selftests/nolibc: Add test for getcwd() and readlink()

Add a test that uses both getcwd() and readlink() so that both
are exercised.

First the happy path is tested by fetching what should be the
same string via getcwd() and readlink() and checking they match.

Then a few different combinations of bad parameters are passed to
getcwd() to make sure it returns NULL and sets errno in those
cases.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
Link: https://patch.msgid.link/20260702085101.3304547-4-daniel@thingy.jp
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

1 files changed, 53 insertions, 0 deletions

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index c1c1ce43a047..996e8d13508e 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -854,6 +854,58 @@ static int test_dirent(void)
 	return 0;
 }
 
+int test_getcwd(void)
+{
+	char cwd_syscall[PATH_MAX];
+	char cwd_proc[PATH_MAX];
+	ssize_t len;
+
+	/* Read where the link /proc/self/cwd points */
+	len = readlink("/proc/self/cwd", cwd_proc, sizeof(cwd_proc) - 1);
+	if (len <= 0)
+		return __LINE__;
+
+	/* Terminate the string from readlink() */
+	cwd_proc[len] = '\0';
+
+	/* Get the cwd via syscall */
+	if (getcwd(cwd_syscall, sizeof(cwd_syscall)) == NULL)
+		return __LINE__;
+
+	/* Fail if they aren't the same */
+	if (strcmp(cwd_proc, cwd_syscall) != 0)
+		return __LINE__;
+
+	/* Try getcwd() with NULL for the buffer,
+	 * should return NULL and an error in errno.
+	 * Other libc's allow this by allocating a buffer
+	 * internally.
+	 */
+	if (is_nolibc) {
+		errno = 0;
+		if (getcwd(NULL, 0) != NULL || !errno)
+			return __LINE__;
+	}
+
+	/* Try getcwd() with a buffer but make the size 0,
+	 * should return NULL and an error in errno.
+	 */
+	errno = 0;
+	if (getcwd(cwd_syscall, 0) != NULL || !errno)
+		return __LINE__;
+
+	/* Try getcwd() with a buffer but make the size 1,
+	 * should return NULL and an error in errno because
+	 * the string written to the buffer is terminated
+	 * so you need at least 2 bytes even for "/".
+	 */
+	errno = 0;
+	if (getcwd(cwd_syscall, 1) != NULL || !errno)
+		return __LINE__;
+
+	return 0;
+}
+
 int test_getrandom(void)
 {
 	uint64_t rng = 0;
@@ -1555,6 +1607,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(clock_getres);      EXPECT_SYSZR(1, clock_getres(CLOCK_MONOTONIC, &ts)); break;
 		CASE_TEST(clock_gettime);     EXPECT_SYSZR(1, clock_gettime(CLOCK_MONOTONIC, &ts)); break;
 		CASE_TEST(clock_settime);     EXPECT_SYSER(1, clock_settime(CLOCK_MONOTONIC, &ts), -1, EINVAL); break;
+		CASE_TEST(getcwd);            EXPECT_SYSZR(proc, test_getcwd()); break;
 		CASE_TEST(getpid);            EXPECT_SYSNE(1, getpid(), -1); break;
 		CASE_TEST(getppid);           EXPECT_SYSNE(1, getppid(), -1); break;
 		CASE_TEST(gettid);            EXPECT_SYSNE(has_gettid, gettid(), -1); break;