path: root/lib/tests/string_kunit.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Test cases for string functions.
 */

#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
#define STRCMP_CHANGE_POINT 1337
#define STRCMP_TEST_EXPECT_EQUAL(test, fn, ...) KUNIT_EXPECT_EQ(test, fn(__VA_ARGS__), 0)
#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

#define STRING_BENCH_SEED	888
#define STRING_BENCH_WORKLOAD	(1 * MEGA)

static void string_test_memset16(struct kunit *test)
{
	unsigned i, j, k;
	u16 v, *p;

	p = kunit_kzalloc(test, 256 * 2 * 2, GFP_KERNEL);
	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, p);

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset16(p + i, 0xb1b2, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1,
						"i:%d j:%d k:%d", i, j, k);
				} else if (k < i + j) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xb1b2,
						"i:%d j:%d k:%d", i, j, k);
				} else {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1,
						"i:%d j:%d k:%d", i, j, k);
				}
			}
		}
	}
}

static void string_test_memset32(struct kunit *test)
{
	unsigned i, j, k;
	u32 v, *p;

	p = kunit_kzalloc(test, 256 * 2 * 4, GFP_KERNEL);
	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, p);

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset32(p + i, 0xb1b2b3b4, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1a1a1,
						"i:%d j:%d k:%d", i, j, k);
				} else if (k < i + j) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xb1b2b3b4,
						"i:%d j:%d k:%d", i, j, k);
				} else {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1a1a1,
						"i:%d j:%d k:%d", i, j, k);
				}
			}
		}
	}
}

static void string_test_memset64(struct kunit *test)
{
	unsigned i, j, k;
	u64 v, *p;

	p = kunit_kzalloc(test, 256 * 2 * 8, GFP_KERNEL);
	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, p);

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset64(p + i, 0xb1b2b3b4b5b6b7b8ULL, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1a1a1a1a1a1a1ULL,
						"i:%d j:%d k:%d", i, j, k);
				} else if (k < i + j) {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xb1b2b3b4b5b6b7b8ULL,
						"i:%d j:%d k:%d", i, j, k);
				} else {
					KUNIT_ASSERT_EQ_MSG(test, v, 0xa1a1a1a1a1a1a1a1ULL,
						"i:%d j:%d k:%d", i, j, k);
				}
			}
		}
	}
}

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_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";
	const char *empty_string = "";
	char *result;
	int i;

	for (i = 0; i < strlen(test_string) + 1; i++) {
		result = strchr(test_string, test_string[i]);
		KUNIT_ASSERT_EQ_MSG(test, result - test_string, i,
				    "char:%c", 'a' + i);
	}

	result = strchr(empty_string, '\0');
	KUNIT_ASSERT_PTR_EQ(test, result, empty_string);

	result = strchr(empty_string, 'a');
	KUNIT_ASSERT_NULL(test, result);

	result = strchr(test_string, 'z');
	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";
	const char *empty_string = "";
	char *result;
	int i, j;

	for (i = 0; i < strlen(test_string) + 1; i++) {
		for (j = 0; j < strlen(test_string) + 2; j++) {
			result = strnchr(test_string, j, test_string[i]);
			if (j <= i) {
				KUNIT_ASSERT_NULL_MSG(test, result,
					"char:%c i:%d j:%d", 'a' + i, i, j);
			} else {
				KUNIT_ASSERT_EQ_MSG(test, result - test_string, i,
					"char:%c i:%d j:%d", 'a' + i, i, j);
			}
		}
	}

	result = strnchr(empty_string, 0, '\0');
	KUNIT_ASSERT_NULL(test, result);

	result = strnchr(empty_string, 1, '\0');
	KUNIT_ASSERT_PTR_EQ(test, result, empty_string);

	result = strnchr(empty_string, 1, 'a');
	KUNIT_ASSERT_NULL(test, result);

