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s390/string: Convert memset() to C

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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>
This commit is contained in:
Heiko Carstens 2026-06-09 12:33:39 +02:00 committed by Alexander Gordeev
parent c3e4b7eb1b
commit 0a8be1f9c7
2 changed files with 61 additions and 63 deletions
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63
arch/s390/lib/mem.S
View File

@ -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
*

61
arch/s390/lib/string.c
View File

@ -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
*/