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192 lines
8.1 KiB
HTML
192 lines
8.1 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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<html>
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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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Observer Mode (Debugging with GDB)</title>
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<meta name="description" content="Observer Mode (Debugging with GDB)">
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<meta name="keywords" content="Observer Mode (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="Thread-Stops.html#Thread-Stops" rel="up" title="Thread Stops">
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<link href="Reverse-Execution.html#Reverse-Execution" rel="next" title="Reverse Execution">
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<link href="Interrupted-System-Calls.html#Interrupted-System-Calls" rel="prev" title="Interrupted System Calls">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Observer-Mode"></a>
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<div class="header">
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<p>
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Previous: <a href="Interrupted-System-Calls.html#Interrupted-System-Calls" accesskey="p" rel="prev">Interrupted System Calls</a>, Up: <a href="Thread-Stops.html#Thread-Stops" accesskey="u" rel="up">Thread Stops</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="Observer-Mode-1"></a>
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<h4 class="subsection">5.5.6 Observer Mode</h4>
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<p>If you want to build on non-stop mode and observe program behavior
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without any chance of disruption by <small>GDB</small>, you can set
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variables to disable all of the debugger’s attempts to modify state,
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whether by writing memory, inserting breakpoints, etc. These operate
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at a low level, intercepting operations from all commands.
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</p>
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<p>When all of these are set to <code>off</code>, then <small>GDB</small> is said to
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be <em>observer mode</em>. As a convenience, the variable
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<code>observer</code> can be set to disable these, plus enable non-stop
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mode.
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</p>
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<p>Note that <small>GDB</small> will not prevent you from making nonsensical
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combinations of these settings. For instance, if you have enabled
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<code>may-insert-breakpoints</code> but disabled <code>may-write-memory</code>,
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then breakpoints that work by writing trap instructions into the code
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stream will still not be able to be placed.
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</p>
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<dl compact="compact">
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<dd>
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<a name="index-observer"></a>
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</dd>
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<dt><code>set observer on</code></dt>
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<dt><code>set observer off</code></dt>
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<dd><p>When set to <code>on</code>, this disables all the permission variables
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below (except for <code>insert-fast-tracepoints</code>), plus enables
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non-stop debugging. Setting this to <code>off</code> switches back to
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normal debugging, though remaining in non-stop mode.
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</p>
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</dd>
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<dt><code>show observer</code></dt>
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<dd><p>Show whether observer mode is on or off.
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</p>
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<a name="index-may_002dwrite_002dregisters"></a>
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</dd>
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<dt><code>set may-write-registers on</code></dt>
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<dt><code>set may-write-registers off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to alter the values of
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registers, such as with assignment expressions in <code>print</code>, or the
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<code>jump</code> command. It defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-write-registers</code></dt>
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<dd><p>Show the current permission to write registers.
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</p>
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<a name="index-may_002dwrite_002dmemory"></a>
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</dd>
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<dt><code>set may-write-memory on</code></dt>
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<dt><code>set may-write-memory off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to alter the contents
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of memory, such as with assignment expressions in <code>print</code>. It
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defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-write-memory</code></dt>
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<dd><p>Show the current permission to write memory.
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</p>
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<a name="index-may_002dinsert_002dbreakpoints"></a>
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</dd>
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<dt><code>set may-insert-breakpoints on</code></dt>
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<dt><code>set may-insert-breakpoints off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to insert breakpoints.
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This affects all breakpoints, including internal breakpoints defined
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by <small>GDB</small>. It defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-insert-breakpoints</code></dt>
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<dd><p>Show the current permission to insert breakpoints.
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</p>
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<a name="index-may_002dinsert_002dtracepoints"></a>
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</dd>
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<dt><code>set may-insert-tracepoints on</code></dt>
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<dt><code>set may-insert-tracepoints off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to insert (regular)
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tracepoints at the beginning of a tracing experiment. It affects only
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non-fast tracepoints, fast tracepoints being under the control of
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<code>may-insert-fast-tracepoints</code>. It defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-insert-tracepoints</code></dt>
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<dd><p>Show the current permission to insert tracepoints.
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</p>
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<a name="index-may_002dinsert_002dfast_002dtracepoints"></a>
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</dd>
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<dt><code>set may-insert-fast-tracepoints on</code></dt>
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<dt><code>set may-insert-fast-tracepoints off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to insert fast
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tracepoints at the beginning of a tracing experiment. It affects only
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fast tracepoints, regular (non-fast) tracepoints being under the
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control of <code>may-insert-tracepoints</code>. It defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-insert-fast-tracepoints</code></dt>
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<dd><p>Show the current permission to insert fast tracepoints.
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</p>
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<a name="index-may_002dinterrupt"></a>
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</dd>
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<dt><code>set may-interrupt on</code></dt>
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<dt><code>set may-interrupt off</code></dt>
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<dd><p>This controls whether <small>GDB</small> will attempt to interrupt or stop
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program execution. When this variable is <code>off</code>, the
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<code>interrupt</code> command will have no effect, nor will
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<kbd>Ctrl-c</kbd>. It defaults to <code>on</code>.
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</p>
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</dd>
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<dt><code>show may-interrupt</code></dt>
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<dd><p>Show the current permission to interrupt or stop the program.
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</p>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Interrupted-System-Calls.html#Interrupted-System-Calls" accesskey="p" rel="prev">Interrupted System Calls</a>, Up: <a href="Thread-Stops.html#Thread-Stops" accesskey="u" rel="up">Thread Stops</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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