[PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Feng Jiang]

This series provides optimized implementations of strnlen(), strchr(),
and strrchr() for the RISC-V architecture. The strnlen() implementation
is derived from the existing optimized strlen(). For strchr() and
strrchr(), the current versions use simple byte-by-byte assembly logic,
which will serve as a baseline for future Zbb-based optimizations.

The patch series is organized into three parts:
1. Correctness Testing: The first three patches add KUnit test cases
   for strlen(), strnlen(), and strrchr() to ensure the baseline and
   optimized versions are functionally correct.
2. Benchmarking Tool: Patches 4 and 5 extend string_kunit to include
   performance measurement capabilities, allowing for comparative
   analysis within the KUnit environment.
3. Architectural Optimizations: The final three patches introduce the
   RISC-V specific assembly implementations.

Following suggestions from Andy Shevchenko, performance benchmarks have
been added to string_kunit.c to provide quantifiable evidence of the
improvements. Andy provided many specific comments on the implementation
of the benchmark logic, which is also inspired by Eric Biggers'
crc_benchmark(). Performance was measured in a QEMU TCG (rv64) environment,
comparing the generic C implementation with the new RISC-V assembly
versions.

Performance Summary (Improvement %):
---------------------------------------------------------------
Function  |  16 B (Short) |  512 B (Mid) |  4096 B (Long)
---------------------------------------------------------------
strnlen   |    +72.6%     |   +350.1%    |    +427.5%
strchr    |    +3.6%      |   +3.5%      |    -0.3%
strrchr   |    +5.3%      |   +5.8%      |    +0.8%
---------------------------------------------------------------
The benchmarks can be reproduced by enabling CONFIG_STRING_KUNIT_BENCH
and running: ./tools/testing/kunit/kunit.py run --arch=riscv \
--cross_compile=riscv64-linux-gnu- --kunitconfig=my_string.kunitconfig \
--raw_output

The strnlen() implementation leverages the Zbb 'orc.b' instruction and
word-at-a-time logic, showing significant gains as the string length
increases. For strchr() and strrchr(), the handwritten assembly reduces
fixed overhead by eliminating stack frame management. The gain is most
prominent on short strings where function call overhead dominates,
while the performance converges with the C implementation for longer
strings in the TCG environment.

I would like to thank Andy Shevchenko for the suggestion to add benchmarks
and for his detailed feedback on the test framework, and Eric Biggers for
the benchmarking approach. I am also grateful to Kees Cook for his
suggestion to use vmalloc-based over-read detection. I am also grateful
to Qingfang Deng for providing the optimized implementation logic for
strnlen(). Thanks also to Joel Stanley for testing support and feedback,
and to David Laight for his suggestions regarding performance measurement.

Changes:

v7:
- Fix build error in 1/8 (call to undeclared function 'PAGE_ALIGN') as
  reported by kernel test robot.
- Link to v6: https://lore.kernel.org/all/20260129070227.220866-1-jiangfeng@kylinos.cn/

v6:
- Use vmalloc() and page-boundary alignment in strlen(), strnlen(), and
  strrchr() correctness tests to ensure over-reads are detected, as
  suggested by Kees Cook. Consequently, previous Acked-by and Tested-by
  tags for these tests have been dropped.
- Added <linux/minmax.h> include.
- Update STRING_BENCH_BUF macro to initialize variables inside the loop.
- Fixed operator positioning and removed redundant blank lines.
- Added warm-up iteration comment.

v5:
- Include <linux/ktime.h> for ktime_get_ns() and <linux/time64.h> 
  for NSEC_PER_SEC.
- Use #if IS_ENABLED(CONFIG_STRING_KUNIT_BENCH) to define the macro 
  instead of using if (!IS_ENABLED(...)) inside the function.
- Declare variables inside for-loops.
- Simplify the for-loop logic in alloc_max_bench_buffer().
- Replace the magic number 1000 with (NSEC_PER_SEC / MEGA) to clarify 
  the bytes/ns to MB/s conversion.

v4:
- Refine formatting and terminology:
  - Refer to '\0' as NUL.
  - Append parentheses () when referencing function names.
  - Ensure trailing commas are present in initializers.
  - Reorder local variable declarations to follow the "reverse Xmas tree" 
    style. (Style-only change; kept existing Acked-by tags).
- Improve documentation: Refine comments and commit messages for better 
  clarity.
- Improve readability by using (1 * MEGA) instead of 1000000UL.
- Replace max_t() with max() where type-casting is unnecessary.
- Simplify the return value check for kunit_kzalloc() in 
  alloc_max_bench_buffer().
- Remove redundant NUL-terminator handling in STRING_BENCH_BUF().
- Optimize strnlen() implementation by replacing bleu/bgeu instructions 
  with minu, as suggested by Qingfang Deng.
- Remove incorrect Suggested-by tags from certain patches.
- Drop Tested-by tags for benchmark-related patches due to significant 
  framework changes since v3.
- Re-run all tests and updated the performance data in the documentation.

v3:
- Re-implement benchmark logic inspired by crc_benchmark().
- Add 'len - 2' test case to strnlen correctness tests.
- Incorporate detailed benchmark data into individual commit messages.

v2: 
- Refactored lib/string.c to export __generic_* functions and added
  corresponding functional/performance tests for strnlen, strchr,
  and strrchr (Andy Shevchenko).
- Replaced magic numbers with STRING_TEST_MAX_LEN etc. (Andy Shevchenko).

v1: Initial submission.

