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<title>Debugging with GDB: Recordings In Python</title>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Recordings-In-Python"></a>
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<div class="header">
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<p>
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Next: <a href="CLI-Commands-In-Python.html#CLI-Commands-In-Python" accesskey="n" rel="next">CLI Commands In Python</a>, Previous: <a href="Threads-In-Python.html#Threads-In-Python" accesskey="p" rel="previous">Threads In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</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>
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</div>
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<hr>
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<a name="Recordings-In-Python-1"></a>
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<h4 class="subsubsection">23.3.2.19 Recordings In Python</h4>
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<a name="index-recordings-in-python"></a>
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<p>The following recordings-related functions
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(see <a href="Process-Record-and-Replay.html#Process-Record-and-Replay">Process Record and Replay</a>) are available in the <code>gdb</code>
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module:
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</p>
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<dl>
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<dt><a name="index-gdb_002estart_005frecording"></a>Function: <strong>gdb.start_recording</strong> <em>(<span class="roman">[</span>method<span class="roman">]</span>, <span class="roman">[</span>format<span class="roman">]</span>)</em></dt>
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<dd><p>Start a recording using the given <var>method</var> and <var>format</var>. If
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no <var>format</var> is given, the default format for the recording method
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is used. If no <var>method</var> is given, the default method will be used.
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Returns a <code>gdb.Record</code> object on success. Throw an exception on
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failure.
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</p>
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<p>The following strings can be passed as <var>method</var>:
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</p>
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<ul>
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<li> <code>"full"</code>
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</li><li> <code>"btrace"</code>: Possible values for <var>format</var>: <code>"pt"</code>,
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<code>"bts"</code> or leave out for default format.
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</li></ul>
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</dd></dl>
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<dl>
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<dt><a name="index-gdb_002ecurrent_005frecording"></a>Function: <strong>gdb.current_recording</strong> <em>()</em></dt>
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<dd><p>Access a currently running recording. Return a <code>gdb.Record</code>
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object on success. Return <code>None</code> if no recording is currently
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active.
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</p></dd></dl>
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<dl>
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<dt><a name="index-gdb_002estop_005frecording"></a>Function: <strong>gdb.stop_recording</strong> <em>()</em></dt>
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<dd><p>Stop the current recording. Throw an exception if no recording is
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currently active. All record objects become invalid after this call.
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</p></dd></dl>
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<p>A <code>gdb.Record</code> object has the following attributes:
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</p>
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<dl>
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<dt><a name="index-Record_002emethod"></a>Variable: <strong>Record.method</strong></dt>
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<dd><p>A string with the current recording method, e.g. <code>full</code> or
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<code>btrace</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002eformat"></a>Variable: <strong>Record.format</strong></dt>
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<dd><p>A string with the current recording format, e.g. <code>bt</code>, <code>pts</code> or
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<code>None</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002ebegin"></a>Variable: <strong>Record.begin</strong></dt>
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<dd><p>A method specific instruction object representing the first instruction
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in this recording.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002eend"></a>Variable: <strong>Record.end</strong></dt>
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<dd><p>A method specific instruction object representing the current
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instruction, that is not actually part of the recording.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002ereplay_005fposition"></a>Variable: <strong>Record.replay_position</strong></dt>
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<dd><p>The instruction representing the current replay position. If there is
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no replay active, this will be <code>None</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002einstruction_005fhistory"></a>Variable: <strong>Record.instruction_history</strong></dt>
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<dd><p>A list with all recorded instructions.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Record_002efunction_005fcall_005fhistory"></a>Variable: <strong>Record.function_call_history</strong></dt>
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<dd><p>A list with all recorded function call segments.
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</p></dd></dl>
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<p>A <code>gdb.Record</code> object has the following methods:
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</p>
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<dl>
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<dt><a name="index-Record_002egoto"></a>Function: <strong>Record.goto</strong> <em>(instruction)</em></dt>
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<dd><p>Move the replay position to the given <var>instruction</var>.
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</p></dd></dl>
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<p>The common <code>gdb.Instruction</code> class that recording method specific
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instruction objects inherit from, has the following attributes:
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</p>
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<dl>
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<dt><a name="index-Instruction_002epc"></a>Variable: <strong>Instruction.pc</strong></dt>
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<dd><p>An integer representing this instruction’s address.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Instruction_002edata"></a>Variable: <strong>Instruction.data</strong></dt>
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<dd><p>A buffer with the raw instruction data. In Python 3, the return value is a
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<code>memoryview</code> object.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Instruction_002edecoded"></a>Variable: <strong>Instruction.decoded</strong></dt>
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<dd><p>A human readable string with the disassembled instruction.
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</p></dd></dl>
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<dl>
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<dt><a name="index-Instruction_002esize"></a>Variable: <strong>Instruction.size</strong></dt>
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<dd><p>The size of the instruction in bytes.
