[MSan][MIPS] VarArgHelper for MIPS64

[eugenis]

LGTM w/ inline comments

lib/Transforms/Instrumentation/MemorySanitizer.cpp

434

Please reuse VAArgSizeTLS instead of creating a new member variable, with a comment somewhere in VarArgHelper that it is used to pass the full argument size (effectively, all arguments on MIPS64 go to the overflow area in terms of X86_64).

It's confusing, unless you want to rename __msan_va_arg_overflow_size_tls as well.

2983

Above, we use the following to check for MIPS64:

case Triple::mips64:
case Triple::mips64el:

Do you need to check for Triple::mips64 here as well?

[mohit.bhakkad]

Changes in this revision:

• removed VAArgSizeTLS
• adding support for mips64 EB (big endian)

[mohit.bhakkad]

@eugenis any comment/suggestion on this? This will provide provide msan for VarArgs on mips64/mips64el.

[eugenis]

Sorry for the delay, I've been travelling for the last 2 weeks.

lib/Transforms/Instrumentation/MemorySanitizer.cpp

2888

Should it be += (8 - ArgSize) ?
I assume each argument is extended to 8 bytes.

[mohit.bhakkad]

lib/Transforms/Instrumentation/MemorySanitizer.cpp

2888

For variable args, types char and short int are automatically promoted to int, so anything less than size 8 is of size 4.
So += (8 - ArgSize) and += ArgSize should work same.

[eugenis]

lib/Transforms/Instrumentation/MemorySanitizer.cpp

2888

If you want to rely on that, then please add a CHECK that ArgSize == 4.

[mohit.bhakkad]

Changes in this revision:

• as per @eugenis suggestion changed += ArgSize to += (8 - ArgSize)

[mohit.bhakkad]

lib/Transforms/Instrumentation/MemorySanitizer.cpp

2888

Going ahead with += (8 - ArgSize) in next revision, as it matches the context, and I don't want another CHECK.

[eugenis]

Looks good.

lib/Transforms/Instrumentation/MemorySanitizer.cpp

2888

Yes, I think it's less confusing.

lib/Transforms/Instrumentation/MemorySanitizer.cpp

private:
   MDNode *ColdCallWeights;
   /// \brief Branch weights for origin store.
   MDNode *OriginStoreWeights;
   /// \brief An empty volatile inline asm that prevents callback merge.
   InlineAsm *EmptyAsm;
 
   friend struct MemorySanitizerVisitor;
   friend struct VarArgAMD64Helper;
+  friend struct VarArgMIPS64Helper;
 };
 }  // namespace
 
 char MemorySanitizer::ID = 0;
 INITIALIZE_PASS(MemorySanitizer, "msan",
                 "MemorySanitizer: detects uninitialized reads.",
                 false, false)
 
ParamOriginTLS = new GlobalVariable(
     M, ArrayType::get(OriginTy, kParamTLSSize / 4), false,
     GlobalVariable::ExternalLinkage, nullptr, "__msan_param_origin_tls",
     nullptr, GlobalVariable::InitialExecTLSModel);
 
   VAArgTLS = new GlobalVariable(
     M, ArrayType::get(IRB.getInt64Ty(), kParamTLSSize / 8), false,
     GlobalVariable::ExternalLinkage, nullptr, "__msan_va_arg_tls", nullptr,
     GlobalVariable::InitialExecTLSModel);
   VAArgOverflowSizeTLS = new GlobalVariable(
     M, IRB.getInt64Ty(), false, GlobalVariable::ExternalLinkage, nullptr,
     "__msan_va_arg_overflow_size_tls", nullptr,
     GlobalVariable::InitialExecTLSModel);
   OriginTLS = new GlobalVariable(
     M, IRB.getInt32Ty(), false, GlobalVariable::ExternalLinkage, nullptr,
     "__msan_origin_tls", nullptr, GlobalVariable::InitialExecTLSModel);
 
   // We insert an empty inline asm after __msan_report* to avoid callback merge.
for (size_t i = 0, n = VAStartInstrumentationList.size(); i < n; i++) {
       Value *OverflowArgAreaShadowPtr =
         MSV.getShadowPtr(OverflowArgAreaPtr, IRB.getInt8Ty(), IRB);
       Value *SrcPtr = IRB.CreateConstGEP1_32(VAArgTLSCopy, AMD64FpEndOffset);
       IRB.CreateMemCpy(OverflowArgAreaShadowPtr, SrcPtr, VAArgOverflowSize, 16);
     }
   }
 };
 
