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<title>Debugging with GDB: Selection</title>
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<a name="Selection"></a>
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<div class="header">
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<p>
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Next: <a href="Frame-Info.html#Frame-Info" accesskey="n" rel="next">Frame Info</a>, Previous: <a href="Backtrace.html#Backtrace" accesskey="p" rel="previous">Backtrace</a>, Up: <a href="Stack.html#Stack" accesskey="u" rel="up">Stack</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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<hr>
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<a name="Selecting-a-Frame"></a>
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<h3 class="section">8.3 Selecting a Frame</h3>
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<p>Most commands for examining the stack and other data in your program work on
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whichever stack frame is selected at the moment. Here are the commands for
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selecting a stack frame; all of them finish by printing a brief description
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of the stack frame just selected.
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</p>
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<dl compact="compact">
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<dd><a name="index-frame_002c-selecting"></a>
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<a name="index-f-_0028frame_0029"></a>
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</dd>
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<dt><code>frame <span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span></code></dt>
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<dt><code>f <span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span></code></dt>
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<dd><p>The <code>frame</code> command allows different stack frames to be
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selected. The <var>frame-selection-spec</var> can be any of the following:
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</p>
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<dl compact="compact">
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<dd><a name="index-frame-level-1"></a>
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</dd>
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<dt><code><var>num</var></code></dt>
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<dt><code>level <var>num</var></code></dt>
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<dd><p>Select frame level <var>num</var>. Recall that frame zero is the innermost
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(currently executing) frame, frame one is the frame that called the
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innermost one, and so on. The highest level frame is usually the one
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for <code>main</code>.
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</p>
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<p>As this is the most common method of navigating the frame stack, the
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string <code>level</code> can be omitted. For example, the following two
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commands are equivalent:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) frame 3
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(gdb) frame level 3
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</pre></div>
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<a name="index-frame-address"></a>
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</dd>
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<dt><code>address <var>stack-address</var></code></dt>
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<dd><p>Select the frame with stack address <var>stack-address</var>. The
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<var>stack-address</var> for a frame can be seen in the output of
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<code>info frame</code>, for example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) info frame
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Stack level 1, frame at 0x7fffffffda30:
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rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
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tail call frame, caller of frame at 0x7fffffffda30
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source language c++.
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Arglist at unknown address.
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Locals at unknown address, Previous frame's sp is 0x7fffffffda30
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</pre></div>
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<p>The <var>stack-address</var> for this frame is <code>0x7fffffffda30</code> as
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indicated by the line:
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</p>
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<div class="smallexample">
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<pre class="smallexample">Stack level 1, frame at 0x7fffffffda30:
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</pre></div>
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<a name="index-frame-function"></a>
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</dd>
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<dt><code>function <var>function-name</var></code></dt>
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<dd><p>Select the stack frame for function <var>function-name</var>. If there are
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multiple stack frames for function <var>function-name</var> then the inner
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most stack frame is selected.
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</p>
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<a name="index-frame-view"></a>
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</dd>
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<dt><code>view <var>stack-address</var> <span class="roman">[</span> <var>pc-addr</var> <span class="roman">]</span></code></dt>
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<dd><p>View a frame that is not part of <small>GDB</small>’s backtrace. The frame
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viewed has stack address <var>stack-addr</var>, and optionally, a program
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counter address of <var>pc-addr</var>.
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</p>
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<p>This is useful mainly if the chaining of stack frames has been
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damaged by a bug, making it impossible for <small>GDB</small> to assign
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numbers properly to all frames. In addition, this can be useful
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when your program has multiple stacks and switches between them.
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</p>
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<p>When viewing a frame outside the current backtrace using
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<code>frame view</code> then you can always return to the original
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stack using one of the previous stack frame selection instructions,
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for example <code>frame level 0</code>.
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</p>
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</dd>
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</dl>
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<a name="index-up"></a>
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</dd>
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<dt><code>up <var>n</var></code></dt>
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<dd><p>Move <var>n</var> frames up the stack; <var>n</var> defaults to 1. For positive
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numbers <var>n</var>, this advances toward the outermost frame, to higher
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frame numbers, to frames that have existed longer.
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</p>
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<a name="index-down"></a>
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<a name="index-do-_0028down_0029"></a>
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</dd>
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<dt><code>down <var>n</var></code></dt>
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<dd><p>Move <var>n</var> frames down the stack; <var>n</var> defaults to 1. For
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positive numbers <var>n</var>, this advances toward the innermost frame, to
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lower frame numbers, to frames that were created more recently.
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You may abbreviate <code>down</code> as <code>do</code>.
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</p></dd>
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</dl>
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<p>All of these commands end by printing two lines of output describing the
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frame. The first line shows the frame number, the function name, the
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arguments, and the source file and line number of execution in that
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frame. The second line shows the text of that source line.
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</p>
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<p>For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) up
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#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
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at env.c:10
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10 read_input_file (argv[i]);
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</pre></div>
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<p>After such a printout, the <code>list</code> command with no arguments
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prints ten lines centered on the point of execution in the frame.
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You can also edit the program at the point of execution with your favorite
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editing program by typing <code>edit</code>.
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See <a href="List.html#List">Printing Source Lines</a>,
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for details.
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</p>
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<dl compact="compact">
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<dd><a name="index-select_002dframe"></a>
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</dd>
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<dt><code>select-frame <span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span></code></dt>
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<dd><p>The <code>select-frame</code> command is a variant of <code>frame</code> that does
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not display the new frame after selecting it. This command is
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intended primarily for use in <small>GDB</small> command scripts, where the
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output might be unnecessary and distracting. The
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<var>frame-selection-spec</var> is as for the <code>frame</code> command
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described in <a href="#Selection">Selecting a Frame</a>.
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</p>
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<a name="index-down_002dsilently"></a>
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<a name="index-up_002dsilently"></a>
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</dd>
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<dt><code>up-silently <var>n</var></code></dt>
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<dt><code>down-silently <var>n</var></code></dt>
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<dd><p>These two commands are variants of <code>up</code> and <code>down</code>,
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respectively; they differ in that they do their work silently, without
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causing display of the new frame. They are intended primarily for use
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in <small>GDB</small> command scripts, where the output might be unnecessary and
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distracting.
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</p></dd>
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</dl>
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<div class="header">
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<p>
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Next: <a href="Frame-Info.html#Frame-Info" accesskey="n" rel="next">Frame Info</a>, Previous: <a href="Backtrace.html#Backtrace" accesskey="p" rel="previous">Backtrace</a>, Up: <a href="Stack.html#Stack" accesskey="u" rel="up">Stack</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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