[PATCH v2] 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 <ndesau...@google.com>
---
Changes v1 -> v2:
* Use __warning__ rather than warning in __has_attribute check, as per
Nathan.
* Don't sort existing __GCC4_has_attribute_* defines.

include/linux/compiler-gcc.h | 3 ---
include/linux/compiler_attributes.h | 24 ++++++++++++++++++++++++
include/linux/compiler_types.h | 6 ------
3 files changed, 24 insertions(+), 9 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 67c5667f8042..fb08b843ab47 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -30,6 +30,7 @@
# 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___no_caller_saved_registers__ 0
# define __GCC4_has_attribute___noclone__ 1
@@ -39,6 +40,7 @@
# define __GCC4_has_attribute___no_sanitize_undefined__ 1
# define __GCC4_has_attribute___no_sanitize_coverage__ 0
# define __GCC4_has_attribute___fallthrough__ 0
+# define __GCC4_has_attribute___warning__ 1
#endif

/*
@@ -138,6 +140,17 @@
# 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
*
@@ -299,6 +312,17 @@
*/
#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) \
--
2.32.0.554.ge1b32706d8-goog

[Nathan Chancellor]

On 8/2/2021 1:23 PM, 'Nick Desaulniers' via Clang Built Linux 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 <ndesau...@google.com>

Reviewed-by: Nathan Chancellor <nat...@kernel.org>

One comment below, please carry my tag forward in further revisions
unless they are significant.

Are you planning on petitioning for D106030 to be applied to
release/13.x when it is merged into main? If not, this should be updated
to 14.0.0 since that is main's current version.

[Kees Cook]

On Mon, Aug 02, 2021 at 01:23:20PM -0700, 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 <ndesau...@google.com>

I'm looking forward to having this working in Clang! :)

Reviewed-by: Kees Cook <kees...@chromium.org>

--
Kees Cook

[Nick Desaulniers]

Ah, I forgot the release/13.x branch was cut before I sent this. I'd
rather this feature "ride the trains" so that it gets more soak time.

Miguel, would you like a v3 updating the comment above (and the
comment below) to s/13.0/14.0/g, or can you simply fold that change
into this one when applying it?

--
Thanks,
~Nick Desaulniers

[Miguel Ojeda]

On Wed, Aug 4, 2021 at 7:44 PM Nick Desaulniers <ndesau...@google.com> wrote:
>
> Ah, I forgot the release/13.x branch was cut before I sent this. I'd
> rather this feature "ride the trains" so that it gets more soak time.
>
> Miguel, would you like a v3 updating the comment above (and the
> comment below) to s/13.0/14.0/g, or can you simply fold that change
> into this one when applying it?

I can do the replacements on my side, no worries!

Cheers,
Miguel

[Nick Desaulniers]

Bump, this has landed in llvm 14 (so needs a fixup when applying locally).
--
Thanks,
~Nick Desaulniers