PR11124: Don't overwrite memory outside of a base class when performing zero-initialization before running its constructor.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@141933 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExprCXX.cpp b/lib/CodeGen/CGExprCXX.cpp
index 8c05b46..78db590 100644
--- a/lib/CodeGen/CGExprCXX.cpp
+++ b/lib/CodeGen/CGExprCXX.cpp
@@ -353,6 +353,49 @@
return CGM.getCUDARuntime().EmitCUDAKernelCallExpr(*this, E, ReturnValue);
}
+static void EmitNullBaseClassInitialization(CodeGenFunction &CGF,
+ llvm::Value *DestPtr,
+ const CXXRecordDecl *Base) {
+ if (Base->isEmpty())
+ return;
+
+ DestPtr = CGF.EmitCastToVoidPtr(DestPtr);
+
+ const ASTRecordLayout &Layout = CGF.getContext().getASTRecordLayout(Base);
+ CharUnits Size = Layout.getNonVirtualSize();
+ CharUnits Align = Layout.getNonVirtualAlign();
+
+ llvm::Value *SizeVal = CGF.CGM.getSize(Size);
+
+ // If the type contains a pointer to data member we can't memset it to zero.
+ // Instead, create a null constant and copy it to the destination.
+ // TODO: there are other patterns besides zero that we can usefully memset,
+ // like -1, which happens to be the pattern used by member-pointers.
+ // TODO: isZeroInitializable can be over-conservative in the case where a
+ // virtual base contains a member pointer.
+ if (!CGF.CGM.getTypes().isZeroInitializable(Base)) {
+ llvm::Constant *NullConstant = CGF.CGM.EmitNullConstantForBase(Base);
+
+ llvm::GlobalVariable *NullVariable =
+ new llvm::GlobalVariable(CGF.CGM.getModule(), NullConstant->getType(),
+ /*isConstant=*/true,
+ llvm::GlobalVariable::PrivateLinkage,
+ NullConstant, Twine());
+ NullVariable->setAlignment(Align.getQuantity());
+ llvm::Value *SrcPtr = CGF.EmitCastToVoidPtr(NullVariable);
+
+ // Get and call the appropriate llvm.memcpy overload.
+ CGF.Builder.CreateMemCpy(DestPtr, SrcPtr, SizeVal, Align.getQuantity());
+ return;
+ }
+
+ // Otherwise, just memset the whole thing to zero. This is legal
+ // because in LLVM, all default initializers (other than the ones we just
+ // handled above) are guaranteed to have a bit pattern of all zeros.
+ CGF.Builder.CreateMemSet(DestPtr, CGF.Builder.getInt8(0), SizeVal,
+ Align.getQuantity());
+}
+
void
CodeGenFunction::EmitCXXConstructExpr(const CXXConstructExpr *E,
AggValueSlot Dest) {
@@ -363,8 +406,19 @@
// constructor, as can be the case with a non-user-provided default
// constructor, emit the zero initialization now, unless destination is
// already zeroed.
- if (E->requiresZeroInitialization() && !Dest.isZeroed())
- EmitNullInitialization(Dest.getAddr(), E->getType());
+ if (E->requiresZeroInitialization() && !Dest.isZeroed()) {
+ switch (E->getConstructionKind()) {
+ case CXXConstructExpr::CK_Delegating:
+ assert(0 && "Delegating constructor should not need zeroing");
+ case CXXConstructExpr::CK_Complete:
+ EmitNullInitialization(Dest.getAddr(), E->getType());
+ break;
+ case CXXConstructExpr::CK_VirtualBase:
+ case CXXConstructExpr::CK_NonVirtualBase:
+ EmitNullBaseClassInitialization(*this, Dest.getAddr(), CD->getParent());
+ break;
+ }
+ }
// If this is a call to a trivial default constructor, do nothing.
if (CD->isTrivial() && CD->isDefaultConstructor())
diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 30c978e..8711c1f 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -1343,3 +1343,8 @@
// A NULL pointer is represented as -1.
return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
}
+
+llvm::Constant *
+CodeGenModule::EmitNullConstantForBase(const CXXRecordDecl *Record) {
+ return ::EmitNullConstant(*this, Record, false);
+}
diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index 48237b9..8e38a89 100644
--- a/lib/CodeGen/CodeGenModule.h
+++ b/lib/CodeGen/CodeGenModule.h
@@ -670,6 +670,11 @@
/// but not always, an LLVM null constant.
llvm::Constant *EmitNullConstant(QualType T);
+ /// EmitNullConstantForBase - Return a null constant appropriate for
+ /// zero-initializing a base class with the given type. This is usually,
+ /// but not always, an LLVM null constant.
+ llvm::Constant *EmitNullConstantForBase(const CXXRecordDecl *Record);
+
/// Error - Emit a general error that something can't be done.
void Error(SourceLocation loc, StringRef error);