<!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>Trace State Variables (Debugging with GDB)</title> <meta name="description" content="Trace State Variables (Debugging with GDB)"> <meta name="keywords" content="Trace State Variables (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="Tracepoint-Actions.html#Tracepoint-Actions" rel="next" title="Tracepoint Actions"> <link href="Tracepoint-Conditions.html#Tracepoint-Conditions" rel="prev" title="Tracepoint Conditions"> <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="Trace-State-Variables"></a> <div class="header"> <p> Next: <a href="Tracepoint-Actions.html#Tracepoint-Actions" accesskey="n" rel="next">Tracepoint Actions</a>, Previous: <a href="Tracepoint-Conditions.html#Tracepoint-Conditions" accesskey="p" rel="prev">Tracepoint Conditions</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="Trace-State-Variables-1"></a> <h4 class="subsection">13.1.5 Trace State Variables</h4> <a name="index-trace-state-variables"></a> <p>A <em>trace state variable</em> is a special type of variable that is created and managed by target-side code. The syntax is the same as that for GDB’s convenience variables (a string prefixed with “$”), but they are stored on the target. They must be created explicitly, using a <code>tvariable</code> command. They are always 64-bit signed integers. </p> <p>Trace state variables are remembered by <small>GDB</small>, and downloaded to the target along with tracepoint information when the trace experiment starts. There are no intrinsic limits on the number of trace state variables, beyond memory limitations of the target. </p> <a name="index-convenience-variables_002c-and-trace-state-variables"></a> <p>Although trace state variables are managed by the target, you can use them in print commands and expressions as if they were convenience variables; <small>GDB</small> will get the current value from the target while the trace experiment is running. Trace state variables share the same namespace as other “$” variables, which means that you cannot have trace state variables with names like <code>$23</code> or <code>$pc</code>, nor can you have a trace state variable and a convenience variable with the same name. </p> <dl compact="compact"> <dt><code>tvariable $<var>name</var> [ = <var>expression</var> ]</code></dt> <dd><a name="index-tvariable"></a> <p>The <code>tvariable</code> command creates a new trace state variable named <code>$<var>name</var></code>, and optionally gives it an initial value of <var>expression</var>. The <var>expression</var> is evaluated when this command is entered; the result will be converted to an integer if possible, otherwise <small>GDB</small> will report an error. A subsequent <code>tvariable</code> command specifying the same name does not create a variable, but instead assigns the supplied initial value to the existing variable of that name, overwriting any previous initial value. The default initial value is 0. </p> </dd> <dt><code>info tvariables</code></dt> <dd><a name="index-info-tvariables"></a> <p>List all the trace state variables along with their initial values. Their current values may also be displayed, if the trace experiment is currently running. </p> </dd> <dt><code>delete tvariable <span class="roman">[</span> $<var>name</var> … <span class="roman">]</span></code></dt> <dd><a name="index-delete-tvariable"></a> <p>Delete the given trace state variables, or all of them if no arguments are specified. </p> </dd> </dl> <hr> <div class="header"> <p> Next: <a href="Tracepoint-Actions.html#Tracepoint-Actions" accesskey="n" rel="next">Tracepoint Actions</a>, Previous: <a href="Tracepoint-Conditions.html#Tracepoint-Conditions" accesskey="p" rel="prev">Tracepoint Conditions</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>