[asan] Fix dynamic allocas unpoisoning on PowerPC{64}.

[m.ostapenko]

Summary

Hi!

As discussed in llvm-dev ML (https://groups.google.com/forum/m/#!topic/llvm-dev/42tNzaHISdk), for PowerPC{64} 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). In particular, to get the pointer to the most recent dynamic alloca, we should add a compile-time-known offset to SP. This offset becomes to be known only on the frame index elimination stage, so we have introduced a special @llvm.get.dynamic.area.offset intrinsic (http://reviews.llvm.org/D14983) to reference it in LLVM. For most targets, this intrinsic is just lowered to zero in backend.

This patch just adds the value returned by @llvm.get.dynamic.area.offset to extracted from @llvm.stackrestore SP, so dynamic allocas unpoisoning stuff would work correctly on PowerPC{64}.

Tested on x86_64-unknown-linux-gnu. Jay, could you please check it on your PPC box?

[foad]

Jay, could you please check it on your PPC box?

Works for me, thanks!

[ygribov]

Kostya, Alexey, is this ok for trunk?

[samsonov]

LGTM (though it would be nice to have llvm test for that as well)

[m.ostapenko]

Thanks! As for test, perhaps I can add it with another commit?

[samsonov]

I'm fine either way.

llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp

struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
 
   // ----------------------- Visitors.
   /// \brief Collect all Ret instructions.
   void visitReturnInst(ReturnInst &RI) { RetVec.push_back(&RI); }
 
   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.
   void unpoisonDynamicAllocas() {
     for (auto &Ret : RetVec)
       unpoisonDynamicAllocasBeforeInst(Ret, DynamicAllocaLayout);
 
     for (auto &StackRestoreInst : StackRestoreVec)