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<title>Caching Target Data (Debugging with GDB)</title>
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<a name="Caching-Target-Data"></a>
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<p>
Next: <a href="Searching-Memory.html#Searching-Memory" accesskey="n" rel="next">Searching Memory</a>, Previous: <a href="Character-Sets.html#Character-Sets" accesskey="p" rel="prev">Character Sets</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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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<hr>
<a name="Caching-Data-of-Targets"></a>
<h3 class="section">10.21 Caching Data of Targets</h3>
<a name="index-caching-data-of-targets"></a>
<p><small>GDB</small> caches data exchanged between the debugger and a target.
Each cache is associated with the address space of the inferior.
See <a href="Inferiors-and-Programs.html#Inferiors-and-Programs">Inferiors and Programs</a>, about inferior and address space.
Such caching generally improves performance in remote debugging
(see <a href="Remote-Debugging.html#Remote-Debugging">Remote Debugging</a>), 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 <small>GDB</small> 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, <small>GDB</small> only caches data
known to be on the stack<a name="DOCF12" href="#FOOT12"><sup>12</sup></a> or
in the code segment.
Other regions of memory can be explicitly marked as
cacheable; see <a href="Memory-Region-Attributes.html#Memory-Region-Attributes">Memory Region Attributes</a>.
</p>
<dl compact="compact">
<dd><a name="index-set-remotecache"></a>
</dd>
<dt><code>set remotecache on</code></dt>
<dt><code>set remotecache off</code></dt>
<dd><p>This option no longer does anything; it exists for compatibility
with old scripts.
</p>
<a name="index-show-remotecache"></a>
</dd>
<dt><code>show remotecache</code></dt>
<dd><p>Show the current state of the obsolete remotecache flag.
</p>
<a name="index-set-stack_002dcache"></a>
</dd>
<dt><code>set stack-cache on</code></dt>
<dt><code>set stack-cache off</code></dt>
<dd><p>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"></a>
</dd>
<dt><code>show stack-cache</code></dt>
<dd><p>Show the current state of data caching for memory accesses.
</p>
<a name="index-set-code_002dcache"></a>
</dd>
<dt><code>set code-cache on</code></dt>
<dt><code>set code-cache off</code></dt>
<dd><p>Enable or disable caching of code segment accesses. When <code>on</code>,
use caching. By default, this option is <code>on</code>. This improves
performance of disassembly in remote debugging.
</p>
<a name="index-show-code_002dcache"></a>
</dd>
<dt><code>show code-cache</code></dt>
<dd><p>Show the current state of target memory cache for code segment
accesses.
</p>
<a name="index-info-dcache"></a>
</dd>
<dt><code>info dcache <span class="roman">[</span>line<span class="roman">]</span></code></dt>
<dd><p>Print the information about the performance of data cache of the
current inferior’s address space. 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>
<p>If a line number is specified, the contents of that line will be
printed in hex.
</p>
</dd>
<dt><code>set dcache size <var>size</var></code></dt>
<dd><a name="index-dcache-size"></a>
<a name="index-set-dcache-size"></a>
<p>Set maximum number of entries in dcache (dcache depth above).
</p>
</dd>
<dt><code>set dcache line-size <var>line-size</var></code></dt>
<dd><a name="index-dcache-line_002dsize"></a>
<a name="index-set-dcache-line_002dsize"></a>
<p>Set number of bytes each dcache entry caches (dcache width above).
Must be a power of 2.
</p>
</dd>
<dt><code>show dcache size</code></dt>
<dd><a name="index-show-dcache-size"></a>
<p>Show maximum number of dcache entries. See <a href="#Caching-Target-Data">info dcache</a>.
</p>
</dd>
<dt><code>show dcache line-size</code></dt>
<dd><a name="index-show-dcache-line_002dsize"></a>
<p>Show default size of dcache lines.
</p>
</dd>
</dl>
<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>
<h3><a name="FOOT12" href="#DOCF12">(12)</a></h3>
<p>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>
</div>
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