> QEMU has a funny new build error message when I use the upstream kernel headers:
>
> CC block/file-posix.o
> In file included from /home/cborntra/REPOS/qemu/include/qemu/timer.h:4,
> from /home/cborntra/REPOS/qemu/include/qemu/timed-average.h:29,
> from /home/cborntra/REPOS/qemu/include/block/accounting.h:28,
> from /home/cborntra/REPOS/qemu/include/block/block_int.h:27,
> from /home/cborntra/REPOS/qemu/block/file-posix.c:30:
> /usr/include/linux/swab.h: In function ‘__swab’:
> /home/cborntra/REPOS/qemu/include/qemu/bitops.h:20:34: error: "sizeof" is not defined, evaluates to 0 [-Werror=undef]
> 20 | #define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE)
> | ^~~~~~
> /home/cborntra/REPOS/qemu/include/qemu/bitops.h:20:41: error: missing binary operator before token "("
> 20 | #define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE)
> | ^
> cc1: all warnings being treated as errors
> make: *** [/home/cborntra/REPOS/qemu/rules.mak:69: block/file-posix.o] Error 1
> rm tests/qemu-iotests/socket_scm_helper.o
>
> This was triggered by commit d5767057c9a ("uapi: rename ext2_swab() to swab() and share globally in swab.h")
> This patch is doing
> +#include <asm/bitsperlong.h>
> but it uses BITS_PER_LONG.
>
> The kernel file asm/bitsperlong.h provide only __BITS_PER_LONG.
>
> Let us use the __ variant in swap.h
> Fixes: d5767057c9a ("uapi: rename ext2_swab() to swab() and share globally in swab.h")
> Cc: Yury Norov <yury.norov@xxxxxxxxx>
> Cc: Allison Randal <allison@xxxxxxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: William Breathitt Gray <vilhelm.gray@xxxxxxxxx>
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> ---
> include/uapi/linux/swab.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
> index fa7f97da5b76..7272f85d6d6a 100644
> --- a/include/uapi/linux/swab.h
> +++ b/include/uapi/linux/swab.h
> @@ -135,9 +135,9 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
>
> static __always_inline unsigned long __swab(const unsigned long y)
> {
> -#if BITS_PER_LONG == 64
> +#if __BITS_PER_LONG == 64
> return __swab64(y);
> -#else /* BITS_PER_LONG == 32 */
> +#else /* __BITS_PER_LONG == 32 */
> return __swab32(y);
> #endif
> }
Cc: <stable@xxxxxxxxxxxxxxx> # 4.19.x: 467d12f5:
include/uapi/linux/swab.h: fix userspace breakage
