[llvm] r188191 - [stackprotector] Added intrinsic llvm.stackprotectorcheck.

[Michael Gottesman]

Author: mgottesman
Date: Mon Aug 12 13:35:32 2013
New Revision: 188191

URL: http://llvm.org/viewvc/llvm-project?rev=188191&view=rev
Log:
[stackprotector] Added intrinsic llvm.stackprotectorcheck.

Modified:
    llvm/trunk/docs/LangRef.rst
    llvm/trunk/include/llvm/IR/Intrinsics.td

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=188191&r1=188190&r2=188191&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Mon Aug 12 13:35:32 2013
@@ -8641,14 +8641,52 @@ enough space to hold the value of the gu
 Semantics:
 """"""""""
 
-This intrinsic causes the prologue/epilogue inserter to force the
-position of the ``AllocaInst`` 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 are different, then the program aborts by calling the
+This intrinsic causes the prologue/epilogue inserter to force the position of
+the ``AllocaInst`` 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 by ``llvm.stackprotectorcheck``. If they are
+different, then ``llvm.stackprotectorcheck`` causes the program to abort by
+calling the ``__stack_chk_fail()`` function.
+
+'``llvm.stackprotectorcheck``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare void @llvm.stackprotectorcheck(i8** <guard>)
+
+Overview:
+"""""""""
+
+The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
+created stack protector and if they do not equal calls the
 ``__stack_chk_fail()`` function.
 
+Arguments:
+""""""""""
+
+The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
+the variable ``@__stack_chk_guard``.
+
+Semantics:
+""""""""""
+
+This intrinsic is provided to perform the stack protector check by comparing
+``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
+values do not match call the ``__stack_chk_fail()`` function.
+
+The reason to provide this as an IR level intrinsic instead of implementing it
+via other IR operations is that in order to perform this operation at the IR
+level without an intrinsic, one would need to create additional basic blocks to
+handle the success/failure cases. This makes it difficult to stop the stack
+protector check from disrupting sibling tail calls in Codegen. With this
+intrinsic, we are able to generate the stack protector basic blocks late in
+codegen after the tail call decision has occured.
+
 '``llvm.objectsize``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

Modified: llvm/trunk/include/llvm/IR/Intrinsics.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Intrinsics.td?rev=188191&r1=188190&r2=188191&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Intrinsics.td (original)
+++ llvm/trunk/include/llvm/IR/Intrinsics.td Mon Aug 12 13:35:32 2013
@@ -258,6 +258,8 @@ def int_readcyclecounter : Intrinsic<[ll
 // Stack Protector Intrinsic - The stackprotector intrinsic writes the stack
 // guard to the correct place on the stack frame.
 def int_stackprotector : Intrinsic<[], [llvm_ptr_ty, llvm_ptrptr_ty], []>;
+def int_stackprotectorcheck : Intrinsic<[], [llvm_ptrptr_ty],
+                                        [IntrReadWriteArgMem]>;
 
 //===------------------- Standard C Library Intrinsics --------------------===//
 //