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</p></dd></dl>
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<p>Additionally <code>gdb.RecordInstruction</code> has the following attributes:
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</p>
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<dl>
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<dt><a name="index-RecordInstruction_002enumber"></a>Variable: <strong>RecordInstruction.number</strong></dt>
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<dd><p>An integer identifying this instruction. <code>number</code> corresponds to
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the numbers seen in <code>record instruction-history</code>
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(see <a href="Process-Record-and-Replay.html#Process-Record-and-Replay">Process Record and Replay</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordInstruction_002esal"></a>Variable: <strong>RecordInstruction.sal</strong></dt>
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<dd><p>A <code>gdb.Symtab_and_line</code> object representing the associated symtab
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and line of this instruction. May be <code>None</code> if no debug information is
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available.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordInstruction_002eis_005fspeculative"></a>Variable: <strong>RecordInstruction.is_speculative</strong></dt>
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<dd><p>A boolean indicating whether the instruction was executed speculatively.
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</p></dd></dl>
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<p>If an error occured during recording or decoding a recording, this error is
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represented by a <code>gdb.RecordGap</code> object in the instruction list. It has
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the following attributes:
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</p>
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<dl>
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<dt><a name="index-RecordGap_002enumber"></a>Variable: <strong>RecordGap.number</strong></dt>
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<dd><p>An integer identifying this gap. <code>number</code> corresponds to the numbers seen
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in <code>record instruction-history</code> (see <a href="Process-Record-and-Replay.html#Process-Record-and-Replay">Process Record and Replay</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordGap_002eerror_005fcode"></a>Variable: <strong>RecordGap.error_code</strong></dt>
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<dd><p>A numerical representation of the reason for the gap. The value is specific to
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the current recording method.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordGap_002eerror_005fstring"></a>Variable: <strong>RecordGap.error_string</strong></dt>
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<dd><p>A human readable string with the reason for the gap.
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</p></dd></dl>
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<p>A <code>gdb.RecordFunctionSegment</code> object has the following attributes:
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</p>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002enumber"></a>Variable: <strong>RecordFunctionSegment.number</strong></dt>
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<dd><p>An integer identifying this function segment. <code>number</code> corresponds to
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the numbers seen in <code>record function-call-history</code>
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(see <a href="Process-Record-and-Replay.html#Process-Record-and-Replay">Process Record and Replay</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002esymbol"></a>Variable: <strong>RecordFunctionSegment.symbol</strong></dt>
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<dd><p>A <code>gdb.Symbol</code> object representing the associated symbol. May be
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<code>None</code> if no debug information is available.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002elevel"></a>Variable: <strong>RecordFunctionSegment.level</strong></dt>
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<dd><p>An integer representing the function call’s stack level. May be
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<code>None</code> if the function call is a gap.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002einstructions"></a>Variable: <strong>RecordFunctionSegment.instructions</strong></dt>
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<dd><p>A list of <code>gdb.RecordInstruction</code> or <code>gdb.RecordGap</code> objects
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associated with this function call.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002eup"></a>Variable: <strong>RecordFunctionSegment.up</strong></dt>
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<dd><p>A <code>gdb.RecordFunctionSegment</code> object representing the caller’s
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function segment. If the call has not been recorded, this will be the
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function segment to which control returns. If neither the call nor the
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return have been recorded, this will be <code>None</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002eprev"></a>Variable: <strong>RecordFunctionSegment.prev</strong></dt>
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<dd><p>A <code>gdb.RecordFunctionSegment</code> object representing the previous
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segment of this function call. May be <code>None</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-RecordFunctionSegment_002enext"></a>Variable: <strong>RecordFunctionSegment.next</strong></dt>
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<dd><p>A <code>gdb.RecordFunctionSegment</code> object representing the next segment of
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this function call. May be <code>None</code>.
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</p></dd></dl>
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<p>The following example demonstrates the usage of these objects and
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functions to create a function that will rewind a record to the last
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time a function in a different file was executed. This would typically
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be used to track the execution of user provided callback functions in a
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library which typically are not visible in a back trace.
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</p>
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<div class="smallexample">
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<pre class="smallexample">def bringback ():
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rec = gdb.current_recording ()
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if not rec:
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return
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insn = rec.instruction_history
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if len (insn) == 0:
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return
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try:
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position = insn.index (rec.replay_position)
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except:
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position = -1
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try:
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filename = insn[position].sal.symtab.fullname ()
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except:
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filename = None
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for i in reversed (insn[:position]):
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try:
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current = i.sal.symtab.fullname ()
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except:
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current = None
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if filename == current:
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continue
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rec.goto (i)
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return
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</pre></div>
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<p>Another possible application is to write a function that counts the
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number of code executions in a given line range. This line range can
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contain parts of functions or span across several functions and is not
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limited to be contiguous.
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</p>
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<div class="smallexample">
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<pre class="smallexample">def countrange (filename, linerange):
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count = 0
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def filter_only (file_name):
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for call in gdb.current_recording ().function_call_history:
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try:
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if file_name in call.symbol.symtab.fullname ():
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yield call
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except:
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pass
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for c in filter_only (filename):
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for i in c.instructions:
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try:
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if i.sal.line in linerange:
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count += 1
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break;
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except:
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pass
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return count
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="CLI-Commands-In-Python.html#CLI-Commands-In-Python" accesskey="n" rel="next">CLI Commands In Python</a>, Previous: <a href="Threads-In-Python.html#Threads-In-Python" accesskey="p" rel="previous">Threads In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</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>
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