---

Feng Jiang (8):
  lib/string_kunit: add correctness test for strlen()
  lib/string_kunit: add correctness test for strnlen()
  lib/string_kunit: add correctness test for strrchr()
  lib/string_kunit: add performance benchmark for strlen()
  lib/string_kunit: extend benchmarks to strnlen() and chr searches
  riscv: lib: add strnlen() implementation
  riscv: lib: add strchr() implementation
  riscv: lib: add strrchr() implementation

 arch/riscv/include/asm/string.h |   9 ++
 arch/riscv/lib/Makefile         |   3 +
 arch/riscv/lib/strchr.S         |  35 ++++
 arch/riscv/lib/strnlen.S        | 164 +++++++++++++++++++
 arch/riscv/lib/strrchr.S        |  37 +++++
 arch/riscv/purgatory/Makefile   |  11 +-
 lib/Kconfig.debug               |  11 ++
 lib/tests/string_kunit.c        | 274 ++++++++++++++++++++++++++++++++
 8 files changed, 543 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/lib/strchr.S
 create mode 100644 arch/riscv/lib/strnlen.S
 create mode 100644 arch/riscv/lib/strrchr.S

-- 
2.25.1

[PATCH v7 1/8] lib/string_kunit: add correctness test for strlen()

[Feng Jiang]

Add a KUnit test for strlen() to verify correctness across
different string lengths and memory alignments. Use vmalloc()
to place the NUL character at the page boundary to ensure
over-reads are detected.

Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 lib/tests/string_kunit.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index f9a8e557ba77..26962118768e 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -6,10 +6,12 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <kunit/test.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/vmalloc.h>
 
 #define STRCMP_LARGE_BUF_LEN 2048
 #define STRCMP_CHANGE_POINT 1337
@@ -17,6 +19,9 @@
 #define STRCMP_TEST_EXPECT_LOWER(test, fn, ...) KUNIT_EXPECT_LT(test, fn(__VA_ARGS__), 0)
 #define STRCMP_TEST_EXPECT_GREATER(test, fn, ...) KUNIT_EXPECT_GT(test, fn(__VA_ARGS__), 0)
 
+#define STRING_TEST_MAX_LEN	128
+#define STRING_TEST_MAX_OFFSET	16
+
 static void string_test_memset16(struct kunit *test)
 {
 	unsigned i, j, k;
@@ -104,6 +109,30 @@ static void string_test_memset64(struct kunit *test)
 	}
 }
 
+static void string_test_strlen(struct kunit *test)
+{
+	size_t buf_size;
+	char *buf, *s;
+
+	buf_size = PAGE_ALIGN(STRING_TEST_MAX_LEN + STRING_TEST_MAX_OFFSET + 1);
+	buf = vmalloc(buf_size);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+	memset(buf, 'A', buf_size);
+
+	for (size_t offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
+		for (size_t len = 0; len <= STRING_TEST_MAX_LEN; len++) {
+			s = buf + buf_size - 1 - offset - len;
+			s[len] = '\0';
+			KUNIT_EXPECT_EQ_MSG(test, strlen(s), len,
+				"offset:%zu len:%zu", offset, len);
+			s[len] = 'A';
+		}
+	}
+
+	vfree(buf);
+}
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -618,6 +647,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset16),
 	KUNIT_CASE(string_test_memset32),
 	KUNIT_CASE(string_test_memset64),
+	KUNIT_CASE(string_test_strlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strspn),
-- 
2.25.1

[PATCH v7 2/8] lib/string_kunit: add correctness test for strnlen()

[Feng Jiang]

Add a KUnit test for strnlen() to verify correctness across
different string lengths and memory alignments. Use vmalloc()
to place the NUL character at the page boundary to ensure
over-reads are detected.

Suggested-by: Andy Shevchenko <andy@kernel.org>
Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 lib/tests/string_kunit.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 26962118768e..1c2d57e05624 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -133,6 +133,40 @@ static void string_test_strlen(struct kunit *test)
 	vfree(buf);
 }
 
+static void string_test_strnlen(struct kunit *test)
+{
+	size_t buf_size;
+	char *buf, *s;
+
+	buf_size = PAGE_ALIGN(STRING_TEST_MAX_LEN + STRING_TEST_MAX_OFFSET + 1);
+	buf = vmalloc(buf_size);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+	memset(buf, 'A', buf_size);
+
+	for (size_t offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
+		for (size_t len = 0; len <= STRING_TEST_MAX_LEN; len++) {
+			s = buf + buf_size - 1 - offset - len;
+			s[len] = '\0';
+
+			if (len > 0)
+				KUNIT_EXPECT_EQ(test, strnlen(s, len - 1), len - 1);
+			if (len > 1)
+				KUNIT_EXPECT_EQ(test, strnlen(s, len - 2), len - 2);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s, len), len);
+
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 1), len);
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 2), len);
+			KUNIT_EXPECT_EQ(test, strnlen(s, len + 10), len);
+
+			s[len] = 'A';
+		}
+	}
+
+	vfree(buf);
+}
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -648,6 +682,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset32),
 	KUNIT_CASE(string_test_memset64),
 	KUNIT_CASE(string_test_strlen),
+	KUNIT_CASE(string_test_strnlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strspn),
-- 
2.25.1

[PATCH v7 3/8] lib/string_kunit: add correctness test for strrchr()

[Feng Jiang]

Add a KUnit test for strrchr() to verify correctness across
different string lengths and memory alignments. Use vmalloc()
to place the NUL character at the page boundary to ensure
over-reads are detected.

Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 lib/tests/string_kunit.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 1c2d57e05624..2bed641e1eae 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -190,6 +190,36 @@ static void string_test_strchr(struct kunit *test)
 	KUNIT_ASSERT_NULL(test, result);
 }
 
+static void string_test_strrchr(struct kunit *test)
+{
+	size_t buf_size;
+	char *buf, *s;
+
+	buf_size = PAGE_ALIGN(STRING_TEST_MAX_LEN + STRING_TEST_MAX_OFFSET + 1);
+	buf = vmalloc(buf_size);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+	memset(buf, 'A', buf_size);
+
+	for (size_t offset = 0; offset < STRING_TEST_MAX_OFFSET; offset++) {
+		for (size_t len = 0; len <= STRING_TEST_MAX_LEN; len++) {
+			s = buf + buf_size - 1 - offset - len;
+			s[len] = '\0';
+
+			KUNIT_EXPECT_PTR_EQ(test, strrchr(s, 'Z'), NULL);
+
+			if (len > 0)
+				KUNIT_EXPECT_PTR_EQ(test, strrchr(s, 'A'), s + len - 1);
+			else
+				KUNIT_EXPECT_PTR_EQ(test, strrchr(s, 'A'), NULL);
+
+			s[len] = 'A';
+		}
+	}
+
+	vfree(buf);
+}
+
 static void string_test_strnchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -685,6 +715,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_strnlen),
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
+	KUNIT_CASE(string_test_strrchr),
 	KUNIT_CASE(string_test_strspn),
 	KUNIT_CASE(string_test_strcmp),
 	KUNIT_CASE(string_test_strcmp_long_strings),
-- 
2.25.1

[PATCH v7 4/8] lib/string_kunit: add performance benchmark for strlen()

[Feng Jiang]

Introduce a benchmarking framework to the string_kunit test suite to
measure the execution efficiency of string functions.

The implementation is inspired by crc_benchmark(), measuring throughput
(MB/s) and latency (ns/call) across a range of string lengths. It
includes a warm-up phase, disables preemption during measurement, and
uses a fixed seed for reproducible results.

This framework allows for comparing different implementations (e.g.,
generic C vs. architecture-optimized assembly) within the KUnit
environment.

Initially, provide a benchmark for strlen().

Suggested-by: Andy Shevchenko <andy@kernel.org>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 lib/Kconfig.debug        |  11 +++
 lib/tests/string_kunit.c | 160 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 171 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ba36939fda79..21b058ae815f 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2475,6 +2475,17 @@ config STRING_HELPERS_KUNIT_TEST
 	depends on KUNIT
 	default KUNIT_ALL_TESTS
 
+config STRING_KUNIT_BENCH
+       bool "Benchmark string functions at runtime"
+       depends on STRING_KUNIT_TEST
+       help
+         Enable performance measurement for string functions.
+
+         This measures the execution efficiency of string functions
+         during the KUnit test run.
+
+         If unsure, say N.
+
 config FFS_KUNIT_TEST
 	tristate "KUnit test ffs-family functions at runtime" if !KUNIT_ALL_TESTS
 	depends on KUNIT
diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 2bed641e1eae..5f6d0409459b 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -6,11 +6,17 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <kunit/test.h>
+#include <linux/ktime.h>
+#include <linux/math64.h>
+#include <linux/minmax.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/prandom.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/time64.h>
+#include <linux/units.h>
 #include <linux/vmalloc.h>
 
 #define STRCMP_LARGE_BUF_LEN 2048
@@ -22,6 +28,9 @@
 #define STRING_TEST_MAX_LEN	128
 #define STRING_TEST_MAX_OFFSET	16
 
+#define STRING_BENCH_SEED	888
+#define STRING_BENCH_WORKLOAD	(1 * MEGA)
+
 static void string_test_memset16(struct kunit *test)
 {
 	unsigned i, j, k;
@@ -707,6 +716,156 @@ static void string_test_strends(struct kunit *test)
 	KUNIT_EXPECT_TRUE(test, strends("", ""));
 }
 
