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223 lines
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223 lines
10 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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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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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Emacs (Debugging with GDB)</title>
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<meta name="description" content="Emacs (Debugging with GDB)">
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<meta name="keywords" content="Emacs (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="GDB_002fMI.html#GDB_002fMI" rel="next" title="GDB/MI">
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<link href="TUI-Configuration.html#TUI-Configuration" rel="prev" title="TUI Configuration">
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</head>
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<body lang="en">
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<a name="Emacs"></a>
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<div class="header">
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<p>
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Next: <a href="GDB_002fMI.html#GDB_002fMI" accesskey="n" rel="next">GDB/MI</a>, Previous: <a href="TUI.html#TUI" accesskey="p" rel="prev">TUI</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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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</div>
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<hr>
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<a name="Using-GDB-under-GNU-Emacs"></a>
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<h2 class="chapter">26 Using <small>GDB</small> under <small>GNU</small> Emacs</h2>
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<a name="index-Emacs"></a>
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<a name="index-GNU-Emacs"></a>
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<p>A special interface allows you to use <small>GNU</small> Emacs to view (and
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edit) the source files for the program you are debugging with
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<small>GDB</small>.
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</p>
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<p>To use this interface, use the command <kbd>M-x gdb</kbd> in Emacs. Give the
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executable file you want to debug as an argument. This command starts
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<small>GDB</small> as a subprocess of Emacs, with input and output through a newly
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created Emacs buffer.
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</p>
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<p>Running <small>GDB</small> under Emacs can be just like running <small>GDB</small> normally except for two
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things:
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</p>
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<ul>
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<li> All “terminal” input and output goes through an Emacs buffer, called
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the GUD buffer.
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<p>This applies both to <small>GDB</small> commands and their output, and to the input
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and output done by the program you are debugging.
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</p>
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<p>This is useful because it means that you can copy the text of previous
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commands and input them again; you can even use parts of the output
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in this way.
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</p>
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<p>All the facilities of Emacs’ Shell mode are available for interacting
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with your program. In particular, you can send signals the usual
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way—for example, <kbd>C-c C-c</kbd> for an interrupt, <kbd>C-c C-z</kbd> for a
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stop.
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</p>
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</li><li> <small>GDB</small> displays source code through Emacs.
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<p>Each time <small>GDB</small> displays a stack frame, Emacs automatically finds the
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source file for that frame and puts an arrow (‘<samp>=></samp>’) at the
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left margin of the current line. Emacs uses a separate buffer for
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source display, and splits the screen to show both your <small>GDB</small> session
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and the source.
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</p>
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<p>Explicit <small>GDB</small> <code>list</code> or search commands still produce output as
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usual, but you probably have no reason to use them from Emacs.
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</p></li></ul>
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<p>We call this <em>text command mode</em>. Emacs 22.1, and later, also uses
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a graphical mode, enabled by default, which provides further buffers
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that can control the execution and describe the state of your program.
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See <a href="../Emacs/GDB-Graphical-Interface.html#GDB-Graphical-Interface">GDB Graphical Interface</a> in <cite>The <small>GNU</small> Emacs Manual</cite>.
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</p>
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<p>If you specify an absolute file name when prompted for the <kbd>M-x
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gdb</kbd> argument, then Emacs sets your current working directory to where
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your program resides. If you only specify the file name, then Emacs
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sets your current working directory to the directory associated
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with the previous buffer. In this case, <small>GDB</small> may find your
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program by searching your environment’s <code>PATH</code> variable, but on
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some operating systems it might not find the source. So, although the
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<small>GDB</small> input and output session proceeds normally, the auxiliary
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buffer does not display the current source and line of execution.
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</p>
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<p>The initial working directory of <small>GDB</small> is printed on the top
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line of the GUD buffer and this serves as a default for the commands
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that specify files for <small>GDB</small> to operate on. See <a href="Files.html#Files">Commands to Specify Files</a>.
