linux-kernel - Re: [PATCH] drm/i915: drop unneeded -Wall addition

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Date:   Wed, 15 May 2019 07:23:12 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        intel-gfx@...ts.freedesktop.org
Cc:     Dave Airlie <airlied@...hat.com>, Sam Ravnborg <sam@...nborg.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/i915: drop unneeded -Wall addition

Quoting Masahiro Yamada (2019-05-15 05:37:53)
> The top level Makefile adds -Wall globally:
> 
>   KBUILD_CFLAGS   := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
> 
> I see two "-Wall" added for compiling under drivers/gpu/drm/i915/.

Does it matter? Is the statement in i915/Makefile not more complete for
saying "-Wall -Wextra -Werror"?

> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
> BTW, I have a question in the comment:
> 
>  "Note the danger in using -Wall -Wextra is that when CI updates gcc we
>   will most likely get a sudden build breakage... Hopefully we will fix
>   new warnings before CI updates!"
> 
> Enabling whatever warning options does not cause build breakage.
> -Werror does.
> 
> So, I think the correct statement is:
> 
>  "Note the danger in using -Werror is that when CI updates gcc we ...

No. CI enforces -Werror and that is constant, so the uncontrolled
variable, the danger, lies in using the unreliable heuristics gcc may
arbitrary enable between versions. That the set of warnings causing an
error may be different between CI and the developer.
-Chris