+#if IS_ENABLED(CONFIG_STRING_KUNIT_BENCH)
+/* Target string lengths for benchmarking */
+static const size_t bench_lens[] = {
+	0, 1, 7, 8, 16, 31, 64, 127, 512, 1024, 3173, 4096,
+};
+
+/**
+ * alloc_max_bench_buffer() - Allocate buffer for the max test case.
+ * @test: KUnit context for managed allocation.
+ * @lens: Array of lengths used in the benchmark cases.
+ * @count: Number of elements in the @lens array.
+ * @buf_len: [out] Pointer to store the actually allocated buffer
+ * size (including NUL character).
+ *
+ * Return: Pointer to the allocated memory, or NULL on failure.
+ */
+static void *alloc_max_bench_buffer(struct kunit *test,
+		const size_t *lens, size_t count, size_t *buf_len)
+{
+	size_t max_len = 0;
+	void *buf;
+
+	for (size_t i = 0; i < count; i++)
+		max_len = max(lens[i], max_len);
+
+	/* Add space for NUL character */
+	max_len += 1;
+
+	buf = kunit_kzalloc(test, max_len, GFP_KERNEL);
+	if (!buf)
+		return NULL;
+
+	if (buf_len)
+		*buf_len = max_len;
+
+	return buf;
+}
+
+/**
+ * fill_random_string() - Populate a buffer with a random NUL-terminated string.
+ * @buf: Buffer to fill.
+ * @len: Length of the buffer in bytes.
+ *
+ * Fills the buffer with random non-NUL bytes and ensures the string is
+ * properly NUL-terminated.
+ */
+static void fill_random_string(char *buf, size_t len)
+{
+	struct rnd_state state;
+
+	if (!buf || !len)
+		return;
+
+	/* Use a fixed seed to ensure deterministic benchmark results */
+	prandom_seed_state(&state, STRING_BENCH_SEED);
+	prandom_bytes_state(&state, buf, len);
+
+	/* Replace NUL characters to avoid early string termination */
+	for (size_t i = 0; i < len; i++) {
+		if (buf[i] == '\0')
+			buf[i] = 0x01;
+	}
+
+	buf[len - 1] = '\0';
+}
+
+/**
+ * STRING_BENCH() - Benchmark string functions.
+ * @iters: Number of iterations to run.
+ * @func: Function to benchmark.
+ * @...: Variable arguments passed to @func.
+ *
+ * Disables preemption and measures the total time in nanoseconds to execute
+ * @func(@__VA_ARGS__) for @iters times, including a small warm-up phase.
+ *
+ * Context: Disables preemption during measurement.
+ * Return: Total execution time in nanoseconds (u64).
+ */
+#define STRING_BENCH(iters, func, ...)					\
+({									\
+	/* Volatile function pointer prevents dead code elimination */	\
+	typeof(func) (* volatile __func) = (func);			\
+	size_t __bn_iters = (iters);					\
+	size_t __bn_warm_iters;						\
+	u64 __bn_t;							\
+									\
+	/* Use 10% of the given iterations (maximum 50) to warm up */	\
+	__bn_warm_iters = max(__bn_iters / 10, 50U);			\
+									\
+	for (size_t __bn_i = 0; __bn_i < __bn_warm_iters; __bn_i++)	\
+		(void)__func(__VA_ARGS__);				\
+									\
+	preempt_disable();						\
+	__bn_t = ktime_get_ns();					\
+	for (size_t __bn_i = 0; __bn_i < __bn_iters; __bn_i++)		\
+		(void)__func(__VA_ARGS__);				\
+	__bn_t = ktime_get_ns() - __bn_t;				\
+	preempt_enable();						\
+	__bn_t;								\
+})
+
+/**
+ * STRING_BENCH_BUF() - Benchmark harness for single-buffer functions.
+ * @test: KUnit context.
+ * @buf_name: Local char * variable name to be defined.
+ * @buf_size: Local size_t variable name to be defined.
+ * @func: Function to benchmark.
+ * @...: Extra arguments for @func.
+ *
+ * Prepares a randomized, NUL-terminated buffer and iterates through lengths
+ * in bench_lens, defining @buf_name and @buf_size in each loop.
+ */
+#define STRING_BENCH_BUF(test, buf_name, buf_size, func, ...)		\
+do {									\
+	size_t _bn_i, _bn_iters, _bn_size = 0;				\
+	u64 _bn_t, _bn_mbps = 0, _bn_lat = 0;				\
+	char *_bn_buf;							\
+									\
+	_bn_buf = alloc_max_bench_buffer(test, bench_lens,		\
+			ARRAY_SIZE(bench_lens), &_bn_size);		\
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, _bn_buf);			\
+									\
+	fill_random_string(_bn_buf, _bn_size);				\
+									\
+	for (_bn_i = 0; _bn_i < ARRAY_SIZE(bench_lens); _bn_i++) {	\
+		size_t buf_size = bench_lens[_bn_i];			\
+		char *buf_name = _bn_buf + _bn_size - buf_size - 1;	\
+		_bn_iters = STRING_BENCH_WORKLOAD / max(buf_size, 1U);	\
+									\
+		_bn_t = STRING_BENCH(_bn_iters, func, ##__VA_ARGS__);	\
+		if (_bn_t > 0) {					\
+			_bn_mbps = (u64)(buf_size) * _bn_iters *	\
+					(NSEC_PER_SEC / MEGA);		\
+			_bn_mbps = div64_u64(_bn_mbps, _bn_t);		\
+			_bn_lat = div64_u64(_bn_t, _bn_iters);		\
+		}							\
+		kunit_info(test, "len=%zu: %llu MB/s (%llu ns/call)\n",	\
+				buf_size, _bn_mbps, _bn_lat);		\
+	}								\
+} while (0)
+#else
+#define STRING_BENCH_BUF(test, buf_name, buf_size, func, ...)		\
+	kunit_skip(test, "not enabled")
+#endif /* IS_ENABLED(CONFIG_STRING_KUNIT_BENCH) */
+
+static void string_bench_strlen(struct kunit *test)
+{
+	STRING_BENCH_BUF(test, buf, len, strlen, buf);
+}
+
 static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset16),
 	KUNIT_CASE(string_test_memset32),
@@ -732,6 +891,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_strtomem),
 	KUNIT_CASE(string_test_memtostr),
 	KUNIT_CASE(string_test_strends),
+	KUNIT_CASE(string_bench_strlen),
 	{}
 };
 
-- 
2.25.1

[PATCH v7 5/8] lib/string_kunit: extend benchmarks to strnlen() and chr searches

[Feng Jiang]

Extend the string benchmarking suite to include strnlen(), strchr(),
and strrchr().