	result = strnchr(NULL, 0, '\0');
	KUNIT_ASSERT_NULL(test, result);
}

static void string_test_strspn(struct kunit *test)
{
	static const struct strspn_test {
		const char str[16];
		const char accept[16];
		const char reject[16];
		unsigned a;
		unsigned r;
	} tests[] = {
		{ "foobar", "", "", 0, 6 },
		{ "abba", "abc", "ABBA", 4, 4 },
		{ "abba", "a", "b", 1, 1 },
		{ "", "abc", "abc", 0, 0},
	};
	const struct strspn_test *s = tests;
	size_t i;

	for (i = 0; i < ARRAY_SIZE(tests); ++i, ++s) {
		KUNIT_ASSERT_EQ_MSG(test, s->a, strspn(s->str, s->accept),
			"i:%zu", i);
		KUNIT_ASSERT_EQ_MSG(test, s->r, strcspn(s->str, s->reject),
			"i:%zu", i);
	}
}

static char strcmp_buffer1[STRCMP_LARGE_BUF_LEN];
static char strcmp_buffer2[STRCMP_LARGE_BUF_LEN];

static void strcmp_fill_buffers(char fill1, char fill2)
{
	memset(strcmp_buffer1, fill1, STRCMP_LARGE_BUF_LEN);
	memset(strcmp_buffer2, fill2, STRCMP_LARGE_BUF_LEN);
	strcmp_buffer1[STRCMP_LARGE_BUF_LEN - 1] = 0;
	strcmp_buffer2[STRCMP_LARGE_BUF_LEN - 1] = 0;
}

static void string_test_strcmp(struct kunit *test)
{
	/* Equal strings */
	STRCMP_TEST_EXPECT_EQUAL(test, strcmp, "Hello, Kernel!", "Hello, Kernel!");
	/* First string is lexicographically less than the second */
	STRCMP_TEST_EXPECT_LOWER(test, strcmp, "Hello, KUnit!", "Hello, Kernel!");
	/* First string is lexicographically larger than the second */
	STRCMP_TEST_EXPECT_GREATER(test, strcmp, "Hello, Kernel!", "Hello, KUnit!");
	/* Empty string is always lexicographically less than any non-empty string */
	STRCMP_TEST_EXPECT_LOWER(test, strcmp, "", "Non-empty string");
	/* Two empty strings should be equal */
	STRCMP_TEST_EXPECT_EQUAL(test, strcmp, "", "");
	/* Compare two strings which have only one char difference */
	STRCMP_TEST_EXPECT_LOWER(test, strcmp, "Abacaba", "Abadaba");
	/* Compare two strings which have the same prefix*/
	STRCMP_TEST_EXPECT_LOWER(test, strcmp, "Just a string", "Just a string and something else");
}

static void string_test_strcmp_long_strings(struct kunit *test)
{
	strcmp_fill_buffers('B', 'B');
	STRCMP_TEST_EXPECT_EQUAL(test, strcmp, strcmp_buffer1, strcmp_buffer2);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'A';
	STRCMP_TEST_EXPECT_LOWER(test, strcmp, strcmp_buffer1, strcmp_buffer2);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'C';
	STRCMP_TEST_EXPECT_GREATER(test, strcmp, strcmp_buffer1, strcmp_buffer2);
}

static void string_test_strncmp(struct kunit *test)
{
	/* Equal strings */
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, "Hello, KUnit!", "Hello, KUnit!", 13);
	/* First string is lexicographically less than the second */
	STRCMP_TEST_EXPECT_LOWER(test, strncmp, "Hello, KUnit!", "Hello, Kernel!", 13);
	/* Result is always 'equal' when count = 0 */
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, "Hello, Kernel!", "Hello, KUnit!", 0);
	/* Strings with common prefix are equal if count = length of prefix */
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, "Abacaba", "Abadaba", 3);
	/* Strings with common prefix are not equal when count = length of prefix + 1 */
	STRCMP_TEST_EXPECT_LOWER(test, strncmp, "Abacaba", "Abadaba", 4);
	/* If one string is a prefix of another, the shorter string is lexicographically smaller */
	STRCMP_TEST_EXPECT_LOWER(test, strncmp, "Just a string", "Just a string and something else",
				 strlen("Just a string and something else"));
	/*
	 * If one string is a prefix of another, and we check first length
	 * of prefix chars, the result is 'equal'
	 */
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, "Just a string", "Just a string and something else",
				 strlen("Just a string"));
}

