From mboxrd@z Thu Jan 1 00:00:00 1970 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2DAB1D7235B for ; Fri, 23 Jan 2026 08:59:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=9fmYNQeFTcnaL0fxHPqP6UlEY3Q6nlTcsYabdUsPJF8=; b=idtpYdm1KFMmqY HNsXLaXoAOdH5cQ3/Lbmcsq967efaGw7Ei8WsgPxMkxT5YGm4MrNI+d6e7YTj5DxKhvI8Yf0IBGUw cH8bkeKt4UVvnaeu1lI6KQ8H1P/xMfzeZX1XrmYFKaRwga7JCzXCVOWGMs89xjXGqS56eFJGpiIzw YjwcgH7qET37wv7r9xXxW0RjzN1/3FS9UvLctY04/qVo0yZ7rF3OC3OQvdbB+5EzV3umtOwZnsCI4 VjfExdW08385E0oDa0FG/ZtL497t2dXNxPCr139NPh/4na9aO/nsILL6CJZIOrXDrR/CLp61rU52w ssVl+Kte6LoE12rnIeGg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vjD0R-00000008VsO-0Peg; Fri, 23 Jan 2026 08:59:03 +0000 Received: from mailgw.kylinos.cn ([124.126.103.232]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vjD0M-00000008VmY-0SMH for linux-riscv@lists.infradead.org; Fri, 23 Jan 2026 08:58:59 +0000 X-UUID: be51dffaf83911f0b0f03b4cfa9209d1-20260123 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.3.6,REQID:e7b31b3c-b674-4a1c-b5d2-71cc865d3b67,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:317e3d8f933718520d277b6c7368d8c6,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: be51dffaf83911f0b0f03b4cfa9209d1-20260123 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 647105484; Fri, 23 Jan 2026 16:58:53 +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, mingo@kernel.org, charlie@rivosinc.com, conor.dooley@microchip.com, samuel.holland@sifive.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 v4 8/8] riscv: lib: add strrchr() implementation Date: Fri, 23 Jan 2026 16:58:41 +0800 Message-Id: <20260123085841.212468-9-jiangfeng@kylinos.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260123085841.212468-1-jiangfeng@kylinos.cn> References: <20260123085841.212468-1-jiangfeng@kylinos.cn> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260123_005858_463359_AAAF7AFB X-CRM114-Status: GOOD ( 13.53 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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/string.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 *, size_t); #define __HAVE_ARCH_STRCHR extern asmlinkage char *strchr(const char *, int); + +#define __HAVE_ARCH_STRRCHR +extern asmlinkage char *strrchr(const char *, int); #endif /* 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 += strlen.o lib-y += strncmp.o lib-y += strnlen.o lib-y += strchr.o +lib-y += strrchr.o endif lib-y += csum.o ifeq ($(CONFIG_MMU), y) diff --git a/arch/riscv/lib/strrchr.S b/arch/riscv/lib/strrchr.S new file mode 100644 index 000000000000..ac58b20ca21d --- /dev/null +++ b/arch/riscv/lib/strrchr.S @@ -0,0 +1,37 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +/* + * Copyright (C) 2025 Feng Jiang + */ + +#include +#include + +/* char *strrchr(const char *s, int c) */ +SYM_FUNC_START(strrchr) + /* + * Parameters + * a0 - The string to be searched + * a1 - The character to seaerch for + * + * Returns + * a0 - Address of last occurrence of 'c' or 0 + * + * Clobbers + * t0, t1 + */ + andi a1, a1, 0xff + mv t1, a0 + li a0, 0 +1: + lbu t0, 0(t1) + bne t0, a1, 2f + mv a0, t1 +2: + addi t1, t1, 1 + bnez t0, 1b + ret +SYM_FUNC_END(strrchr) + +SYM_FUNC_ALIAS_WEAK(__pi_strrchr, strrchr) +EXPORT_SYMBOL(strrchr) diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile index e7b3d748c913..b0358a78f11a 100644 --- a/arch/riscv/purgatory/Makefile +++ b/arch/riscv/purgatory/Makefile @@ -2,7 +2,7 @@ purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),) -purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o strchr.o +purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o strchr.o strrchr.o endif targets += $(purgatory-y) @@ -38,6 +38,9 @@ $(obj)/strnlen.o: $(srctree)/arch/riscv/lib/strnlen.S FORCE $(obj)/strchr.o: $(srctree)/arch/riscv/lib/strchr.S FORCE $(call if_changed_rule,as_o_S) +$(obj)/strrchr.o: $(srctree)/arch/riscv/lib/strrchr.S FORCE + $(call if_changed_rule,as_o_S) + CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY CFLAGS_string.o := -D__DISABLE_EXPORTS CFLAGS_ctype.o := -D__DISABLE_EXPORTS -- 2.25.1 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv