Add support for the file descriptor based variant of chdir().

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 tools/include/nolibc/sys.h                   | 13 +++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index c5564f57deec88b8aa70291fcf6f9ca4dbc1d03f..a4b0fdb9b641230174f5e62d62762f59af81a00e 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -118,6 +118,7 @@ void *sbrk(intptr_t inc)
 
 /*
  * int chdir(const char *path);
+ * int fchdir(int fildes);
  */
 
 static __attribute__((unused))
@@ -132,6 +133,18 @@ int chdir(const char *path)
 	return __sysret(sys_chdir(path));
 }
 
+static __attribute__((unused))
+int sys_fchdir(int fildes)
+{
+	return my_syscall1(__NR_fchdir, fildes);
+}
+
+static __attribute__((unused))
+int fchdir(int fildes)
+{
+	return __sysret(sys_fchdir(fildes));
+}
+
 
 /*
  * int chmod(const char *path, mode_t mode);
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 29de21595fc95341c2aa975375a8d471cb3933fc..5927a84466cc0ede3b99611e134a8c6b8ab91e72 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1343,6 +1343,8 @@ int run_syscall(int min, int max)
 		CASE_TEST(dup3_0);            tmp = dup3(0, 100, 0);  EXPECT_SYSNE(1, tmp, -1); close(tmp); break;
 		CASE_TEST(dup3_m1);           tmp = dup3(-1, 100, 0); EXPECT_SYSER(1, tmp, -1, EBADF); if (tmp != -1) close(tmp); break;
 		CASE_TEST(execve_root);       EXPECT_SYSER(1, execve("/", (char*[]){ [0] = "/", [1] = NULL }, NULL), -1, EACCES); break;
+		CASE_TEST(fchdir_stdin);      EXPECT_SYSER(1, fchdir(STDIN_FILENO), -1, ENOTDIR); break;
+		CASE_TEST(fchdir_badfd);      EXPECT_SYSER(1, fchdir(-1), -1, EBADF); break;
 		CASE_TEST(file_stream);       EXPECT_SYSZR(1, test_file_stream()); break;
 		CASE_TEST(fork);              EXPECT_SYSZR(1, test_fork(FORK_STANDARD)); break;
 		CASE_TEST(getdents64_root);   EXPECT_SYSNE(1, test_getdents64("/"), -1); break;

---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251107-nolibc-fchdir-2645c298a538

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@linutronix.de>

Hi Thomas,

On Fri, Nov 07, 2025 at 03:13:38PM +0100, Thomas Weißschuh wrote:
> Add support for the file descriptor based variant of chdir().
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
>  tools/include/nolibc/sys.h                   | 13 +++++++++++++
>  tools/testing/selftests/nolibc/nolibc-test.c |  2 ++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> index c5564f57deec88b8aa70291fcf6f9ca4dbc1d03f..a4b0fdb9b641230174f5e62d62762f59af81a00e 100644
> --- a/tools/include/nolibc/sys.h
> +++ b/tools/include/nolibc/sys.h
> @@ -118,6 +118,7 @@ void *sbrk(intptr_t inc)
>  
>  /*
>   * int chdir(const char *path);
> + * int fchdir(int fildes);
>   */
>  
>  static __attribute__((unused))
> @@ -132,6 +133,18 @@ int chdir(const char *path)
>  	return __sysret(sys_chdir(path));
>  }
>  
> +static __attribute__((unused))
> +int sys_fchdir(int fildes)
> +{
> +	return my_syscall1(__NR_fchdir, fildes);
> +}
> +
> +static __attribute__((unused))
> +int fchdir(int fildes)
> +{
> +	return __sysret(sys_fchdir(fildes));
> +}
> +
>  
>  /*
>   * int chmod(const char *path, mode_t mode);
> diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> index 29de21595fc95341c2aa975375a8d471cb3933fc..5927a84466cc0ede3b99611e134a8c6b8ab91e72 100644
> --- a/tools/testing/selftests/nolibc/nolibc-test.c
> +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> @@ -1343,6 +1343,8 @@ int run_syscall(int min, int max)
>  		CASE_TEST(dup3_0);            tmp = dup3(0, 100, 0);  EXPECT_SYSNE(1, tmp, -1); close(tmp); break;
>  		CASE_TEST(dup3_m1);           tmp = dup3(-1, 100, 0); EXPECT_SYSER(1, tmp, -1, EBADF); if (tmp != -1) close(tmp); break;
>  		CASE_TEST(execve_root);       EXPECT_SYSER(1, execve("/", (char*[]){ [0] = "/", [1] = NULL }, NULL), -1, EACCES); break;
> +		CASE_TEST(fchdir_stdin);      EXPECT_SYSER(1, fchdir(STDIN_FILENO), -1, ENOTDIR); break;
> +		CASE_TEST(fchdir_badfd);      EXPECT_SYSER(1, fchdir(-1), -1, EBADF); break;
>  		CASE_TEST(file_stream);       EXPECT_SYSZR(1, test_file_stream()); break;
>  		CASE_TEST(fork);              EXPECT_SYSZR(1, test_fork(FORK_STANDARD)); break;
>  		CASE_TEST(getdents64_root);   EXPECT_SYSNE(1, test_getdents64("/"), -1); break;
> 
> ---
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
> change-id: 20251107-nolibc-fchdir-2645c298a538

Looks good to me!

Acked-by: Willy Tarreau <w@1wt.eu>
Willy