static void string_test_strncmp_long_strings(struct kunit *test)
{
	strcmp_fill_buffers('B', 'B');
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_LARGE_BUF_LEN);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'A';
	STRCMP_TEST_EXPECT_LOWER(test, strncmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_LARGE_BUF_LEN);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'C';
	STRCMP_TEST_EXPECT_GREATER(test, strncmp, strcmp_buffer1,
				   strcmp_buffer2, STRCMP_LARGE_BUF_LEN);
	/* the strings are equal up to STRCMP_CHANGE_POINT */
	STRCMP_TEST_EXPECT_EQUAL(test, strncmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_CHANGE_POINT);
	STRCMP_TEST_EXPECT_GREATER(test, strncmp, strcmp_buffer1,
				   strcmp_buffer2, STRCMP_CHANGE_POINT + 1);
}

static void string_test_strcasecmp(struct kunit *test)
{
	/* Same strings in different case should be equal */
	STRCMP_TEST_EXPECT_EQUAL(test, strcasecmp, "Hello, Kernel!", "HeLLO, KErNeL!");
	/* Empty strings should be equal */
	STRCMP_TEST_EXPECT_EQUAL(test, strcasecmp, "", "");
	/* Despite ascii code for 'a' is larger than ascii code for 'B', 'a' < 'B' */
	STRCMP_TEST_EXPECT_LOWER(test, strcasecmp, "a", "B");
	STRCMP_TEST_EXPECT_GREATER(test, strcasecmp, "B", "a");
	/* Special symbols and numbers should be processed correctly */
	STRCMP_TEST_EXPECT_EQUAL(test, strcasecmp, "-+**.1230ghTTT~^", "-+**.1230Ghttt~^");
}

static void string_test_strcasecmp_long_strings(struct kunit *test)
{
	strcmp_fill_buffers('b', 'B');
	STRCMP_TEST_EXPECT_EQUAL(test, strcasecmp, strcmp_buffer1, strcmp_buffer2);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'a';
	STRCMP_TEST_EXPECT_LOWER(test, strcasecmp, strcmp_buffer1, strcmp_buffer2);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'C';
	STRCMP_TEST_EXPECT_GREATER(test, strcasecmp, strcmp_buffer1, strcmp_buffer2);
}

static void string_test_strncasecmp(struct kunit *test)
{
	/* Same strings in different case should be equal */
	STRCMP_TEST_EXPECT_EQUAL(test, strncasecmp, "AbAcAbA", "Abacaba", strlen("Abacaba"));
	/* strncasecmp should check 'count' chars only */
	STRCMP_TEST_EXPECT_EQUAL(test, strncasecmp, "AbaCaBa", "abaCaDa", 5);
	STRCMP_TEST_EXPECT_LOWER(test, strncasecmp, "a", "B", 1);
	STRCMP_TEST_EXPECT_GREATER(test, strncasecmp, "B", "a", 1);
	/* Result is always 'equal' when count = 0 */
	STRCMP_TEST_EXPECT_EQUAL(test, strncasecmp, "Abacaba", "Not abacaba", 0);
}

static void string_test_strncasecmp_long_strings(struct kunit *test)
{
	strcmp_fill_buffers('b', 'B');
	STRCMP_TEST_EXPECT_EQUAL(test, strncasecmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_LARGE_BUF_LEN);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'a';
	STRCMP_TEST_EXPECT_LOWER(test, strncasecmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_LARGE_BUF_LEN);

	strcmp_buffer1[STRCMP_CHANGE_POINT] = 'C';
	STRCMP_TEST_EXPECT_GREATER(test, strncasecmp, strcmp_buffer1,
				   strcmp_buffer2, STRCMP_LARGE_BUF_LEN);

