119 lines
6.4 KiB
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119 lines
6.4 KiB
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<title>Caching Target Data - Debugging with GDB</title>
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<link rel="up" href="Data.html#Data" title="Data">
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<link rel="prev" href="Character-Sets.html#Character-Sets" title="Character Sets">
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<div class="node">
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<a name="Caching-Target-Data"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Searching-Memory.html#Searching-Memory">Searching Memory</a>,
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Previous: <a rel="previous" accesskey="p" href="Character-Sets.html#Character-Sets">Character Sets</a>,
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Up: <a rel="up" accesskey="u" href="Data.html#Data">Data</a>
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<hr>
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</div>
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<h3 class="section">10.21 Caching Data of Targets</h3>
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<p><a name="index-caching-data-of-targets-816"></a>
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<span class="sc">gdb</span> caches data exchanged between the debugger and a target.
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Each cache is associated with the address space of the inferior.
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See <a href="Inferiors-and-Programs.html#Inferiors-and-Programs">Inferiors and Programs</a>, about inferior and address space.
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Such caching generally improves performance in remote debugging
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(see <a href="Remote-Debugging.html#Remote-Debugging">Remote Debugging</a>), because it reduces the overhead of the
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remote protocol by bundling memory reads and writes into large chunks.
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Unfortunately, simply caching everything would lead to incorrect results,
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since <span class="sc">gdb</span> does not necessarily know anything about volatile
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values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode
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(see <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>) memory can be changed <em>while</em> a gdb command
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is executing.
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Therefore, by default, <span class="sc">gdb</span> only caches data
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known to be on the stack<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a> or
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in the code segment.
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Other regions of memory can be explicitly marked as
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cacheable; see <a href="Memory-Region-Attributes.html#Memory-Region-Attributes">Memory Region Attributes</a>.
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<a name="index-set-remotecache-817"></a>
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<dl><dt><code>set remotecache on</code><dt><code>set remotecache off</code><dd>This option no longer does anything; it exists for compatibility
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with old scripts.
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<p><a name="index-show-remotecache-818"></a><br><dt><code>show remotecache</code><dd>Show the current state of the obsolete remotecache flag.
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<p><a name="index-set-stack_002dcache-819"></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
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caching. By default, this option is <code>on</code>.
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<p><a name="index-show-stack_002dcache-820"></a><br><dt><code>show stack-cache</code><dd>Show the current state of data caching for memory accesses.
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<p><a name="index-set-code_002dcache-821"></a><br><dt><code>set code-cache on</code><dt><code>set code-cache off</code><dd>Enable or disable caching of code segment accesses. When <code>on</code>,
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use caching. By default, this option is <code>on</code>. This improves
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performance of disassembly in remote debugging.
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<p><a name="index-show-code_002dcache-822"></a><br><dt><code>show code-cache</code><dd>Show the current state of target memory cache for code segment
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accesses.
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<p><a name="index-info-dcache-823"></a><br><dt><code>info dcache </code><span class="roman">[</span><code>line</code><span class="roman">]</span><dd>Print the information about the performance of data cache of the
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current inferior's address space. The information displayed
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includes the dcache width and depth, and for each cache line, its
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number, address, and how many times it was referenced. This
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command is useful for debugging the data cache operation.
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<p>If a line number is specified, the contents of that line will be
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printed in hex.
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<br><dt><code>set dcache size </code><var>size</var><dd><a name="index-dcache-size-824"></a><a name="index-set-dcache-size-825"></a>Set maximum number of entries in dcache (dcache depth above).
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<br><dt><code>set dcache line-size </code><var>line-size</var><dd><a name="index-dcache-line_002dsize-826"></a><a name="index-set-dcache-line_002dsize-827"></a>Set number of bytes each dcache entry caches (dcache width above).
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Must be a power of 2.
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<br><dt><code>show dcache size</code><dd><a name="index-show-dcache-size-828"></a>Show maximum number of dcache entries. See <a href="Caching-Target-Data.html#Caching-Target-Data">info dcache</a>.
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<br><dt><code>show dcache line-size</code><dd><a name="index-show-dcache-line_002dsize-829"></a>Show default size of dcache lines.
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</dl>
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<div class="footnote">
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<hr>
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<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> In non-stop mode, it is moderately
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rare for a running thread to modify the stack of a stopped thread
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in a way that would interfere with a backtrace, and caching of
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stack reads provides a significant speed up of remote backtraces.</p>
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<hr></div>
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</body></html>
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