Add a new builtin: __builtin_dynamic_object_size
This builtin has the same UI as __builtin_object_size, but has the
potential to be evaluated dynamically. It is meant to be used as a
drop-in replacement for libraries that use __builtin_object_size when
a dynamic checking mode is enabled. For instance,
__builtin_object_size fails to provide any extra checking in the
following function:
void f(size_t alloc) {
char* p = malloc(alloc);
strcpy(p, "foobar"); // expands to __builtin___strcpy_chk(p, "foobar", __builtin_object_size(p, 0))
}
This is an overflow if alloc < 7, but because LLVM can't fold the
object size intrinsic statically, it folds __builtin_object_size to
-1. With __builtin_dynamic_object_size, alloc is passed through to
__builtin___strcpy_chk.
rdar://32212419
Differential revision: https://reviews.llvm.org/D56760
llvm-svn: 352665
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index f1014b6..93b5775 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -494,10 +494,11 @@
llvm::Value *
CodeGenFunction::evaluateOrEmitBuiltinObjectSize(const Expr *E, unsigned Type,
llvm::IntegerType *ResType,
- llvm::Value *EmittedE) {
+ llvm::Value *EmittedE,
+ bool IsDynamic) {
uint64_t ObjectSize;
if (!E->tryEvaluateObjectSize(ObjectSize, getContext(), Type))
- return emitBuiltinObjectSize(E, Type, ResType, EmittedE);
+ return emitBuiltinObjectSize(E, Type, ResType, EmittedE, IsDynamic);
return ConstantInt::get(ResType, ObjectSize, /*isSigned=*/true);
}
@@ -513,7 +514,7 @@
llvm::Value *
CodeGenFunction::emitBuiltinObjectSize(const Expr *E, unsigned Type,
llvm::IntegerType *ResType,
- llvm::Value *EmittedE) {
+ llvm::Value *EmittedE, bool IsDynamic) {
// We need to reference an argument if the pointer is a parameter with the
// pass_object_size attribute.
if (auto *D = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts())) {
@@ -549,7 +550,7 @@
Value *Min = Builder.getInt1((Type & 2) != 0);
// For GCC compatibility, __builtin_object_size treat NULL as unknown size.
Value *NullIsUnknown = Builder.getTrue();
- Value *Dynamic = Builder.getFalse();
+ Value *Dynamic = Builder.getInt1(IsDynamic);
return Builder.CreateCall(F, {Ptr, Min, NullIsUnknown, Dynamic});
}
@@ -1978,6 +1979,7 @@
Result = Builder.CreateIntCast(Result, ResultType, /*isSigned*/false);
return RValue::get(Result);
}
+ case Builtin::BI__builtin_dynamic_object_size:
case Builtin::BI__builtin_object_size: {
unsigned Type =
E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();
@@ -1985,8 +1987,9 @@
// We pass this builtin onto the optimizer so that it can figure out the
// object size in more complex cases.
+ bool IsDynamic = BuiltinID == Builtin::BI__builtin_dynamic_object_size;
return RValue::get(emitBuiltinObjectSize(E->getArg(0), Type, ResType,
- /*EmittedE=*/nullptr));
+ /*EmittedE=*/nullptr, IsDynamic));
}
case Builtin::BI__builtin_prefetch: {
Value *Locality, *RW, *Address = EmitScalarExpr(E->getArg(0));