For character search functions strchr() and strrchr(), the benchmark
targets the NUL character. This ensures the entire string is scanned,
providing a consistent measure of full-length processing efficiency
comparable to strlen().

Suggested-by: Andy Shevchenko <andy@kernel.org>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
Acked-by: Andy Shevchenko <andy@kernel.org>
---
 lib/tests/string_kunit.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 5f6d0409459b..a8d430aa5466 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -866,6 +866,21 @@ static void string_bench_strlen(struct kunit *test)
 	STRING_BENCH_BUF(test, buf, len, strlen, buf);
 }
 
+static void string_bench_strnlen(struct kunit *test)
+{
+	STRING_BENCH_BUF(test, buf, len, strnlen, buf, len);
+}
+
+static void string_bench_strchr(struct kunit *test)
+{
+	STRING_BENCH_BUF(test, buf, len, strchr, buf, '\0');
+}
+
+static void string_bench_strrchr(struct kunit *test)
+{
+	STRING_BENCH_BUF(test, buf, len, strrchr, buf, '\0');
+}
+
 static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset16),
 	KUNIT_CASE(string_test_memset32),
@@ -892,6 +907,9 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memtostr),
 	KUNIT_CASE(string_test_strends),
 	KUNIT_CASE(string_bench_strlen),
+	KUNIT_CASE(string_bench_strnlen),
+	KUNIT_CASE(string_bench_strchr),
+	KUNIT_CASE(string_bench_strrchr),
 	{}
 };
 
-- 
2.25.1

[PATCH v7 6/8] riscv: lib: add strnlen() implementation

[Feng Jiang]

Add an optimized strnlen() implementation for RISC-V. This version
includes a generic optimization and a Zbb-powered optimization using
the 'orc.b' instruction, derived from the strlen() implementation.

Benchmark results (QEMU TCG, rv64):
  Length | Original (MB/s) | Optimized (MB/s) | Improvement
  -------|-----------------|------------------|------------
  16 B   | 179             | 309              | +72.6%
  512 B  | 347             | 1562             | +350.1%
  4096 B | 356             | 1878             | +427.5%

Suggested-by: Qingfang Deng <dqfext@gmail.com>
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 arch/riscv/include/asm/string.h |   3 +
 arch/riscv/lib/Makefile         |   1 +
 arch/riscv/lib/strnlen.S        | 164 ++++++++++++++++++++++++++++++++
 arch/riscv/purgatory/Makefile   |   5 +-
 4 files changed, 172 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/lib/strnlen.S

diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 5ba77f60bf0b..16634d67c217 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -28,6 +28,9 @@ extern asmlinkage __kernel_size_t strlen(const char *);
 
 #define __HAVE_ARCH_STRNCMP
 extern asmlinkage int strncmp(const char *cs, const char *ct, size_t count);
+
+#define __HAVE_ARCH_STRNLEN
+extern asmlinkage __kernel_size_t strnlen(const char *, size_t);
 #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 bbc031124974..0969d8136df0 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -7,6 +7,7 @@ ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
 lib-y			+= strcmp.o
 lib-y			+= strlen.o
 lib-y			+= strncmp.o
+lib-y			+= strnlen.o
 endif
 lib-y			+= csum.o
 ifeq ($(CONFIG_MMU), y)
diff --git a/arch/riscv/lib/strnlen.S b/arch/riscv/lib/strnlen.S
new file mode 100644
index 000000000000..53afa7b5b314
--- /dev/null
+++ b/arch/riscv/lib/strnlen.S
@@ -0,0 +1,164 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/*
+ * Base on arch/riscv/lib/strlen.S
+ *
+ * Copyright (C) Feng Jiang <jiangfeng@kylinos.cn>
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/alternative-macros.h>
+#include <asm/hwcap.h>
+
+/* size_t strnlen(const char *s, size_t count) */
+SYM_FUNC_START(strnlen)
+
+	__ALTERNATIVE_CFG("nop", "j strnlen_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
+
+
+	/*
+	 * Returns
+	 *   a0 - String length
+	 *
+	 * Parameters
+	 *   a0 - String to measure
+	 *   a1 - Max length of string
+	 *
+	 * Clobbers
+	 *   t0, t1, t2
+	 */
+	addi	t1, a0, -1
+	add	t2, a0, a1
+1:
+	addi	t1, t1, 1
+	beq	t1, t2, 2f
+	lbu	t0, 0(t1)
+	bnez	t0, 1b
+2:
+	sub	a0, t1, a0
+	ret
+
+
+/*
+ * Variant of strnlen using the ZBB extension if available
+ */
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
+strnlen_zbb:
+
+#ifdef CONFIG_CPU_BIG_ENDIAN
+# define CZ	clz
+# define SHIFT	sll
+#else
+# define CZ	ctz
+# define SHIFT	srl
+#endif
+
+.option push
+.option arch,+zbb
+
+	/*
+	 * Returns
+	 *   a0 - String length
+	 *
+	 * Parameters
+	 *   a0 - String to measure
+	 *   a1 - Max length of string
+	 *
+	 * Clobbers
+	 *   t0, t1, t2, t3, t4
+	 */
+
+	/* If maxlen is 0, return 0. */
+	beqz	a1, 3f
+
+	/* Number of irrelevant bytes in the first word. */
+	andi	t2, a0, SZREG-1
+
+	/* Align pointer. */
+	andi	t0, a0, -SZREG
+
+	li	t3, SZREG
+	sub	t3, t3, t2
+	slli	t2, t2, 3
+
+	/* Aligned boundary. */
+	add	t4, a0, a1
+	andi	t4, t4, -SZREG
+
+	/* Get the first word.  */
+	REG_L	t1, 0(t0)
+
+	/*
+	 * Shift away the partial data we loaded to remove the irrelevant bytes
+	 * preceding the string with the effect of adding NUL bytes at the
+	 * end of the string's first word.
+	 */
+	SHIFT	t1, t1, t2
+
+	/* Convert non-NUL into 0xff and NUL into 0x00. */
+	orc.b	t1, t1
+
+	/* Convert non-NUL into 0x00 and NUL into 0xff. */
+	not	t1, t1
+
+	/*
+	 * Search for the first set bit (corresponding to a NUL byte in the
+	 * original chunk).
+	 */
+	CZ	t1, t1
+
+	/*
+	 * The first chunk is special: compare against the number
+	 * of valid bytes in this chunk.
+	 */
+	srli	a0, t1, 3
+
+	/* Limit the result by maxlen. */
+	minu	a0, a0, a1
+
+	bgtu	t3, a0, 2f
+
+	/* Prepare for the word comparison loop. */
+	addi	t2, t0, SZREG
+	li	t3, -1
+
+	/*
+	 * Our critical loop is 4 instructions and processes data in
+	 * 4 byte or 8 byte chunks.
+	 */
+	.p2align 3
+1:
+	REG_L	t1, SZREG(t0)
+	addi	t0, t0, SZREG
+	orc.b	t1, t1
+	bgeu	t0, t4, 4f
+	beq	t1, t3, 1b
+4:
+	not	t1, t1
+	CZ	t1, t1
+	srli	t1, t1, 3
+
+	/* Get number of processed bytes. */
+	sub	t2, t0, t2
+
+	/* Add number of characters in the first word.  */
+	add	a0, a0, t2
+
+	/* Add number of characters in the last word.  */
+	add	a0, a0, t1
+
+	/* Ensure the final result does not exceed maxlen. */
+	minu	a0, a0, a1
+2:
+	ret
+3:
+	mv	a0, a1
+	ret
+
+.option pop
+#endif
+SYM_FUNC_END(strnlen)
+SYM_FUNC_ALIAS(__pi_strnlen, strnlen)
+EXPORT_SYMBOL(strnlen)
diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
index 530e497ca2f9..d7c0533108be 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
+purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o
 endif
 
