include/arch/x86/swab.h badness?

From: PaweÅ Sikora
Date: Fri Oct 07 2011 - 15:13:20 EST


during compiling some byte-order related code for 32-bit x86 which uses glibc's
#include <byteorder.h> i've noticed that __be*_to_cpu uses a generic i386 (ror+xchg) impl.
quick investigation shows that #include <linux/asm/swab.h> sucks a little ;)

please look at the current linux implementation:

static __inline__ __u32 __arch_swab32(__u32 val)
#ifdef __i386__
# ifdef CONFIG_X86_BSWAP
__asm__("bswap %0" : "=r" (val) : "0" (val));
# else
__asm__("xchgb %b0,%h0\n\t" /* swap lower bytes */
"rorl $16,%0\n\t" /* swap words */
"xchgb %b0,%h0" /* swap higher bytes */
: "=q" (val)
: "0" (val));
# endif

#else /* __i386__ */
__asm__("bswapl %0"
: "=r" (val)
: "0" (val));
return val;

in the userspace, the __i386__ is always defined by gcc for any -march=i486/i586/...
and the CONFIG_X86_BSWAP is never defined, so the userspace always ends with inlined
assembly with generic i386 implementation :(

could you please improve this #ifdefs to get bswap opcodes for i486+ ?
maybe the __builtin_bswap* should be used in recent kernel tree?


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