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127 lines
5.4 KiB
HTML
127 lines
5.4 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) 1988-2018 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 "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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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>x86 control-flow protection intrinsics (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="x86 control-flow protection intrinsics (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="x86 control-flow protection intrinsics (Using the GNU Compiler Collection (GCC))">
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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="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Target-Builtins.html#Target-Builtins" rel="up" title="Target Builtins">
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<link href="Target-Format-Checks.html#Target-Format-Checks" rel="next" title="Target Format Checks">
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<link href="x86-transactional-memory-intrinsics.html#x86-transactional-memory-intrinsics" rel="prev" title="x86 transactional memory intrinsics">
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a.summary-letter {text-decoration: none}
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</style>
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</head>
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<body lang="en">
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<a name="x86-control_002dflow-protection-intrinsics"></a>
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<div class="header">
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<p>
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Previous: <a href="x86-transactional-memory-intrinsics.html#x86-transactional-memory-intrinsics" accesskey="p" rel="prev">x86 transactional memory intrinsics</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="x86-Control_002dFlow-Protection-Intrinsics"></a>
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<h4 class="subsection">6.59.35 x86 Control-Flow Protection Intrinsics</h4>
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<dl>
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<dt><a name="index-_005fget_005fssp"></a>CET Function: <em>ret_type</em> <strong>_get_ssp</strong> <em>(void)</em></dt>
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<dd><p>Get the current value of shadow stack pointer if shadow stack support
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from Intel CET is enabled in the hardware or <code>0</code> otherwise.
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The <code>ret_type</code> is <code>unsigned long long</code> for 64-bit targets
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and <code>unsigned int</code> for 32-bit targets.
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</p></dd></dl>
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<dl>
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<dt><a name="index-_005finc_005fssp"></a>CET Function: <em>void</em> <strong>_inc_ssp</strong> <em>(unsigned int)</em></dt>
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<dd><p>Increment the current shadow stack pointer by the size specified by the
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function argument. The argument is masked to a byte value for security
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reasons, so to increment by more than 255 bytes you must call the function
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multiple times.
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</p></dd></dl>
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<p>The shadow stack unwind code looks like:
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</p>
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<div class="smallexample">
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<pre class="smallexample">#include <immintrin.h>
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/* Unwind the shadow stack for EH. */
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#define _Unwind_Frames_Extra(x) \
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do \
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{ \
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_Unwind_Word ssp = _get_ssp (); \
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if (ssp != 0) \
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{ \
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_Unwind_Word tmp = (x); \
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while (tmp > 255) \
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{ \
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_inc_ssp (tmp); \
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tmp -= 255; \
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} \
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_inc_ssp (tmp); \
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} \
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} \
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while (0)
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</pre></div>
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<p>This code runs unconditionally on all 64-bit processors. For 32-bit
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processors the code runs on those that support multi-byte NOP instructions.
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</p>
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</body>
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</html>
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