	STRCMP_TEST_EXPECT_EQUAL(test, strncasecmp, strcmp_buffer1,
				 strcmp_buffer2, STRCMP_CHANGE_POINT);
	STRCMP_TEST_EXPECT_GREATER(test, strncasecmp, strcmp_buffer1,
				   strcmp_buffer2, STRCMP_CHANGE_POINT + 1);
}

/**
 * strscpy_check() - Run a specific test case.
 * @test: KUnit test context pointer
 * @src: Source string, argument to strscpy_pad()
 * @count: Size of destination buffer, argument to strscpy_pad()
 * @expected: Expected return value from call to strscpy_pad()
 * @chars: Number of characters from the src string expected to be
 *         written to the dst buffer.
 * @terminator: 1 if there should be a terminating null byte 0 otherwise.
 * @pad: Number of pad characters expected (in the tail of dst buffer).
 *       (@pad does not include the null terminator byte.)
 *
 * Calls strscpy_pad() and verifies the return value and state of the
 * destination buffer after the call returns.
 */
static void strscpy_check(struct kunit *test, char *src, int count,
			  int expected, int chars, int terminator, int pad)
{
	int nr_bytes_poison;
	int max_expected;
	int max_count;
	int written;
	char buf[6];
	int index, i;
	const char POISON = 'z';

	KUNIT_ASSERT_TRUE_MSG(test, src != NULL,
			      "null source string not supported");

	memset(buf, POISON, sizeof(buf));
	/* Future proofing test suite, validate args */
	max_count = sizeof(buf) - 2; /* Space for null and to verify overflow */
	max_expected = count - 1;    /* Space for the null */

	KUNIT_ASSERT_LE_MSG(test, count, max_count,
		"count (%d) is too big (%d) ... aborting", count, max_count);
	KUNIT_EXPECT_LE_MSG(test, expected, max_expected,
		"expected (%d) is bigger than can possibly be returned (%d)",
		expected, max_expected);

	written = strscpy_pad(buf, src, count);
	KUNIT_ASSERT_EQ(test, written, expected);

	if (count && written == -E2BIG) {
		KUNIT_ASSERT_EQ_MSG(test, 0, strncmp(buf, src, count - 1),
			"buffer state invalid for -E2BIG");
		KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
			"too big string is not null terminated correctly");
	}

	for (i = 0; i < chars; i++)
		KUNIT_ASSERT_EQ_MSG(test, buf[i], src[i],
			"buf[i]==%c != src[i]==%c", buf[i], src[i]);

	if (terminator)
		KUNIT_ASSERT_EQ_MSG(test, buf[count - 1], '\0',
			"string is not null terminated correctly");

	for (i = 0; i < pad; i++) {
		index = chars + terminator + i;
		KUNIT_ASSERT_EQ_MSG(test, buf[index], '\0',
			"padding missing at index: %d", i);
	}

	nr_bytes_poison = sizeof(buf) - chars - terminator - pad;
	for (i = 0; i < nr_bytes_poison; i++) {
		index = sizeof(buf) - 1 - i; /* Check from the end back */
		KUNIT_ASSERT_EQ_MSG(test, buf[index], POISON,
			"poison value missing at index: %d", i);
	}
}

static void string_test_strscpy(struct kunit *test)
{
	char dest[8];

	/*
	 * strscpy_check() uses a destination buffer of size 6 and needs at
	 * least 2 characters spare (one for null and one to check for
	 * overflow).  This means we should only call tc() with
	 * strings up to a maximum of 4 characters long and 'count'
	 * should not exceed 4.  To test with longer strings increase
	 * the buffer size in tc().
	 */

