* [PATCH 1/2] riscv: lib: add memchr() implementation
2026-05-20 15:55 [PATCH 0/2] riscv: lib: add optimized memchr() and extend KUnit tests Milan Tripkovic
@ 2026-05-20 15:55 ` Milan Tripkovic
2026-05-20 15:55 ` [PATCH 2/2] lib/string_kunit: extend benchmarks and unit test to memchr() Milan Tripkovic
1 sibling, 0 replies; 4+ messages in thread
From: Milan Tripkovic @ 2026-05-20 15:55 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou, Kees Cook
Cc: Alexandre Ghiti, Andy Shevchenko, linux-riscv, linux-kernel,
linux-hardening, Dusan Stojkovic, Milan Tripkovic
From: Milan Tripkovic <Milan.Tripkovic@rt-rk.com>
This implementation leverages word-at-a-time comparisons and the RISC-V
Zbb extension to accelerate character searching, falling back to a
generic byte-by-byte loop on systems without Zbb support.
Benchmark results (QEMU TCG, rv64):
| len | zbb | Wozbb | default | % Wozbb | % zbb |
|------|--------|-------|---------|---------|---------|
| 1 | 22.9 | 26 | 22.1 | 17.64 % | 3.62 %|
| 7 | 115.5 | 130.6 | 100.1 | 30.46 % | 15.38 %|
| 8 | 184.3 | 143.3 | 117.2 | 22.26 % | 57.25 %|
| 16 | 322 | 205.1 | 179.7 | 14.13 % | 79.19 %|
| 31 | 361 | 247.4 | 221.7 | 11.59 % | 62.83 %|
| 64 | 880 | 280.6 | 233.2 | 20.32 % | 277.35 %|
| 127 | 961.3 | 307.9 | 271.4 | 13.44 % | 254.20 %|
| 512 | 1812.9 | 325.6 | 294.1 | 10.71 % | 516.42 %|
| 1024 | 1973.2 | 335.4 | 273.8 | 22.49 % | 620.67 %|
| 3173 | 2245.9 | 338.7 | 288.6 | 17.35 % | 678.20 %|
| 4096 | 2327.5 | 345 | 317.5 | 8.661 % | 633.07 %|
Signed-off-by: Milan Tripkovic <Milan.Tripkovic@rt-rk.com>
---
arch/riscv/include/asm/string.h | 3 +-
arch/riscv/lib/Makefile | 1 +
arch/riscv/lib/memchr.S | 126 ++++++++++++++++++++++++++++++++
arch/riscv/purgatory/Makefile | 5 +-
4 files changed, 133 insertions(+), 2 deletions(-)
create mode 100644 arch/riscv/lib/memchr.S
diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 764ffe8f6479..cfcf1193b446 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -18,7 +18,8 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
#define __HAVE_ARCH_MEMMOVE
extern asmlinkage void *memmove(void *, const void *, size_t);
extern asmlinkage void *__memmove(void *, const void *, size_t);
-
+#define __HAVE_ARCH_MEMCHR
+extern asmlinkage void *memchr(const void *s, int c, size_t n);
#if !(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS))
#define __HAVE_ARCH_STRCMP
extern asmlinkage int strcmp(const char *cs, const char *ct);
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 6f767b2a349d..bbc54dabbb81 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -3,6 +3,7 @@ lib-y += delay.o
lib-y += memcpy.o
lib-y += memset.o
lib-y += memmove.o
+lib-y += memchr.o
ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
lib-y += strcmp.o
lib-y += strlen.o
diff --git a/arch/riscv/lib/memchr.S b/arch/riscv/lib/memchr.S
new file mode 100644
index 000000000000..0e971cf51410
--- /dev/null
+++ b/arch/riscv/lib/memchr.S
@@ -0,0 +1,126 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/alternative-macros.h>
+#include <asm/hwcap.h>
+
+/* void *memchr(const void *s, int c, size_t n) */
+SYM_FUNC_START(memchr)
+
+ __ALTERNATIVE_CFG("nop", "j memchr_zbb", 0, RISCV_ISA_EXT_ZBB,
+ IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
+/*
+ *
+ * Parameters
+ * a0 - Pointer to memory area (s), also return value
+ * a1 - Character to search for (c)
+ * a2 - Number of bytes to search (n)
+ *
+ * Returns
+ * a0 - Pointer to the matched character, or NULL (0) if not found
+ *
+ * Clobbers
+ * t0, t1
+ */
+ beqz a2, 3f
+ andi a1, a1, 0xff
+ add t1, a0, a2
+
+1:
+ lbu t0, 0(a0)
+ beq t0, a1, 4f
+ addi a0, a0, 1
+ bne a0, t1, 1b
+
+3:
+ li a0, 0
+4:
+ ret
+
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
+.balign 4
+memchr_zbb:
+.option push
+.option arch, +zbb
+/*
+ * Parameters
+ * a0 - Pointer to memory area (s), also return value
+ * a1 - Character to search for (c)
+ * a2 - Number of bytes to search (n)
+ *
+ * Returns
+ * a0 - Pointer to the matched character, or NULL (0) if not found
+ *
+ * Clobbers
+ * t0, t1, t2, t3, t4, t5, t6
+ */
+ beqz a2, 3b
+ add t6, a0, a2
+ andi t3, a1, 0xff
+
+ li t0, SZREG
+ bltu a2, t0, 8f
+
+#if __riscv_xlen == 64
+ li t0, 0x0101010101010101
+#else
+ li t0, 0x01010101
+#endif
+ mul a1, t3, t0
+
+ andi t1, a0, SZREG - 1
+ beqz t1, 5f
