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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 18 Nov 2021 08:57:49 -0800
Message-ID: <CANn89i+K6=Kc0weayD_phAPn9YT=2UUje+1BZfg=kUiLp7ELqQ@mail.gmail.com>
Subject: Re: [tip:x86/core 1/1] arch/x86/um/../lib/csum-partial_64.c:98:12:
 error: implicit declaration of function 'load_unaligned_zeropad'
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        kernel test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Alexander Duyck <alexanderduyck@fb.com>,
        linux-um@lists.infradead.org
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Precedence: bulk

On Thu, Nov 18, 2021 at 8:27 AM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Thu, 2021-11-18 at 17:00 +0100, Peter Zijlstra wrote:
> > On Wed, Nov 17, 2021 at 11:40:35AM -0800, Eric Dumazet wrote:
> > > On Wed, Nov 17, 2021 at 10:55 AM Eric Dumazet <edumazet@google.com> wrote:
> > > >
> > > > On Wed, Nov 17, 2021 at 10:46 AM kernel test robot <lkp@intel.com> wrote:
> > > > >
> > > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/core
> > > > > head:   d31c3c683ee668ba5d87c0730610442fd672525f
> > > > > commit: d31c3c683ee668ba5d87c0730610442fd672525f [1/1] x86/csum: Rewrite/optimize csum_partial()
> > > > > config: um-x86_64_defconfig (attached as .config)
> > > > > compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> > > > > reproduce (this is a W=1 build):
> > > > >         # https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=d31c3c683ee668ba5d87c0730610442fd672525f
> > > > >         git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
> > > > >         git fetch --no-tags tip x86/core
> > > > >         git checkout d31c3c683ee668ba5d87c0730610442fd672525f
> > > > >         # save the attached .config to linux build tree
> > > > >         make W=1 ARCH=um SUBARCH=x86_64
> > > > >
> > > > > If you fix the issue, kindly add following tag as appropriate
> > > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > >
> > > > > All errors (new ones prefixed by >>):
> > > > >
> > > > >    arch/x86/um/../lib/csum-partial_64.c: In function 'csum_partial':
> > > > > > > arch/x86/um/../lib/csum-partial_64.c:98:12: error: implicit declaration of function 'load_unaligned_zeropad' [-Werror=implicit-function-declaration]
> > > > >       98 |   trail = (load_unaligned_zeropad(buff) << shift) >> shift;
> > > > >          |            ^~~~~~~~~~~~~~~~~~~~~~
> > > > >    cc1: some warnings being treated as errors
> > > > >
> > > > >
> > > >
> > > > Hmmm... it seems we need to guard this with CONFIG_DCACHE_WORD_ACCESS ?
> > >
> > > Perhaps something like the following ?
> >
> > Dear um folks, is this indeed the best solution? It's a bit sad to have
> > to add this to x86_64, but if that's the way it is...
> >
>
> I guess we can add load_unaligned_zeropad() or even just somehow add the
> include with it (asm/word-at-a-time.h) from x86?

Unless fixups can be handled, the signature of the function needs to
be different.

In UM, we would need to provide a number of bytes that can be read.