You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
249 lines
12 KiB
HTML
249 lines
12 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2019 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 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>Create and Delete Tracepoints (Debugging with GDB)</title>
|
|
|
|
<meta name="description" content="Create and Delete Tracepoints (Debugging with GDB)">
|
|
<meta name="keywords" content="Create and Delete Tracepoints (Debugging with GDB)">
|
|
<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="Set-Tracepoints.html#Set-Tracepoints" rel="up" title="Set Tracepoints">
|
|
<link href="Enable-and-Disable-Tracepoints.html#Enable-and-Disable-Tracepoints" rel="next" title="Enable and Disable Tracepoints">
|
|
<link href="Set-Tracepoints.html#Set-Tracepoints" rel="prev" title="Set Tracepoints">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
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.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<a name="Create-and-Delete-Tracepoints"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Enable-and-Disable-Tracepoints.html#Enable-and-Disable-Tracepoints" accesskey="n" rel="next">Enable and Disable Tracepoints</a>, Up: <a href="Set-Tracepoints.html#Set-Tracepoints" accesskey="u" rel="up">Set Tracepoints</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="Create-and-Delete-Tracepoints-1"></a>
|
|
<h4 class="subsection">13.1.1 Create and Delete Tracepoints</h4>
|
|
|
|
<dl compact="compact">
|
|
<dd><a name="index-set-tracepoint"></a>
|
|
<a name="index-trace"></a>
|
|
</dd>
|
|
<dt><code>trace <var>location</var></code></dt>
|
|
<dd><p>The <code>trace</code> command is very similar to the <code>break</code> command.
|
|
Its argument <var>location</var> can be any valid location.
|
|
See <a href="Specify-Location.html#Specify-Location">Specify Location</a>. The <code>trace</code> command defines a tracepoint,
|
|
which is a point in the target program where the debugger will briefly stop,
|
|
collect some data, and then allow the program to continue. Setting a tracepoint
|
|
or changing its actions takes effect immediately if the remote stub
|
|
supports the ‘<samp>InstallInTrace</samp>’ feature (see <a href="General-Query-Packets.html#install-tracepoint-in-tracing">install tracepoint in tracing</a>).
|
|
If remote stub doesn’t support the ‘<samp>InstallInTrace</samp>’ feature, all
|
|
these changes don’t take effect until the next <code>tstart</code>
|
|
command, and once a trace experiment is running, further changes will
|
|
not have any effect until the next trace experiment starts. In addition,
|
|
<small>GDB</small> supports <em>pending tracepoints</em>—tracepoints whose
|
|
address is not yet resolved. (This is similar to pending breakpoints.)
|
|
Pending tracepoints are not downloaded to the target and not installed
|
|
until they are resolved. The resolution of pending tracepoints requires
|
|
<small>GDB</small> support—when debugging with the remote target, and
|
|
<small>GDB</small> disconnects from the remote stub (see <a href="Starting-and-Stopping-Trace-Experiments.html#disconnected-tracing">disconnected tracing</a>), pending tracepoints can not be resolved (and downloaded to
|
|
the remote stub) while <small>GDB</small> is disconnected.
|
|
</p>
|
|
<p>Here are some examples of using the <code>trace</code> command:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">(gdb) <b>trace foo.c:121</b> // a source file and line number
|
|
|
|
(gdb) <b>trace +2</b> // 2 lines forward
|
|
|
|
(gdb) <b>trace my_function</b> // first source line of function
|
|
|
|
(gdb) <b>trace *my_function</b> // EXACT start address of function
|
|
|
|
(gdb) <b>trace *0x2117c4</b> // an address
|
|
</pre></div>
|
|
|
|
<p>You can abbreviate <code>trace</code> as <code>tr</code>.
|
|
</p>
|
|
</dd>
|
|
<dt><code>trace <var>location</var> if <var>cond</var></code></dt>
|
|
<dd><p>Set a tracepoint with condition <var>cond</var>; evaluate the expression
|
|
<var>cond</var> each time the tracepoint is reached, and collect data only
|
|
if the value is nonzero—that is, if <var>cond</var> evaluates as true.
|
|
See <a href="Tracepoint-Conditions.html#Tracepoint-Conditions">Tracepoint Conditions</a>, for more
|
|
information on tracepoint conditions.
|
|
</p>
|
|
</dd>
|
|
<dt><code>ftrace <var>location</var> [ if <var>cond</var> ]</code></dt>
|
|
<dd><a name="index-set-fast-tracepoint"></a>
|
|
<a name="index-fast-tracepoints_002c-setting"></a>
|
|
<a name="index-ftrace"></a>
|
|
<p>The <code>ftrace</code> command sets a fast tracepoint. For targets that
|
|
support them, fast tracepoints will use a more efficient but possibly
|
|
less general technique to trigger data collection, such as a jump
|
|
instruction instead of a trap, or some sort of hardware support. It
|
|
may not be possible to create a fast tracepoint at the desired
|
|
location, in which case the command will exit with an explanatory
|
|
message.
|
|
</p>
|
|
<p><small>GDB</small> handles arguments to <code>ftrace</code> exactly as for
|
|
<code>trace</code>.