+/// \brief MIPS64-specific implementation of VarArgHelper.
+struct VarArgMIPS64Helper : public VarArgHelper {
+  Function &F;
+  MemorySanitizer &MS;
+  MemorySanitizerVisitor &MSV;
+  Value *VAArgTLSCopy;
+  Value *VAArgSize;
+
+  SmallVector<CallInst*, 16> VAStartInstrumentationList;
+
+  VarArgMIPS64Helper(Function &F, MemorySanitizer &MS,
+                    MemorySanitizerVisitor &MSV)
+    : F(F), MS(MS), MSV(MSV), VAArgTLSCopy(nullptr),
+      VAArgSize(nullptr) {}
+
+  void visitCallSite(CallSite &CS, IRBuilder<> &IRB) override {
+    unsigned VAArgOffset = 0;
+    for (CallSite::arg_iterator ArgIt = CS.arg_begin() + 1, End = CS.arg_end();
+         ArgIt != End; ++ArgIt) {
+      Value *A = *ArgIt;
+      Value *Base;
+      uint64_t ArgSize = MS.DL->getTypeAllocSize(A->getType());
+#if defined(__MIPSEB__) || defined(MIPSEB)
+      // Adjusting the shadow for argument with size < 8 to match the placement
+      // of bits in big endian system
+      if (ArgSize < 8)
+        VAArgOffset += (8 - ArgSize);
+#endif
+      Base = getShadowPtrForVAArgument(A->getType(), IRB, VAArgOffset);
+      VAArgOffset += ArgSize;
+      VAArgOffset = RoundUpToAlignment(VAArgOffset, 8);
+      IRB.CreateAlignedStore(MSV.getShadow(A), Base, kShadowTLSAlignment);
+    }
+
+    Constant *TotalVAArgSize = ConstantInt::get(IRB.getInt64Ty(), VAArgOffset);
+    // Here using VAArgOverflowSizeTLS as VAArgSizeTLS to avoid creation of
+    // a new class member i.e. it is the total size of all VarArgs.
+    IRB.CreateStore(TotalVAArgSize, MS.VAArgOverflowSizeTLS);
+  }
+
+  /// \brief Compute the shadow address for a given va_arg.
+  Value *getShadowPtrForVAArgument(Type *Ty, IRBuilder<> &IRB,
+                                   int ArgOffset) {
+    Value *Base = IRB.CreatePointerCast(MS.VAArgTLS, MS.IntptrTy);
+    Base = IRB.CreateAdd(Base, ConstantInt::get(MS.IntptrTy, ArgOffset));
+    return IRB.CreateIntToPtr(Base, PointerType::get(MSV.getShadowTy(Ty), 0),
+                              "_msarg");
+  }
+
+  void visitVAStartInst(VAStartInst &I) override {
+    IRBuilder<> IRB(&I);
+    VAStartInstrumentationList.push_back(&I);
+    Value *VAListTag = I.getArgOperand(0);
+    Value *ShadowPtr = MSV.getShadowPtr(VAListTag, IRB.getInt8Ty(), IRB);
+    IRB.CreateMemSet(ShadowPtr, Constant::getNullValue(IRB.getInt8Ty()),
+                     /* size */8, /* alignment */8, false);
+  }
+
+  void visitVACopyInst(VACopyInst &I) override {
+    IRBuilder<> IRB(&I);
+    Value *VAListTag = I.getArgOperand(0);
+    Value *ShadowPtr = MSV.getShadowPtr(VAListTag, IRB.getInt8Ty(), IRB);
+    // Unpoison the whole __va_list_tag.
+    // FIXME: magic ABI constants.
+    IRB.CreateMemSet(ShadowPtr, Constant::getNullValue(IRB.getInt8Ty()),
+                     /* size */8, /* alignment */8, false);
+  }
+
+  void finalizeInstrumentation() override {
+    assert(!VAArgSize && !VAArgTLSCopy &&
+           "finalizeInstrumentation called twice");
+    IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+    VAArgSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
+    Value *CopySize = IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, 0),
+                                    VAArgSize);
+
+    if (!VAStartInstrumentationList.empty()) {
+      // If there is a va_start in this function, make a backup copy of
+      // va_arg_tls somewhere in the function entry block.
+      VAArgTLSCopy = IRB.CreateAlloca(Type::getInt8Ty(*MS.C), CopySize);
+      IRB.CreateMemCpy(VAArgTLSCopy, MS.VAArgTLS, CopySize, 8);
+    }
+
+    // Instrument va_start.
+    // Copy va_list shadow from the backup copy of the TLS contents.
+    for (size_t i = 0, n = VAStartInstrumentationList.size(); i < n; i++) {
+      CallInst *OrigInst = VAStartInstrumentationList[i];
+      IRBuilder<> IRB(OrigInst->getNextNode());
+      Value *VAListTag = OrigInst->getArgOperand(0);
+      Value *RegSaveAreaPtrPtr =
+        IRB.CreateIntToPtr(IRB.CreatePtrToInt(VAListTag, MS.IntptrTy),
+                        Type::getInt64PtrTy(*MS.C));
+      Value *RegSaveAreaPtr = IRB.CreateLoad(RegSaveAreaPtrPtr);
+      Value *RegSaveAreaShadowPtr =
+      MSV.getShadowPtr(RegSaveAreaPtr, IRB.getInt8Ty(), IRB);
+      IRB.CreateMemCpy(RegSaveAreaShadowPtr, VAArgTLSCopy, CopySize, 8);
+    }
+  }
+};
+
 /// \brief A no-op implementation of VarArgHelper.
 struct VarArgNoOpHelper : public VarArgHelper {
   VarArgNoOpHelper(Function &F, MemorySanitizer &MS,
                    MemorySanitizerVisitor &MSV) {}
 
   void visitCallSite(CallSite &CS, IRBuilder<> &IRB) override {}
 
   void visitVAStartInst(VAStartInst &I) override {}
 
   void visitVACopyInst(VACopyInst &I) override {}
 
   void finalizeInstrumentation() override {}
 };
 
 VarArgHelper *CreateVarArgHelper(Function &Func, MemorySanitizer &Msan,
                                  MemorySanitizerVisitor &Visitor) {
   // VarArg handling is only implemented on AMD64. False positives are possible
   // on other platforms.
   llvm::Triple TargetTriple(Func.getParent()->getTargetTriple());
   if (TargetTriple.getArch() == llvm::Triple::x86_64)
     return new VarArgAMD64Helper(Func, Msan, Visitor);
+  else if (TargetTriple.getArch() == llvm::Triple::mips64 ||
+           TargetTriple.getArch() == llvm::Triple::mips64el)
+    return new VarArgMIPS64Helper(Func, Msan, Visitor);
   else
     return new VarArgNoOpHelper(Func, Msan, Visitor);
 }
 
 }  // namespace
 
 bool MemorySanitizer::runOnFunction(Function &F) {
   MemorySanitizerVisitor Visitor(F, *this);