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| <title>Debugging with GDB: Memory Region Attributes</title> |
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| <a name="Memory-Region-Attributes"></a> |
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| <a name="Memory-Region-Attributes-1"></a> |
| <h3 class="section">10.17 Memory Region Attributes</h3> |
| <a name="index-memory-region-attributes"></a> |
| |
| <p><em>Memory region attributes</em> allow you to describe special handling |
| required by regions of your target’s memory. <small>GDB</small> uses |
| attributes to determine whether to allow certain types of memory |
| accesses; whether to use specific width accesses; and whether to cache |
| target memory. By default the description of memory regions is |
| fetched from the target (if the current target supports this), but the |
| user can override the fetched regions. |
| </p> |
| <p>Defined memory regions can be individually enabled and disabled. When a |
| memory region is disabled, <small>GDB</small> uses the default attributes when |
| accessing memory in that region. Similarly, if no memory regions have |
| been defined, <small>GDB</small> uses the default attributes when accessing |
| all memory. |
| </p> |
| <p>When a memory region is defined, it is given a number to identify it; |
| to enable, disable, or remove a memory region, you specify that number. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-mem"></a> |
| </dd> |
| <dt><code>mem <var>lower</var> <var>upper</var> <var>attributes</var>…</code></dt> |
| <dd><p>Define a memory region bounded by <var>lower</var> and <var>upper</var> with |
| attributes <var>attributes</var>…, and add it to the list of regions |
| monitored by <small>GDB</small>. Note that <var>upper</var> == 0 is a special |
| case: it is treated as the target’s maximum memory address. |
| (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.) |
| </p> |
| </dd> |
| <dt><code>mem auto</code></dt> |
| <dd><p>Discard any user changes to the memory regions and use target-supplied |
| regions, if available, or no regions if the target does not support. |
| </p> |
| <a name="index-delete-mem"></a> |
| </dd> |
| <dt><code>delete mem <var>nums</var>…</code></dt> |
| <dd><p>Remove memory regions <var>nums</var>… from the list of regions |
| monitored by <small>GDB</small>. |
| </p> |
| <a name="index-disable-mem"></a> |
| </dd> |
| <dt><code>disable mem <var>nums</var>…</code></dt> |
| <dd><p>Disable monitoring of memory regions <var>nums</var>…. |
| A disabled memory region is not forgotten. |
| It may be enabled again later. |
| </p> |
| <a name="index-enable-mem"></a> |
| </dd> |
| <dt><code>enable mem <var>nums</var>…</code></dt> |
| <dd><p>Enable monitoring of memory regions <var>nums</var>…. |
| </p> |
| <a name="index-info-mem"></a> |
| </dd> |
| <dt><code>info mem</code></dt> |
| <dd><p>Print a table of all defined memory regions, with the following columns |
| for each region: |
| </p> |
| <dl compact="compact"> |
| <dt><em>Memory Region Number</em></dt> |
| <dt><em>Enabled or Disabled.</em></dt> |
| <dd><p>Enabled memory regions are marked with ‘<samp>y</samp>’. |
| Disabled memory regions are marked with ‘<samp>n</samp>’. |
| </p> |
| </dd> |
| <dt><em>Lo Address</em></dt> |
| <dd><p>The address defining the inclusive lower bound of the memory region. |
| </p> |
| </dd> |
| <dt><em>Hi Address</em></dt> |
| <dd><p>The address defining the exclusive upper bound of the memory region. |
| </p> |
| </dd> |
| <dt><em>Attributes</em></dt> |
| <dd><p>The list of attributes set for this memory region. |
| </p></dd> |
| </dl> |
| </dd> |
| </dl> |
| |
| |
| <a name="Attributes"></a> |
| <h4 class="subsection">10.17.1 Attributes</h4> |
| |
| <a name="Memory-Access-Mode"></a> |
| <h4 class="subsubsection">10.17.1.1 Memory Access Mode</h4> |
| <p>The access mode attributes set whether <small>GDB</small> may make read or |
| write accesses to a memory region. |
| </p> |
| <p>While these attributes prevent <small>GDB</small> from performing invalid |
| memory accesses, they do nothing to prevent the target system, I/O DMA, |
| etc. from accessing memory. |
| </p> |
| <dl compact="compact"> |
| <dt><code>ro</code></dt> |
| <dd><p>Memory is read only. |
| </p></dd> |
| <dt><code>wo</code></dt> |
| <dd><p>Memory is write only. |
| </p></dd> |
| <dt><code>rw</code></dt> |
| <dd><p>Memory is read/write. This is the default. |
| </p></dd> |
| </dl> |
| |
| <a name="Memory-Access-Size"></a> |
| <h4 class="subsubsection">10.17.1.2 Memory Access Size</h4> |
| <p>The access size attribute tells <small>GDB</small> to use specific sized |
| accesses in the memory region. Often memory mapped device registers |
| require specific sized accesses. If no access size attribute is |
| specified, <small>GDB</small> may use accesses of any size. |
| </p> |
| <dl compact="compact"> |
| <dt><code>8</code></dt> |
| <dd><p>Use 8 bit memory accesses. |
| </p></dd> |
| <dt><code>16</code></dt> |
| <dd><p>Use 16 bit memory accesses. |
| </p></dd> |
| <dt><code>32</code></dt> |
| <dd><p>Use 32 bit memory accesses. |
| </p></dd> |
| <dt><code>64</code></dt> |
| <dd><p>Use 64 bit memory accesses. |
| </p></dd> |
| </dl> |
| |
| |
| <a name="Data-Cache"></a> |
| <h4 class="subsubsection">10.17.1.3 Data Cache</h4> |
| <p>The data cache attributes set whether <small>GDB</small> will cache target |
| memory. While this generally improves performance by reducing debug |
| protocol overhead, it can lead to incorrect results because <small>GDB</small> |
| does not know about volatile variables or memory mapped device |
| registers. |
| </p> |
| <dl compact="compact"> |
| <dt><code>cache</code></dt> |
| <dd><p>Enable <small>GDB</small> to cache target memory. |
| </p></dd> |
| <dt><code>nocache</code></dt> |
| <dd><p>Disable <small>GDB</small> from caching target memory. This is the default. |
| </p></dd> |
| </dl> |
| |
| <a name="Memory-Access-Checking"></a> |
| <h4 class="subsection">10.17.2 Memory Access Checking</h4> |
| <p><small>GDB</small> can be instructed to refuse accesses to memory that is |
| not explicitly described. This can be useful if accessing such |
| regions has undesired effects for a specific target, or to provide |
| better error checking. The following commands control this behaviour. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-set-mem-inaccessible_002dby_002ddefault"></a> |
| </dd> |
| <dt><code>set mem inaccessible-by-default [on|off]</code></dt> |
| <dd><p>If <code>on</code> is specified, make <small>GDB</small> treat memory not |
| explicitly described by the memory ranges as non-existent and refuse accesses |
| to such memory. The checks are only performed if there’s at least one |
| memory range defined. If <code>off</code> is specified, make <small>GDB</small> |
| treat the memory not explicitly described by the memory ranges as RAM. |
| The default value is <code>on</code>. |
| <a name="index-show-mem-inaccessible_002dby_002ddefault"></a> |
| </p></dd> |
| <dt><code>show mem inaccessible-by-default</code></dt> |
| <dd><p>Show the current handling of accesses to unknown memory. |
| </p></dd> |
| </dl> |
| |
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