From: Ammar Faizi <[email protected]>
To: "Willy Tarreau" <[email protected]>, "Thomas Weißschuh" <[email protected]>
Cc: Ammar Faizi <[email protected]>,
David Laight <[email protected]>,
Nicholas Rosenberg <[email protected]>,
Alviro Iskandar Setiawan <[email protected]>,
Michael William Jonathan <[email protected]>,
GNU/Weeb Mailing List <[email protected]>,
Linux Kernel Mailing List <[email protected]>
Subject: [RFC PATCH v3 2/4] tools/nolibc: x86-64: Use `rep stosb` for `memset()`
Date: Sat, 2 Sep 2023 20:35:03 +0700 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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/[email protected]
Suggested-by: Alviro Iskandar Setiawan <[email protected]>
Suggested-by: Willy Tarreau <[email protected]>
Signed-off-by: Ammar Faizi <[email protected]>
---
tools/include/nolibc/arch-x86_64.h | 13 +++++++++++++
tools/include/nolibc/string.h | 2 ++
2 files changed, 15 insertions(+)
diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index aece7d8951535a36..1502db5c58fc0c87 100644
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -162,44 +162,57 @@
*
*/
void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
{
__asm__ volatile (
"xor %ebp, %ebp\n" /* zero the stack frame */
"mov %rsp, %rdi\n" /* save stack pointer to %rdi, as arg1 of _start_c */
"and $-16, %rsp\n" /* %rsp must be 16-byte aligned before call */
"call _start_c\n" /* transfer to c runtime */
"hlt\n" /* ensure it does not return */
);
__builtin_unreachable();
}
#define NOLIBC_ARCH_HAS_MEMMOVE
void *memmove(void *dst, const void *src, size_t len);
#define NOLIBC_ARCH_HAS_MEMCPY
void *memcpy(void *dst, const void *src, size_t len);
+#define NOLIBC_ARCH_HAS_MEMSET
+void *memset(void *dst, int c, size_t len);
+
__asm__ (
".section .text.nolibc_memmove_memcpy\n"
".weak memmove\n"
".weak memcpy\n"
"memmove:\n"
"memcpy:\n"
"movq %rdx, %rcx\n\t"
"movq %rdi, %rax\n\t"
"movq %rdi, %rdx\n\t"
"subq %rsi, %rdx\n\t"
"cmpq %rcx, %rdx\n\t"
"jb .Lbackward_copy\n\t"
"rep movsb\n\t"
"retq\n"
".Lbackward_copy:"
"leaq -1(%rdi, %rcx, 1), %rdi\n\t"
"leaq -1(%rsi, %rcx, 1), %rsi\n\t"
"std\n\t"
"rep movsb\n\t"
"cld\n\t"
"retq\n"
+
+".section .text.nolibc_memset\n"
+".weak memset\n"
+"memset:\n"
+ "xchgl %eax, %esi\n"
+ "movq %rdx, %rcx\n"
+ "pushq %rdi\n"
+ "rep stosb\n"
+ "popq %rax\n"
+ "retq\n"
);
#endif /* _NOLIBC_ARCH_X86_64_H */
diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 6eca267ec6fa7177..1bad6121ef8c4ab5 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -67,55 +67,57 @@ void *memmove(void *dst, const void *src, size_t len)
}
while (len) {
pos += dir;
((char *)dst)[pos] = ((const char *)src)[pos];
len--;
}
return dst;
}
#endif /* #ifndef NOLIBC_ARCH_HAS_MEMMOVE */
#ifndef NOLIBC_ARCH_HAS_MEMCPY
/* must be exported, as it's used by libgcc on ARM */
__attribute__((weak,unused,section(".text.nolibc_memcpy")))
void *memcpy(void *dst, const void *src, size_t len)
{
return _nolibc_memcpy_up(dst, src, len);
}
#endif /* #ifndef NOLIBC_ARCH_HAS_MEMCPY */
+#ifndef NOLIBC_ARCH_HAS_MEMSET
/* might be ignored by the compiler without -ffreestanding, then found as
* missing.
*/
__attribute__((weak,unused,section(".text.nolibc_memset")))
void *memset(void *dst, int b, size_t len)
{
char *p = dst;
while (len--) {
/* prevent gcc from recognizing memset() here */
__asm__ volatile("");
*(p++) = b;
}
return dst;
}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMSET */
static __attribute__((unused))
char *strchr(const char *s, int c)
{
while (*s) {
if (*s == (char)c)
return (char *)s;
s++;
}
return NULL;
}
static __attribute__((unused))
int strcmp(const char *a, const char *b)
{
unsigned int c;
int diff;
while (!(diff = (unsigned char)*a++ - (c = (unsigned char)*b++)) && c)
;
--
Ammar Faizi
next prev parent reply other threads:[~2023-09-02 13:35 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-02 13:35 [RFC PATCH v3 0/4] nolibc x86-64 string functions Ammar Faizi
2023-09-02 13:35 ` [RFC PATCH v3 1/4] tools/nolibc: x86-64: Use `rep movsb` for `memcpy()` and `memmove()` Ammar Faizi
2023-09-02 13:35 ` Ammar Faizi [this message]
2023-09-02 19:28 ` [RFC PATCH v3 2/4] tools/nolibc: x86-64: Use `rep stosb` for `memset()` Alviro Iskandar Setiawan
2023-09-02 19:34 ` Ammar Faizi
2023-09-02 19:38 ` Alviro Iskandar Setiawan
2023-09-02 19:39 ` Ammar Faizi
2023-09-03 8:17 ` Willy Tarreau
2023-09-03 8:34 ` Ammar Nofan Faizi
2023-09-03 8:39 ` Ammar Faizi
2023-09-03 9:55 ` Willy Tarreau
2023-09-02 13:35 ` [RFC PATCH v3 3/4] tools/nolibc: string: Remove the `_nolibc_memcpy_down()` function Ammar Faizi
2023-09-02 19:24 ` Alviro Iskandar Setiawan
2023-09-02 13:35 ` [RFC PATCH v3 4/4] tools/nolibc: string: Remove the `_nolibc_memcpy_up()` function Ammar Faizi
2023-09-02 19:26 ` Alviro Iskandar Setiawan
2023-09-03 20:38 ` [RFC PATCH v3 0/4] nolibc x86-64 string functions David Laight
2023-09-03 21:19 ` Willy Tarreau
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