linux-kernel - Re: [PATCH] zlib: define get_unaligned16() only when used

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Message-ID: <CAKXUXMxfPqn4hG-QCtQM1qrK7Vck2hHRycb5VZBYHf4-ezkiGA@mail.gmail.com>
Date:   Tue, 24 Nov 2020 13:00:30 +0100
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Tom Rix <trix@...hat.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        kernel-janitors@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zlib: define get_unaligned16() only when used

On Tue, Nov 24, 2020 at 12:56 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Tue, Nov 24, 2020 at 12:51 PM Christoph Hellwig <hch@...radead.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 Since commit acaab7335bd6 ("lib/zlib: remove outdated and incorrect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@...il.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.
>

Jann, Christoph, Arnd, thanks for the advice. I will start to look
into this immediately.

Lukas