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From:   Florian Weimer <fweimer@redhat.com>
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Kees Cook <keescook@chromium.org>,
        Mark Brown <broonie@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vipin Sharma <vipinsh@google.com>,
        Chris Down <chris@chrisdown.name>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Vlastimil Babka <vbabka@suse.cz>,
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Subject: Re: [PATCH] Revert "Enable '-Werror' by default for all kernel builds"
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        <c8fb537f-26e5-b305-6bc5-06f0d27a4029@infradead.org>
        <20210913093256.GA12225@amd>
Date:   Mon, 13 Sep 2021 11:50:31 +0200
In-Reply-To: <20210913093256.GA12225@amd> (Pavel Machek's message of "Mon, 13
        Sep 2021 11:32:56 +0200")
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* Pavel Machek:

> Do we really want developers treat warnings as errors? When the code
> is okay but some random version of gcc dislikes it...

There are some warnings-as-errors which are quite reasonable, like
-Werror=implicit-function-declaration (which we can't make the compiler
default without cleaning up userspace first) and perhaps
-Werror=implicit-int.  Some other warnings can be used to enforce coding
style, and there -Werror could make sense as well (-Werror=vla and
others).

But there are also warnings which are emitted by the GCC middle-end (the
optimizers), and turning on -Werror for those is very problematic.
These warnings are very target-specific and also depend on compiler
version and optimization parameters.  Unfortunately that includes the
buffer size warnings based on function attributes (which would otherwise
be a good fit for the kernel because it uses few external headers).

GCC also lacks a facility to suppress warnings if they concern code that
was introduced during optimization and removed again later
(e.g. inlining, constant propagation, dead code removal).

Thanks,
Florian