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From:   Jani Nikula <jani.nikula@intel.com>
To:     linux-kernel@vger.kernel.org, workflows@vger.kernel.org,
        linux-kbuild@vger.kernel.org, intel-gfx@lists.freedesktop.org
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Masahiro Yamada <masahiroy@kernel.org>
Subject: __diag_ignore_all(), GCC < 8, extra warnings, and -Werror
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Date:   Wed, 05 Jul 2023 12:54:35 +0300
Message-ID: <87wmzezns4.fsf@intel.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk


For a long time now, i915 has enabled a bunch of W=1 style warnings
locally, and we try hard to keep i915 warning free.

One of the warnings is -Woverride-init from -Wextra. We need to bypass
that in a few cases, and used to do this for the relevant files:

	CFLAGS_file.o = $(call cc-disable-warning, override-init)

Recently, we switched from the above to a more localized version in each
file.c:

	__diag_push();
	__diag_ignore_all("-Woverride-init", "Allow overriding inherited members");
	...
        __diag_pop();

We now got a report that this fails the build with CONFIG_WERROR=y or
W=e when using GCC version < 8. Indeed, __diag_ignore_all() requires GCC
version 8 or later.

Should we now revert back to disabling -Woverride-init on a file
granularity? Should we consider breaking the build for CONFIG_WERROR=y
or W=e on older compilers a regression?

I'll note that with the current usage of __diag_ignore_all() elsewhere
in kernel, CONFIG_WERROR=y or W=e with W=1 will never pass on older
compilers. But then again, it has never passed on any compiler, so it
can't be a regression.


BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center