[libc] Add Linux implementations of POSIX chdir, fchdir, chmod and fchmod.

[michaelrj]

LGTM

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.sprintf
     libc.src.stdio.snprintf
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.mmap
     libc.src.sys.mman.munmap
 
     # sys/stat.h entrypoints
+    libc.src.sys.stat.chmod
+    libc.src.sys.stat.fchmod
     libc.src.sys.stat.mkdir
     libc.src.sys.stat.mkdirat
 
     # unistd.h entrypoints
+    libc.src.unistd.chdir
     libc.src.unistd.close
+    libc.src.unistd.fchdir
     libc.src.unistd.fsync
     libc.src.unistd.lseek
     libc.src.unistd.read
     libc.src.unistd.rmdir
     libc.src.unistd.unlink
     libc.src.unistd.unlinkat
     libc.src.unistd.write
 )

libc/include/llvm-libc-macros/linux/fcntl-macros.h

 //===-- Definition of macros from fcntl.h ---------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef __LLVM_LIBC_MACROS_LINUX_FCNTL_MACROS_H
 #define __LLVM_LIBC_MACROS_LINUX_FCNTL_MACROS_H
 
 // File creation flags
 #define O_CLOEXEC 02000000
 #define O_CREAT 00000100
+#define O_PATH 010000000
 
 #ifdef __aarch64__
 #define O_DIRECTORY 040000
 #else
 #define O_DIRECTORY 00200000
 #endif
 
 #define O_EXCL 00000200

libc/spec/posix.td

HeaderSpec UniStd = HeaderSpec<
     [
       OffTType,
       SSizeTType,
       SizeTType,
     ],
     [], // Enumerations
     [
         FunctionSpec<
+          "chdir",
+          RetValSpec<IntType>,
+          [ArgSpec<ConstCharPtr>]
+        >,
+        FunctionSpec<
+          "fchdir",
+          RetValSpec<IntType>,
+          [ArgSpec<IntType>]
+        >,
+        FunctionSpec<
           "close",
           RetValSpec<IntType>,
           [ArgSpec<IntType>]
         >,
         FunctionSpec<
           "fsync",
           RetValSpec<IntType>,
           [ArgSpec<IntType>]
def POSIX : StandardSpec<"POSIX"> {
 
   HeaderSpec SysStat = HeaderSpec<
     "sys/stat.h",
     [], // Macros
     [ModeTType], // Types
     [], // Enumerations
     [
         FunctionSpec<
+          "chmod",
+          RetValSpec<IntType>,
+          [ArgSpec<ConstCharPtr>]
+        >,
+        FunctionSpec<
+          "fchmod",
+          RetValSpec<IntType>,
+          [ArgSpec<IntType>]
+        >,
+        FunctionSpec<
             "mkdir",
             RetValSpec<IntType>,
             [ArgSpec<ConstCharPtr>, ArgSpec<ModeTType>]
         >,
         FunctionSpec<
             "mkdirat",
             RetValSpec<IntType>,
             [ArgSpec<IntType>, ArgSpec<ConstCharPtr>, ArgSpec<ModeTType>]

libc/src/sys/stat/CMakeLists.txt

 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
 endif()
 
 add_entrypoint_object(
+  chmod
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.chmod
+)
+
+add_entrypoint_object(
+  fchmod
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.fchmod
+)
+
+add_entrypoint_object(
   mkdir
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.mkdir
 )
 
 add_entrypoint_object(
   mkdirat
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.mkdirat
 )

libc/src/sys/stat/chmod.h

+//===-- Implementation header for chmod -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_STAT_CHMOD_H
+#define LLVM_LIBC_SRC_SYS_STAT_CHMOD_H
+
+#include <sys/stat.h>
+
+namespace __llvm_libc {
+
+int chmod(const char *path, mode_t mode);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SYS_STAT_CHMOD_H

libc/src/sys/stat/fchmod.h

+//===-- Implementation header for fchmod ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_STAT_FCHMOD_H
+#define LLVM_LIBC_SRC_SYS_STAT_FCHMOD_H
+
+#include <sys/stat.h>
+
+namespace __llvm_libc {
+
+int fchmod(int fd, mode_t mode);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SYS_STAT_FCHMOD_H

libc/src/sys/stat/linux/CMakeLists.txt

 add_entrypoint_object(
+  chmod
+  SRCS
+    chmod.cpp
+  HDRS
+    ../chmod.h
+  DEPENDS
+    libc.include.fcntl
+    libc.include.sys_stat
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  fchmod
+  SRCS
+    fchmod.cpp
+  HDRS
+    ../fchmod.h
+  DEPENDS
+    libc.include.sys_stat
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
   mkdir
   SRCS
     mkdir.cpp
   HDRS
     ../mkdir.h
   DEPENDS
     libc.include.fcntl
     libc.include.sys_stat

libc/src/sys/stat/linux/chmod.cpp

+//===-- Linux implementation of chmod -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/stat/chmod.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, chmod, (const char *path, mode_t mode)) {
+#ifdef SYS_chmod
+  long ret = __llvm_libc::syscall(SYS_chmod, path, mode);
+#elif defined(SYS_chmodat)
+  long ret = __llvm_libc::syscall(SYS_chmodat, AT_FDCWD, path, mode);
+#else
+#error "chmod and chmodat syscalls not available."
+#endif
+
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/src/sys/stat/linux/fchmod.cpp

