Messages in this thread | | | From | Paweł Sikora <> | Subject | include/arch/x86/swab.h badness? | Date | Fri, 7 Oct 2011 21:13:09 +0200 |
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Hi,
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)); #endif 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?
BR, Paweł.
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