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184 lines
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<title>Memory Region Attributes - Debugging with GDB</title>
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<div class="node">
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<a name="Memory-Region-Attributes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Dump_002fRestore-Files.html#Dump_002fRestore-Files">Dump/Restore Files</a>,
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Previous: <a rel="previous" accesskey="p" href="OS-Information.html#OS-Information">OS Information</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">10.17 Memory Region Attributes</h3>
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<p><a name="index-memory-region-attributes-783"></a>
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<dfn>Memory region attributes</dfn> allow you to describe special handling
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required by regions of your target's memory. <span class="sc">gdb</span> uses
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attributes to determine whether to allow certain types of memory
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accesses; whether to use specific width accesses; and whether to cache
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target memory. By default the description of memory regions is
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fetched from the target (if the current target supports this), but the
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user can override the fetched regions.
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<p>Defined memory regions can be individually enabled and disabled. When a
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memory region is disabled, <span class="sc">gdb</span> uses the default attributes when
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accessing memory in that region. Similarly, if no memory regions have
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been defined, <span class="sc">gdb</span> uses the default attributes when accessing
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all memory.
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<p>When a memory region is defined, it is given a number to identify it;
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to enable, disable, or remove a memory region, you specify that number.
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<a name="index-mem-784"></a>
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<dl><dt><code>mem </code><var>lower</var> <var>upper</var> <var>attributes</var><code>...</code><dd>Define a memory region bounded by <var>lower</var> and <var>upper</var> with
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attributes <var>attributes</var><small class="dots">...</small>, and add it to the list of regions
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monitored by <span class="sc">gdb</span>. Note that <var>upper</var> == 0 is a special
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case: it is treated as the target's maximum memory address.
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(0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
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<br><dt><code>mem auto</code><dd>Discard any user changes to the memory regions and use target-supplied
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regions, if available, or no regions if the target does not support.
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<p><a name="index-delete-mem-785"></a><br><dt><code>delete mem </code><var>nums</var><code>...</code><dd>Remove memory regions <var>nums</var><small class="dots">...</small> from the list of regions
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monitored by <span class="sc">gdb</span>.
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<p><a name="index-disable-mem-786"></a><br><dt><code>disable mem </code><var>nums</var><code>...</code><dd>Disable monitoring of memory regions <var>nums</var><small class="dots">...</small>.
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A disabled memory region is not forgotten.
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It may be enabled again later.
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<p><a name="index-enable-mem-787"></a><br><dt><code>enable mem </code><var>nums</var><code>...</code><dd>Enable monitoring of memory regions <var>nums</var><small class="dots">...</small>.
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<p><a name="index-info-mem-788"></a><br><dt><code>info mem</code><dd>Print a table of all defined memory regions, with the following columns
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for each region:
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<dl>
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<dt><em>Memory Region Number</em><br><dt><em>Enabled or Disabled.</em><dd>Enabled memory regions are marked with ‘<samp><span class="samp">y</span></samp>’.
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Disabled memory regions are marked with ‘<samp><span class="samp">n</span></samp>’.
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<br><dt><em>Lo Address</em><dd>The address defining the inclusive lower bound of the memory region.
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<br><dt><em>Hi Address</em><dd>The address defining the exclusive upper bound of the memory region.
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<br><dt><em>Attributes</em><dd>The list of attributes set for this memory region.
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</dl>
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</dl>
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<h4 class="subsection">10.17.1 Attributes</h4>
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<h5 class="subsubsection">10.17.1.1 Memory Access Mode</h5>
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<p>The access mode attributes set whether <span class="sc">gdb</span> may make read or
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write accesses to a memory region.
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<p>While these attributes prevent <span class="sc">gdb</span> from performing invalid
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memory accesses, they do nothing to prevent the target system, I/O DMA,
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etc. from accessing memory.
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<dl>
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<dt><code>ro</code><dd>Memory is read only.
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<br><dt><code>wo</code><dd>Memory is write only.
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<br><dt><code>rw</code><dd>Memory is read/write. This is the default.
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</dl>
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<h5 class="subsubsection">10.17.1.2 Memory Access Size</h5>
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<p>The access size attribute tells <span class="sc">gdb</span> to use specific sized
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accesses in the memory region. Often memory mapped device registers
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require specific sized accesses. If no access size attribute is
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specified, <span class="sc">gdb</span> may use accesses of any size.
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<dl>
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<dt><code>8</code><dd>Use 8 bit memory accesses.
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<br><dt><code>16</code><dd>Use 16 bit memory accesses.
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<br><dt><code>32</code><dd>Use 32 bit memory accesses.
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<br><dt><code>64</code><dd>Use 64 bit memory accesses.
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</dl>
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<!-- @subsubsection Hardware/Software Breakpoints -->
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<!-- The hardware/software breakpoint attributes set whether @value{GDBN} -->
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<!-- will use hardware or software breakpoints for the internal breakpoints -->
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<!-- used by the step, next, finish, until, etc. commands. -->
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<!-- @table @code -->
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<!-- @item hwbreak -->
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<!-- Always use hardware breakpoints -->
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<!-- @item swbreak (default) -->
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<!-- @end table -->
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<h5 class="subsubsection">10.17.1.3 Data Cache</h5>
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<p>The data cache attributes set whether <span class="sc">gdb</span> will cache target
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memory. While this generally improves performance by reducing debug
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protocol overhead, it can lead to incorrect results because <span class="sc">gdb</span>
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does not know about volatile variables or memory mapped device
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registers.
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<dl>
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<dt><code>cache</code><dd>Enable <span class="sc">gdb</span> to cache target memory.
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<br><dt><code>nocache</code><dd>Disable <span class="sc">gdb</span> from caching target memory. This is the default.
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</dl>
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<h4 class="subsection">10.17.2 Memory Access Checking</h4>
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<p><span class="sc">gdb</span> can be instructed to refuse accesses to memory that is
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not explicitly described. This can be useful if accessing such
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regions has undesired effects for a specific target, or to provide
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better error checking. The following commands control this behaviour.
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<a name="index-set-mem-inaccessible_002dby_002ddefault-789"></a>
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<dl><dt><code>set mem inaccessible-by-default [on|off]</code><dd>If <code>on</code> is specified, make <span class="sc">gdb</span> treat memory not
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explicitly described by the memory ranges as non-existent and refuse accesses
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to such memory. The checks are only performed if there's at least one
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memory range defined. If <code>off</code> is specified, make <span class="sc">gdb</span>
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treat the memory not explicitly described by the memory ranges as RAM.
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The default value is <code>on</code>.
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<a name="index-show-mem-inaccessible_002dby_002ddefault-790"></a><br><dt><code>show mem inaccessible-by-default</code><dd>Show the current handling of accesses to unknown memory.
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</dl>
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<!-- @subsubsection Memory Write Verification -->
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<!-- The memory write verification attributes set whether @value{GDBN} -->
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<!-- will re-reads data after each write to verify the write was successful. -->
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<!-- @table @code -->
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<!-- @item verify -->
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<!-- @item noverify (default) -->
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<!-- @end table -->
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</body></html>
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