s390: provide memmove implementation

Provide an s390 specific memmove implementation which is faster than
the generic implementation which copies byte-wise.

For non-destructive (as defined by the mvc instruction) memmove
operations the following table compares the old default implementation
versus the new s390 specific implementation:

size     old   new
   1     1ns   8ns
   2     2ns   8ns
   4     4ns   8ns
   8     7ns   8ns
  16    17ns   8ns
  32    35ns   8ns
  64    65ns   9ns
 128   146ns  10ns
 256   298ns  11ns
 512   537ns  11ns
1024  1193ns  19ns
2048  2405ns  36ns

So only for very small sizes the old implementation is faster. For
overlapping memmoves, where the mvc instruction can't be used, the new
implementation is as slow as the old one.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/string.h

@@ -14,6 +14,7 @@
 #define __HAVE_ARCH_MEMCHR	/* inline & arch function */
 #define __HAVE_ARCH_MEMCMP	/* arch function */
 #define __HAVE_ARCH_MEMCPY	/* gcc builtin & arch function */
+#define __HAVE_ARCH_MEMMOVE	/* gcc builtin & arch function */
 #define __HAVE_ARCH_MEMSCAN	/* inline & arch function */
 #define __HAVE_ARCH_MEMSET	/* gcc builtin & arch function */
 #define __HAVE_ARCH_STRCAT	/* inline & arch function */
@@ -32,6 +33,7 @@
 extern int memcmp(const void *, const void *, size_t);
 extern void *memcpy(void *, const void *, size_t);
 extern void *memset(void *, int, size_t);
+extern void *memmove(void *, const void *, size_t);
 extern int strcmp(const char *,const char *);
 extern size_t strlcat(char *, const char *, size_t);
 extern size_t strlcpy(char *, const char *, size_t);
@@ -40,7 +42,6 @@ extern char *strncpy(char *, const char *, size_t);
 extern char *strrchr(const char *, int);
 extern char *strstr(const char *, const char *);
 
-#undef __HAVE_ARCH_MEMMOVE
 #undef __HAVE_ARCH_STRCHR
 #undef __HAVE_ARCH_STRNCHR
 #undef __HAVE_ARCH_STRNCMP

arch/s390/lib/mem.S

@@ -7,6 +7,45 @@
 #include <linux/linkage.h>
 #include <asm/export.h>
 
+/*
+ * void *memmove(void *dest, const void *src, size_t n)
+ */
+ENTRY(memmove)
+	ltgr	%r4,%r4
+	lgr	%r1,%r2
+	bzr	%r14
+	clgr	%r2,%r3
+	jnh	.Lmemmove_forward
+	la	%r5,0(%r4,%r3)
+	clgr	%r2,%r5
+	jl	.Lmemmove_reverse
+.Lmemmove_forward:
+	aghi	%r4,-1
+	srlg	%r0,%r4,8
+	ltgr	%r0,%r0
+	jz	.Lmemmove_rest
+.Lmemmove_loop:
+	mvc	0(256,%r1),0(%r3)
+	la	%r1,256(%r1)
+	la	%r3,256(%r3)
+	brctg	%r0,.Lmemmove_loop
+.Lmemmove_rest:
+	larl	%r5,.Lmemmove_mvc
+	ex	%r4,0(%r5)
+	br	%r14
+.Lmemmove_reverse:
+	aghi	%r4,-1
+.Lmemmove_reverse_loop:
+	ic	%r0,0(%r4,%r3)
+	stc	%r0,0(%r4,%r1)
+	brctg	%r4,.Lmemmove_reverse_loop
+	ic	%r0,0(%r4,%r3)
+	stc	%r0,0(%r4,%r1)
+	br	%r14
+.Lmemmove_mvc:
+	mvc	0(1,%r1),0(%r3)
+EXPORT_SYMBOL(memmove)
+
 /*
  * memset implementation
  *