252 lines
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HTML
252 lines
12 KiB
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<html lang="en">
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<head>
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<title>Frames In Python - Debugging with GDB</title>
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Python-API.html#Python-API" title="Python API">
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<link rel="prev" href="Objfiles-In-Python.html#Objfiles-In-Python" title="Objfiles In Python">
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<link rel="next" href="Blocks-In-Python.html#Blocks-In-Python" title="Blocks In Python">
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Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Frames-In-Python"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Blocks-In-Python.html#Blocks-In-Python">Blocks In Python</a>,
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Previous: <a rel="previous" accesskey="p" href="Objfiles-In-Python.html#Objfiles-In-Python">Objfiles In Python</a>,
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Up: <a rel="up" accesskey="u" href="Python-API.html#Python-API">Python API</a>
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<hr>
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</div>
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<h5 class="subsubsection">23.2.2.25 Accessing inferior stack frames from Python</h5>
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<p><a name="index-frames-in-python-2264"></a>When the debugged program stops, <span class="sc">gdb</span> is able to analyze its call
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stack (see <a href="Frames.html#Frames">Stack frames</a>). The <code>gdb.Frame</code> class
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represents a frame in the stack. A <code>gdb.Frame</code> object is only valid
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while its corresponding frame exists in the inferior's stack. If you try
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to use an invalid frame object, <span class="sc">gdb</span> will throw a <code>gdb.error</code>
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exception (see <a href="Exception-Handling.html#Exception-Handling">Exception Handling</a>).
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<p>Two <code>gdb.Frame</code> objects can be compared for equality with the <code>==</code>
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operator, like:
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<pre class="smallexample"> (gdb) python print gdb.newest_frame() == gdb.selected_frame ()
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True
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</pre>
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<p>The following frame-related functions are available in the <code>gdb</code> module:
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<p><a name="index-gdb_002eselected_005fframe-2265"></a>
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<div class="defun">
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— Function: <b>gdb.selected_frame</b> ()<var><a name="index-gdb_002eselected_005fframe-2266"></a></var><br>
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<blockquote><p>Return the selected frame object. (see <a href="Selection.html#Selection">Selecting a Frame</a>).
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</p></blockquote></div>
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<p><a name="index-gdb_002enewest_005fframe-2267"></a>
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<div class="defun">
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— Function: <b>gdb.newest_frame</b> ()<var><a name="index-gdb_002enewest_005fframe-2268"></a></var><br>
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<blockquote><p>Return the newest frame object for the selected thread.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>gdb.frame_stop_reason_string</b> (<var>reason</var>)<var><a name="index-gdb_002eframe_005fstop_005freason_005fstring-2269"></a></var><br>
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<blockquote><p>Return a string explaining the reason why <span class="sc">gdb</span> stopped unwinding
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frames, as expressed by the given <var>reason</var> code (an integer, see the
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<code>unwind_stop_reason</code> method further down in this section).
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</p></blockquote></div>
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<p><a name="index-gdb_002einvalidate_005fcached_005fframes-2270"></a>
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<div class="defun">
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— Function: <b>gdb.invalidate_cached_frames</b><var><a name="index-gdb_002einvalidate_005fcached_005fframes-2271"></a></var><br>
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<blockquote><p><span class="sc">gdb</span> internally keeps a cache of the frames that have been
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unwound. This function invalidates this cache.
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<p>This function should not generally be called by ordinary Python code.
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It is documented for the sake of completeness.
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</p></blockquote></div>
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<p>A <code>gdb.Frame</code> object has the following methods:
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<div class="defun">
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— Function: <b>Frame.is_valid</b> ()<var><a name="index-Frame_002eis_005fvalid-2272"></a></var><br>
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<blockquote><p>Returns true if the <code>gdb.Frame</code> object is valid, false if not.
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A frame object can become invalid if the frame it refers to doesn't
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exist anymore in the inferior. All <code>gdb.Frame</code> methods will throw
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an exception if it is invalid at the time the method is called.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.name</b> ()<var><a name="index-Frame_002ename-2273"></a></var><br>
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<blockquote><p>Returns the function name of the frame, or <code>None</code> if it can't be
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obtained.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.architecture</b> ()<var><a name="index-Frame_002earchitecture-2274"></a></var><br>
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<blockquote><p>Returns the <code>gdb.Architecture</code> object corresponding to the frame's
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architecture. See <a href="Architectures-In-Python.html#Architectures-In-Python">Architectures In Python</a>.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.type</b> ()<var><a name="index-Frame_002etype-2275"></a></var><br>
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<blockquote><p>Returns the type of the frame. The value can be one of:
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<dl>
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<dt><code>gdb.NORMAL_FRAME</code><dd>An ordinary stack frame.
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<br><dt><code>gdb.DUMMY_FRAME</code><dd>A fake stack frame that was created by <span class="sc">gdb</span> when performing an
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inferior function call.
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<br><dt><code>gdb.INLINE_FRAME</code><dd>A frame representing an inlined function. The function was inlined
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into a <code>gdb.NORMAL_FRAME</code> that is older than this one.
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<br><dt><code>gdb.TAILCALL_FRAME</code><dd>A frame representing a tail call. See <a href="Tail-Call-Frames.html#Tail-Call-Frames">Tail Call Frames</a>.
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<br><dt><code>gdb.SIGTRAMP_FRAME</code><dd>A signal trampoline frame. This is the frame created by the OS when
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it calls into a signal handler.
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<br><dt><code>gdb.ARCH_FRAME</code><dd>A fake stack frame representing a cross-architecture call.
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<br><dt><code>gdb.SENTINEL_FRAME</code><dd>This is like <code>gdb.NORMAL_FRAME</code>, but it is only used for the
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newest frame.
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</dl>
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.unwind_stop_reason</b> ()<var><a name="index-Frame_002eunwind_005fstop_005freason-2276"></a></var><br>
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<blockquote><p>Return an integer representing the reason why it's not possible to find
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more frames toward the outermost frame. Use
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<code>gdb.frame_stop_reason_string</code> to convert the value returned by this
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function to a string. The value can be one of:
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<dl>
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<dt><code>gdb.FRAME_UNWIND_NO_REASON</code><dd>No particular reason (older frames should be available).
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<br><dt><code>gdb.FRAME_UNWIND_NULL_ID</code><dd>The previous frame's analyzer returns an invalid result. This is no
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longer used by <span class="sc">gdb</span>, and is kept only for backward
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compatibility.
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<br><dt><code>gdb.FRAME_UNWIND_OUTERMOST</code><dd>This frame is the outermost.
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<br><dt><code>gdb.FRAME_UNWIND_UNAVAILABLE</code><dd>Cannot unwind further, because that would require knowing the
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values of registers or memory that have not been collected.
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<br><dt><code>gdb.FRAME_UNWIND_INNER_ID</code><dd>This frame ID looks like it ought to belong to a NEXT frame,
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but we got it for a PREV frame. Normally, this is a sign of
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unwinder failure. It could also indicate stack corruption.
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<br><dt><code>gdb.FRAME_UNWIND_SAME_ID</code><dd>This frame has the same ID as the previous one. That means
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that unwinding further would almost certainly give us another
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frame with exactly the same ID, so break the chain. Normally,
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this is a sign of unwinder failure. It could also indicate
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stack corruption.
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<br><dt><code>gdb.FRAME_UNWIND_NO_SAVED_PC</code><dd>The frame unwinder did not find any saved PC, but we needed
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one to unwind further.
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<br><dt><code>gdb.FRAME_UNWIND_MEMORY_ERROR</code><dd>The frame unwinder caused an error while trying to access memory.
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<br><dt><code>gdb.FRAME_UNWIND_FIRST_ERROR</code><dd>Any stop reason greater or equal to this value indicates some kind
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of error. This special value facilitates writing code that tests
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for errors in unwinding in a way that will work correctly even if
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the list of the other values is modified in future <span class="sc">gdb</span>
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versions. Using it, you could write:
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<pre class="smallexample"> reason = gdb.selected_frame().unwind_stop_reason ()
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reason_str = gdb.frame_stop_reason_string (reason)
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if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
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print "An error occured: %s" % reason_str
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</pre>
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</dl>
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</blockquote></div>
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<div class="defun">
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— Function: <b>Frame.pc</b> ()<var><a name="index-Frame_002epc-2277"></a></var><br>
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<blockquote><p>Returns the frame's resume address.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.block</b> ()<var><a name="index-Frame_002eblock-2278"></a></var><br>
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<blockquote><p>Return the frame's code block. See <a href="Blocks-In-Python.html#Blocks-In-Python">Blocks In Python</a>. If the frame
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does not have a block – for example, if there is no debugging
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information for the code in question – then this will throw an
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exception.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.function</b> ()<var><a name="index-Frame_002efunction-2279"></a></var><br>
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<blockquote><p>Return the symbol for the function corresponding to this frame.
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See <a href="Symbols-In-Python.html#Symbols-In-Python">Symbols In Python</a>.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.older</b> ()<var><a name="index-Frame_002eolder-2280"></a></var><br>
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<blockquote><p>Return the frame that called this frame.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.newer</b> ()<var><a name="index-Frame_002enewer-2281"></a></var><br>
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<blockquote><p>Return the frame called by this frame.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.find_sal</b> ()<var><a name="index-Frame_002efind_005fsal-2282"></a></var><br>
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<blockquote><p>Return the frame's symtab and line object.
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See <a href="Symbol-Tables-In-Python.html#Symbol-Tables-In-Python">Symbol Tables In Python</a>.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.read_register</b> (<var>register</var>)<var><a name="index-Frame_002eread_005fregister-2283"></a></var><br>
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<blockquote><p>Return the value of <var>register</var> in this frame. The <var>register</var>
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argument must be a string (e.g., <code>'sp'</code> or <code>'rax'</code>).
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Returns a <code>Gdb.Value</code> object. Throws an exception if <var>register</var>
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does not exist.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.read_var</b> (<var>variable </var><span class="roman">[</span><var>, block</var><span class="roman">]</span>)<var><a name="index-Frame_002eread_005fvar-2284"></a></var><br>
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<blockquote><p>Return the value of <var>variable</var> in this frame. If the optional
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argument <var>block</var> is provided, search for the variable from that
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block; otherwise start at the frame's current block (which is
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determined by the frame's current program counter). The <var>variable</var>
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argument must be a string or a <code>gdb.Symbol</code> object; <var>block</var> must be a
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<code>gdb.Block</code> object.
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</p></blockquote></div>
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<div class="defun">
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— Function: <b>Frame.select</b> ()<var><a name="index-Frame_002eselect-2285"></a></var><br>
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<blockquote><p>Set this frame to be the selected frame. See <a href="Stack.html#Stack">Examining the Stack</a>.
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</p></blockquote></div>
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</body></html>
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