	/* strscpy_check(test, src, count, expected, chars, terminator, pad) */
	strscpy_check(test, "a", 0, -E2BIG, 0, 0, 0);
	strscpy_check(test, "",  0, -E2BIG, 0, 0, 0);

	strscpy_check(test, "a", 1, -E2BIG, 0, 1, 0);
	strscpy_check(test, "",  1, 0,	 0, 1, 0);

	strscpy_check(test, "ab", 2, -E2BIG, 1, 1, 0);
	strscpy_check(test, "a",  2, 1,	  1, 1, 0);
	strscpy_check(test, "",   2, 0,	  0, 1, 1);

	strscpy_check(test, "abc", 3, -E2BIG, 2, 1, 0);
	strscpy_check(test, "ab",  3, 2,	   2, 1, 0);
	strscpy_check(test, "a",   3, 1,	   1, 1, 1);
	strscpy_check(test, "",    3, 0,	   0, 1, 2);

	strscpy_check(test, "abcd", 4, -E2BIG, 3, 1, 0);
	strscpy_check(test, "abc",  4, 3,	    3, 1, 0);
	strscpy_check(test, "ab",   4, 2,	    2, 1, 1);
	strscpy_check(test, "a",    4, 1,	    1, 1, 2);
	strscpy_check(test, "",     4, 0,	    0, 1, 3);

	/* Compile-time-known source strings. */
	KUNIT_EXPECT_EQ(test, strscpy(dest, "", ARRAY_SIZE(dest)), 0);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "", 3), 0);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "", 1), 0);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "", 0), -E2BIG);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", ARRAY_SIZE(dest)), 5);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 3), -E2BIG);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 1), -E2BIG);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 0), -E2BIG);
	KUNIT_EXPECT_EQ(test, strscpy(dest, "This is too long", ARRAY_SIZE(dest)), -E2BIG);
}

static volatile int unconst;

static void string_test_strcat(struct kunit *test)
{
	char dest[8];

	/* Destination is terminated. */
	memset(dest, 0, sizeof(dest));
	KUNIT_EXPECT_EQ(test, strlen(dest), 0);
	/* Empty copy does nothing. */
	KUNIT_EXPECT_TRUE(test, strcat(dest, "") == dest);
	KUNIT_EXPECT_STREQ(test, dest, "");
	/* 4 characters copied in, stops at %NUL. */
	KUNIT_EXPECT_TRUE(test, strcat(dest, "four\000123") == dest);
	KUNIT_EXPECT_STREQ(test, dest, "four");
	KUNIT_EXPECT_EQ(test, dest[5], '\0');
	/* 2 more characters copied in okay. */
	KUNIT_EXPECT_TRUE(test, strcat(dest, "AB") == dest);
	KUNIT_EXPECT_STREQ(test, dest, "fourAB");
}

static void string_test_strncat(struct kunit *test)
{
	char dest[8];

	/* Destination is terminated. */
	memset(dest, 0, sizeof(dest));
	KUNIT_EXPECT_EQ(test, strlen(dest), 0);
	/* Empty copy of size 0 does nothing. */
	KUNIT_EXPECT_TRUE(test, strncat(dest, "", 0 + unconst) == dest);
	KUNIT_EXPECT_STREQ(test, dest, "");
	/* Empty copy of size 1 does nothing too. */
	KUNIT_EXPECT_TRUE(test, strncat(dest, "", 1 + unconst) == dest);
	KUNIT_EXPECT_STREQ(test, dest, "");
	/* Copy of max 0 characters should do nothing. */
	KUNIT_EXPECT_TRUE(test, strncat(dest, "asdf", 0 + unconst) == dest);
	KUNIT_EXPECT_STREQ(test, dest, "");

