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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 20 Jul 2021 13:56:51 -0700
Message-ID: <CAKwvOd=Lh4mLjcNKLn_-s2249zpuEY_ijC6sijRY9QaWSNVvYA@mail.gmail.com>
Subject: Re: [PATCH] compiler_attributes.h: move __compiletime_{error|warning}
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Marco Elver <elver@google.com>, Will Deacon <will@kernel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Sami Tolvanen <samitolvanen@google.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com
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On Tue, Jul 20, 2021 at 12:07 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> 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@google.com>
> > ---
> > 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__)
>
> ?

Yes. :-X

>
> > +# 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)               \
> >


-- 
Thanks,
~Nick Desaulniers