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<title>Frames In Guile - Debugging with GDB</title>
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<a name="Frames-In-Guile"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Blocks-In-Guile.html#Blocks-In-Guile">Blocks In Guile</a>,
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Previous: <a rel="previous" accesskey="p" href="Objfiles-In-Guile.html#Objfiles-In-Guile">Objfiles In Guile</a>,
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Up: <a rel="up" accesskey="u" href="Guile-API.html#Guile-API">Guile API</a>
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<h5 class="subsubsection">23.3.3.15 Accessing inferior stack frames from Guile.</h5>
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<p><a name="index-frames-in-guile-2674"></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
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<code>gdb:invalid-object</code> exception (see <a href="Guile-Exception-Handling.html#Guile-Exception-Handling">Guile Exception Handling</a>).
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<p>Two <code><gdb:frame></code> objects can be compared for equality with the
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<code>equal?</code> function, like:
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<pre class="smallexample"> (gdb) guile (equal? (newest-frame) (selected-frame))
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#t
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</pre>
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<p>The following frame-related procedures are provided by the
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<code>(gdb)</code> module:
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<div class="defun">
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— Scheme Procedure: <b>frame?</b><var> object<a name="index-frame_003f-2675"></a></var><br>
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<blockquote><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:frame></code> object.
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Otherwise return <code>#f</code>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-valid?</b><var> frame<a name="index-frame_002dvalid_003f-2676"></a></var><br>
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<blockquote><p>Returns <code>#t</code> if <var>frame</var> is valid, <code>#f</code> 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> procedures will throw
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an exception if the frame is invalid at the time the procedure is called.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-name</b><var> frame<a name="index-frame_002dname-2677"></a></var><br>
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<blockquote><p>Return the function name of <var>frame</var>, or <code>#f</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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— Scheme Procedure: <b>frame-arch</b><var> frame<a name="index-frame_002darch-2678"></a></var><br>
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<blockquote><p>Return the <code><gdb:architecture></code> object corresponding to <var>frame</var>'s
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architecture. See <a href="Architectures-In-Guile.html#Architectures-In-Guile">Architectures In Guile</a>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-type</b><var> frame<a name="index-frame_002dtype-2679"></a></var><br>
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<blockquote><p>Return the type of <var>frame</var>. The value can be one of:
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<dl>
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<dt><code>NORMAL_FRAME</code><dd>An ordinary stack frame.
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<br><dt><code>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>INLINE_FRAME</code><dd>A frame representing an inlined function. The function was inlined
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into a <code>NORMAL_FRAME</code> that is older than this one.
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<br><dt><code>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>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>ARCH_FRAME</code><dd>A fake stack frame representing a cross-architecture call.
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<br><dt><code>SENTINEL_FRAME</code><dd>This is like <code>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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— Scheme Procedure: <b>frame-unwind-stop-reason</b><var> frame<a name="index-frame_002dunwind_002dstop_002dreason-2680"></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>unwind-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>FRAME_UNWIND_NO_REASON</code><dd>No particular reason (older frames should be available).
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<br><dt><code>FRAME_UNWIND_NULL_ID</code><dd>The previous frame's analyzer returns an invalid result.
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<br><dt><code>FRAME_UNWIND_OUTERMOST</code><dd>This frame is the outermost.
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<br><dt><code>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>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>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>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>FRAME_UNWIND_MEMORY_ERROR</code><dd>The frame unwinder caused an error while trying to access memory.
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<br><dt><code>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"> (define reason (frame-unwind-stop-readon (selected-frame)))
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(define reason-str (unwind-stop-reason-string reason))
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(if (>= reason FRAME_UNWIND_FIRST_ERROR)
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(format #t "An error occured: ~s\n" reason-str))
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</pre>
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</dl>
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-pc</b><var> frame<a name="index-frame_002dpc-2681"></a></var><br>
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<blockquote><p>Return the frame's resume address.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-block</b><var> frame<a name="index-frame_002dblock-2682"></a></var><br>
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<blockquote><p>Return the frame's code block as a <code><gdb:block></code> object.
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See <a href="Blocks-In-Guile.html#Blocks-In-Guile">Blocks In Guile</a>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-function</b><var> frame<a name="index-frame_002dfunction-2683"></a></var><br>
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<blockquote><p>Return the symbol for the function corresponding to this frame
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as a <code><gdb:symbol></code> object, or <code>#f</code> if there isn't one.
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See <a href="Symbols-In-Guile.html#Symbols-In-Guile">Symbols In Guile</a>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-older</b><var> frame<a name="index-frame_002dolder-2684"></a></var><br>
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<blockquote><p>Return the frame that called <var>frame</var>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-newer</b><var> frame<a name="index-frame_002dnewer-2685"></a></var><br>
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<blockquote><p>Return the frame called by <var>frame</var>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-sal</b><var> frame<a name="index-frame_002dsal-2686"></a></var><br>
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<blockquote><p>Return the frame's <code><gdb:sal></code> (symtab and line) object.
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See <a href="Symbol-Tables-In-Guile.html#Symbol-Tables-In-Guile">Symbol Tables In Guile</a>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-read-register</b><var> frame register<a name="index-frame_002dread_002dregister-2687"></a></var><br>
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<blockquote><p>Return the value of <var>register</var> in <var>frame</var>. <var>register</var>
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should be a string, like ‘<samp><span class="samp">pc</span></samp>’.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-read-var</b><var> frame variable </var><span class="roman">[</span><var>#:block block</var><span class="roman">]</span><var><a name="index-frame_002dread_002dvar-2688"></a></var><br>
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<blockquote><p>Return the value of <var>variable</var> in <var>frame</var>. 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
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<var>variable</var> must be given as a string or a <code><gdb:symbol></code>
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object, and <var>block</var> must be a <code><gdb:block></code> object.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>frame-select</b><var> frame<a name="index-frame_002dselect-2689"></a></var><br>
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<blockquote><p>Set <var>frame</var> 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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<div class="defun">
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— Scheme Procedure: <b>selected-frame</b><var><a name="index-selected_002dframe-2690"></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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<div class="defun">
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— Scheme Procedure: <b>newest-frame</b><var><a name="index-newest_002dframe-2691"></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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— Scheme Procedure: <b>unwind-stop-reason-string</b><var> reason<a name="index-unwind_002dstop_002dreason_002dstring-2692"></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>frame-unwind-stop-reason</code> procedure above in this section).
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</p></blockquote></div>
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