95 lines
4.9 KiB
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95 lines
4.9 KiB
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<title>Trace State Variables - Debugging with GDB</title>
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<link rel="up" href="Set-Tracepoints.html#Set-Tracepoints" title="Set Tracepoints">
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<link rel="prev" href="Tracepoint-Conditions.html#Tracepoint-Conditions" title="Tracepoint Conditions">
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<div class="node">
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<a name="Trace-State-Variables"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Tracepoint-Actions.html#Tracepoint-Actions">Tracepoint Actions</a>,
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Previous: <a rel="previous" accesskey="p" href="Tracepoint-Conditions.html#Tracepoint-Conditions">Tracepoint Conditions</a>,
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Up: <a rel="up" accesskey="u" href="Set-Tracepoints.html#Set-Tracepoints">Set Tracepoints</a>
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<hr>
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</div>
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<h4 class="subsection">13.1.5 Trace State Variables</h4>
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<p><a name="index-trace-state-variables-884"></a>
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A <dfn>trace state variable</dfn> is a special type of variable that is
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created and managed by target-side code. The syntax is the same as
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that for GDB's convenience variables (a string prefixed with “$”),
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but they are stored on the target. They must be created explicitly,
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using a <code>tvariable</code> command. They are always 64-bit signed
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integers.
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<p>Trace state variables are remembered by <span class="sc">gdb</span>, and downloaded
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to the target along with tracepoint information when the trace
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experiment starts. There are no intrinsic limits on the number of
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trace state variables, beyond memory limitations of the target.
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<p><a name="index-convenience-variables_002c-and-trace-state-variables-885"></a>Although trace state variables are managed by the target, you can use
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them in print commands and expressions as if they were convenience
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variables; <span class="sc">gdb</span> will get the current value from the target
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while the trace experiment is running. Trace state variables share
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the same namespace as other “$” variables, which means that you
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cannot have trace state variables with names like <code>$23</code> or
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<code>$pc</code>, nor can you have a trace state variable and a convenience
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variable with the same name.
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<dl>
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<dt><code>tvariable $</code><var>name</var><code> [ = </code><var>expression</var><code> ]</code><dd><a name="index-tvariable-886"></a>The <code>tvariable</code> command creates a new trace state variable named
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<code>$</code><var>name</var>, and optionally gives it an initial value of
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<var>expression</var>. The <var>expression</var> is evaluated when this command is
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entered; the result will be converted to an integer if possible,
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otherwise <span class="sc">gdb</span> will report an error. A subsequent
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<code>tvariable</code> command specifying the same name does not create a
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variable, but instead assigns the supplied initial value to the
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existing variable of that name, overwriting any previous initial
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value. The default initial value is 0.
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<br><dt><code>info tvariables</code><dd><a name="index-info-tvariables-887"></a>List all the trace state variables along with their initial values.
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Their current values may also be displayed, if the trace experiment is
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currently running.
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<br><dt><code>delete tvariable </code><span class="roman">[</span><code> $</code><var>name</var><code> ... </code><span class="roman">]</span><dd><a name="index-delete-tvariable-888"></a>Delete the given trace state variables, or all of them if no arguments
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are specified.
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</dl>
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</body></html>
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