From: Feng Jiang Date: Sat, 4 Apr 2026 01:28:47 +0000 (-0600) Subject: riscv: lib: add strrchr() implementation X-Git-Tag: v7.1-rc1~27^2~6 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=bef64bcb940269a503d12eb1bc180d1aa9adf74d;p=thirdparty%2Fkernel%2Flinux.git riscv: lib: add strrchr() implementation 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 Tested-by: Joel Stanley Link: https://patch.msgid.link/20260130025018.172925-9-jiangfeng@kylinos.cn Signed-off-by: Paul Walmsley --- 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