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</p>
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<p>By default, <kbd>M-x gdb</kbd> calls the program called <samp>gdb</samp>. If you
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need to call <small>GDB</small> by a different name (for example, if you
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keep several configurations around, with different names) you can
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customize the Emacs variable <code>gud-gdb-command-name</code> to run the
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one you want.
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</p>
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<p>In the GUD buffer, you can use these special Emacs commands in
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addition to the standard Shell mode commands:
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</p>
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<dl compact="compact">
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<dt><kbd>C-h m</kbd></dt>
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<dd><p>Describe the features of Emacs’ GUD Mode.
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</p>
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</dd>
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<dt><kbd>C-c C-s</kbd></dt>
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<dd><p>Execute to another source line, like the <small>GDB</small> <code>step</code> command; also
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update the display window to show the current file and location.
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</p>
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</dd>
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<dt><kbd>C-c C-n</kbd></dt>
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<dd><p>Execute to next source line in this function, skipping all function
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calls, like the <small>GDB</small> <code>next</code> command. Then update the display window
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to show the current file and location.
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</p>
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</dd>
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<dt><kbd>C-c C-i</kbd></dt>
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<dd><p>Execute one instruction, like the <small>GDB</small> <code>stepi</code> command; update
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display window accordingly.
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</p>
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</dd>
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<dt><kbd>C-c C-f</kbd></dt>
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<dd><p>Execute until exit from the selected stack frame, like the <small>GDB</small>
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<code>finish</code> command.
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</p>
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</dd>
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<dt><kbd>C-c C-r</kbd></dt>
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<dd><p>Continue execution of your program, like the <small>GDB</small> <code>continue</code>
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command.
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</p>
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</dd>
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<dt><kbd>C-c <</kbd></dt>
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<dd><p>Go up the number of frames indicated by the numeric argument
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(see <a href="../Emacs/Arguments.html#Arguments">Numeric Arguments</a> in <cite>The <small>GNU</small> Emacs Manual</cite>),
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like the <small>GDB</small> <code>up</code> command.
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</p>
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</dd>
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<dt><kbd>C-c ></kbd></dt>
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<dd><p>Go down the number of frames indicated by the numeric argument, like the
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<small>GDB</small> <code>down</code> command.
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</p></dd>
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</dl>
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<p>In any source file, the Emacs command <kbd>C-x <span class="key">SPC</span></kbd> (<code>gud-break</code>)
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tells <small>GDB</small> to set a breakpoint on the source line point is on.
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</p>
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<p>In text command mode, if you type <kbd>M-x speedbar</kbd>, Emacs displays a
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separate frame which shows a backtrace when the GUD buffer is current.
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Move point to any frame in the stack and type <tt class="key">RET</tt> to make it
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become the current frame and display the associated source in the
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source buffer. Alternatively, click <kbd>Mouse-2</kbd> to make the
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selected frame become the current one. In graphical mode, the
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speedbar displays watch expressions.
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</p>
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<p>If you accidentally delete the source-display buffer, an easy way to get
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it back is to type the command <code>f</code> in the <small>GDB</small> buffer, to
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request a frame display; when you run under Emacs, this recreates
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the source buffer if necessary to show you the context of the current
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frame.
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</p>
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<p>The source files displayed in Emacs are in ordinary Emacs buffers
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which are visiting the source files in the usual way. You can edit
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the files with these buffers if you wish; but keep in mind that <small>GDB</small>
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communicates with Emacs in terms of line numbers. If you add or
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delete lines from the text, the line numbers that <small>GDB</small> knows cease
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to correspond properly with the code.
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</p>
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<p>A more detailed description of Emacs’ interaction with <small>GDB</small> is
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given in the Emacs manual (see <a href="../Emacs/Debuggers.html#Debuggers">Debuggers</a> in <cite>The <small>GNU</small>
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Emacs Manual</cite>).
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="GDB_002fMI.html#GDB_002fMI" accesskey="n" rel="next">GDB/MI</a>, Previous: <a href="TUI.html#TUI" accesskey="p" rel="prev">TUI</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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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</div>
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</body>
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</html>
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