 targets += $(purgatory-y)
@@ -32,6 +32,9 @@ $(obj)/strncmp.o: $(srctree)/arch/riscv/lib/strncmp.S FORCE
 $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
+$(obj)/strnlen.o: $(srctree)/arch/riscv/lib/strnlen.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

[PATCH v7 7/8] riscv: lib: add strchr() implementation

[Feng Jiang]

Add an assembly implementation of strchr() for RISC-V.

By eliminating stack frame management (prologue/epilogue) and optimizing
the function entries, the assembly version provides significant relative
gains for short strings where the fixed overhead of the C function is
most prominent. As string length increases, performance converges with
the generic C implementation.

Benchmark results (QEMU TCG, rv64):
  Length | Original (MB/s) | Optimized (MB/s) | Improvement
  -------|-----------------|------------------|------------
  1 B    | 21              | 22               | +4.8%
  7 B    | 113             | 121              | +7.1%
  16 B   | 195             | 202              | +3.6%
  512 B  | 376             | 389              | +3.5%
  4096 B | 394             | 393              | -0.3%

Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
 arch/riscv/include/asm/string.h |  3 +++
 arch/riscv/lib/Makefile         |  1 +
 arch/riscv/lib/strchr.S         | 35 +++++++++++++++++++++++++++++++++
 arch/riscv/purgatory/Makefile   |  5 ++++-
 4 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/lib/strchr.S

diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 16634d67c217..ca3ade82b124 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -31,6 +31,9 @@ extern asmlinkage int strncmp(const char *cs, const char *ct, size_t count);
 
 #define __HAVE_ARCH_STRNLEN
 extern asmlinkage __kernel_size_t strnlen(const char *, size_t);
+
+#define __HAVE_ARCH_STRCHR
+extern asmlinkage char *strchr(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 0969d8136df0..b7f804dce1c3 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -8,6 +8,7 @@ lib-y			+= strcmp.o
 lib-y			+= strlen.o
 lib-y			+= strncmp.o
 lib-y			+= strnlen.o
+lib-y			+= strchr.o
 endif
 lib-y			+= csum.o
 ifeq ($(CONFIG_MMU), y)
diff --git a/arch/riscv/lib/strchr.S b/arch/riscv/lib/strchr.S
new file mode 100644
index 000000000000..48c3a9da53e3
--- /dev/null
+++ b/arch/riscv/lib/strchr.S
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/*
+ * Copyright (C) 2025 Feng Jiang <jiangfeng@kylinos.cn>
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+/* char *strchr(const char *s, int c) */
+SYM_FUNC_START(strchr)
+	/*
+	 * Parameters
+	 *   a0 - The string to be searched
+	 *   a1 - The character to search for
+	 *
+	 * Returns
+	 *   a0 - Address of first occurrence of 'c' or 0
+	 *
+	 * Clobbers
+	 *   t0
+	 */
+	andi	a1, a1, 0xff
+1:
+	lbu	t0, 0(a0)
+	beq	t0, a1, 2f
+	addi	a0, a0, 1
+	bnez	t0, 1b
+	li	a0, 0
+2:
+	ret
+SYM_FUNC_END(strchr)
+
+SYM_FUNC_ALIAS_WEAK(__pi_strchr, strchr)
+EXPORT_SYMBOL(strchr)
diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
index d7c0533108be..e7b3d748c913 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
+purgatory-y += strcmp.o strlen.o strncmp.o strnlen.o strchr.o
 endif
 
 targets += $(purgatory-y)
@@ -35,6 +35,9 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
 $(obj)/strnlen.o: $(srctree)/arch/riscv/lib/strnlen.S FORCE
 	$(call if_changed_rule,as_o_S)
 
