[PATCH 0/3] nolibc: Add getcwd() and readlink()

[PATCH 0/3] nolibc: Add getcwd() and readlink()

[Daniel Palmer]

Me again :)

I needed getcwd() for something. So I added that, then realised
I also needed readlink() to test the result of getcwd().

This adds getcwd() and readlink() then adds a test that uses
both.

nolibc selftest passed on: i386 x86_64 x32 arm64 arm armthumb mips32le
mips32be mipsn32le mipsn32be mips64le mips64be ppc ppc64 ppc64le riscv32
riscv64 sparc32 sparc64 m68k

Daniel Palmer (3):
  tools/nolibc: unistd: Add getcwd()
  tools/nolibc: unistd: Add readlink()
  selftests/nolibc: Add test for getcwd() and readlink()

 tools/include/nolibc/unistd.h                | 42 ++++++++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c | 26 ++++++++++++
 2 files changed, 68 insertions(+)


base-commit: 266df86c4893fed1a7f027e767fe1c7f6456b100
-- 
2.53.0

[PATCH 1/3] tools/nolibc: unistd: Add getcwd()

[Daniel Palmer]

Add getcwd() for getting the current working directory.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 tools/include/nolibc/unistd.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
index 5882a6862066..c7f89c56bc9b 100644
--- a/tools/include/nolibc/unistd.h
+++ b/tools/include/nolibc/unistd.h
@@ -48,6 +48,28 @@ int access(const char *path, int amode)
 	return faccessat(AT_FDCWD, path, amode, 0);
 }
 
+/*
+ * char *getcwd(char *buf, size_t size);
+ */
+
+static __attribute__((unused))
+int _sys_getcwd(char *buf, size_t size)
+{
+	return __nolibc_syscall2(__NR_getcwd, buf, size);
+}
+
+static __attribute__((unused))
+char *getcwd(char *buf, size_t size)
+{
+	/* If successful we get the number of bytes written into
+	 * the buffer, so check the result is positive.
+	 */
+	if (__sysret(_sys_getcwd(buf, size)) > 0)
+		return buf;
+
+	/* On error return NULL, __sysret() above will have set errno */
+	return NULL;
+}
 
 static __attribute__((unused))
 int msleep(unsigned int msecs)
-- 
2.53.0

Re: [PATCH 1/3] tools/nolibc: unistd: Add getcwd()

[Thomas Weißschuh]

May 2, 2026 09:25:43 Daniel Palmer <daniel@thingy.jp>:

> Add getcwd() for getting the current working directory.
>
> Signed-off-by: Daniel Palmer <daniel@thingy.jp>
> ---
> tools/include/nolibc/unistd.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
> index 5882a6862066..c7f89c56bc9b 100644
> --- a/tools/include/nolibc/unistd.h
> +++ b/tools/include/nolibc/unistd.h
> @@ -48,6 +48,28 @@ int access(const char *path, int amode)
>     return faccessat(AT_FDCWD, path, amode, 0);
> }
>
> +/*
> + * char *getcwd(char *buf, size_t size);
> + */
> +
> +static __attribute__((unused))
> +int _sys_getcwd(char *buf, size_t size)
> +{
> +   return __nolibc_syscall2(__NR_getcwd, buf, size);
> +}
> +
> +static __attribute__((unused))
> +char *getcwd(char *buf, size_t size)
> +{
> +   /* If successful we get the number of bytes written into
> +    * the buffer, so check the result is positive.
> +    */
> +   if (__sysret(_sys_getcwd(buf, size)) > 0)

According to the comment before the system call implementation this should be '>= 0'.

> +       return buf;
> +
> +   /* On error return NULL, __sysret() above will have set errno */
> +   return NULL;
> +}
>
> static __attribute__((unused))
> int msleep(unsigned int msecs)
> --
> 2.53.0

Re: [PATCH 1/3] tools/nolibc: unistd: Add getcwd()

[Daniel Palmer]

Hi Thomas,

On Sat, 2 May 2026 at 22:41, Thomas Weißschuh <linux@weissschuh.net> wrote:
> > +{
> > +   /* If successful we get the number of bytes written into
> > +    * the buffer, so check the result is positive.
> > +    */
> > +   if (__sysret(_sys_getcwd(buf, size)) > 0)
>
> According to the comment before the system call implementation this should be '>= 0'.

I think 0 is an error and the comment I wrote is a bit off. I think it
should be "result is greater than 0".
Anyhow, I wondered what musl and glibc were doing around this as I
couldn't work it out from the manpage.
Long story short I have adjusted this so the logic follows what musl
is doing and I'll send a v2.

Thanks,

Daniel.

