Re: [PATCH bpf-next v4 6/8] compiler_types.h: Add unified __diag_ignore_all for GCC/LLVM

[Nick Desaulniers <ndesaulniers@google.com>]

On Sat, Mar 05, 2022 at 04:16:43AM +0530, Kumar Kartikeya Dwivedi wrote:
> Add a __diag_ignore_all macro, to ignore warnings for both GCC and LLVM,
> without having to specify the compiler type and version. By default, GCC
> 8 and clang 11 are used. This will be used by bpf subsystem to ignore
> -Wmissing-prototypes warning for functions that are meant to be global
> functions so that they are in vmlinux BTF, but don't have a prototype.
> 
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  include/linux/compiler-clang.h | 3 +++
>  include/linux/compiler-gcc.h   | 3 +++
>  include/linux/compiler_types.h | 4 ++++
>  3 files changed, 10 insertions(+)
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index f1aa41d520bd..babb1347148c 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -90,3 +90,6 @@
>  #else
>  #define __diag_clang_11(s)
>  #endif
> +
> +#define __diag_ignore_all(option, comment) \
> +	__diag_clang(11, ignore, option)
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index ccbbd31b3aae..d364c98a4a80 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -151,6 +151,9 @@
>  #define __diag_GCC_8(s)
>  #endif
>  
> +#define __diag_ignore_all(option, comment) \
> +	__diag_GCC(8, ignore, option)

While this approach will work for clang, it doesn't seem scalable for
GCC. Documentation/process/changes.rst documents that we support gcc
5.1+. This approach will only disable diagnostics for gcc 8+.

> +
>  /*
>   * Prior to 9.1, -Wno-alloc-size-larger-than (and therefore the "alloc_size"
>   * attribute) do not work, and must be disabled.
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 3f31ff400432..8e5d2f50f951 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -371,4 +371,8 @@ struct ftrace_likely_data {
>  #define __diag_error(compiler, version, option, comment) \
>  	__diag_ ## compiler(version, error, option)
>  
> +#ifndef __diag_ignore_all
> +#define __diag_ignore_all(option, comment)
> +#endif
> +
>  #endif /* __LINUX_COMPILER_TYPES_H */
> -- 
> 2.35.1
>