+$(obj)/strchr.o: $(srctree)/arch/riscv/lib/strchr.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

[PATCH v7 8/8] riscv: lib: add strrchr() implementation

[Feng Jiang]

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 <jiangfeng@kylinos.cn>
---
 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 <jiangfeng@kylinos.cn>
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+/* 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

Re: [PATCH v7 1/8] lib/string_kunit: add correctness test for strlen()

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:11AM +0800, Feng Jiang wrote:
> Add a KUnit test for strlen() to verify correctness across
> different string lengths and memory alignments. Use vmalloc()
> to place the NUL character at the page boundary to ensure
> over-reads are detected.
> 
> Suggested-by: Kees Cook <kees@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v7 2/8] lib/string_kunit: add correctness test for strnlen()

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:12AM +0800, Feng Jiang wrote:
> Add a KUnit test for strnlen() to verify correctness across
> different string lengths and memory alignments. Use vmalloc()
> to place the NUL character at the page boundary to ensure
> over-reads are detected.
> 
> Suggested-by: Andy Shevchenko <andy@kernel.org>
> Suggested-by: Kees Cook <kees@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v7 3/8] lib/string_kunit: add correctness test for strrchr()

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:13AM +0800, Feng Jiang wrote:
> Add a KUnit test for strrchr() to verify correctness across
> different string lengths and memory alignments. Use vmalloc()
> to place the NUL character at the page boundary to ensure
> over-reads are detected.
> 
> Suggested-by: Kees Cook <kees@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v7 4/8] lib/string_kunit: add performance benchmark for strlen()

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:14AM +0800, Feng Jiang wrote:
> Introduce a benchmarking framework to the string_kunit test suite to
> measure the execution efficiency of string functions.
> 
> The implementation is inspired by crc_benchmark(), measuring throughput
> (MB/s) and latency (ns/call) across a range of string lengths. It
> includes a warm-up phase, disables preemption during measurement, and
> uses a fixed seed for reproducible results.
> 
> This framework allows for comparing different implementations (e.g.,
> generic C vs. architecture-optimized assembly) within the KUnit
> environment.
> 
> Initially, provide a benchmark for strlen().
> 
> Suggested-by: Andy Shevchenko <andy@kernel.org>
> Suggested-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v7 5/8] lib/string_kunit: extend benchmarks to strnlen() and chr searches

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:15AM +0800, Feng Jiang wrote:
> Extend the string benchmarking suite to include strnlen(), strchr(),
> and strrchr().
> 
> For character search functions strchr() and strrchr(), the benchmark
> targets the NUL character. This ensures the entire string is scanned,
> providing a consistent measure of full-length processing efficiency
> comparable to strlen().
> 
> Suggested-by: Andy Shevchenko <andy@kernel.org>
> Suggested-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Kees Cook]

On Fri, Jan 30, 2026 at 10:50:10AM +0800, Feng Jiang wrote:
> This series provides optimized implementations of strnlen(), strchr(),
> and strrchr() for the RISC-V architecture. The strnlen() implementation
> is derived from the existing optimized strlen(). For strchr() and
> strrchr(), the current versions use simple byte-by-byte assembly logic,
> which will serve as a baseline for future Zbb-based optimizations.

I'm happy with the Kunit elements here, so unless Andy has other
feedback, please feel free to take this via the riscv tree. (Or if riscv
maintainers would prefer, I can take it via string.)

Thanks for working on this!

-Kees

-- 
Kees Cook

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Andy Shevchenko]

On Fri, Jan 30, 2026 at 09:37:36AM -0800, Kees Cook wrote:
> On Fri, Jan 30, 2026 at 10:50:10AM +0800, Feng Jiang wrote:
> > This series provides optimized implementations of strnlen(), strchr(),
> > and strrchr() for the RISC-V architecture. The strnlen() implementation
> > is derived from the existing optimized strlen(). For strchr() and
> > strrchr(), the current versions use simple byte-by-byte assembly logic,
> > which will serve as a baseline for future Zbb-based optimizations.
> 
> I'm happy with the Kunit elements here, so unless Andy has other
> feedback, please feel free to take this via the riscv tree. (Or if riscv
> maintainers would prefer, I can take it via string.)

