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187 lines
7.9 KiB
HTML
187 lines
7.9 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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<html>
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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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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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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>Caching Target Data (Debugging with GDB)</title>
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<meta name="description" content="Caching Target Data (Debugging with GDB)">
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<meta name="keywords" content="Caching Target Data (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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="Searching-Memory.html#Searching-Memory" rel="next" title="Searching Memory">
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<link href="Character-Sets.html#Character-Sets" rel="prev" title="Character Sets">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Caching-Target-Data"></a>
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<div class="header">
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<p>
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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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</div>
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<hr>
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<a name="Caching-Data-of-Targets"></a>
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<h3 class="section">10.21 Caching Data of Targets</h3>
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<a name="index-caching-data-of-targets"></a>
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<p><small>GDB</small> 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 <small>GDB</small> 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, <small>GDB</small> only caches data
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known to be on the stack<a name="DOCF12" href="#FOOT12"><sup>12</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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</p>
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<dl compact="compact">
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<dd><a name="index-set-remotecache"></a>
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</dd>
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<dt><code>set remotecache on</code></dt>
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<dt><code>set remotecache off</code></dt>
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<dd><p>This option no longer does anything; it exists for compatibility
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with old scripts.
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</p>
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<a name="index-show-remotecache"></a>
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</dd>
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<dt><code>show remotecache</code></dt>
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<dd><p>Show the current state of the obsolete remotecache flag.
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</p>
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<a name="index-set-stack_002dcache"></a>
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</dd>
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<dt><code>set stack-cache on</code></dt>
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<dt><code>set stack-cache off</code></dt>
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<dd><p>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>
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<a name="index-show-stack_002dcache"></a>
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</dd>
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<dt><code>show stack-cache</code></dt>
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<dd><p>Show the current state of data caching for memory accesses.
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</p>
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<a name="index-set-code_002dcache"></a>
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</dd>
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<dt><code>set code-cache on</code></dt>
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<dt><code>set code-cache off</code></dt>
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<dd><p>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>
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<a name="index-show-code_002dcache"></a>
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</dd>
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<dt><code>show code-cache</code></dt>
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<dd><p>Show the current state of target memory cache for code segment
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accesses.
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</p>
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<a name="index-info-dcache"></a>
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</dd>
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<dt><code>info dcache <span class="roman">[</span>line<span class="roman">]</span></code></dt>
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<dd><p>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>
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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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</p>
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</dd>
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<dt><code>set dcache size <var>size</var></code></dt>
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<dd><a name="index-dcache-size"></a>
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<a name="index-set-dcache-size"></a>
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<p>Set maximum number of entries in dcache (dcache depth above).
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</p>
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</dd>
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<dt><code>set dcache line-size <var>line-size</var></code></dt>
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<dd><a name="index-dcache-line_002dsize"></a>
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<a name="index-set-dcache-line_002dsize"></a>
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<p>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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</p>
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</dd>
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<dt><code>show dcache size</code></dt>
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<dd><a name="index-show-dcache-size"></a>
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<p>Show maximum number of dcache entries. See <a href="#Caching-Target-Data">info dcache</a>.
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</p>
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</dd>
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<dt><code>show dcache line-size</code></dt>
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<dd><a name="index-show-dcache-line_002dsize"></a>
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<p>Show default size of dcache lines.
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</p>
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</dd>
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</dl>
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<div class="footnote">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h3><a name="FOOT12" href="#DOCF12">(12)</a></h3>
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<p>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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</div>
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<hr>
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<div class="header">
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<p>
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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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</div>
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</body>
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</html>
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