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252 lines
9.9 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Memory Region Attributes (Debugging with GDB)</title>
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<meta name="description" content="Memory Region Attributes (Debugging with GDB)">
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<meta name="keywords" content="Memory Region Attributes (Debugging with GDB)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Data.html#Data" rel="up" title="Data">
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<link href="Dump_002fRestore-Files.html#Dump_002fRestore-Files" rel="next" title="Dump/Restore Files">
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</head>
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<body lang="en">
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<a name="Memory-Region-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="Dump_002fRestore-Files.html#Dump_002fRestore-Files" accesskey="n" rel="next">Dump/Restore Files</a>, Previous: <a href="OS-Information.html#OS-Information" accesskey="p" rel="prev">OS Information</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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</div>
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<hr>
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<a name="Memory-Region-Attributes-1"></a>
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<h3 class="section">10.17 Memory Region Attributes</h3>
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<a name="index-memory-region-attributes"></a>
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<p><em>Memory region attributes</em> allow you to describe special handling
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required by regions of your target’s memory. <small>GDB</small> 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>
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<p>Defined memory regions can be individually enabled and disabled. When a
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memory region is disabled, <small>GDB</small> 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, <small>GDB</small> uses the default attributes when accessing
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all memory.
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</p>
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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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</p>
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<dl compact="compact">
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<dd><a name="index-mem"></a>
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</dd>
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<dt><code>mem <var>lower</var> <var>upper</var> <var>attributes</var>…</code></dt>
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<dd><p>Define a memory region bounded by <var>lower</var> and <var>upper</var> with
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attributes <var>attributes</var>…, and add it to the list of regions
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monitored by <small>GDB</small>. 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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</p>
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</dd>
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<dt><code>mem auto</code></dt>
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<dd><p>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>
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<a name="index-delete-mem"></a>
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</dd>
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<dt><code>delete mem <var>nums</var>…</code></dt>
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<dd><p>Remove memory regions <var>nums</var>… from the list of regions
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monitored by <small>GDB</small>.
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</p>
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<a name="index-disable-mem"></a>
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</dd>
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<dt><code>disable mem <var>nums</var>…</code></dt>
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<dd><p>Disable monitoring of memory regions <var>nums</var>….
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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>
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<a name="index-enable-mem"></a>
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</dd>
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<dt><code>enable mem <var>nums</var>…</code></dt>
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<dd><p>Enable monitoring of memory regions <var>nums</var>….
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</p>
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<a name="index-info-mem"></a>
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</dd>
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<dt><code>info mem</code></dt>
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<dd><p>Print a table of all defined memory regions, with the following columns
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for each region:
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</p>
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<dl compact="compact">
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<dt><em>Memory Region Number</em></dt>
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<dt><em>Enabled or Disabled.</em></dt>
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<dd><p>Enabled memory regions are marked with ‘<samp>y</samp>’.
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Disabled memory regions are marked with ‘<samp>n</samp>’.
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</p>
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</dd>
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<dt><em>Lo Address</em></dt>
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<dd><p>The address defining the inclusive lower bound of the memory region.
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</p>
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</dd>
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<dt><em>Hi Address</em></dt>
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<dd><p>The address defining the exclusive upper bound of the memory region.
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</p>
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</dd>
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<dt><em>Attributes</em></dt>
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<dd><p>The list of attributes set for this memory region.
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</p></dd>
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</dl>
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</dd>
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</dl>
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<a name="Attributes"></a>
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<h4 class="subsection">10.17.1 Attributes</h4>
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<a name="Memory-Access-Mode"></a>
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<h4 class="subsubsection">10.17.1.1 Memory Access Mode</h4>
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<p>The access mode attributes set whether <small>GDB</small> may make read or
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write accesses to a memory region.
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</p>
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<p>While these attributes prevent <small>GDB</small> 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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</p>
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<dl compact="compact">
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<dt><code>ro</code></dt>
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<dd><p>Memory is read only.
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</p></dd>
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<dt><code>wo</code></dt>
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<dd><p>Memory is write only.
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</p></dd>
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<dt><code>rw</code></dt>
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<dd><p>Memory is read/write. This is the default.
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</p></dd>
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</dl>
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<a name="Memory-Access-Size"></a>
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<h4 class="subsubsection">10.17.1.2 Memory Access Size</h4>
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<p>The access size attribute tells <small>GDB</small> 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, <small>GDB</small> may use accesses of any size.
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</p>
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<dl compact="compact">
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<dt><code>8</code></dt>
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<dd><p>Use 8 bit memory accesses.
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</p></dd>
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<dt><code>16</code></dt>
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<dd><p>Use 16 bit memory accesses.
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</p></dd>
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<dt><code>32</code></dt>
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<dd><p>Use 32 bit memory accesses.
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</p></dd>
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<dt><code>64</code></dt>
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<dd><p>Use 64 bit memory accesses.
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</p></dd>
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</dl>
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<a name="Data-Cache"></a>
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<h4 class="subsubsection">10.17.1.3 Data Cache</h4>
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<p>The data cache attributes set whether <small>GDB</small> 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 <small>GDB</small>
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does not know about volatile variables or memory mapped device
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registers.
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</p>
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<dl compact="compact">
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<dt><code>cache</code></dt>
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<dd><p>Enable <small>GDB</small> to cache target memory.
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</p></dd>
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<dt><code>nocache</code></dt>
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<dd><p>Disable <small>GDB</small> from caching target memory. This is the default.
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</p></dd>
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</dl>
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<a name="Memory-Access-Checking"></a>
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<h4 class="subsection">10.17.2 Memory Access Checking</h4>
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<p><small>GDB</small> 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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</p>
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<dl compact="compact">
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<dd><a name="index-set-mem-inaccessible_002dby_002ddefault"></a>
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</dd>
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<dt><code>set mem inaccessible-by-default [on|off]</code></dt>
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<dd><p>If <code>on</code> is specified, make <small>GDB</small> 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 <small>GDB</small>
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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"></a>
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</p></dd>
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<dt><code>show mem inaccessible-by-default</code></dt>
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<dd><p>Show the current handling of accesses to unknown memory.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Dump_002fRestore-Files.html#Dump_002fRestore-Files" accesskey="n" rel="next">Dump/Restore Files</a>, Previous: <a href="OS-Information.html#OS-Information" accesskey="p" rel="prev">OS Information</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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</div>
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</body>
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