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McKenney" To: linux-kernel@vger.kernel.org Cc: gwml@vger.gnuweeb.org, kernel-team@meta.com, w@lwt.eu, Ammar Faizi , Alviro Iskandar Setiawan , Willy Tarreau , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= Subject: [PATCH nolibc 07/19] tools/nolibc: x86-64: Use `rep stosb` for `memset()` Date: Thu, 12 Oct 2023 12:32:21 -0700 Message-Id: <20231012193233.207857-7-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit List-Id: From: Ammar Faizi 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 : 10c9: 48 89 f8 mov %rdi,%rax 10cc: 48 85 d2 test %rdx,%rdx 10cf: 74 0e je 10df 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 10df: c3 ret ``` After this patch: ``` 0000000000001511 : 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 Suggested-by: Willy Tarreau Signed-off-by: Ammar Faizi Reviewed-by: Alviro Iskandar Setiawan Signed-off-by: Willy Tarreau Signed-off-by: Thomas Weißschuh --- 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 aece7d895153..68609f421934 100644 --- a/tools/include/nolibc/arch-x86_64.h +++ b/tools/include/nolibc/arch-x86_64.h @@ -179,6 +179,9 @@ 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" @@ -200,6 +203,16 @@ __asm__ ( "rep movsb\n\t" "cld\n\t" "retq\n" + +".section .text.nolibc_memset\n" +".weak memset\n" +"memset:\n" + "xchgl %eax, %esi\n\t" + "movq %rdx, %rcx\n\t" + "pushq %rdi\n\t" + "rep stosb\n\t" + "popq %rax\n\t" + "retq\n" ); #endif /* _NOLIBC_ARCH_X86_64_H */ 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) -- 2.40.1