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| <h4 class="subsection">5.4.6 Observer Mode</h4> |
| |
| <p>If you want to build on non-stop mode and observe program behavior |
| without any chance of disruption by <span class="sc">gdb</span>, you can set |
| variables to disable all of the debugger's attempts to modify state, |
| whether by writing memory, inserting breakpoints, etc. These operate |
| at a low level, intercepting operations from all commands. |
| |
| <p>When all of these are set to <code>off</code>, then <span class="sc">gdb</span> is said to |
| be <dfn>observer mode</dfn>. As a convenience, the variable |
| <code>observer</code> can be set to disable these, plus enable non-stop |
| mode. |
| |
| <p>Note that <span class="sc">gdb</span> 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. |
| |
| |
| <a name="index-observer-351"></a> |
| <dl><dt><code>set observer on</code><dt><code>set observer off</code><dd>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. |
| |
| <br><dt><code>show observer</code><dd>Show whether observer mode is on or off. |
| |
| <p><a name="index-may_002dwrite_002dregisters-352"></a><br><dt><code>set may-write-registers on</code><dt><code>set may-write-registers off</code><dd>This controls whether <span class="sc">gdb</span> 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>. |
| |
| <br><dt><code>show may-write-registers</code><dd>Show the current permission to write registers. |
| |
| <p><a name="index-may_002dwrite_002dmemory-353"></a><br><dt><code>set may-write-memory on</code><dt><code>set may-write-memory off</code><dd>This controls whether <span class="sc">gdb</span> will attempt to alter the contents |
| of memory, such as with assignment expressions in <code>print</code>. It |
| defaults to <code>on</code>. |
| |
| <br><dt><code>show may-write-memory</code><dd>Show the current permission to write memory. |
| |
| <p><a name="index-may_002dinsert_002dbreakpoints-354"></a><br><dt><code>set may-insert-breakpoints on</code><dt><code>set may-insert-breakpoints off</code><dd>This controls whether <span class="sc">gdb</span> will attempt to insert breakpoints. |
| This affects all breakpoints, including internal breakpoints defined |
| by <span class="sc">gdb</span>. It defaults to <code>on</code>. |
| |
| <br><dt><code>show may-insert-breakpoints</code><dd>Show the current permission to insert breakpoints. |
| |
| <p><a name="index-may_002dinsert_002dtracepoints-355"></a><br><dt><code>set may-insert-tracepoints on</code><dt><code>set may-insert-tracepoints off</code><dd>This controls whether <span class="sc">gdb</span> 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>. |
| |
| <br><dt><code>show may-insert-tracepoints</code><dd>Show the current permission to insert tracepoints. |
| |
| <p><a name="index-may_002dinsert_002dfast_002dtracepoints-356"></a><br><dt><code>set may-insert-fast-tracepoints on</code><dt><code>set may-insert-fast-tracepoints off</code><dd>This controls whether <span class="sc">gdb</span> 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>. |
| |
| <br><dt><code>show may-insert-fast-tracepoints</code><dd>Show the current permission to insert fast tracepoints. |
| |
| <p><a name="index-may_002dinterrupt-357"></a><br><dt><code>set may-interrupt on</code><dt><code>set may-interrupt off</code><dd>This controls whether <span class="sc">gdb</span> 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>. |
| |
| <br><dt><code>show may-interrupt</code><dd>Show the current permission to interrupt or stop the program. |
| |
| </dl> |
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