From nobody Sat Feb 7 23:49:01 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7AF74CA0FFD for ; Sat, 2 Sep 2023 05:51:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351592AbjIBFvS (ORCPT ); Sat, 2 Sep 2023 01:51:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351582AbjIBFvP (ORCPT ); Sat, 2 Sep 2023 01:51:15 -0400 Received: from gnuweeb.org (gnuweeb.org [51.81.211.47]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F55510F6 for ; Fri, 1 Sep 2023 22:51:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1693633872; bh=x9sDKPf10aSubQx2+ufgoe1wqMoNjeL92ALh+yOhHx4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=o4zLcBRCrL11CYdrGjjX08nuRkrk+qRYSsiofmENoJwnRI3qMFfSlW3dPmKX7ikJe D1O7lw53EpIDE5jAlrAAQiSm/ypgfp1nnd6zka7mf6bKzzu+hNA1FSJGo8zt+c3Vvt sQJDXVDYq2wshI46JktOqy+8wSgbJR2BYMi4fbt7XybqhB2j5uSibWY8qsHVjyEAxX 7WpcJNZvJHAAPoFWao9Jyalab+t4IJqMMetzKzRTLB6gAn3Zvjyyc9fFQr4MSXOd7P 0HvQktXpoIhNfCNH2+PRh/xHZANu2iqNSe4Mgz4WQdjJNbC4HLkXDuOPjHR7pKc2Pu b8z8wkOXW4JtQ== Received: from localhost.localdomain (unknown [182.253.126.208]) by gnuweeb.org (Postfix) with ESMTPSA id A5B8624B3A7; Sat, 2 Sep 2023 12:51:08 +0700 (WIB) From: Ammar Faizi To: Willy Tarreau , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= Cc: Ammar Faizi , David Laight , Nicholas Rosenberg , Alviro Iskandar Setiawan , Michael William Jonathan , GNU/Weeb Mailing List , Linux Kernel Mailing List Subject: [RFC PATCH v2 2/4] tools/nolibc: x86-64: Use `rep stosb` for `memset()` Date: Sat, 2 Sep 2023 12:50:43 +0700 Message-Id: <20230902055045.2138405-3-ammarfaizi2@gnuweeb.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230902055045.2138405-1-ammarfaizi2@gnuweeb.org> References: <20230902055045.2138405-1-ammarfaizi2@gnuweeb.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 =3D value (just like the second argument of memset()) %rdi =3D destination %rcx =3D 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 code size shrink: - 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 --- 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 297ffa364b2312eb..ed01b130e25c6740 100644 --- a/tools/include/nolibc/arch-x86_64.h +++ b/tools/include/nolibc/arch-x86_64.h @@ -162,50 +162,63 @@ * */ 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 _sta= rt_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(); } =20 #define NOLIBC_ARCH_HAS_MEMMOVE void *memmove(void *dst, const void *src, size_t len); =20 #define NOLIBC_ARCH_HAS_MEMCPY void *memcpy(void *dst, const void *src, size_t len); =20 +#define NOLIBC_ARCH_HAS_MEMSET +void *memset(void *dst, int c, size_t len); + __asm__ ( ".section .text.nolibc_memmove\n" ".weak memmove\n" "memmove:\n" "movq %rdx, %rcx\n" "movq %rdi, %rdx\n" "movq %rdi, %rax\n" "subq %rsi, %rdx\n" "cmpq %rcx, %rdx\n" "jnb .Lforward_copy\n" "leaq -1(%rdi, %rcx, 1), %rdi\n" "leaq -1(%rsi, %rcx, 1), %rsi\n" "std\n" "rep movsb\n" "cld\n" "retq\n" ".Lforward_copy:\n" "rep movsb\n" "retq\n" =20 ".section .text.nolibc_memcpy\n" ".weak memcpy\n" "memcpy:\n" "movq %rdi, %rax\n" "movq %rdx, %rcx\n" "rep movsb\n" "retq\n" + +".section .text.nolibc_memset\n" +".weak memset\n" +"memset:\n" + "xchg %eax, %esi\n" + "movq %rdx, %rcx\n" + "pushq %rdi\n" + "rep stosb\n" + "popq %rax\n" + "retq\n" ); =20 #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) } =20 while (len) { pos +=3D dir; ((char *)dst)[pos] =3D ((const char *)src)[pos]; len--; } return dst; } #endif /* #ifndef NOLIBC_ARCH_HAS_MEMMOVE */ =20 #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 */ =20 +#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 =3D dst; =20 while (len--) { /* prevent gcc from recognizing memset() here */ __asm__ volatile(""); *(p++) =3D b; } return dst; } +#endif /* #ifndef NOLIBC_ARCH_HAS_MEMSET */ =20 static __attribute__((unused)) char *strchr(const char *s, int c) { while (*s) { if (*s =3D=3D (char)c) return (char *)s; s++; } return NULL; } =20 static __attribute__((unused)) int strcmp(const char *a, const char *b) { unsigned int c; int diff; =20 while (!(diff =3D (unsigned char)*a++ - (c =3D (unsigned char)*b++)) && c) ; --=20 Ammar Faizi