[msan] Reset shadow of byval before call

[vitalybuka]

Summary

If function is not sanitized we must reset shadow, not copy.

Depends on D117285

[vitalybuka]

rebase

[eugenis]

Is this necessary if we zero byval pointee shadow in the other patch?

[vitalybuka]

In D117286#3244655, @eugenis wrote:

Is this necessary if we zero byval pointee shadow in the other patch?

without the patch:

1. test line 82 with byval -> reset and then copy shadow
2. test line 82 without byval -> copy shadow

with the patch:

1. test line 82 with byval -> reset shadow
2. test line 82 without byval -> reset shadow

[eugenis]

LGTM

[kda]

LGTM
and clean up formatting.

[vitalybuka]

rebase

[vitalybuka]

rebase

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

for (auto ArgIt = CB.arg_begin(), End = CB.arg_end(); ArgIt != End;
           const MaybeAlign ParamAlignment(CB.getParamAlign(i));
           MaybeAlign Alignment = llvm::None;
           if (ParamAlignment)
             Alignment = std::min(*ParamAlignment, kShadowTLSAlignment);
           Value *AShadowPtr =
               getShadowOriginPtr(A, IRB, IRB.getInt8Ty(), Alignment,
                                  /*isStore*/ false)
                   .first;
-
+          if (!PropagateShadow) {
+            Store = IRB.CreateMemSet(ArgShadowBase,
+                                     Constant::getNullValue(IRB.getInt8Ty()),
+                                     Size, Alignment);
+          } else {
             Store = IRB.CreateMemCpy(ArgShadowBase, Alignment, AShadowPtr,
                                      Alignment, Size);
-          // TODO(glider): need to copy origins.
+          }
         } else {
           // Any other parameters mean we need bit-grained tracking of uninit
           // data
           Size = DL.getTypeAllocSize(A->getType());
           if (ArgOffset + Size > kParamTLSSize)
             break;
           Store = IRB.CreateAlignedStore(ArgShadow, ArgShadowBase,
                                          kShadowTLSAlignment);

llvm/test/Instrumentation/MemorySanitizer/byval.ll

 ; CHECK-NEXT:    call void @FnByVal(
 ; CHECK-NEXT:    ret void
 ;
 entry:
   call void @FnByVal(i128* byval(i128) %p)
   ret void
 }
 
-; FIXME: Shadow for byval should be reset not copied before the call.
 define void @ByValForwardByValNoSanitize(i32, i128* byval(i128) %p) {
 ; CHECK-LABEL: @ByValForwardByValNoSanitize(
 ; CHECK-NEXT:  entry:
 ; CHECK:         call void @llvm.memset.p0i8.i64(i8* align 8 {{.*}}, i8 0, i64 16, i1 false)
-; CHECK:         call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast ([100 x i64]* @__msan_param_tls to i8*), i8* {{.*}}, i64 16, i1 false) 
+; CHECK:         call void @llvm.memset.p0i8.i64(i8* bitcast ([100 x i64]* @__msan_param_tls to i8*), i8 0, i64 16, i1 false)
 ; CHECK:         store i32 0, i32* getelementptr inbounds ([200 x i32], [200 x i32]* @__msan_param_origin_tls, i32 0, i32 0)
 ; CHECK-NEXT:    call void @FnByVal(
 ; CHECK-NEXT:    ret void
 ;
 entry:
   call void @FnByVal(i128* byval(i128) %p)
   ret void
 }