Compiler Attributes: Add __overloadable for Clang

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@kernel.org>
Cc: llvm@lists.linux.dev
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220208225350.1331628-4-keescook@chromium.org

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index d0c503772061e4e445fad0235031817df09ac5d6..dcaf55f5d1ae9c78878e41252d3949bc86fae11e 100644 (file)
--- 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