[PATCH v3 4/9] s390/string: Convert memmove() to C

[Heiko Carstens <hca@linux.ibm.com>]

Convert memmove() from assembler to C, which should make it easier to
read and change, if required. And it allows the compiler to optimize
the code, and use different instructions, except for the used inline
assemblies.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/lib/mem.S    | 41 -------------------------------------
 arch/s390/lib/string.c | 46 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 41 deletions(-)

diff --git a/arch/s390/lib/mem.S b/arch/s390/lib/mem.S
index d026debf250c..712b955ea9b4 100644
--- a/arch/s390/lib/mem.S
+++ b/arch/s390/lib/mem.S
@@ -11,47 +11,6 @@
 
 	GEN_BR_THUNK %r14
 
-/*
- * void *memmove(void *dest, const void *src, size_t n)
- */
-SYM_FUNC_START(__memmove)
-	ltgr	%r4,%r4
-	lgr	%r1,%r2
-	jz	.Lmemmove_exit
-	aghi	%r4,-1
-	clgr	%r2,%r3
-	jnh	.Lmemmove_forward
-	la	%r5,1(%r4,%r3)
-	clgr	%r2,%r5
-	jl	.Lmemmove_reverse
-.Lmemmove_forward:
-	srlg	%r0,%r4,8
-	ltgr	%r0,%r0
-	jz	.Lmemmove_forward_remainder
-.Lmemmove_forward_loop:
-	mvc	0(256,%r1),0(%r3)
-	la	%r1,256(%r1)
-	la	%r3,256(%r3)
-	brctg	%r0,.Lmemmove_forward_loop
-.Lmemmove_forward_remainder:
-	exrl	%r4,.Lmemmove_mvc
-.Lmemmove_exit:
-	BR_EX	%r14
-.Lmemmove_reverse:
-	ic	%r0,0(%r4,%r3)
-	stc	%r0,0(%r4,%r1)
-	brctg	%r4,.Lmemmove_reverse
-	ic	%r0,0(%r4,%r3)
-	stc	%r0,0(%r4,%r1)
-	BR_EX	%r14
-.Lmemmove_mvc:
-	mvc	0(1,%r1),0(%r3)
-SYM_FUNC_END(__memmove)
-EXPORT_SYMBOL(__memmove)
-
-SYM_FUNC_ALIAS(memmove, __memmove)
-EXPORT_SYMBOL(memmove)
-
 /*
  * memset implementation
  *
diff --git a/arch/s390/lib/string.c b/arch/s390/lib/string.c
index 757f58960198..66286d486ef8 100644
--- a/arch/s390/lib/string.c
+++ b/arch/s390/lib/string.c
@@ -17,6 +17,52 @@
 #include <linux/export.h>
 #include <asm/asm.h>
 
+#define SYMBOL_FUNCTION_ALIAS(alias, name)		\
+asm(".globl " __stringify(alias) "\n\t"			\
+    ".set   " __stringify(alias) "," __stringify(name))
+
+#ifdef __HAVE_ARCH_MEMMOVE
+noinstr void *__memmove(void *dest, const void *src, size_t n)
+{
+	const char *s = src;
+	char *d = dest;
+
+	if (!n)
+		return dest;
+	if ((d <= s || d >= s + n)) {
+		/* Forward copy */
+		while (n >= 256) {
+			asm volatile(
+				"	mvc	0(256,%[d]),0(%[s])\n"
+				:
+				: [d] "a" (d), [s] "a" (s)
+				: "memory");
+			d += 256;
+			s += 256;
+			n -= 256;
+		}
+		if (n) {
+			asm volatile(
+				"	exrl	%[n],0f\n"
+				"	j	1f\n"
+				"0:	mvc	0(1,%[d]),0(%[s])\n"
+				"1:"
+				:
+				: [d] "a" (d), [s] "a" (s), [n] "a" (n - 1)
+				: "memory");
+		}
+	} else {
+		/* Backward copy */
+		while (n--)
+			d[n] = s[n];
+	}
+	return dest;
+}
+SYMBOL_FUNCTION_ALIAS(memmove, __memmove);
+EXPORT_SYMBOL(__memmove);
+EXPORT_SYMBOL(memmove);
+#endif
+
 /*
  * Helper functions to find the end of a string
  */
-- 
2.53.0