Re: [PATCH 1/2] drm/i915: drop -Wall and related disables from cflags as redundant

[Jani Nikula <jani.nikula@intel.com>]

On Mon, 09 Oct 2023, Nathan Chancellor <nathan@kernel.org> wrote:
> On Sun, Oct 08, 2023 at 12:28:46AM +0900, Masahiro Yamada wrote:
>> On Fri, Oct 6, 2023 at 9:35 PM Jani Nikula <jani.nikula@intel.com> wrote:
>> >
>> > The kernel top level Makefile, and recently scripts/Makefile.extrawarn,
>> > have included -Wall, and the disables -Wno-format-security and
>> > $(call cc-disable-warning,frame-address,) for a very long time. They're
>> > redundant in our local subdir-ccflags-y and can be dropped.
>> >
>> > Cc: Arnd Bergmann <arnd@arndb.de>
>> > Cc: Nick Desaulniers <ndesaulniers@google.com>
>> > Cc: Nathan Chancellor <nathan@kernel.org>
>> > Cc: Masahiro Yamada <masahiroy@kernel.org>
>> > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> 
>> 
>> I made a similar suggestion in the past
>> https://lore.kernel.org/dri-devel/20190515043753.9853-1-yamada.masahiro@socionext.com/
>> 
>> So, I am glad that Intel has decided to de-duplicate the flags.
>> 
>> 
>> 
>> I think you can drop more flags.
>> 
>> For example,
>> 
>>  subdir-ccflags-y += -Wno-sign-compare
>> 
>> 
>> It is set by scripts/Makefile.extrawarn
>> unless W=3 is passed.
>> 
>> 
>> If W=3 is set by a user, -Wsign-compare should be warned
>> as it is the user's request.
>> 
>> 
>> drivers/gpu/drm/i915/Makefile negates W=3.
>> There is no good reason to do so.
>> 
>> 
>> Same applied to
>> 
>> 
>> subdir-ccflags-y += -Wno-shift-negative-value
>
> As I point out in my review of the second patch [1], I am not sure these
> should be dropped because -Wextra turns these warnings back on, at least
> for clang according to this build report [2] and my own testing, so they
> need to be disabled again.

Yeah. The focus is on enabling W=1 warnings by default for i915. I get
that the disables we have to add to achieve that also disable some W=2
and W=3 warnings. But taking all of that into account requires
duplicating even more of Makefile.extrawarn (checking for warning
levels, maintaining parity with the different levels, etc.).

I guess we could check if KBUILD_EXTRA_WARN does not have any of 1, 2,
or 3, but very few places outside of the build system look at
KBUILD_EXTRA_WARN, so feels wrong.

BR,
Jani.


>
> [1]: https://lore.kernel.org/20231006174550.GC3359308@dev-arch.thelio-3990X/
> [2]: https://lore.kernel.org/202310070011.Fji48IBk-lkp@intel.com/
>
> Cheers,
> Nathan.

-- 
Jani Nikula, Intel