[MSan] [X86] Fix vararg helper for fixed arguments in overflow area.

[• koriakin]

Summary

This fixes http://llvm.org/PR27646 on x86_64.

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

void visitCallSite(CallSite &CS, IRBuilder<> &IRB) override {
     unsigned GpOffset = 0;
     unsigned FpOffset = AMD64GpEndOffset;
     unsigned OverflowOffset = AMD64FpEndOffset;
     const DataLayout &DL = F.getParent()->getDataLayout();
     for (CallSite::arg_iterator ArgIt = CS.arg_begin(), End = CS.arg_end();
          ArgIt != End; ++ArgIt) {
       Value *A = *ArgIt;
       unsigned ArgNo = CS.getArgumentNo(ArgIt);
+      bool IsFixed = ArgNo < CS.getFunctionType()->getNumParams();
       bool IsByVal = CS.paramHasAttr(ArgNo + 1, Attribute::ByVal);
       if (IsByVal) {
         // ByVal arguments always go to the overflow area.
+        // Fixed arguments passed through the overflow area will be stepped
+        // over by va_start, so don't count them towards the offset.
+        if (IsFixed)
+          continue;
         assert(A->getType()->isPointerTy());
         Type *RealTy = A->getType()->getPointerElementType();
         uint64_t ArgSize = DL.getTypeAllocSize(RealTy);
         Value *Base = getShadowPtrForVAArgument(RealTy, IRB, OverflowOffset);
         OverflowOffset += alignTo(ArgSize, 8);
         IRB.CreateMemCpy(Base, MSV.getShadowPtr(A, IRB.getInt8Ty(), IRB),
                          ArgSize, kShadowTLSAlignment);
       } else {
         ArgKind AK = classifyArgument(A);
         if (AK == AK_GeneralPurpose && GpOffset >= AMD64GpEndOffset)
           AK = AK_Memory;
         if (AK == AK_FloatingPoint && FpOffset >= AMD64FpEndOffset)
           AK = AK_Memory;
         Value *Base;
         switch (AK) {
           case AK_GeneralPurpose:
             Base = getShadowPtrForVAArgument(A->getType(), IRB, GpOffset);
             GpOffset += 8;
             break;
           case AK_FloatingPoint:
             Base = getShadowPtrForVAArgument(A->getType(), IRB, FpOffset);
             FpOffset += 16;
             break;
           case AK_Memory:
+            if (IsFixed)
+              continue;
             uint64_t ArgSize = DL.getTypeAllocSize(A->getType());
             Base = getShadowPtrForVAArgument(A->getType(), IRB, OverflowOffset);
             OverflowOffset += alignTo(ArgSize, 8);
         }
+        // Take fixed arguments into account for GpOffset and FpOffset,
+        // but don't actually store shadows for them.
+        if (IsFixed)
+          continue;
         IRB.CreateAlignedStore(MSV.getShadow(A), Base, kShadowTLSAlignment);
       }
     }
     Constant *OverflowSize =
       ConstantInt::get(IRB.getInt64Ty(), OverflowOffset - AMD64FpEndOffset);
     IRB.CreateStore(OverflowSize, MS.VAArgOverflowSizeTLS);
   }
 

llvm/trunk/test/Instrumentation/MemorySanitizer/msan_basic.ll

entry:
   call void (i32, ...) @VAArgStructFn(i32 undef, i64 %agg.tmp.sroa.0.0.copyload, i64 %agg.tmp.sroa.2.0.copyload, i64 %agg.tmp.sroa.0.0.copyload, i64 %agg.tmp.sroa.2.0.copyload, %struct.StructByVal* byval align 8 %agg.tmp2)
   ret void
 }
 
 ; "undef" and the first 2 structs go to general purpose registers;
 ; the third struct goes to the overflow area byval
 
 ; CHECK-LABEL: @VAArgStruct
-; undef
-; CHECK: store i32 -1, i32* {{.*}}@__msan_va_arg_tls {{.*}}, align 8
+; undef not stored to __msan_va_arg_tls - it's a fixed argument
 ; first struct through general purpose registers
 ; CHECK: store i64 {{.*}}, i64* {{.*}}@__msan_va_arg_tls{{.*}}, i64 8){{.*}}, align 8
 ; CHECK: store i64 {{.*}}, i64* {{.*}}@__msan_va_arg_tls{{.*}}, i64 16){{.*}}, align 8
 ; second struct through general purpose registers
 ; CHECK: store i64 {{.*}}, i64* {{.*}}@__msan_va_arg_tls{{.*}}, i64 24){{.*}}, align 8
 ; CHECK: store i64 {{.*}}, i64* {{.*}}@__msan_va_arg_tls{{.*}}, i64 32){{.*}}, align 8
 ; third struct through the overflow area byval
 ; CHECK: ptrtoint %struct.StructByVal* {{.*}} to i64