Re: [akpm-mm:mm-nonmm-unstable 52/52] lib/bch.c:317:undefined reference to `__paritydi2'

[Pedro Falcato <pedro.falcato@gmail.com>]

On Fri, Jan 31, 2025 at 1:23 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Fri, Jan 31, 2025 at 2:12 PM kernel test robot <lkp@intel.com> wrote:
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-nonmm-unstable
> > head:   1b9f78ccbffefb107cd92e20cfccd03ff2fa9d0e
> > commit: 1b9f78ccbffefb107cd92e20cfccd03ff2fa9d0e [52/52] lib/bch.c: use __builtin_parity() when available
> > config: arm64-randconfig-002-20250131 (https://download.01.org/0day-ci/archive/20250131/202501312159.l6jNRaYy-lkp@intel.com/config)
> > compiler: aarch64-linux-gcc (GCC) 14.2.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250131/202501312159.l6jNRaYy-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202501312159.l6jNRaYy-lkp@intel.com/
> >
> > All errors (new ones prefixed by >>):
> >
> >    aarch64-linux-ld: lib/bch.o: in function `parity':
> > >> lib/bch.c:317:(.text+0x10e8): undefined reference to `__paritydi2'
> > >> lib/bch.c:317:(.text+0x10e8): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `__paritydi2'
>
> This config for some reason generates a call to the library function.
> But I have tested this with a crosscompiler:
>
>        fmov    s31, w0
>        cnt     v31.8b, v31.8b
>        addv    b31, v31.8b
>        fmov    w0, s31
>        and     w0, w0, 1
>        ret
>
> It looks that __has_builtin() does not mean that there will be no call
> to a library function?!

Yep, __builtin functions aren't strictly required to be inlined and
can generate a library call if the compiler so chooses (how often this
happens depends on the optimization level and architecture).
e.g: https://godbolt.org/z/zKPb9hbaM

-- 
Pedro