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127 lines
5.4 KiB
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127 lines
5.4 KiB
HTML
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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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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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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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