	/* 4 characters copied in, even if max is 8. */
	KUNIT_EXPECT_TRUE(test, strncat(dest, "four\000123", 8 + unconst) == dest);
	KUNIT_EXPECT_STREQ(test, dest, "four");
	KUNIT_EXPECT_EQ(test, dest[5], '\0');
	KUNIT_EXPECT_EQ(test, dest[6], '\0');
	/* 2 characters copied in okay, 2 ignored. */
	KUNIT_EXPECT_TRUE(test, strncat(dest, "ABCD", 2 + unconst) == dest);
	KUNIT_EXPECT_STREQ(test, dest, "fourAB");
}

static void string_test_strlcat(struct kunit *test)
{
	char dest[8] = "";
	int len = sizeof(dest) + unconst;

	/* Destination is terminated. */
	KUNIT_EXPECT_EQ(test, strlen(dest), 0);
	/* Empty copy is size 0. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "", len), 0);
	KUNIT_EXPECT_STREQ(test, dest, "");
	/* Size 1 should keep buffer terminated, report size of source only. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "four", 1 + unconst), 4);
	KUNIT_EXPECT_STREQ(test, dest, "");

	/* 4 characters copied in. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "four", len), 4);
	KUNIT_EXPECT_STREQ(test, dest, "four");
	/* 2 characters copied in okay, gets to 6 total. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "AB", len), 6);
	KUNIT_EXPECT_STREQ(test, dest, "fourAB");
	/* 2 characters ignored if max size (7) reached. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "CD", 7 + unconst), 8);
	KUNIT_EXPECT_STREQ(test, dest, "fourAB");
	/* 1 of 2 characters skipped, now at true max size. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "EFG", len), 9);
	KUNIT_EXPECT_STREQ(test, dest, "fourABE");
	/* Everything else ignored, now at full size. */
	KUNIT_EXPECT_EQ(test, strlcat(dest, "1234", len), 11);
	KUNIT_EXPECT_STREQ(test, dest, "fourABE");
}

static void string_test_strtomem(struct kunit *test)
{
	static const char input[sizeof(unsigned long)] = "hi";
	static const char truncate[] = "this is too long";
	struct {
		unsigned long canary1;
		unsigned char output[sizeof(unsigned long)] __nonstring;
		unsigned long canary2;
	} wrap;

	memset(&wrap, 0xFF, sizeof(wrap));
	KUNIT_EXPECT_EQ_MSG(test, wrap.canary1, ULONG_MAX,
			    "bad initial canary value");
	KUNIT_EXPECT_EQ_MSG(test, wrap.canary2, ULONG_MAX,
			    "bad initial canary value");

	/* Check unpadded copy leaves surroundings untouched. */
	strtomem(wrap.output, input);
	KUNIT_EXPECT_EQ(test, wrap.canary1, ULONG_MAX);
	KUNIT_EXPECT_EQ(test, wrap.output[0], input[0]);
	KUNIT_EXPECT_EQ(test, wrap.output[1], input[1]);
	for (size_t i = 2; i < sizeof(wrap.output); i++)
		KUNIT_EXPECT_EQ(test, wrap.output[i], 0xFF);
	KUNIT_EXPECT_EQ(test, wrap.canary2, ULONG_MAX);

	/* Check truncated copy leaves surroundings untouched. */
	memset(&wrap, 0xFF, sizeof(wrap));
	strtomem(wrap.output, truncate);
	KUNIT_EXPECT_EQ(test, wrap.canary1, ULONG_MAX);
	for (size_t i = 0; i < sizeof(wrap.output); i++)
		KUNIT_EXPECT_EQ(test, wrap.output[i], truncate[i]);
	KUNIT_EXPECT_EQ(test, wrap.canary2, ULONG_MAX);

