[asan] Fix dynamic allocas unpoisoning on PowerPC64.

For PowerPC64 we cannot just pass SP extracted from @llvm.stackrestore to
_asan_allocas_unpoison due to specific ABI requirements
(http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#DYNAM-STACK).
This patch adds the value returned by @llvm.get.dynamic.area.offset to
extracted from @llvm.stackrestore stack pointer, so dynamic allocas unpoisoning
stuff would work correctly on PowerPC64.

Patch by Max Ostapenko.

Differential Revision: http://reviews.llvm.org/D15108

llvm-svn: 254707

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -624,9 +624,24 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
   void unpoisonDynamicAllocasBeforeInst(Instruction *InstBefore,
                                         Value *SavedStack) {
     IRBuilder<> IRB(InstBefore);
+    Value *DynamicAreaPtr = IRB.CreatePtrToInt(SavedStack, IntptrTy);
+    // When we insert _asan_allocas_unpoison before @llvm.stackrestore, we
+    // need to adjust extracted SP to compute the address of the most recent
+    // alloca. We have a special @llvm.get.dynamic.area.offset intrinsic for
+    // this purpose.
+    if (!isa<ReturnInst>(InstBefore)) {
+      Function *DynamicAreaOffsetFunc = Intrinsic::getDeclaration(
+          InstBefore->getModule(), Intrinsic::get_dynamic_area_offset,
+          {IntptrTy});
+
+      Value *DynamicAreaOffset = IRB.CreateCall(DynamicAreaOffsetFunc, {});
+
+      DynamicAreaPtr = IRB.CreateAdd(IRB.CreatePtrToInt(SavedStack, IntptrTy),
+                                     DynamicAreaOffset);
+    }
+
     IRB.CreateCall(AsanAllocasUnpoisonFunc,
-                   {IRB.CreateLoad(DynamicAllocaLayout),
-                    IRB.CreatePtrToInt(SavedStack, IntptrTy)});
+                   {IRB.CreateLoad(DynamicAllocaLayout), DynamicAreaPtr});
   }
 
   // Unpoison dynamic allocas redzones.