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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Tue, 24 Nov 2020 12:56:30 +0100
Message-ID: <CAK8P3a2rVKQ5UHzcycu=0QpjtSQ3Nne4Xre-7+V27vmCe9yfKg@mail.gmail.com>
Subject: Re: [PATCH] zlib: define get_unaligned16() only when used
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jann Horn <jannh@google.com>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>, Tom Rix <trix@redhat.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        kernel-janitors@vger.kernel.org,
        kernel list <linux-kernel@vger.kernel.org>
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Precedence: bulk

On Tue, Nov 24, 2020 at 12:51 PM Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Nov 24, 2020 at 12:08:40PM +0100, Jann Horn wrote:
> > > Since commit acaab7335bd6 ("lib/zlib: remove outdated and incorrect
> > > pre-increment optimization"), get_unaligned16() is only used when
> > > !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
> > >
> > > Hence, make CC=clang W=1 warns:
> > >
> > >   lib/zlib_inflate/inffast.c:20:1:
> > >     warning: unused function 'get_unaligned16' [-Wunused-function]
> > >
> > > Define get_unaligned16() only when it is actually used.
> > >
> > > Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
> >
> > AFAICS a nicer option would be to "#include <asm/unaligned.h>" and
> > then use "get_unaligned", which should automatically do the right
> > thing everywhere and remove the need for defining get_unaligned16()
> > and checking CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS entirely?
>
> Yes, that is the right thing to do.

It's possible that this didn't work when the code was originally added:
The decompressor functions are called from the compressed boot path,
which is a bit limited regarding which headers it can include, at least
on some architectures.

I would recommend test-building this for all architectures that include
../../../../lib/decompress_inflate.c from their boot code.

     Arnd