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