On Thu, Apr 28, 2016 at 12:00:36AM +0200, Arnd Bergmann wrote:
> This is another attempt to avoid a regression in wwn_to_u64()
> after that started using get_unaligned_be64(), which in turn
> ran into a bug on gcc-4.9 through 6.1.
>
> As part of the problem is how __builtin_constant_p gets evaluated
> on an argument passed by reference into an inline function, this
> avoids the use of __builtin_constant_p() for all architectures
> that set CONFIG_ARCH_USE_BUILTIN_BSWAP. Most architectures do not
> set ARCH_SUPPORTS_OPTIMIZED_INLINING, which means they probably
> do not suffer from the problem in the qla2xxx driver, but they
> might still run into it elsewhere.
>
> I have not been able to reproduce the original problem, so I don't
> know if this patch solves it, but at least it leads to simpler
> code doing the same thing, so at least there should be no downsides.
>
> Please test.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Nice patch. I can confirm it fixes the issue with gcc 5.3.1.
Tested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
> index 3f10e5317b46..de56fd54428d 100644
> --- a/include/uapi/linux/swab.h
> +++ b/include/uapi/linux/swab.h
> @@ -45,9 +45,7 @@
>
> static inline __attribute_const__ __u16 __fswab16(__u16 val)
> {
> -#ifdef __HAVE_BUILTIN_BSWAP16__
> - return __builtin_bswap16(val);
> -#elif defined (__arch_swab16)
> +#if defined (__arch_swab16)
> return __arch_swab16(val);
> #else
> return ___constant_swab16(val);
> @@ -56,9 +54,7 @@ static inline __attribute_const__ __u16 __fswab16(__u16 val)
>
> static inline __attribute_const__ __u32 __fswab32(__u32 val)
> {
> -#ifdef __HAVE_BUILTIN_BSWAP32__
> - return __builtin_bswap32(val);
> -#elif defined(__arch_swab32)
> +#if defined(__arch_swab32)
> return __arch_swab32(val);
> #else
> return ___constant_swab32(val);
> @@ -67,9 +63,7 @@ static inline __attribute_const__ __u32 __fswab32(__u32 val)
>
> static inline __attribute_const__ __u64 __fswab64(__u64 val)
> {
> -#ifdef __HAVE_BUILTIN_BSWAP64__
> - return __builtin_bswap64(val);
> -#elif defined (__arch_swab64)
> +#if defined (__arch_swab64)
> return __arch_swab64(val);
> #elif defined(__SWAB_64_THRU_32__)
> __u32 h = val >> 32;
> @@ -102,28 +96,40 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
> * __swab16 - return a byteswapped 16-bit value
> * @x: value to byteswap
> */
> +#ifdef __HAVE_BUILTIN_BSWAP16__
> +#define __swab16(x) __builtin_bswap16((__u16)(x))
> +#else
> #define __swab16(x) \
> (__builtin_constant_p((__u16)(x)) ? \
> ___constant_swab16(x) : \
> __fswab16(x))
> +#endif
>
> /**
> * __swab32 - return a byteswapped 32-bit value
> * @x: value to byteswap
> */
> +#ifdef __HAVE_BUILTIN_BSWAP32__
> +#define __swab32(x) __builtin_bswap32((__u32)(x))
> +#else
> #define __swab32(x) \
> (__builtin_constant_p((__u32)(x)) ? \
> ___constant_swab32(x) : \
> __fswab32(x))
> +#endif
>
> /**
> * __swab64 - return a byteswapped 64-bit value
> * @x: value to byteswap
> */
> +#ifdef __HAVE_BUILTIN_BSWAP64__
> +#define __swab64(x) __builtin_bswap64((__u64)(x))
> +#else
> #define __swab64(x) \
> (__builtin_constant_p((__u64)(x)) ? \
> ___constant_swab64(x) : \
> __fswab64(x))
> +#endif
>
> /**
> * __swahw32 - return a word-swapped 32-bit value
>
--
Josh
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