Documentation for the llvm.stackprotector intrinsic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59557 91177308-0d34-0410-b5e6-96231b3b80d8

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           <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
         </ol>
       </li>
-          <li><a href="#int_atomics">Atomic intrinsics</a>
-            <ol>
-              <li><a href="#int_memory_barrier"><tt>llvm.memory_barrier</tt></a></li>
-              <li><a href="#int_atomic_cmp_swap"><tt>llvm.atomic.cmp.swap</tt></a></li>
-              <li><a href="#int_atomic_swap"><tt>llvm.atomic.swap</tt></a></li>
-              <li><a href="#int_atomic_load_add"><tt>llvm.atomic.load.add</tt></a></li>
-              <li><a href="#int_atomic_load_sub"><tt>llvm.atomic.load.sub</tt></a></li>
-              <li><a href="#int_atomic_load_and"><tt>llvm.atomic.load.and</tt></a></li>
-              <li><a href="#int_atomic_load_nand"><tt>llvm.atomic.load.nand</tt></a></li>
-              <li><a href="#int_atomic_load_or"><tt>llvm.atomic.load.or</tt></a></li>
-              <li><a href="#int_atomic_load_xor"><tt>llvm.atomic.load.xor</tt></a></li>
-              <li><a href="#int_atomic_load_max"><tt>llvm.atomic.load.max</tt></a></li>
-              <li><a href="#int_atomic_load_min"><tt>llvm.atomic.load.min</tt></a></li>
-              <li><a href="#int_atomic_load_umax"><tt>llvm.atomic.load.umax</tt></a></li>
-              <li><a href="#int_atomic_load_umin"><tt>llvm.atomic.load.umin</tt></a></li>
-            </ol>
-          </li>
+      <li><a href="#int_stackprotect">Stack Protector Intrinsic</a>
+        <ol>
+          <li><a href="#int_ssp">'<tt>llvm.stackprotector</tt>' Intrinsic</a></li>
+        </ol>
+      </li>
+      <li><a href="#int_atomics">Atomic intrinsics</a>
+        <ol>
+          <li><a href="#int_memory_barrier"><tt>llvm.memory_barrier</tt></a></li>
+          <li><a href="#int_atomic_cmp_swap"><tt>llvm.atomic.cmp.swap</tt></a></li>
+          <li><a href="#int_atomic_swap"><tt>llvm.atomic.swap</tt></a></li>
+          <li><a href="#int_atomic_load_add"><tt>llvm.atomic.load.add</tt></a></li>
+          <li><a href="#int_atomic_load_sub"><tt>llvm.atomic.load.sub</tt></a></li>
+          <li><a href="#int_atomic_load_and"><tt>llvm.atomic.load.and</tt></a></li>
+          <li><a href="#int_atomic_load_nand"><tt>llvm.atomic.load.nand</tt></a></li>
+          <li><a href="#int_atomic_load_or"><tt>llvm.atomic.load.or</tt></a></li>
+          <li><a href="#int_atomic_load_xor"><tt>llvm.atomic.load.xor</tt></a></li>
+          <li><a href="#int_atomic_load_max"><tt>llvm.atomic.load.max</tt></a></li>
+          <li><a href="#int_atomic_load_min"><tt>llvm.atomic.load.min</tt></a></li>
+          <li><a href="#int_atomic_load_umax"><tt>llvm.atomic.load.umax</tt></a></li>
+          <li><a href="#int_atomic_load_umin"><tt>llvm.atomic.load.umin</tt></a></li>
+        </ol>
+      </li>
       <li><a href="#int_general">General intrinsics</a>
         <ol>
           <li><a href="#int_var_annotation">
@@ -5802,6 +5807,54 @@ declare i8* @llvm.init.trampoline(i8* &lt;tramp&gt;, i8* &lt;func&gt;, i8* &lt;n
 </p>
 </div>
 
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+  <a name="int_stackprotect">Stack Protector Intrinsic</a>
+</div>
+
+<div class="doc_text">
+<p>
+  This intrinsic is used when stack protectors are required. LLVM generates a
+  call to load the randomized stack protector guard's value. The intrinsic is
+  used so that LLVM can ensure that the stack guard is placed onto the stack in
+  the appropriate place&mdash;before local variables are allocated on the stack.
+</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+  <a name="int_ssp">'<tt>llvm.stackprotector</tt>' Intrinsic</a>
+</div>
+<div class="doc_text">
+<h5>Syntax:</h5>
+<pre>
+declare void @llvm.stackprotector( i8* &lt;guard&gt;, i8** &lt;slot&gt; )
+
+</pre>
+<h5>Overview:</h5>
+<p>
+  The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and stores
+  it onto the stack at <tt>slot</tt>. The stack slot is adjusted to ensure that
+  it's before local variables are allocated on the stack.
+</p>
+<h5>Arguments:</h5>
+<p>
+  The <tt>llvm.stackprotector</tt> intrinsic requires two pointer arguments. The
+  first argument is the value loaded from the stack guard
+  <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt> that
+  has enough space to hold the value of the guard.
+</p>
+<h5>Semantics:</h5>
+<p>
+  This intrinsic causes the prologue/epilogue inserter to force the position of
+  the <tt>AllocaInst</tt> stack slot to be before local variables on the
+  stack. This is to ensure that if a local variable on the stack is overwritten,
+  it will destroy the value of the guard. When the function exits, the guard on
+  the stack is checked against the original guard. If they're different, then
+  the program aborts by calling the <tt>__stack_chk_fail()</tt> function.
+</p>
+</div>
+
 <!-- ======================================================================= -->
 <div class="doc_subsection">
   <a name="int_atomics">Atomic Operations and Synchronization Intrinsics</a>