[PATCH v7 3/8] Compiler Attributes: Add __overloadable for Clang

[Kees Cook]

In order for FORTIFY_SOURCE to use __pass_object_size on an "extern
inline" function, as all the fortified string functions are, the functions
must be marked as being overloadable (i.e. different prototypes due
to the implicitly injected object size arguments). This allows the
__pass_object_size versions to take precedence.

Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: llvm@xxxxxxxxxxxxxxx
Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/compiler_attributes.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index d0c503772061..dcaf55f5d1ae 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -257,6 +257,18 @@
  */
 #define __noreturn                      __attribute__((__noreturn__))
 
+/*
+ * Optional: not supported by gcc.
+ * Optional: not supported by icc.
+ *
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#overloadable
+ */
+#if __has_attribute(__overloadable__)
+# define __overloadable			__attribute__((__overloadable__))
+#else
+# define __overloadable
+#endif
+
 /*
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
  * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
-- 
2.30.2