Re: [PATCH] kbuild: Disable two Clang specific enumeration warnings

[Yonghong Song <yonghong.song@linux.dev>]

On 3/5/24 9:42 AM, Nathan Chancellor wrote:
> Clang enables -Wenum-enum-conversion and -Wenum-compare-conditional
> under -Wenum-conversion. A recent change in Clang strengthened these
> warnings and they appear frequently in common builds, primarily due to
> several instances in common headers but there are quite a few drivers
> that have individual instances as well.
>
>    include/linux/vmstat.h:508:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
>      508 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
>          |                            ~~~~~~~~~~~~~~~~~~~~~ ^
>      509 |                            item];
>          |                            ~~~~
>
>    drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c:955:24: warning: conditional expression between different enumeration types ('enum iwl_mac_beacon_flags' and 'enum iwl_mac_beacon_flags_v1') [-Wenum-compare-conditional]
>      955 |                 flags |= is_new_rate ? IWL_MAC_BEACON_CCK
>          |                                      ^ ~~~~~~~~~~~~~~~~~~
>      956 |                           : IWL_MAC_BEACON_CCK_V1;
>          |                             ~~~~~~~~~~~~~~~~~~~~~
>    drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c:1120:21: warning: conditional expression between different enumeration types ('enum iwl_mac_beacon_flags' and 'enum iwl_mac_beacon_flags_v1') [-Wenum-compare-conditional]
>     1120 |                                                0) > 10 ?
>          |                                                        ^
>     1121 |                         IWL_MAC_BEACON_FILS :
>          |                         ~~~~~~~~~~~~~~~~~~~
>     1122 |                         IWL_MAC_BEACON_FILS_V1;
>          |                         ~~~~~~~~~~~~~~~~~~~~~~
>
> While doing arithmetic with different types of enums may be potentially
> problematic, inspecting several instances of the warning does not reveal
> any obvious problems. To silence the warnings at the source level, an
> integral cast must be added to each mismatched enum (which is incredibly
> ugly when done frequently) or the value must moved out of the enum to a
> macro, which can remove the type safety offered by enums in other
> places, such as assignments that would trigger -Wenum-conversion.
>
> As the warnings do not appear to have a high signal to noise ratio and
> the source level silencing options are not sustainable, disable the
> warnings unconditionally, as they will be enabled with -Wenum-conversion
> and are supported in all versions of clang that can build the kernel.
>
> Cc: stable@vger.kernel.org
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2002
> Link: https://github.com/llvm/llvm-project/commit/8c2ae42b3e1c6aa7c18f873edcebff7c0b45a37e
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the fix. LGTM.

Acked-by: Yonghong Song <yonghong.song@linux.dev>