From nobody Mon Feb 9 17:23:17 2026 Received: from mailgw.kylinos.cn (mailgw.kylinos.cn [124.126.103.232]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82F8237AA66; Thu, 29 Jan 2026 07:02:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=124.126.103.232 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769670164; cv=none; b=sEapI+6RdQBCXm2BNlwRkisGpelrKpS5wHhMdpGMKU/JiYuu1msy+T1DaCvo7cZJl8Ha1TxLiHwTa3MUZS7I3OC36e2dC0hSUqtA0q8HpBBqPl+PSWKlyiL4Dw53Qmzr7kkrO8nbrqLOuR0U0MgseA+RDk7JWISmwxr/fme/M4Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769670164; c=relaxed/simple; bh=AMLyJP13lq5q9yfPKhQ9OMAfBqXzPWDIhUThsyomljo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=MzxY52mN8USiZscMadT3ykEvBx2TNsnFso7TTrxLVJQeGu50hdHDl2LeaTMqibLjVVb0NwXi7+cgz9b6+ejiKXF/5SXthVmpWJqjhIoY77RnLYwNoSj7uo+dc43VMCveda6kb3VEkEJgFwxfUSK1noQ5ZEco4LYVTB3hDU1zh2I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn; spf=pass smtp.mailfrom=kylinos.cn; arc=none smtp.client-ip=124.126.103.232 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kylinos.cn X-UUID: 7f11e190fce011f0b0f03b4cfa9209d1-20260129 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.3.6,REQID:52c21111-b78e-47bf-9cc4-dbb2c974de95,IP:0,UR L:0,TC:0,Content:-25,EDM:0,RT:0,SF:0,FILE:0,BULK:0,RULE:Release_Ham,ACTION :release,TS:-25 X-CID-META: VersionHash:a9d874c,CLOUDID:e4807e3fb9f05e0e6227c83d5eadcc8a,BulkI D:nil,BulkQuantity:0,Recheck:0,SF:81|82|102|850|898,TC:nil,Content:0|15|50 ,EDM:-3,IP:nil,URL:0,File:nil,RT:nil,Bulk:nil,QS:nil,BEC:nil,COL:0,OSI:0,O SA:0,AV:0,LES:1,SPR:NO,DKR:0,DKP:0,BRR:0,BRE:0,ARC:0 X-CID-BVR: 2,SSN|SDN X-CID-BAS: 2,SSN|SDN,0,_ X-CID-FACTOR: TF_CID_SPAM_SNR X-CID-RHF: D41D8CD98F00B204E9800998ECF8427E X-UUID: 7f11e190fce011f0b0f03b4cfa9209d1-20260129 X-User: jiangfeng@kylinos.cn Received: from localhost.localdomain [(10.44.16.150)] by mailgw.kylinos.cn (envelope-from ) (Generic MTA with TLSv1.3 TLS_AES_256_GCM_SHA384 256/256) with ESMTP id 283613446; Thu, 29 Jan 2026 15:02:38 +0800 From: Feng Jiang To: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, akpm@linux-foundation.org, kees@kernel.org, andy@kernel.org, jiangfeng@kylinos.cn, ebiggers@kernel.org, martin.petersen@oracle.com, herbert@gondor.apana.org.au, samuel.holland@sifive.com, ajones@ventanamicro.com, charlie@rivosinc.com, conor.dooley@microchip.com, linus.walleij@linaro.org, nathan@kernel.org Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v6 8/8] riscv: lib: add strrchr() implementation Date: Thu, 29 Jan 2026 15:02:27 +0800 Message-Id: <20260129070227.220866-9-jiangfeng@kylinos.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260129070227.220866-1-jiangfeng@kylinos.cn> References: <20260129070227.220866-1-jiangfeng@kylinos.