[MSAN] Never allow checking calls to __sanitizer_unaligned_{load,store}

[guiand]

Summary

These functions expect the caller to always pass shadows over TLS.

Split off of https://reviews.llvm.org/D83427.

[guiand]

This patch actually has no dependency on clang emitting noundef, so it should be good to go.

[eugenis]

Please add a test (instrumentation only, no need for a compiler-rt test).

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

3592

add another underscore at the end

[guiand]

Added a test case

[eugenis]

LGTM

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

if (auto *Call = dyn_cast<CallInst>(&CB)) {
             .addAttribute(Attribute::ArgMemOnly)
             .addAttribute(Attribute::Speculatable);
         Func->removeAttributes(AttributeList::FunctionIndex, B);
       }
 
       maybeMarkSanitizerLibraryCallNoBuiltin(Call, TLI);
     }
     IRBuilder<> IRB(&CB);
+    bool MayCheckCall = ClEagerChecks;
+    if (Function *Func = CB.getCalledFunction()) {
+      // __sanitizer_unaligned_{load,store} functions may be called by users
+      // and always expects shadows in the TLS. So don't check them.
+      MayCheckCall &= !Func->getName().startswith("__sanitizer_unaligned");
+    }
 
     unsigned ArgOffset = 0;
     LLVM_DEBUG(dbgs() << "  CallSite: " << CB << "\n");
     for (auto ArgIt = CB.arg_begin(), End = CB.arg_end(); ArgIt != End;
          ++ArgIt) {
       Value *A = *ArgIt;
       unsigned i = ArgIt - CB.arg_begin();
       if (!A->getType()->isSized()) {
for (auto ArgIt = CB.arg_begin(), End = CB.arg_end(); ArgIt != End;
       Value *ArgShadowBase = getShadowPtrForArgument(A, IRB, ArgOffset);
       LLVM_DEBUG(dbgs() << "  Arg#" << i << ": " << *A
                         << " Shadow: " << *ArgShadow << "\n");
       bool ArgIsInitialized = false;
       const DataLayout &DL = F.getParent()->getDataLayout();
 
       bool ByVal = CB.paramHasAttr(i, Attribute::ByVal);
       bool NoUndef = CB.paramHasAttr(i, Attribute::NoUndef);
-      bool EagerCheck = ClEagerChecks && !ByVal && NoUndef;
+      bool EagerCheck = MayCheckCall && !ByVal && NoUndef;
 
       if (EagerCheck) {
         insertShadowCheck(A, &CB);
         continue;
       }
       if (ByVal) {
         // ByVal requires some special handling as it's too big for a single
         // load
void visitCallBase(CallBase &CB) {
 
     // Now, get the shadow for the RetVal.
     if (!CB.getType()->isSized())
       return;
     // Don't emit the epilogue for musttail call returns.
     if (isa<CallInst>(CB) && cast<CallInst>(CB).isMustTailCall())
       return;
 
-    if (ClEagerChecks && CB.hasRetAttr(Attribute::NoUndef)) {
+    if (MayCheckCall && CB.hasRetAttr(Attribute::NoUndef)) {
       setShadow(&CB, getCleanShadow(&CB));
       setOrigin(&CB, getCleanOrigin());
       return;
     }
 
     IRBuilder<> IRBBefore(&CB);
     // Until we have full dynamic coverage, make sure the retval shadow is 0.
     Value *Base = getShadowPtrForRetval(&CB, IRBBefore);