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150 lines
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<title>tfind - Debugging with GDB</title>
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<a name="tfind"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="tdump.html#tdump">tdump</a>,
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Up: <a rel="up" accesskey="u" href="Analyze-Collected-Data.html#Analyze-Collected-Data">Analyze Collected Data</a>
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<h4 class="subsection">13.2.1 <code>tfind </code><var>n</var></h4>
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<p><a name="index-tfind-927"></a><a name="index-select-trace-snapshot-928"></a><a name="index-find-trace-snapshot-929"></a>The basic command for selecting a trace snapshot from the buffer is
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<code>tfind </code><var>n</var>, which finds trace snapshot number <var>n</var>,
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counting from zero. If no argument <var>n</var> is given, the next
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snapshot is selected.
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<p>Here are the various forms of using the <code>tfind</code> command.
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<dl>
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<dt><code>tfind start</code><dd>Find the first snapshot in the buffer. This is a synonym for
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<code>tfind 0</code> (since 0 is the number of the first snapshot).
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<br><dt><code>tfind none</code><dd>Stop debugging trace snapshots, resume <em>live</em> debugging.
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<br><dt><code>tfind end</code><dd>Same as ‘<samp><span class="samp">tfind none</span></samp>’.
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<br><dt><code>tfind</code><dd>No argument means find the next trace snapshot or find the first
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one if no trace snapshot is selected.
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<br><dt><code>tfind -</code><dd>Find the previous trace snapshot before the current one. This permits
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retracing earlier steps.
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<br><dt><code>tfind tracepoint </code><var>num</var><dd>Find the next snapshot associated with tracepoint <var>num</var>. Search
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proceeds forward from the last examined trace snapshot. If no
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argument <var>num</var> is given, it means find the next snapshot collected
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for the same tracepoint as the current snapshot.
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<br><dt><code>tfind pc </code><var>addr</var><dd>Find the next snapshot associated with the value <var>addr</var> of the
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program counter. Search proceeds forward from the last examined trace
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snapshot. If no argument <var>addr</var> is given, it means find the next
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snapshot with the same value of PC as the current snapshot.
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<br><dt><code>tfind outside </code><var>addr1</var><code>, </code><var>addr2</var><dd>Find the next snapshot whose PC is outside the given range of
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addresses (exclusive).
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<br><dt><code>tfind range </code><var>addr1</var><code>, </code><var>addr2</var><dd>Find the next snapshot whose PC is between <var>addr1</var> and
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<var>addr2</var> (inclusive).
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<br><dt><code>tfind line </code><span class="roman">[</span><var>file</var><code>:</code><span class="roman">]</span><var>n</var><dd>Find the next snapshot associated with the source line <var>n</var>. If
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the optional argument <var>file</var> is given, refer to line <var>n</var> in
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that source file. Search proceeds forward from the last examined
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trace snapshot. If no argument <var>n</var> is given, it means find the
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next line other than the one currently being examined; thus saying
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<code>tfind line</code> repeatedly can appear to have the same effect as
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stepping from line to line in a <em>live</em> debugging session.
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</dl>
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<p>The default arguments for the <code>tfind</code> commands are specifically
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designed to make it easy to scan through the trace buffer. For
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instance, <code>tfind</code> with no argument selects the next trace
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snapshot, and <code>tfind -</code> with no argument selects the previous
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trace snapshot. So, by giving one <code>tfind</code> command, and then
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simply hitting <RET> repeatedly you can examine all the trace
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snapshots in order. Or, by saying <code>tfind -</code> and then hitting
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<RET> repeatedly you can examine the snapshots in reverse order.
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The <code>tfind line</code> command with no argument selects the snapshot
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for the next source line executed. The <code>tfind pc</code> command with
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no argument selects the next snapshot with the same program counter
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(PC) as the current frame. The <code>tfind tracepoint</code> command with
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no argument selects the next trace snapshot collected by the same
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tracepoint as the current one.
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<p>In addition to letting you scan through the trace buffer manually,
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these commands make it easy to construct <span class="sc">gdb</span> scripts that
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scan through the trace buffer and print out whatever collected data
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you are interested in. Thus, if we want to examine the PC, FP, and SP
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registers from each trace frame in the buffer, we can say this:
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<pre class="smallexample"> (gdb) <b>tfind start</b>
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(gdb) <b>while ($trace_frame != -1)</b>
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> printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
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$trace_frame, $pc, $sp, $fp
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> tfind
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> end
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Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
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Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
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Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
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Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
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Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
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Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
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Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
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Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
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Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
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Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
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Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
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</pre>
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<p>Or, if we want to examine the variable <code>X</code> at each source line in
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the buffer:
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<pre class="smallexample"> (gdb) <b>tfind start</b>
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(gdb) <b>while ($trace_frame != -1)</b>
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> printf "Frame %d, X == %d\n", $trace_frame, X
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> tfind line
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> end
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Frame 0, X = 1
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Frame 7, X = 2
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Frame 13, X = 255
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</pre>
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