|
|
</p>
|
|
<p>On 32-bit x86-architecture systems, fast tracepoints normally need to
|
|
be placed at an instruction that is 5 bytes or longer, but can be
|
|
placed at 4-byte instructions if the low 64K of memory of the target
|
|
program is available to install trampolines. Some Unix-type systems,
|
|
such as <small>GNU</small>/Linux, exclude low addresses from the program’s
|
|
address space; but for instance with the Linux kernel it is possible
|
|
to let <small>GDB</small> use this area by doing a <code>sysctl</code> command
|
|
to set the <code>mmap_min_addr</code> kernel parameter, as in
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">sudo sysctl -w vm.mmap_min_addr=32768
|
|
</pre></div>
|
|
|
|
<p>which sets the low address to 32K, which leaves plenty of room for
|
|
trampolines. The minimum address should be set to a page boundary.
|
|
</p>
|
|
</dd>
|
|
<dt><code>strace <var>location</var> [ if <var>cond</var> ]</code></dt>
|
|
<dd><a name="index-set-static-tracepoint"></a>
|
|
<a name="index-static-tracepoints_002c-setting"></a>
|
|
<a name="index-probe-static-tracepoint-marker"></a>
|
|
<a name="index-strace"></a>
|
|
<p>The <code>strace</code> command sets a static tracepoint. For targets that
|
|
support it, setting a static tracepoint probes a static
|
|
instrumentation point, or marker, found at <var>location</var>. It may not
|
|
be possible to set a static tracepoint at the desired location, in
|
|
which case the command will exit with an explanatory message.
|
|
</p>
|
|
<p><small>GDB</small> handles arguments to <code>strace</code> exactly as for
|
|
<code>trace</code>, with the addition that the user can also specify
|
|
<code>-m <var>marker</var></code> as <var>location</var>. This probes the marker
|
|
identified by the <var>marker</var> string identifier. This identifier
|
|
depends on the static tracepoint backend library your program is
|
|
using. You can find all the marker identifiers in the ‘<samp>ID</samp>’ field
|
|
of the <code>info static-tracepoint-markers</code> command output.
|
|
See <a href="Listing-Static-Tracepoint-Markers.html#Listing-Static-Tracepoint-Markers">Listing Static Tracepoint
|
|
Markers</a>. For example, in the following small program using the UST
|
|
tracing engine:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">main ()
|
|
{
|
|
trace_mark(ust, bar33, "str %s", "FOOBAZ");
|
|
}
|
|
</pre></div>
|
|
|
|
<p>the marker id is composed of joining the first two arguments to the
|
|
<code>trace_mark</code> call with a slash, which translates to:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">(gdb) info static-tracepoint-markers
|
|
Cnt Enb ID Address What
|
|
1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22
|
|
Data: "str %s"
|
|
[etc...]
|
|
</pre></div>
|
|
|
|
<p>so you may probe the marker above with:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">(gdb) strace -m ust/bar33
|
|
</pre></div>
|
|
|
|
<p>Static tracepoints accept an extra collect action — <code>collect
|
|
$_sdata</code>. This collects arbitrary user data passed in the probe point
|
|
call to the tracing library. In the UST example above, you’ll see
|
|
that the third argument to <code>trace_mark</code> is a printf-like format
|
|
string. The user data is then the result of running that formating
|
|
string against the following arguments. Note that <code>info
|
|
static-tracepoint-markers</code> command output lists that format string in
|
|
the ‘<samp>Data:</samp>’ field.
|
|
</p>
|
|
<p>You can inspect this data when analyzing the trace buffer, by printing
|
|
the $_sdata variable like any other variable available to
|
|
<small>GDB</small>. See <a href="Tracepoint-Actions.html#Tracepoint-Actions">Tracepoint Action Lists</a>.
|
|
</p>
|
|
<a name="index-_0024tpnum"></a>
|
|
<a name="index-last-tracepoint-number"></a>
|
|
<a name="index-recent-tracepoint-number"></a>
|
|
<a name="index-tracepoint-number"></a>
|
|
<p>The convenience variable <code>$tpnum</code> records the tracepoint number
|
|
of the most recently set tracepoint.
|
|
</p>
|
|
<a name="index-delete-tracepoint"></a>
|
|
<a name="index-tracepoint-deletion"></a>
|
|
</dd>
|
|
<dt><code>delete tracepoint <span class="roman">[</span><var>num</var><span class="roman">]</span></code></dt>
|
|
<dd><p>Permanently delete one or more tracepoints. With no argument, the
|
|
default is to delete all tracepoints. Note that the regular
|
|
<code>delete</code> command can remove tracepoints also.
|
|
</p>
|
|
<p>Examples:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">(gdb) <b>delete trace 1 2 3</b> // remove three tracepoints
|
|
|
|
(gdb) <b>delete trace</b> // remove all tracepoints
|
|
</pre></div>
|
|
|
|
<p>You can abbreviate this command as <code>del tr</code>.
|
|
</p></dd>
|
|
</dl>
|
|
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Enable-and-Disable-Tracepoints.html#Enable-and-Disable-Tracepoints" accesskey="n" rel="next">Enable and Disable Tracepoints</a>, Up: <a href="Set-Tracepoints.html#Set-Tracepoints" accesskey="u" rel="up">Set Tracepoints</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>
|