[Xen-devel] [PATCH] x86-32: use __builtin_{memcpy,memset}

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

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.

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__ */

Attachment: x86-memcpy.patch
Description: Text document

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