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

[Uros Bizjak <ubizjak@gmail.com>]

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?!

Uros.

>
> vim +317 lib/bch.c
>
>    313
>    314  static inline int parity(unsigned int x)
>    315  {
>    316  #if __has_builtin(__builtin_parity)
>  > 317          return __builtin_parity(x);
>    318  #else
>    319          /*
>    320           * public domain code snippet, lifted from
>    321           * http://www-graphics.stanford.edu/~seander/bithacks.html
>    322           */
>    323          x ^= x >> 1;
>    324          x ^= x >> 2;
>    325          x = (x & 0x11111111U) * 0x11111111U;
>    326          return (x >> 28) & 1;
>    327  #endif
>    328  }
>    329
>
> --
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