[PATCH v3] Compiler Attributes: remove CONFIG_ENABLE_MUST_CHECK

[Nick Desaulniers]

On Sat, Nov 28, 2020 at 11:34 AM Masahiro Yamada <masahiroy at kernel.org> wrote:
>
> Revert commit cebc04ba9aeb ("add CONFIG_ENABLE_MUST_CHECK").
>
> A lot of warn_unused_result warnings existed in 2006, but until now
> they have been fixed thanks to people doing allmodconfig tests.
>
> Our goal is to always enable __must_check where appropriate, so this
> CONFIG option is no longer needed.
>
> I see a lot of defconfig (arch/*/configs/*_defconfig) files having:
>
>     # CONFIG_ENABLE_MUST_CHECK is not set
>
> I did not touch them for now since it would be a big churn. If arch
> maintainers want to clean them up, please go ahead.
>
> While I was here, I also moved __must_check to compiler_attributes.h
> from compiler_types.h
>
> Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
> Acked-by: Jason A. Donenfeld <Jason at zx2c4.com>

Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>

> ---
>
> Changes in v3:
>   - Fix a typo
>
> Changes in v2:
>   - Move __must_check to compiler_attributes.h
>
>  include/linux/compiler_attributes.h                 | 7 +++++++
>  include/linux/compiler_types.h                      | 6 ------
>  lib/Kconfig.debug                                   | 8 --------
>  tools/testing/selftests/wireguard/qemu/debug.config | 1 -
>  4 files changed, 7 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index b2a3f4f641a7..5f3b7edad1a7 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -171,6 +171,13 @@
>   */
>  #define __mode(x)                       __attribute__((__mode__(x)))
>
> +/*
> + *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
> + *
> + */
> +#define __must_check                    __attribute__((__warn_unused_result__))
> +
>  /*
>   * Optional: only supported since gcc >= 7
>   *
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index ac3fa37a84f9..7ef20d1a6c28 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -110,12 +110,6 @@ struct ftrace_likely_data {
>         unsigned long                   constant;
>  };
>
> -#ifdef CONFIG_ENABLE_MUST_CHECK
> -#define __must_check           __attribute__((__warn_unused_result__))
> -#else
> -#define __must_check
> -#endif
> -
>  #if defined(CC_USING_HOTPATCH)
>  #define notrace                        __attribute__((hotpatch(0, 0)))
>  #elif defined(CC_USING_PATCHABLE_FUNCTION_ENTRY)
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index c789b39ed527..cb8ef4fd0d02 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -286,14 +286,6 @@ config GDB_SCRIPTS
>
>  endif # DEBUG_INFO
>
> -config ENABLE_MUST_CHECK
> -       bool "Enable __must_check logic"
> -       default y
> -       help
> -         Enable the __must_check logic in the kernel build.  Disable this to
> -         suppress the "warning: ignoring return value of 'foo', declared with
> -         attribute warn_unused_result" messages.
> -
>  config FRAME_WARN
>         int "Warn for stack frames larger than"
>         range 0 8192
> diff --git a/tools/testing/selftests/wireguard/qemu/debug.config b/tools/testing/selftests/wireguard/qemu/debug.config
> index b50c2085c1ac..fe07d97df9fa 100644
> --- a/tools/testing/selftests/wireguard/qemu/debug.config
> +++ b/tools/testing/selftests/wireguard/qemu/debug.config
> @@ -1,5 +1,4 @@
>  CONFIG_LOCALVERSION="-debug"
> -CONFIG_ENABLE_MUST_CHECK=y
>  CONFIG_FRAME_POINTER=y
>  CONFIG_STACK_VALIDATION=y
>  CONFIG_DEBUG_KERNEL=y
> --
> 2.27.0
>


-- 
Thanks,
~Nick Desaulniers