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| -rw-r--r-- | docs/LangRef.rst | 50 | ||||
| -rw-r--r-- | include/llvm/IR/Intrinsics.td | 2 |
2 files changed, 46 insertions, 6 deletions
diff --git a/docs/LangRef.rst b/docs/LangRef.rst index a8feb12..8b0be1b 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -8641,14 +8641,52 @@ enough space to hold the value of the guard. 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 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/include/llvm/IR/Intrinsics.td b/include/llvm/IR/Intrinsics.td index ffa121d..18f56d2 100644 --- a/include/llvm/IR/Intrinsics.td +++ b/include/llvm/IR/Intrinsics.td @@ -258,6 +258,8 @@ def int_readcyclecounter : Intrinsic<[llvm_i64_ty]>; // 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 --------------------===// // |