From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: [PATCH, RFT] byteswap: try to avoid __builtin_constant_p gcc bug Date: Thu, 28 Apr 2016 00:00:36 +0200 Message-ID: <25937441.NbUvhTZ9vo@wuerfel> References: <20160419085221.GA29087@gmail.com> <5298237.1Guzp0G04x@wuerfel> <20160427110503.GB24887@virgil.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20160427110503.GB24887@virgil.suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Martin Jambor Cc: "Martin K. Petersen" , James Bottomley , Josh Poimboeuf , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Denys Vlasenko , Thomas Graf , Peter Zijlstra , David Rientjes , Andrew Morton , Ingo Molnar , Himanshu Madhani , qla2xxx-upstream@qlogic.com, Jan Hubicka List-Id: linux-scsi@vger.kernel.org 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 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