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Date:   Fri, 13 Dec 2019 23:19:01 +0200
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Max Filippov <jcmvbkbc@gmail.com>
Cc:     kbuild test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: WARNING: lib/test_bitmap.o(.text.unlikely+0x5c): Section
 mismatch in reference from the function bitmap_copy_clear_tail() to the
 variable .init.rodata:clump_exp
Message-ID: <20191213211901.GL32742@smile.fi.intel.com>
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 <CAMo8BfKhSkHapX=mDhauZz8pAwR+1DtDNL=oE_RNhmaSQ9V_Zw@mail.gmail.com>
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On Fri, Dec 13, 2019 at 01:08:08PM -0800, Max Filippov wrote:
> On Fri, Dec 13, 2019 at 3:16 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Tue, Dec 10, 2019 at 04:17:03AM +0800, kbuild test robot wrote:
> >
> > +Cc: Max for xtensa matters, perhaps he has an idea.
> >
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   e42617b825f8073569da76dc4510bfa019b1c35a
> > > commit: 30544ed5de431fe25d3793e4dd5a058d877c4d77 lib/bitmap: introduce bitmap_replace() helper
> > > date:   5 days ago
> > > config: xtensa-randconfig-a001-20191209 (attached as .config)
> > > compiler: xtensa-linux-gcc (GCC) 7.5.0
> > > reproduce:
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         git checkout 30544ed5de431fe25d3793e4dd5a058d877c4d77
> > >         # save the attached .config to linux build tree
> > >         GCC_VERSION=7.5.0 make.cross ARCH=xtensa
> > >
> > > If you fix the issue, kindly add following tag
> > > Reported-by: kbuild test robot <lkp@intel.com>
> > >
> > > All warnings (new ones prefixed by >>):
> >
> > I'm not sure I got this (esp. relation to my patch).
> > The mentioned code definitely compiled for 32-bit (since only then mentioned
> > bitmap API is in use). I have tried to reproduce on i386 compilation (gcc 9.x),
> > but can't.
> 
> I was able to reproduce it on xtensa with gcc-9.
> The issue comes from the test "test_replace", specifically
> from the following call:
>   bitmap_replace(bmap, &exp2[0], &exp2[1], exp2_to_exp3_mask, nbits);
> 
> An invariable part of the call sequence used here is instantiated in
> the section .text.unlikely with a reference to exp2_to_exp3_mask built
> into it and it's called from the test_replace. It looks like a compiler bug
> to me, I'd expect this code to be emitted to the .init.text, i.e the same
> section where the function it was hoisted from resides.
> And why "unlikely"? This code is definitely executed.
> 
> I'll file a bug against gcc.

Thanks for an analysis and quick response!

-- 
With Best Regards,
Andy Shevchenko