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| <h3 class="section">8.3 Selecting a Frame</h3> |
| |
| <p>Most commands for examining the stack and other data in your program work on |
| whichever stack frame is selected at the moment. Here are the commands for |
| selecting a stack frame; all of them finish by printing a brief description |
| of the stack frame just selected. |
| |
| |
| <a name="index-frame_0040r_007b_002c-selecting_007d-529"></a> |
| <a name="index-f-_0040r_007b_0028_0040code_007bframe_007d_0029_007d-530"></a> |
| <dl><dt><code>frame </code><span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span><br><dt><code>f </code><span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span><dd>The <samp><span class="command">frame</span></samp> command allows different stack frames to be |
| selected. The <var>frame-selection-spec</var> can be any of the following: |
| |
| |
| <a name="index-frame-level-531"></a> |
| <dl><dt><var>num</var><br><dt><code>level </code><var>num</var><dd>Select frame level <var>num</var>. Recall that frame zero is the innermost |
| (currently executing) frame, frame one is the frame that called the |
| innermost one, and so on. The highest level frame is usually the one |
| for <code>main</code>. |
| |
| <p>As this is the most common method of navigating the frame stack, the |
| string <samp><span class="command">level</span></samp> can be omitted. For example, the following two |
| commands are equivalent: |
| |
| <pre class="smallexample"> (gdb) frame 3 |
| (gdb) frame level 3 |
| </pre> |
| <p><a name="index-frame-address-532"></a><br><dt><code>address </code><var>stack-address</var><dd>Select the frame with stack address <var>stack-address</var>. The |
| <var>stack-address</var> for a frame can be seen in the output of |
| <samp><span class="command">info frame</span></samp>, for example: |
| |
| <pre class="smallexample"> (gdb) info frame |
| Stack level 1, frame at 0x7fffffffda30: |
| rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5 |
| tail call frame, caller of frame at 0x7fffffffda30 |
| source language c++. |
| Arglist at unknown address. |
| Locals at unknown address, Previous frame's sp is 0x7fffffffda30 |
| </pre> |
| <p>The <var>stack-address</var> for this frame is <code>0x7fffffffda30</code> as |
| indicated by the line: |
| |
| <pre class="smallexample"> Stack level 1, frame at 0x7fffffffda30: |
| </pre> |
| <p><a name="index-frame-function-533"></a><br><dt><code>function </code><var>function-name</var><dd>Select the stack frame for function <var>function-name</var>. If there are |
| multiple stack frames for function <var>function-name</var> then the inner |
| most stack frame is selected. |
| |
| <p><a name="index-frame-view-534"></a><br><dt><code>view </code><var>stack-address</var> <span class="roman">[</span> <var>pc-addr</var> <span class="roman">]</span><dd>View a frame that is not part of <span class="sc">gdb</span>'s backtrace. The frame |
| viewed has stack address <var>stack-addr</var>, and optionally, a program |
| counter address of <var>pc-addr</var>. |
| |
| <p>This is useful mainly if the chaining of stack frames has been |
| damaged by a bug, making it impossible for <span class="sc">gdb</span> to assign |
| numbers properly to all frames. In addition, this can be useful |
| when your program has multiple stacks and switches between them. |
| |
| <p>When viewing a frame outside the current backtrace using |
| <samp><span class="command">frame view</span></samp> then you can always return to the original |
| stack using one of the previous stack frame selection instructions, |
| for example <samp><span class="command">frame level 0</span></samp>. |
| |
| </dl> |
| |
| <p><a name="index-up-535"></a><br><dt><code>up </code><var>n</var><dd>Move <var>n</var> frames up the stack; <var>n</var> defaults to 1. For positive |
| numbers <var>n</var>, this advances toward the outermost frame, to higher |
| frame numbers, to frames that have existed longer. |
| |
| <p><a name="index-down-536"></a><a name="index-do-_0040r_007b_0028_0040code_007bdown_007d_0029_007d-537"></a><br><dt><code>down </code><var>n</var><dd>Move <var>n</var> frames down the stack; <var>n</var> defaults to 1. For |
| positive numbers <var>n</var>, this advances toward the innermost frame, to |
| lower frame numbers, to frames that were created more recently. |
| You may abbreviate <code>down</code> as <code>do</code>. |
| </dl> |
| |
| <p>All of these commands end by printing two lines of output describing the |
| frame. The first line shows the frame number, the function name, the |
| arguments, and the source file and line number of execution in that |
| frame. The second line shows the text of that source line. |
| |
| <p>For example: |
| |
| <pre class="smallexample"> (gdb) up |
| #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) |
| at env.c:10 |
| 10 read_input_file (argv[i]); |
| </pre> |
| <p>After such a printout, the <code>list</code> command with no arguments |
| prints ten lines centered on the point of execution in the frame. |
| You can also edit the program at the point of execution with your favorite |
| editing program by typing <code>edit</code>. |
| See <a href="List.html#List">Printing Source Lines</a>, |
| for details. |
| |
| |
| <a name="index-select_002dframe-538"></a> |
| <dl><dt><code>select-frame </code><span class="roman">[</span> <var>frame-selection-spec</var> <span class="roman">]</span><dd>The <code>select-frame</code> command is a variant of <code>frame</code> that does |
| not display the new frame after selecting it. This command is |
| intended primarily for use in <span class="sc">gdb</span> command scripts, where the |
| output might be unnecessary and distracting. The |
| <var>frame-selection-spec</var> is as for the <samp><span class="command">frame</span></samp> command |
| described in <a href="Selection.html#Selection">Selecting a Frame</a>. |
| |
| <p><a name="index-down_002dsilently-539"></a><a name="index-up_002dsilently-540"></a><br><dt><code>up-silently </code><var>n</var><dt><code>down-silently </code><var>n</var><dd>These two commands are variants of <code>up</code> and <code>down</code>, |
| respectively; they differ in that they do their work silently, without |
| causing display of the new frame. They are intended primarily for use |
| in <span class="sc">gdb</span> command scripts, where the output might be unnecessary and |
| distracting. |
| </dl> |
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