160 lines
8.4 KiB
HTML
160 lines
8.4 KiB
HTML
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<html lang="en">
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<head>
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<title>Selection - Debugging with GDB</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Debugging with GDB">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Stack.html#Stack" title="Stack">
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<link rel="prev" href="Backtrace.html#Backtrace" title="Backtrace">
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<link rel="next" href="Frame-Info.html#Frame-Info" title="Frame Info">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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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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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Free Software'' and ``Free Software Needs
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Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom.''
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span.sc { font-variant:small-caps }
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span.roman { font-family:serif; font-weight:normal; }
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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="Selection"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Frame-Info.html#Frame-Info">Frame Info</a>,
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Previous: <a rel="previous" accesskey="p" href="Backtrace.html#Backtrace">Backtrace</a>,
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Up: <a rel="up" accesskey="u" href="Stack.html#Stack">Stack</a>
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<hr>
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</div>
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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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<a name="index-frame_0040r_007b_002c-selecting_007d-529"></a>
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<a name="index-f-_0040r_007b_0028_0040code_007bframe_007d_0029_007d-530"></a>
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<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
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selected. The <var>frame-selection-spec</var> can be any of the following:
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<a name="index-frame-level-531"></a>
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<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
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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>As this is the most common method of navigating the frame stack, the
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string <samp><span class="command">level</span></samp> can be omitted. For example, the following two
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commands are equivalent:
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<pre class="smallexample"> (gdb) frame 3
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(gdb) frame level 3
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</pre>
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<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
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<var>stack-address</var> for a frame can be seen in the output of
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<samp><span class="command">info frame</span></samp>, for example:
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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>
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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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<pre class="smallexample"> Stack level 1, frame at 0x7fffffffda30:
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</pre>
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<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
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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><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
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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>This is useful mainly if the chaining of stack frames has been
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damaged by a bug, making it impossible for <span class="sc">gdb</span> 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>When viewing a frame outside the current backtrace using
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<samp><span class="command">frame view</span></samp> 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 <samp><span class="command">frame level 0</span></samp>.
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</dl>
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<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
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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><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
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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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</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>For example:
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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>
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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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<a name="index-select_002dframe-538"></a>
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<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
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not display the new frame after selecting it. This command is
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intended primarily for use in <span class="sc">gdb</span> 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 <samp><span class="command">frame</span></samp> command
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described in <a href="Selection.html#Selection">Selecting a Frame</a>.
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<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>,
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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 <span class="sc">gdb</span> command scripts, where the output might be unnecessary and
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distracting.
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</dl>
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</body></html>
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