linux-kernel - Re: [PATCH] Compiler Attributes: counted_by: Adjust name and identifier expansion

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Message-ID: <20230817201304.GA2714089@dev-arch.thelio-3990X>
Date:   Thu, 17 Aug 2023 13:13:04 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Compiler Attributes: counted_by: Adjust name and
 identifier expansion

On Thu, Aug 17, 2023 at 01:06:03PM -0700, Kees Cook wrote:
> GCC and Clang's current RFCs name this attribute "counted_by", and have
> moved away from using a string for the member name. Update the kernel's
> macros to match. Additionally provide a UAPI no-op macro for UAPI structs
> that will gain annotations.
> 
> Cc: Miguel Ojeda <ojeda@...nel.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Fixes: dd06e72e68bc ("Compiler Attributes: Add __counted_by macro")
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

One comment below.

> ---
>  include/linux/compiler_attributes.h | 26 +++++++++++++-------------
>  include/uapi/linux/stddef.h         |  4 ++++
>  2 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 00efa35c350f..74716a407aac 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -94,6 +94,19 @@
>  # define __copy(symbol)
>  #endif
>  
> +/*
> + * Optional: only supported since gcc >= 14
> + * Optional: only supported since clang >= 17

Since you are in the area, should the supported clang version be
optimistically updated to '18'? 17.x has already branched and I suspect
it would be too late in the release cycle to cherry-pick that change
from main if it were landed today (which seems pretty unlikely, given
there do not appear to be many reviews from high profile clang folks
yet).

> + *
> + *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> + * clang: https://reviews.llvm.org/D148381
> + */
> +#if __has_attribute(__counted_by__)
> +# define __counted_by(member)		__attribute__((__counted_by__(member)))
> +#else
> +# define __counted_by(member)
> +#endif
> +
>  /*
>   * Optional: not supported by gcc
>   * Optional: only supported since clang >= 14.0
> @@ -129,19 +142,6 @@
>  # define __designated_init
>  #endif
>  
> -/*
> - * Optional: only supported since gcc >= 14
> - * Optional: only supported since clang >= 17
> - *
> - *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
> - * clang: https://reviews.llvm.org/D148381
> - */
> -#if __has_attribute(__element_count__)
> -# define __counted_by(member)		__attribute__((__element_count__(#member)))
> -#else
> -# define __counted_by(member)
> -#endif
> -
>  /*
>   * Optional: only supported since clang >= 14.0
>   *
> diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
> index 7837ba4fe728..7c3fc3980881 100644
> --- a/include/uapi/linux/stddef.h
> +++ b/include/uapi/linux/stddef.h
> @@ -45,3 +45,7 @@
>  		TYPE NAME[]; \
>  	}
>  #endif
> +
> +#ifndef __counted_by
> +#define __counted_by(m)
> +#endif
> -- 
> 2.34.1
>