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142 lines
7.2 KiB
HTML
142 lines
7.2 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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Asynchronous and non-stop modes (Debugging with GDB)</title>
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<meta name="description" content="Asynchronous and non-stop modes (Debugging with GDB)">
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<meta name="keywords" content="Asynchronous and non-stop modes (Debugging with GDB)">
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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="GDB_002fMI-General-Design.html#GDB_002fMI-General-Design" rel="up" title="GDB/MI General Design">
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<link href="Thread-groups.html#Thread-groups" rel="next" title="Thread groups">
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<link href="Context-management.html#Context-management" rel="prev" title="Context management">
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</head>
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<body lang="en">
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<a name="Asynchronous-and-non_002dstop-modes"></a>
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<div class="header">
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<p>
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Next: <a href="Thread-groups.html#Thread-groups" accesskey="n" rel="next">Thread groups</a>, Previous: <a href="Context-management.html#Context-management" accesskey="p" rel="prev">Context management</a>, Up: <a href="GDB_002fMI-General-Design.html#GDB_002fMI-General-Design" accesskey="u" rel="up">GDB/MI General Design</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="Asynchronous-command-execution-and-non_002dstop-mode"></a>
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<h4 class="subsection">27.1.2 Asynchronous command execution and non-stop mode</h4>
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<p>On some targets, <small>GDB</small> is capable of processing MI commands
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even while the target is running. This is called <em>asynchronous
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command execution</em> (see <a href="Background-Execution.html#Background-Execution">Background Execution</a>). The frontend may
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specify a preferrence for asynchronous execution using the
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<code>-gdb-set mi-async 1</code> command, which should be emitted before
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either running the executable or attaching to the target. After the
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frontend has started the executable or attached to the target, it can
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find if asynchronous execution is enabled using the
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<code>-list-target-features</code> command.
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</p>
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<dl compact="compact">
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<dt><code>-gdb-set mi-async on</code></dt>
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<dt><code>-gdb-set mi-async off</code></dt>
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<dd><p>Set whether MI is in asynchronous mode.
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</p>
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<p>When <code>off</code>, which is the default, MI execution commands (e.g.,
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<code>-exec-continue</code>) are foreground commands, and <small>GDB</small> waits
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for the program to stop before processing further commands.
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</p>
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<p>When <code>on</code>, MI execution commands are background execution
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commands (e.g., <code>-exec-continue</code> becomes the equivalent of the
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<code>c&</code> CLI command), and so <small>GDB</small> is capable of processing
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MI commands even while the target is running.
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</p>
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</dd>
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<dt><code>-gdb-show mi-async</code></dt>
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<dd><p>Show whether MI asynchronous mode is enabled.
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</p></dd>
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</dl>
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<p>Note: In <small>GDB</small> version 7.7 and earlier, this option was called
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<code>target-async</code> instead of <code>mi-async</code>, and it had the effect
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of both putting MI in asynchronous mode and making CLI background
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commands possible. CLI background commands are now always possible
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“out of the box” if the target supports them. The old spelling is
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kept as a deprecated alias for backwards compatibility.
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</p>
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<p>Even if <small>GDB</small> can accept a command while target is running,
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many commands that access the target do not work when the target is
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running. Therefore, asynchronous command execution is most useful
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when combined with non-stop mode (see <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>). Then,
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it is possible to examine the state of one thread, while other threads
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are running.
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</p>
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<p>When a given thread is running, MI commands that try to access the
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target in the context of that thread may not work, or may work only on
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some targets. In particular, commands that try to operate on thread’s
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stack will not work, on any target. Commands that read memory, or
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modify breakpoints, may work or not work, depending on the target. Note
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that even commands that operate on global state, such as <code>print</code>,
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<code>set</code>, and breakpoint commands, still access the target in the
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context of a specific thread, so frontend should try to find a
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stopped thread and perform the operation on that thread (using the
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‘<samp>--thread</samp>’ option).
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</p>
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<p>Which commands will work in the context of a running thread is
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highly target dependent. However, the two commands
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<code>-exec-interrupt</code>, to stop a thread, and <code>-thread-info</code>,
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to find the state of a thread, will always work.
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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="Thread-groups.html#Thread-groups" accesskey="n" rel="next">Thread groups</a>, Previous: <a href="Context-management.html#Context-management" accesskey="p" rel="prev">Context management</a>, Up: <a href="GDB_002fMI-General-Design.html#GDB_002fMI-General-Design" accesskey="u" rel="up">GDB/MI General Design</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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