[RFC] arm: use built-in byte swap function
From: Russell King - ARM Linux <hidden>
Date: 2013-01-31 09:28:51
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On Wed, Jan 30, 2013 at 08:09:00PM -0600, Kim Phillips wrote:
The savings come mostly from device-tree related code, and some from drivers.
You forget that IP networking is all big endian, so these will be using the byte swapping too (search it for htons/ntohs/htonl/ntohl).
v2: - at91 and lpd270 builds fixed by limiting to ARMv6 and above (i.e., ARM cores that have support for the 'rev' instruction). Otherwise, the compiler emits calls to libgcc's __bswapsi2 on these ARMv4/v5 builds (and arch ARM doesn't link with libgcc).
Which compiler version? gcc 4.5.4 doesn't do this, except for the 16-bit swap, so I doubt that any later compiler does.
quoted hunk ↗ jump to hunk
--- a/arch/arm/include/uapi/asm/swab.h +++ b/arch/arm/include/uapi/asm/swab.h@@ -50,4 +50,14 @@ static inline __attribute_const__ __u32 __arch_swab32(__u32 x) #endif +#if defined(__KERNEL__) && __LINUX_ARM_ARCH__ >= 6 +#if GCC_VERSION >= 40600 +#define __HAVE_BUILTIN_BSWAP32__ +#define __HAVE_BUILTIN_BSWAP64__ +#endif +#if GCC_VERSION >= 40800 +#define __HAVE_BUILTIN_BSWAP16__ +#endif +#endif
If this is __KERNEL__ only, it should not be in a uapi header. UAPI headers get exported to userland, this is not userland interface code. IT should be in arch/arm/include/asm/swab.h