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| <h3 class="section">10.20 Caching Data of Remote Targets</h3> |
| |
| <p><a name="index-caching-data-of-remote-targets-653"></a> |
| <span class="sc">gdb</span> caches data exchanged between the debugger and a |
| remote target (see <a href="Remote-Debugging.html#Remote-Debugging">Remote Debugging</a>). Such caching generally improves |
| performance, because it reduces the overhead of the remote protocol by |
| bundling memory reads and writes into large chunks. Unfortunately, simply |
| caching everything would lead to incorrect results, since <span class="sc">gdb</span> |
| does not necessarily know anything about volatile values, memory-mapped I/O |
| addresses, etc. Furthermore, in non-stop mode (see <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>) |
| memory can be changed <em>while</em> a gdb command is executing. |
| Therefore, by default, <span class="sc">gdb</span> only caches data |
| known to be on the stack<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>. |
| Other regions of memory can be explicitly marked as |
| cacheable; see see <a href="Memory-Region-Attributes.html#Memory-Region-Attributes">Memory Region Attributes</a>. |
| |
| |
| <a name="index-set-remotecache-654"></a> |
| <dl><dt><code>set remotecache on</code><dt><code>set remotecache off</code><dd>This option no longer does anything; it exists for compatibility |
| with old scripts. |
| |
| <p><a name="index-show-remotecache-655"></a><br><dt><code>show remotecache</code><dd>Show the current state of the obsolete remotecache flag. |
| |
| <p><a name="index-set-stack_002dcache-656"></a><br><dt><code>set stack-cache on</code><dt><code>set stack-cache off</code><dd>Enable or disable caching of stack accesses. When <code>ON</code>, use |
| caching. By default, this option is <code>ON</code>. |
| |
| <p><a name="index-show-stack_002dcache-657"></a><br><dt><code>show stack-cache</code><dd>Show the current state of data caching for memory accesses. |
| |
| <p><a name="index-info-dcache-658"></a><br><dt><code>info dcache </code><span class="roman">[</span><code>line</code><span class="roman">]</span><dd>Print the information about the data cache performance. The |
| information displayed includes the dcache width and depth, and for |
| each cache line, its number, address, and how many times it was |
| referenced. This command is useful for debugging the data cache |
| operation. |
| |
| <p>If a line number is specified, the contents of that line will be |
| printed in hex. |
| </dl> |
| |
| <div class="footnote"> |
| <hr> |
| <h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> In non-stop mode, it is moderately |
| rare for a running thread to modify the stack of a stopped thread |
| in a way that would interfere with a backtrace, and caching of |
| stack reads provides a significant speed up of remote backtraces.</p> |
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