[PATCH 2/3] tools/nolibc: unistd: Add readlink()

[Daniel Palmer]

Add readlink(). This is needed to test getcwd();

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 tools/include/nolibc/unistd.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
index c7f89c56bc9b..309a4e0e65d2 100644
--- a/tools/include/nolibc/unistd.h
+++ b/tools/include/nolibc/unistd.h
@@ -84,6 +84,26 @@ int msleep(unsigned int msecs)
 		return 0;
 }
 
+/*
+ * ssize_t readlink(const char *path, char *buf, size_t bufsiz);
+ */
+
+static __attribute__((unused))
+ssize_t _sys_readlink(const char *path, char *buf, size_t bufsiz)
+{
+#ifdef __NR_readlink
+	return __nolibc_syscall3(__NR_readlink, path, buf, bufsiz);
+#else
+	return __nolibc_syscall4(__NR_readlinkat, AT_FDCWD, path, buf, bufsiz);
+#endif
+}
+
+static __attribute__((unused))
+ssize_t readlink(const char *path, char *buf, size_t bufsiz)
+{
+	return __sysret(_sys_readlink(path, buf, bufsiz));
+}
+
 static __attribute__((unused))
 unsigned int sleep(unsigned int seconds)
 {
-- 
2.53.0

Re: [PATCH 2/3] tools/nolibc: unistd: Add readlink()

[Thomas Weißschuh]

May 2, 2026 09:25:44 Daniel Palmer <daniel@thingy.jp>:

> Add readlink(). This is needed to test getcwd();
>
> Signed-off-by: Daniel Palmer <daniel@thingy.jp>
> ---
> tools/include/nolibc/unistd.h | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
> index c7f89c56bc9b..309a4e0e65d2 100644
> --- a/tools/include/nolibc/unistd.h
> +++ b/tools/include/nolibc/unistd.h
> @@ -84,6 +84,26 @@ int msleep(unsigned int msecs)
>         return 0;
> }
>
> +/*
> + * ssize_t readlink(const char *path, char *buf, size_t bufsiz);
> + */
> +
> +static __attribute__((unused))
> +ssize_t _sys_readlink(const char *path, char *buf, size_t bufsiz)
> +{
> +#ifdef __NR_readlink
> +   return __nolibc_syscall3(__NR_readlink, path, buf, bufsiz);
> +#else
> +   return __nolibc_syscall4(__NR_readlinkat, AT_FDCWD, path, buf, bufsiz);
> +#endif

Every architecture should have readli kat, no?
Then I think we can drop the fallback to regular readlink.

> +}
> +
> +static __attribute__((unused))
> +ssize_t readlink(const char *path, char *buf, size_t bufsiz)
> +{
> +   return __sysret(_sys_readlink(path, buf, bufsiz));
> +}
> +
> static __attribute__((unused))
> unsigned int sleep(unsigned int seconds)
> {
> --
> 2.53.0

[PATCH 3/3] selftests/nolibc: Add test for getcwd() and readlink()

[Daniel Palmer]

Add a test for getcwd() that uses readlink() so tests that
at the same time.

This is very basic, just getting what should be the same
string via getcwd() and readlink() and then checking they
are the same.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 26 ++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 08610cacf030..54513fb9a16a 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -849,6 +849,31 @@ static int test_dirent(void)
 	return 0;
 }
 
+static int test_getcwd(void)
+{
+	char cwd_syscall[1024];
+	char cwd_proc[1024];
+	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 -1;
+
+	/* Terminate the string from readlink() */
+	cwd_proc[len] = '\0';
+
+	/* Get the cwd via syscall */
+	if (getcwd(cwd_syscall, sizeof(cwd_syscall)) == NULL)
+		return -1;
+
+	/* Fail if they aren't the same */
+	if (strcmp(cwd_proc, cwd_syscall) != 0)
+		return -1;
+
+	return 0;
+}
+
 int test_getrandom(void)
 {
 	uint64_t rng = 0;
@@ -1477,6 +1502,7 @@ 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(1, 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;
-- 
2.53.0

Re: [PATCH 3/3] selftests/nolibc: Add test for getcwd() and readlink()

[Thomas Weißschuh]

May 2, 2026 09:25:45 Daniel Palmer <daniel@thingy.jp>:

> Add a test for getcwd() that uses readlink() so tests that
> at the same time.
>
> This is very basic, just getting what should be the same
> string via getcwd() and readlink() and then checking they
> are the same.
>
> Signed-off-by: Daniel Palmer <daniel@thingy.jp>
> ---
> tools/testing/selftests/nolibc/nolibc-test.c | 26 ++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> index 08610cacf030..54513fb9a16a 100644
> --- a/tools/testing/selftests/nolibc/nolibc-test.c
> +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> @@ -849,6 +849,31 @@ static int test_dirent(void)
>     return 0;
> }
>
> +static int test_getcwd(void)
> +{
> +   char cwd_syscall[1024];
> +   char cwd_proc[1024];
> +   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 -1;
> +
> +   /* Terminate the string from readlink() */
> +   cwd_proc[len] = '\0';
> +
> +   /* Get the cwd via syscall */
> +   if (getcwd(cwd_syscall, sizeof(cwd_syscall)) == NULL)
> +       return -1;
> +
> +   /* Fail if they aren't the same */
> +   if (strcmp(cwd_proc, cwd_syscall) != 0)
> +       return -1;
> +
> +   return 0;
> +}
> +
> int test_getrandom(void)
> {
>     uint64_t rng = 0;
> @@ -1477,6 +1502,7 @@ 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(1, test_getcwd()); break;

EXPECT_SYSZR(proc, ...)

>         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;
> --
> 2.53.0