On 11/05/2010 10:05, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> Following a change in Linux 2.6.33, make x86-32 always use
> __builtin_mem{cpy,set}() on gcc 4.0+. This particularly works around
> certain intermediate gcc revisions generating out-of-range-array-index
> warnings with the current inline implementation.
>
> It may be worthwhile considering to make this the case for x86-64 too.
>
> At the same time eliminate the redundant inline assembly in the C
> file, and instead use the inline functions coming from the header.
Hm, well, I hate having to change this stuff as we always seem to end up
broken on some gcc or other. But otoh this will eliminate a bunch of code if
we do this unconditionally, and I'm particularly not keen on doing this only
for x86-32 and particular versions of gcc. I suggest the attached patch: it
should work fine so long as all our supported versions of gcc have
__builtin_memcpy and __builtin_memset. Given we nowadays only support GCC
3.4+, I imagine we are okay in this regard.
What do you think to this alternative patch?
-- Keir
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>
> --- 2010-05-04.orig/xen/arch/x86/string.c 2007-11-26 16:57:03.000000000 +0100
> +++ 2010-05-04/xen/arch/x86/string.c 2010-05-11 09:45:27.000000000 +0200
> @@ -11,44 +11,13 @@
> #undef memcpy
> void *memcpy(void *dest, const void *src, size_t n)
> {
> - long d0, d1, d2;
> -
> - asm volatile (
> -#ifdef __i386__
> - " rep movsl ; "
> -#else
> - " rep movsq ; "
> - " testb $4,%b4 ; "
> - " je 0f ; "
> - " movsl ; "
> - "0: ; "
> -#endif
> - " testb $2,%b4 ; "
> - " je 1f ; "
> - " movsw ; "
> - "1: testb $1,%b4 ; "
> - " je 2f ; "
> - " movsb ; "
> - "2: "
> - : "=&c" (d0), "=&D" (d1), "=&S" (d2)
> - : "0" (n/sizeof(long)), "q" (n), "1" (dest), "2" (src)
> - : "memory");
> -
> - return dest;
> + return __variable_memcpy(dest, src, n);
> }
>
> #undef memset
> void *memset(void *s, int c, size_t n)
> {
> - long d0, d1;
> -
> - asm volatile (
> - "rep stosb"
> - : "=&c" (d0), "=&D" (d1)
> - : "a" (c), "1" (s), "0" (n)
> - : "memory");
> -
> - return s;
> + return __memset_generic(s, c, n);
> }
>
> #undef memmove
> --- 2010-05-04.orig/xen/include/asm-x86/string.h 2009-10-07 13:31:36.000000000
> +0200
> +++ 2010-05-04/xen/include/asm-x86/string.h 2010-05-11 10:21:04.000000000
> +0200
> @@ -16,6 +16,11 @@ static inline void *__variable_memcpy(vo
> return to;
> }
>
> +#define __HAVE_ARCH_MEMCPY
> +#if defined(__i386__) && __GNUC__ >= 4
> +#define memcpy(t, f, n) __builtin_memcpy(t, f, n)
> +#else
> +
> /*
> * This looks horribly ugly, but the compiler can optimize it totally,
> * as the count is constant.
> @@ -95,7 +100,6 @@ static always_inline void * __constant_m
> return to;
> }
>
> -#define __HAVE_ARCH_MEMCPY
> /* align source to a 64-bit boundary */
> static always_inline
> void *__var_memcpy(void *t, const void *f, size_t n)
> @@ -121,11 +125,13 @@ void *__memcpy(void *t, const void *f, s
> __var_memcpy((t),(f),(n)));
> }
>
> +#endif /* !__i386__ || __GNUC__ < 4 */
> +
> /* Some version of gcc don't have this builtin. It's non-critical anyway. */
> #define __HAVE_ARCH_MEMMOVE
> extern void *memmove(void *dest, const void *src, size_t n);
>
> -static inline void *__memset_generic(void *s, char c, size_t count)
> +static inline void *__memset_generic(void *s, int c, size_t count)
> {
> long d0, d1;
> __asm__ __volatile__ (
> @@ -134,6 +140,11 @@ static inline void *__memset_generic(voi
> return s;
> }
>
> +#define __HAVE_ARCH_MEMSET
> +#if defined(__i386__) && __GNUC__ >= 4
> +#define memset(s, c, n) __builtin_memset(s, c, n)
> +#else
> +
> /* we might want to write optimized versions of these later */
> #define __constant_count_memset(s,c,count) __memset_generic((s),(c),(count))
>
> @@ -238,11 +249,12 @@ static always_inline void *__constant_c_
> #define MEMSET_PATTERN_MUL 0x01010101UL
> #endif
>
> -#define __HAVE_ARCH_MEMSET
> #define memset(s, c, count) (__memset((s),(c),(count)))
> #define __memset(s, c, count) \
> (__builtin_constant_p(c) ? \
> __constant_c_x_memset((s),(MEMSET_PATTERN_MUL*(unsigned char)(c)),(count)) :
> \
> __var_x_memset((s),(c),(count)))
>
> +#endif /* !__i386__ || __GNUC__ < 4 */
> +
> #endif /* __X86_STRING_H__ */
>
>
>
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