native mode and +<code>target extended-remote</code> mode. +</p> +<p>You can use the <code>catch</code> command to make <small>GDB</small> stop whenever +a <code>fork</code>, <code>vfork</code>, or <code>exec</code> call is made. See <a href="Set-Catchpoints.html#Set-Catchpoints">Setting Catchpoints</a>. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Checkpoint_002fRestart.html#Checkpoint_002fRestart" accesskey="n" rel="next">Checkpoint/Restart</a>, Previous: <a href="Threads.html#Threads" accesskey="p" rel="previous">Threads</a>, Up: <a href="Running.html#Running" accesskey="u" rel="up">Running</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> |