linux-kernel - Re: [PATCH v2] compiler_attributes.h: move __compiletime

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Date:   Wed, 4 Aug 2021 10:43:51 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Will Deacon <will@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Tom Stellard <tstellar@...hat.com>
Subject: Re: [PATCH v2] compiler_attributes.h: move __compiletime_{error|warning}

On Mon, Aug 2, 2021 at 1:29 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> 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 <ndesaulniers@...gle.com>
>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
>
> One comment below, please carry my tag forward in further revisions
> unless they are significant.
>
> > ---
> > 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
>
> 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.

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?

>
> > + *
> > + *   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)               \
> >



-- 
Thanks,
~Nick Desaulniers