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

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 829821a156d..893a6f2f902 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -3459,7 +3459,8 @@ void CodeGenFunction::EmitCallArgs(
     auto T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
     assert(EmittedArg.getScalarVal() && "We emitted nothing for the arg?");
     llvm::Value *V = evaluateOrEmitBuiltinObjectSize(Arg, PS->getType(), T,
-                                                     EmittedArg.getScalarVal());
+                                                     EmittedArg.getScalarVal(),
+                                                     /*IsDynamic=*/false);
     Args.add(RValue::get(V), SizeTy);
     // If we're emitting args in reverse, be sure to do so with
     // pass_object_size, as well.