Re: [PATCH] compiler_attributes.h: move __compiletime_{error|warning}

From: Nathan Chancellor
Date: Tue Jul 20 2021 - 15:07:48 EST


On 7/20/2021 11:04 AM, Nick Desaulniers wrote:
I'm working on adding support for __attribute__((__error__(""))) and
__attribute__((__warning__(""))) to Clang. To make use of these in
__compiletime_error and __compiletime_warning (as used by BUILD_BUG and
friends) for newer clang and detect/fallback for older versions of
clang, move these to compiler_attributes.h and guard them with
__has_attribute preprocessor guards.

Link: https://reviews.llvm.org/D106030
Link: https://bugs.llvm.org/show_bug.cgi?id=16428
Link: https://github.com/ClangBuiltLinux/linux/issues/1173
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
Note that this feature hasn't landed yet in clang! I expect it to land
in clang-13 though soon. We can still move this in anticipation of the
feature landing, though perhaps the versions might not be precise if it
slips to clang-14 (though I don't anticipate that).

include/linux/compiler-gcc.h | 3 ---
include/linux/compiler_attributes.h | 30 ++++++++++++++++++++++++++---
include/linux/compiler_types.h | 6 ------
3 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index cb9217fc60af..21c36b69eb06 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -43,9 +43,6 @@
#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
-#define __compiletime_warning(message) __attribute__((__warning__(message)))
-#define __compiletime_error(message) __attribute__((__error__(message)))
-
#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
#define __latent_entropy __attribute__((latent_entropy))
#endif
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 2487be0e7199..5f474b593425 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -30,14 +30,16 @@
# define __GCC4_has_attribute___assume_aligned__ 1
# define __GCC4_has_attribute___copy__ 0
# define __GCC4_has_attribute___designated_init__ 0
+# define __GCC4_has_attribute___error__ 1
# define __GCC4_has_attribute___externally_visible__ 1
+# define __GCC4_has_attribute___fallthrough__ 0
# define __GCC4_has_attribute___no_caller_saved_registers__ 0
-# define __GCC4_has_attribute___noclone__ 1
# define __GCC4_has_attribute___no_profile_instrument_function__ 0
-# define __GCC4_has_attribute___nonstring__ 0
# define __GCC4_has_attribute___no_sanitize_address__ 1
# define __GCC4_has_attribute___no_sanitize_undefined__ 1
-# define __GCC4_has_attribute___fallthrough__ 0
+# define __GCC4_has_attribute___noclone__ 1
+# define __GCC4_has_attribute___nonstring__ 0
+# define __GCC4_has_attribute___warning__ 1
#endif
/*
@@ -137,6 +139,17 @@
# define __designated_init
#endif
+/*
+ * Optional: only supported since clang >= 13.0
+ *
+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
+ */
+#if __has_attribute(__error__)
+# define __compiletime_error(msg) __attribute__((__error__(msg)))
+#else
+# define __compiletime_error(msg)
+#endif
+
/*
* Optional: not supported by clang
*
@@ -298,6 +311,17 @@
*/
#define __must_check __attribute__((__warn_unused_result__))
+/*
+ * Optional: only supported since clang >= 13.0
+ *
+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
+ */
+#if __has_attribute(warning)

Should this be

#if __has_attribute(__warning__)

?

+# define __compiletime_warning(msg) __attribute__((__warning__(msg)))
+#else
+# define __compiletime_warning(msg)
+#endif
+
/*
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index e4ea86fc584d..b6ff83a714ca 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -294,12 +294,6 @@ struct ftrace_likely_data {
#ifndef __compiletime_object_size
# define __compiletime_object_size(obj) -1
#endif
-#ifndef __compiletime_warning
-# define __compiletime_warning(message)
-#endif
-#ifndef __compiletime_error
-# define __compiletime_error(message)
-#endif
#ifdef __OPTIMIZE__
# define __compiletime_assert(condition, msg, prefix, suffix) \