[safestack] Support safestack in stack size diagnostics

Current stack size diagnostics ignore the size of the unsafe stack.
This patch attaches the size of the static portion of the unsafe stack
to the function as metadata, which can be used by the backend to emit
diagnostics regarding stack usage.

Reviewed By: phosek, mcgrathr

Differential Revision: https://reviews.llvm.org/D119996

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SafeStack.cpp b/llvm/lib/CodeGen/SafeStack.cpp
index 1f7eac4..2c16c191 100644
--- a/llvm/lib/CodeGen/SafeStack.cpp
+++ b/llvm/lib/CodeGen/SafeStack.cpp
@@ -48,6 +48,7 @@
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Use.h"
@@ -633,6 +634,13 @@ Value *SafeStack::moveStaticAllocasToUnsafeStack(
   // FIXME: no need to update BasePointer in leaf functions.
   unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
 
+  MDBuilder MDB(F.getContext());
+  SmallVector<Metadata *, 2> Data;
+  Data.push_back(MDB.createString("unsafe-stack-size"));
+  Data.push_back(MDB.createConstant(ConstantInt::get(Int32Ty, FrameSize)));
+  MDNode *MD = MDTuple::get(F.getContext(), Data);
+  F.setMetadata(LLVMContext::MD_annotation, MD);
+
   // Update shadow stack pointer in the function epilogue.
   IRB.SetInsertPoint(BasePointer->getNextNode());