	/* Check padded copy leaves only string padded. */
	memset(&wrap, 0xFF, sizeof(wrap));
	strtomem_pad(wrap.output, input, 0xAA);
	KUNIT_EXPECT_EQ(test, wrap.canary1, ULONG_MAX);
	KUNIT_EXPECT_EQ(test, wrap.output[0], input[0]);
	KUNIT_EXPECT_EQ(test, wrap.output[1], input[1]);
	for (size_t i = 2; i < sizeof(wrap.output); i++)
		KUNIT_EXPECT_EQ(test, wrap.output[i], 0xAA);
	KUNIT_EXPECT_EQ(test, wrap.canary2, ULONG_MAX);

	/* Check truncated padded copy has no padding. */
	memset(&wrap, 0xFF, sizeof(wrap));
	strtomem(wrap.output, truncate);
	KUNIT_EXPECT_EQ(test, wrap.canary1, ULONG_MAX);
	for (size_t i = 0; i < sizeof(wrap.output); i++)
		KUNIT_EXPECT_EQ(test, wrap.output[i], truncate[i]);
	KUNIT_EXPECT_EQ(test, wrap.canary2, ULONG_MAX);
}


static void string_test_memtostr(struct kunit *test)
{
	char nonstring[7] __nonstring = { 'a', 'b', 'c', 'd', 'e', 'f', 'g' };
	char nonstring_small[3] __nonstring = { 'a', 'b', 'c' };
	char dest[sizeof(nonstring) + 1];

	/* Copy in a non-NUL-terminated string into exactly right-sized dest. */
	KUNIT_EXPECT_EQ(test, sizeof(dest), sizeof(nonstring) + 1);
	memset(dest, 'X', sizeof(dest));
	memtostr(dest, nonstring);
	KUNIT_EXPECT_STREQ(test, dest, "abcdefg");
	memset(dest, 'X', sizeof(dest));
	memtostr(dest, nonstring_small);
	KUNIT_EXPECT_STREQ(test, dest, "abc");
	KUNIT_EXPECT_EQ(test, dest[7], 'X');

	memset(dest, 'X', sizeof(dest));
	memtostr_pad(dest, nonstring);
	KUNIT_EXPECT_STREQ(test, dest, "abcdefg");
	memset(dest, 'X', sizeof(dest));
	memtostr_pad(dest, nonstring_small);
	KUNIT_EXPECT_STREQ(test, dest, "abc");
	KUNIT_EXPECT_EQ(test, dest[7], '\0');
}

static void string_test_strends(struct kunit *test)
{
	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "bar"));
	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "-bar"));
	KUNIT_EXPECT_TRUE(test, strends("foobar", "foobar"));
	KUNIT_EXPECT_TRUE(test, strends("foobar", ""));
	KUNIT_EXPECT_FALSE(test, strends("bar", "foobar"));
	KUNIT_EXPECT_FALSE(test, strends("", "foo"));
	KUNIT_EXPECT_FALSE(test, strends("foobar", "ba"));
	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 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),
	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_strrchr),
	KUNIT_CASE(string_test_strspn),
	KUNIT_CASE(string_test_strcmp),
	KUNIT_CASE(string_test_strcmp_long_strings),
	KUNIT_CASE(string_test_strncmp),
	KUNIT_CASE(string_test_strncmp_long_strings),
	KUNIT_CASE(string_test_strcasecmp),
	KUNIT_CASE(string_test_strcasecmp_long_strings),
	KUNIT_CASE(string_test_strncasecmp),
	KUNIT_CASE(string_test_strncasecmp_long_strings),
	KUNIT_CASE(string_test_strscpy),
	KUNIT_CASE(string_test_strcat),
	KUNIT_CASE(string_test_strncat),
	KUNIT_CASE(string_test_strlcat),
	KUNIT_CASE(string_test_strtomem),
	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),
	{}
};

static struct kunit_suite string_test_suite = {
	.name = "string",
	.test_cases = string_test_cases,
};

kunit_test_suites(&string_test_suite);

MODULE_DESCRIPTION("Test cases for string functions");
MODULE_LICENSE("GPL v2");