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, 4 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 87d141fe6f0..a989a0e46ca 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -4177,14 +4177,16 @@ private:
   /// If EmittedExpr is non-null, this will use that instead of re-emitting E.
   llvm::Value *evaluateOrEmitBuiltinObjectSize(const Expr *E, unsigned Type,
                                                llvm::IntegerType *ResType,
-                                               llvm::Value *EmittedE);
+                                               llvm::Value *EmittedE,
+                                               bool IsDynamic);
 
   /// Emits the size of E, as required by __builtin_object_size. This
   /// function is aware of pass_object_size parameters, and will act accordingly
   /// if E is a parameter with the pass_object_size attribute.
   llvm::Value *emitBuiltinObjectSize(const Expr *E, unsigned Type,
                                      llvm::IntegerType *ResType,
-                                     llvm::Value *EmittedE);
+                                     llvm::Value *EmittedE,
+                                     bool IsDynamic);
 
 public:
 #ifndef NDEBUG