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

[Nick Desaulniers]

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)
+# 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)		\
-- 
2.32.0.402.g57bb445576-goog