On Mon, 9 Oct 2017 10:40:49 +0200, Geert Uytterhoeven wrote:
> On most architectures[*], gcc turns __builtin_ffsll() into a call to
> __ffsdi2(), which is not provided by any architecture, leading to
> failures like:
>
> rcar-gen3-cpg.c:(.text+0x289): undefined reference to `__ffsdi2'
>
> To fix this, use __ffs64() instead, which is available on all
> architectures.
>
> [*] Known exceptions are some 64-bit architectures like amd64, arm64,
> ia64, powerpc64, and tilegx.
>
> Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
> Fixes: 3e9b3112ec74f192 ("add basic register-field manipulation macros")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> include/linux/bitfield.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 8b9d6fff002db113..0a827677372756fa 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -15,6 +15,7 @@
> #ifndef _LINUX_BITFIELD_H
> #define _LINUX_BITFIELD_H
>
> +#include <linux/bitops.h>
> #include <linux/bug.h>
>
> /*
> @@ -46,7 +47,7 @@
> * reg |= FIELD_PREP(REG_FIELD_C, c);
> */
>
> -#define __bf_shf(x) (__builtin_ffsll(x) - 1)
> +#define __bf_shf(x) __ffs64(x)
Hm. The build bot failure made me think. I think rcar-gen3-cpg.c may
be doing something wrong here, could you point me at the patch in
question? I don't see any FIELD_* there in Linus's tree.
__bf_shf() is supposed to be used with constant masks only, therefore
the call must be optimized away completely.
> #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \
> ({ \
