devdocs/gcc~13/x86-control-flow-protection-intrinsics.html


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<div class="subsection-level-extent" id="x86-control-flow-protection-intrinsics"> <div class="nav-panel"> <p> Previous: <a href="x86-transactional-memory-intrinsics" accesskey="p" rel="prev">x86 Transactional Memory Intrinsics</a>, Up: <a href="target-builtins" accesskey="u" rel="up">Built-in Functions Specific to Particular Target Machines</a> [<a href="index#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="indices" title="Index" rel="index">Index</a>]</p> </div>  <h1 class="subsection" id="x86-Control-Flow-Protection-Intrinsics"><span>6.60.37 x86 Control-Flow Protection Intrinsics<a class="copiable-link" href="#x86-Control-Flow-Protection-Intrinsics"> ¶</a></span></h1> <dl class="first-deftypefn"> <dt class="deftypefn" id="index-_005fget_005fssp">
<span class="category-def">CET Function: </span><span><code class="def-type">ret_type</code> <strong class="def-name">_get_ssp</strong> <code class="def-code-arguments">(void)</code><a class="copiable-link" href="#index-_005fget_005fssp"> ¶</a></span>
</dt> <dd><p>Get the current value of shadow stack pointer if shadow stack support from Intel CET is enabled in the hardware or <code class="code">0</code> otherwise. The <code class="code">ret_type</code> is <code class="code">unsigned long long</code> for 64-bit targets and <code class="code">unsigned int</code> for 32-bit targets. </p></dd>
</dl> <dl class="first-deftypefn"> <dt class="deftypefn" id="index-_005finc_005fssp">
<span class="category-def">CET Function: </span><span><code class="def-type">void</code> <strong class="def-name">_inc_ssp</strong> <code class="def-code-arguments">(unsigned int)</code><a class="copiable-link" href="#index-_005finc_005fssp"> ¶</a></span>
</dt> <dd><p>Increment the current shadow stack pointer by the size specified by the function argument. The argument is masked to a byte value for security reasons, so to increment by more than 255 bytes you must call the function multiple times. </p></dd>
</dl> <p>The shadow stack unwind code looks like: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">#include &lt;immintrin.h&gt;

/* Unwind the shadow stack for EH.  */
#define _Unwind_Frames_Extra(x)       \
  do                                  \
    {                                \
      _Unwind_Word ssp = _get_ssp (); \
      if (ssp != 0)                   \
        {                            \
          _Unwind_Word tmp = (x);     \
          while (tmp &gt; 255)           \
            {                        \
              _inc_ssp (tmp);         \
              tmp -= 255;             \
            }                        \
          _inc_ssp (tmp);             \
        }                            \
    }                                \
    while (0)</pre>
</div> <p>This code runs unconditionally on all 64-bit processors. For 32-bit processors the code runs on those that support multi-byte NOP instructions. </p> </div><div class="_attribution">
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