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add an assembly implementation of strrchr() for RISC-V. This implementation minimizes instruction count and avoids unnecessary memory access to the stack. The performance benefits are most visible on small workloads (1-16 bytes) where the architectural savings in function overhead outweigh the execution time of the scan loop. Benchmark results (QEMU TCG, rv64): Length | Original (MB/s) | Optimized (MB/s) | Improvement -------|-----------------|------------------|------------ 1 B | 20 | 21 | +5.0% 7 B | 111 | 120 | +8.1% 16 B | 189 | 199 | +5.3% 512 B | 361 | 382 | +5.8% 4096 B | 388 | 391 | +0.8% Signed-off-by: Feng Jiang --- arch/riscv/include/asm/string.h | 3 +++ arch/riscv/lib/Makefile | 1 + arch/riscv/lib/strrchr.S | 37 +++++++++++++++++++++++++++++++++ arch/riscv/purgatory/Makefile | 5 ++++- 4 files changed, 45 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/lib/strrchr.S diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/strin= g.h index ca3ade82b124..764ffe8f6479 100644 --- a/arch/riscv/include/asm/string.h +++ b/arch/riscv/include/asm/string.h @@ -34,6 +34,9 @@ extern asmlinkage __kernel_size_t strnlen(const char *, s= ize_t); =20 #define __HAVE_ARCH_STRCHR extern asmlinkage char *strchr(const char *, int); + +#define __HAVE_ARCH_STRRCHR +extern asmlinkage char *strrchr(const char *, int); #endif =20 /* For those files which don't want to check by kasan. */ diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile index b7f804dce1c3..735d0b665536 100644 --- a/arch/riscv/lib/Makefile +++ b/arch/riscv/lib/Makefile @@ -9,6 +9,7 @@ lib-y +=3D strlen.o lib-y +=3D strncmp.o lib-y +=3D strnlen.o lib-y +=3D strchr.o +lib-y +=3D strrchr.o endif lib-y +=3D csum.o ifeq ($(CONFIG_MMU), y) diff --git a/arch/riscv/lib/strrchr.S b/arch/riscv/lib/strrchr.S new file mode 100644 index 000000000000..ac58b20ca21d --- /dev/null +++ b/arch/riscv/lib/strrchr.S @@ -0,0 +1,37 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +/* + * Copyright (C) 2025 Feng Jiang + */ + +#include +#include + +/* char *strrchr(const char *s, int c) */ +SYM_FUNC_START(strrchr) + /* + * Parameters + * a0 - The string to be searched + * a1 - The character to seaerch for + * + * Returns + * a0 - Address of last occurrence of 'c' or 0 + * + * Clobbers + * t0, t1 + */ + andi a1, a1, 0xff + mv t1, a0 + li a0, 0 +1: + lbu t0, 0(t1) + bne t0, a1, 2f + mv a0, t1 +2: + addi t1, t1, 1 + bnez t0, 1b + ret +SYM_FUNC_END(strrchr) + +SYM_FUNC_ALIAS_WEAK(__pi_strrchr, strrchr) +EXPORT_SYMBOL(strrchr) diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile index e7b3d748c913..b0358a78f11a 100644 --- a/arch/riscv/purgatory/Makefile +++ b/arch/riscv/purgatory/Makefile @@ -2,7 +2,7 @@ =20 purgatory-y :=3D purgatory.o sha256.o entry.o string.o ctype.o memcpy.o me= mset.o ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) -purgatory-y +=3D strcmp.o strlen.o strncmp.o strnlen.o strchr.o +purgatory-y +=3D strcmp.o strlen.o strncmp.o strnlen.o strchr.o strrchr.o endif =20 targets +=3D $(purgatory-y) @@ -38,6 +38,9 @@ $(obj)/strnlen.o: $(srctree)/arch/riscv/lib/strnlen.S FOR= CE $(obj)/strchr.o: $(srctree)/arch/riscv/lib/strchr.S FORCE $(call if_changed_rule,as_o_S) =20 +$(obj)/strrchr.o: $(srctree)/arch/riscv/lib/strrchr.S FORCE + $(call if_changed_rule,as_o_S) + CFLAGS_sha256.o :=3D -D__DISABLE_EXPORTS -D__NO_FORTIFY CFLAGS_string.o :=3D -D__DISABLE_EXPORTS CFLAGS_ctype.o :=3D -D__DISABLE_EXPORTS --=20 2.25.1