I have an impression that I already gave some tag. Why aren't not here?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Feng Jiang]

On 2026/1/31 17:52, Andy Shevchenko wrote:
> On Fri, Jan 30, 2026 at 09:37:36AM -0800, Kees Cook wrote:
>> On Fri, Jan 30, 2026 at 10:50:10AM +0800, Feng Jiang wrote:
>>> This series provides optimized implementations of strnlen(), strchr(),
>>> and strrchr() for the RISC-V architecture. The strnlen() implementation
>>> is derived from the existing optimized strlen(). For strchr() and
>>> strrchr(), the current versions use simple byte-by-byte assembly logic,
>>> which will serve as a baseline for future Zbb-based optimizations.
>>
>> I'm happy with the Kunit elements here, so unless Andy has other
>> feedback, please feel free to take this via the riscv tree. (Or if riscv
>> maintainers would prefer, I can take it via string.)
> 
> I have an impression that I already gave some tag. Why aren't not here?
> 

I apologize for the confusion.

In v6, following Kees Cook's suggestion, I introduced a significant change to
the correctness test logic—using vmalloc() and page-boundary alignment to
detect over-reads. Since this part of the code was substantially rewritten,
I felt it was more responsible to drop the previous Acked-by and Tested-by
tags for the affected patches.

I would be very grateful if you could take a quick look at the new test
implementation in v7. If you are satisfied with the changes, I would be
honored to add your tags back.

-- 
With Best Regards,
Feng Jiang

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Feng Jiang]

On 2026/1/31 01:37, Kees Cook wrote:
> On Fri, Jan 30, 2026 at 10:50:10AM +0800, Feng Jiang wrote:
>> This series provides optimized implementations of strnlen(), strchr(),
>> and strrchr() for the RISC-V architecture. The strnlen() implementation
>> is derived from the existing optimized strlen(). For strchr() and
>> strrchr(), the current versions use simple byte-by-byte assembly logic,
>> which will serve as a baseline for future Zbb-based optimizations.
> 
> I'm happy with the Kunit elements here, so unless Andy has other
> feedback, please feel free to take this via the riscv tree. (Or if riscv
> maintainers would prefer, I can take it via string.)
> 
> Thanks for working on this!

Thank you very much for your review and the previous suggestions for improvement.
I truly appreciate your patience and guidance throughout this process!

-- 
With Best Regards,
Feng Jiang

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Feng Jiang]

On 2026/1/30 10:50, Feng Jiang wrote:
> This series provides optimized implementations of strnlen(), strchr(),
> and strrchr() for the RISC-V architecture. The strnlen() implementation
> is derived from the existing optimized strlen(). For strchr() and
> strrchr(), the current versions use simple byte-by-byte assembly logic,
> which will serve as a baseline for future Zbb-based optimizations.

Hi Palmer,

Just a gentle ping on this v7 series.

Kees is happy for this to go through the riscv tree. I've also followed up
with Andy regarding the tags for v7 on the mailing list.

Is there anything else needed for this series to be picked up?

-- 
With Best Regards,
Feng Jiang

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[Feng Jiang]

On 2026/1/30 10:50, Feng Jiang wrote:
> This series provides optimized implementations of strnlen(), strchr(),
> and strrchr() for the RISC-V architecture. The strnlen() implementation
> is derived from the existing optimized strlen(). For strchr() and
> strrchr(), the current versions use simple byte-by-byte assembly logic,
> which will serve as a baseline for future Zbb-based optimizations.

Hi Paul,

I'm very sorry, I dropped you from the 'To' list by mistake in v7.
Adding you back now for visibility.

-- 
With Best Regards,
Feng Jiang

Re: [PATCH v7 0/8] riscv: optimize string functions and add kunit tests

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Paul Walmsley <pjw@kernel.org>:

On Fri, 30 Jan 2026 10:50:10 +0800 you wrote:
> This series provides optimized implementations of strnlen(), strchr(),
> and strrchr() for the RISC-V architecture. The strnlen() implementation
> is derived from the existing optimized strlen(). For strchr() and
> strrchr(), the current versions use simple byte-by-byte assembly logic,
> which will serve as a baseline for future Zbb-based optimizations.
> 
> The patch series is organized into three parts:
> 1. Correctness Testing: The first three patches add KUnit test cases
>    for strlen(), strnlen(), and strrchr() to ensure the baseline and
>    optimized versions are functionally correct.
> 2. Benchmarking Tool: Patches 4 and 5 extend string_kunit to include
>    performance measurement capabilities, allowing for comparative
>    analysis within the KUnit environment.
> 3. Architectural Optimizations: The final three patches introduce the
>    RISC-V specific assembly implementations.
> 
> [...]

Here is the summary with links:
  - [v7,1/8] lib/string_kunit: add correctness test for strlen()
    https://git.kernel.org/riscv/c/abd6819bbf5b
  - [v7,2/8] lib/string_kunit: add correctness test for strnlen()
    https://git.kernel.org/riscv/c/31a361f466a2
  - [v7,3/8] lib/string_kunit: add correctness test for strrchr()
    https://git.kernel.org/riscv/c/68768cdba710
  - [v7,4/8] lib/string_kunit: add performance benchmark for strlen()
    https://git.kernel.org/riscv/c/54a7a0ca4b60
  - [v7,5/8] lib/string_kunit: extend benchmarks to strnlen() and chr searches
    https://git.kernel.org/riscv/c/d52a2222768b
  - [v7,6/8] riscv: lib: add strnlen() implementation
    https://git.kernel.org/riscv/c/018ffd93d25f
  - [v7,7/8] riscv: lib: add strchr() implementation
    https://git.kernel.org/riscv/c/bf74efe28f7c
  - [v7,8/8] riscv: lib: add strrchr() implementation
    https://git.kernel.org/riscv/c/3dcf058583a1

You are awesome, thank you!
-- 
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