From 0a8be1f9c7100fff7ef13ad0a82d41b3b18996f9 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Tue, 9 Jun 2026 12:33:39 +0200
Subject: [PATCH] s390/string: Convert memset() to C

Convert memset() 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>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
 arch/s390/lib/mem.S    | 63 ------------------------------------------
 arch/s390/lib/string.c | 61 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 63 deletions(-)

diff --git a/arch/s390/lib/mem.S b/arch/s390/lib/mem.S
index 712b955ea9b4..a27b103d7450 100644
--- a/arch/s390/lib/mem.S
+++ b/arch/s390/lib/mem.S
@@ -11,69 +11,6 @@
 
 	GEN_BR_THUNK %r14
 
-/*
- * memset implementation
- *
- * This code corresponds to the C construct below. We do distinguish
- * between clearing (c == 0) and setting a memory array (c != 0) simply
- * because nearly all memset invocations in the kernel clear memory and
- * the xc instruction is preferred in such cases.
- *
- * void *memset(void *s, int c, size_t n)
- * {
- *	if (likely(c == 0))
- *		return __builtin_memset(s, 0, n);
- *	return __builtin_memset(s, c, n);
- * }
- */
-SYM_FUNC_START(__memset)
-	ltgr	%r4,%r4
-	jz	.Lmemset_exit
-	ltgr	%r3,%r3
-	jnz	.Lmemset_fill
-	aghi	%r4,-1
-	srlg	%r3,%r4,8
-	ltgr	%r3,%r3
-	lgr	%r1,%r2
-	jz	.Lmemset_clear_remainder
-.Lmemset_clear_loop:
-	xc	0(256,%r1),0(%r1)
-	la	%r1,256(%r1)
-	brctg	%r3,.Lmemset_clear_loop
-.Lmemset_clear_remainder:
-	exrl	%r4,.Lmemset_xc
-.Lmemset_exit:
-	BR_EX	%r14
-.Lmemset_fill:
-	cghi	%r4,1
-	lgr	%r1,%r2
-	je	.Lmemset_fill_exit
-	aghi	%r4,-2
-	srlg	%r5,%r4,8
-	ltgr	%r5,%r5
-	jz	.Lmemset_fill_remainder
-.Lmemset_fill_loop:
-	stc	%r3,0(%r1)
-	mvc	1(255,%r1),0(%r1)
-	la	%r1,256(%r1)
-	brctg	%r5,.Lmemset_fill_loop
-.Lmemset_fill_remainder:
-	stc	%r3,0(%r1)
-	exrl	%r4,.Lmemset_mvc
-	BR_EX	%r14
-.Lmemset_fill_exit:
-	stc	%r3,0(%r1)
-	BR_EX	%r14
-.Lmemset_xc:
-	xc	0(1,%r1),0(%r1)
-.Lmemset_mvc:
-	mvc	1(1,%r1),0(%r1)
-SYM_FUNC_END(__memset)
-EXPORT_SYMBOL(__memset)
-
-SYM_FUNC_ALIAS(memset, __memset)
-EXPORT_SYMBOL(memset)
-
 /*
  * memcpy implementation
  *
diff --git a/arch/s390/lib/string.c b/arch/s390/lib/string.c
index 648d5a66484d..f59d67925e77 100644
--- a/arch/s390/lib/string.c
+++ b/arch/s390/lib/string.c
@@ -63,6 +63,67 @@ EXPORT_SYMBOL(__memmove);
 EXPORT_SYMBOL(memmove);
 #endif
 
+#ifdef __HAVE_ARCH_MEMSET
+noinstr void *__memset(void *s, int c, size_t n)
+{
+	char *xs = s;
+
+	if (!n)
+		return s;
+	if (!c) {
+		/* Clear memory */
+		while (n >= 256) {
+			asm volatile(
+				"	xc	 0(256,%[xs]),0(%[xs])"
+				:
+				: [xs] "a" (xs)
+				: "cc", "memory");
+			xs += 256;
+			n -= 256;
+		}
+		if (!n)
+			return s;
+		asm volatile(
+			"	exrl	%[n],0f\n"
+			"	j	1f\n"
+			"0:	xc	0(1,%[xs]),0(%[xs])\n"
+			"1:"
+			:
+			: [xs] "a" (xs), [n] "a" (n - 1)
+			: "cc", "memory");
+	} else {
+		/* Fill memory */
+		while (n >= 256) {
+			*xs = c;
+			asm volatile(
+				"	mvc	1(255,%[xs]),0(%[xs])"
+				:
+				: [xs] "a" (xs)
+				: "memory");
+			xs += 256;
+			n -= 256;
+		}
+		if (!n)
+			return s;
+		*xs = c;
+		if (n == 1)
+			return s;
+		asm volatile(
+			"	exrl	%[n],0f\n"
+			"	j	1f\n"
+			"0:	mvc	1(1,%[xs]),0(%[xs])\n"
+			"1:"
+			:
+			: [xs] "a" (xs), [n] "a" (n - 2)
+			: "memory");
+	}
+	return s;
+}
+SYMBOL_FUNCTION_ALIAS(memset, __memset);
+EXPORT_SYMBOL(__memset);
+EXPORT_SYMBOL(memset);
+#endif
+
 /*
  * Helper functions to find the end of a string
  */