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<a name="x86-Control_002dFlow-Protection-Intrinsics"></a>
<h4 class="subsection">6.60.36 x86 Control-Flow Protection Intrinsics</h4>

<dl>
<dt><a name="index-_005fget_005fssp"></a>CET Function: <em>ret_type</em> <strong>_get_ssp</strong> <em>(void)</em></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>0</code> otherwise.
The <code>ret_type</code> is <code>unsigned long long</code> for 64-bit targets 
and <code>unsigned int</code> for 32-bit targets.
</p></dd></dl>

<dl>
<dt><a name="index-_005finc_005fssp"></a>CET Function: <em>void</em> <strong>_inc_ssp</strong> <em>(unsigned int)</em></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="smallexample">
<pre class="smallexample">#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>


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