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| <h4 class="subsection">13.1.5 Trace State Variables</h4> |
| |
| <p><a name="index-trace-state-variables-884"></a> |
| A <dfn>trace state variable</dfn> 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 “$”), |
| but they are stored on the target. They must be created explicitly, |
| using a <code>tvariable</code> command. They are always 64-bit signed |
| integers. |
| |
| <p>Trace state variables are remembered by <span class="sc">gdb</span>, and downloaded |
| to the target along with tracepoint information when the trace |
| experiment starts. There are no intrinsic limits on the number of |
| trace state variables, beyond memory limitations of the target. |
| |
| <p><a name="index-convenience-variables_002c-and-trace-state-variables-885"></a>Although trace state variables are managed by the target, you can use |
| them in print commands and expressions as if they were convenience |
| variables; <span class="sc">gdb</span> will get the current value from the target |
| while the trace experiment is running. Trace state variables share |
| the same namespace as other “$” 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. |
| |
| <dl> |
| <dt><code>tvariable $</code><var>name</var><code> [ = </code><var>expression</var><code> ]</code><dd><a name="index-tvariable-886"></a>The <code>tvariable</code> command creates a new trace state variable named |
| <code>$</code><var>name</var>, 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 <span class="sc">gdb</span> 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. |
| |
| <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. |
| Their current values may also be displayed, if the trace experiment is |
| currently running. |
| |
| <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 |
| are specified. |
| |
| </dl> |
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