diff options
| author | Ammar Faizi <ammarfaizi2@gnuweeb.org> | 2023-09-02 20:35:03 +0700 |
|---|---|---|
| committer | Thomas Weißschuh <linux@weissschuh.net> | 2023-10-12 21:14:00 +0200 |
| commit | 12108aa8c1a13bdf4024f1e2e94a6121ac644d2c (patch) | |
| tree | 71b6ca3c3c91a2cbff6aba3024fd86eadb4fb71a /tools/include/nolibc/string.h | |
| parent | 553845eebd6003314bde2f40c1721275bfd2bfcd (diff) | |
tools/nolibc: x86-64: Use `rep stosb` for `memset()`
Simplify memset() on the x86-64 arch.
The x86-64 arch has a 'rep stosb' instruction, which can perform
memset() using only a single instruction, given:
%al = value (just like the second argument of memset())
%rdi = destination
%rcx = length
Before this patch:
```
00000000000010c9 <memset>:
10c9: 48 89 f8 mov %rdi,%rax
10cc: 48 85 d2 test %rdx,%rdx
10cf: 74 0e je 10df <memset+0x16>
10d1: 31 c9 xor %ecx,%ecx
10d3: 40 88 34 08 mov %sil,(%rax,%rcx,1)
10d7: 48 ff c1 inc %rcx
10da: 48 39 ca cmp %rcx,%rdx
10dd: 75 f4 jne 10d3 <memset+0xa>
10df: c3 ret
```
After this patch:
```
0000000000001511 <memset>:
1511: 96 xchg %eax,%esi
1512: 48 89 d1 mov %rdx,%rcx
1515: 57 push %rdi
1516: f3 aa rep stos %al,%es:(%rdi)
1518: 58 pop %rax
1519: c3 ret
```
v2:
- Use pushq %rdi / popq %rax (Alviro).
- Use xchg %eax, %esi (Willy).
Link: https://lore.kernel.org/lkml/ZO9e6h2jjVIMpBJP@1wt.eu
Suggested-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Suggested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Reviewed-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Diffstat (limited to 'tools/include/nolibc/string.h')
| -rw-r--r-- | tools/include/nolibc/string.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h index 6eca267ec6fa..1bad6121ef8c 100644 --- a/tools/include/nolibc/string.h +++ b/tools/include/nolibc/string.h @@ -84,6 +84,7 @@ void *memcpy(void *dst, const void *src, size_t len) } #endif /* #ifndef NOLIBC_ARCH_HAS_MEMCPY */ +#ifndef NOLIBC_ARCH_HAS_MEMSET /* might be ignored by the compiler without -ffreestanding, then found as * missing. */ @@ -99,6 +100,7 @@ void *memset(void *dst, int b, size_t len) } return dst; } +#endif /* #ifndef NOLIBC_ARCH_HAS_MEMSET */ static __attribute__((unused)) char *strchr(const char *s, int c) |