+
+1:
+ lbu t2, 0(a0)
+ beq t2, t3, 4b
+ addi a0, a0, 1
+ andi t1, a0, SZREG - 1
+ bnez t1, 1b
+
+5:
+ sub t5, t6, a0
+ andi t5, t5, -SZREG
+ add t5, a0, t5
+
+ li t4, -1
+
+ beq a0, t5, 8f
+
+6:
+ REG_L t0, 0(a0)
+ xor t1, t0, a1
+ orc.b t1, t1
+ bne t1, t4, 7f
+ addi a0, a0, SZREG
+ bltu a0, t5, 6b
+
+8:
+ beq a0, t6, 3b
+
+2:
+ lbu t0, 0(a0)
+ beq t0, t3, 4b
+ addi a0, a0, 1
+ bltu a0, t6, 2b
+
+ j 3b
+
+7:
+ not t1, t1
+#ifndef CONFIG_CPU_BIG_ENDIAN
+ ctz t1, t1
+#else
+ clz t1, t1
+#endif
+ srli t1, t1, 3
+ add a0, a0, t1
+ ret
+
+.option pop
+#endif
+
+SYM_FUNC_END(memchr)
+SYM_FUNC_ALIAS(__pi_memchr, memchr)
+EXPORT_SYMBOL(memchr)
diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
index b0358a78f11a..42e840fad6df 100644
--- a/arch/riscv/purgatory/Makefile
+++ b/arch/riscv/purgatory/Makefile
@@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
-purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o
+purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o memchr.o
ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o strchr.o strrchr.o
endif
@@ -17,6 +17,9 @@ $(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE
$(obj)/memcpy.o: $(srctree)/arch/riscv/lib/memcpy.S FORCE
$(call if_changed_rule,as_o_S)
+$(obj)/memchr.o: $(srctree)/arch/riscv/lib/memchr.S FORCE
+ $(call if_changed_rule,as_o_S)
+
$(obj)/memset.o: $(srctree)/arch/riscv/lib/memset.S FORCE
$(call if_changed_rule,as_o_S)
--
2.43.0
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 2/2] lib/string_kunit: extend benchmarks and unit test to memchr()
2026-05-20 15:55 [PATCH 0/2] riscv: lib: add optimized memchr() and extend KUnit tests Milan Tripkovic
2026-05-20 15:55 ` [PATCH 1/2] riscv: lib: add memchr() implementation Milan Tripkovic
@ 2026-05-20 15:55 ` Milan Tripkovic
2026-08-06 17:52 ` Paul Walmsley
1 sibling, 1 reply; 4+ messages in thread
From: Milan Tripkovic @ 2026-05-20 15:55 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou, Kees Cook
Cc: Alexandre Ghiti, Andy Shevchenko, linux-riscv, linux-kernel,
linux-hardening, Dusan Stojkovic, Milan Tripkovic
From: Milan Tripkovic <Milan.Tripkovic@rt-rk.com>
Extend the string benchmarking suite to include memchr().
Extend the string unit test to include memchr()
Signed-off-by: Milan Tripkovic <Milan.Tripkovic@rt-rk.com>
---
lib/tests/string_kunit.c | 53 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)
diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 0819ace5b027..3a7d96e292da 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -881,6 +881,57 @@ static void string_bench_strrchr(struct kunit *test)
STRING_BENCH_BUF(test, buf, len, strrchr, buf, '\0');
}
+static void string_test_memchr(struct kunit *test)
+{
+ char *buf;
+ size_t max_len = 128;
+ size_t off, len, match_pos;
+ char *res;
+ char target = 0x88;
+
+ buf = kunit_kzalloc(test, max_len + 64, GFP_KERNEL);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+ memset(buf, 'A', max_len + 64);
+
+ for (off = 0; off < 16; off++) {
+ for (len = 1; len < max_len; len++) {
+ match_pos = len / 2;
+ buf[off + match_pos] = target;
+
+ res = memchr(buf + off, target, len);
+ KUNIT_EXPECT_PTR_EQ_MSG(test, res, buf + off + match_pos,
+ "Failed at:%zu len:%zu pos:%zu", off, len,
+ match_pos);
+
+ buf[off + match_pos] = 'A';
+ }
+ }
+
+ memset(buf, 'A', max_len);
+ buf[10] = 'B';
+ buf[20] = 'B';
+ res = memchr(buf, 'B', max_len);
+ KUNIT_EXPECT_PTR_EQ(test, res, &buf[10]);
+
+ buf[50] = (char)0xFF;
+ res = memchr(buf, 0xFF, max_len);
+ KUNIT_EXPECT_PTR_EQ(test, res, &buf[50]);
+
+ buf[60] = '\0';
+ res = memchr(buf, '\0', max_len);
+ KUNIT_EXPECT_PTR_EQ(test, res, &buf[60]);
+
+ buf[max_len - 1] = 'Z';
+ res = memchr(buf, 'Z', max_len);
+ KUNIT_EXPECT_PTR_EQ(test, res, &buf[max_len - 1]);
+}
+
+static void string_bench_memchr(struct kunit *test)
+{
+ STRING_BENCH_BUF(test, buf, len, memchr, buf, '\0', len);
+}
+
static struct kunit_case string_test_cases[] = {
KUNIT_CASE(string_test_memset16),
KUNIT_CASE(string_test_memset32),
@@ -910,6 +961,8 @@ static struct kunit_case string_test_cases[] = {
KUNIT_CASE(string_bench_strnlen),
KUNIT_CASE(string_bench_strchr),
KUNIT_CASE(string_bench_strrchr),
+ KUNIT_CASE(string_test_memchr),
+ KUNIT_CASE(string_bench_memchr),
{}
};
--
2.43.0
^ permalink raw reply [flat|nested] 4+ messages in thread