+//===-- Linux implementation of fchmod ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sys/stat/fchmod.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, fchmod, (int fd, mode_t mode)) {
+  long ret = __llvm_libc::syscall(SYS_fchmod, fd, mode);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/src/unistd/CMakeLists.txt

 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
 endif()
 
 add_entrypoint_object(
+  chdir
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.chdir
+)
+
+add_entrypoint_object(
   close
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.close
 )
 
 add_entrypoint_object(
+  fchdir
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.fchdir
+)
+
+add_entrypoint_object(
   fsync
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.fsync
 )
 
 add_entrypoint_object(
   lseek

libc/src/unistd/chdir.h

+//===-- Implementation header for chdir -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_CHDIR_H
+#define LLVM_LIBC_SRC_UNISTD_CHDIR_H
+
+namespace __llvm_libc {
+
+int chdir(const char *path);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_CHDIR_H

libc/src/unistd/fchdir.h

+//===-- Implementation header for fchdir ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_FCHDIR_H
+#define LLVM_LIBC_SRC_UNISTD_FCHDIR_H
+
+namespace __llvm_libc {
+
+int fchdir(int fd);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_FCHDIR_H

libc/src/unistd/linux/CMakeLists.txt

 add_entrypoint_object(
+  chdir
+  SRCS
+    chdir.cpp
+  HDRS
+    ../chdir.h
+  DEPENDS
+    libc.include.unistd
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
   close
   SRCS
     close.cpp
   HDRS
     ../close.h
   DEPENDS
     libc.include.unistd
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
+  fchdir
+  SRCS
+    fchdir.cpp
+  HDRS
+    ../fchdir.h
+  DEPENDS
+    libc.include.unistd
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
   fsync
   SRCS
     fsync.cpp
   HDRS
     ../fsync.h
   DEPENDS
     libc.include.unistd
     libc.include.sys_syscall

libc/src/unistd/linux/chdir.cpp

+//===-- Linux implementation of chdir -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/chdir.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, chdir, (const char *path)) {
+  long ret = __llvm_libc::syscall(SYS_chdir, path);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/src/unistd/linux/fchdir.cpp

+//===-- Linux implementation of fchdir ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/fchdir.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, fchdir, (int fd)) {
+  long ret = __llvm_libc::syscall(SYS_fchdir, fd);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/test/src/sys/stat/CMakeLists.txt

 add_libc_testsuite(libc_sys_stat_unittests)
 
 add_subdirectory(testdata)
 
 add_libc_unittest(
+  chmod_test
+  SUITE
+    libc_sys_stat_unittests
+  SRCS
+    chmod_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.fcntl
+    libc.include.sys_stat
+    libc.src.fcntl.open
+    libc.src.sys.stat.chmod
+    libc.src.unistd.close
+    libc.src.unistd.write
+)
+
+add_libc_unittest(
+  fchmod_test
+  SUITE
+    libc_sys_stat_unittests
+  SRCS
+    fchmod_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.fcntl
+    libc.include.sys_stat
+    libc.src.fcntl.open
+    libc.src.sys.stat.fchmod
+    libc.src.unistd.close
+    libc.src.unistd.write
+)
+
+add_libc_unittest(
   mkdirat_test
   SUITE
     libc_sys_stat_unittests
   SRCS
     mkdirat_test.cpp
   DEPENDS
     libc.include.errno
     libc.include.fcntl
     libc.include.sys_stat
     libc.src.sys.stat.mkdirat
     libc.src.unistd.rmdir
 )

libc/test/src/sys/stat/chmod_test.cpp

+//===-- Unittests for chmod -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/sys/stat/chmod.h"
+#include "src/unistd/close.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+TEST(LlvmLibcChmodTest, ChangeAndOpen) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
+  // The test file is initially writable. We open it for writing and ensure
+  // that it indeed can be opened for writing. Next, we close the file and
+  // make it readonly using chmod. We test that chmod actually succeeded by
+  // trying to open the file for writing and failing.
+  constexpr const char *TEST_FILE = "testdata/chmod.test";
+  const char WRITE_DATA[] = "test data";
+  constexpr ssize_t WRITE_SIZE = ssize_t(sizeof(WRITE_DATA));
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::write(fd, WRITE_DATA, sizeof(WRITE_DATA)), WRITE_SIZE);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::chmod(TEST_FILE, S_IRUSR), Succeeds(0));
+
+  // Opening for writing should fail.
+  EXPECT_EQ(__llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY), -1);
+  EXPECT_NE(errno, 0);
+  errno = 0;
+  // But opening for reading should succeed.
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_RDONLY);
+  EXPECT_GT(fd, 0);
+  EXPECT_EQ(errno, 0);
+
+  EXPECT_THAT(__llvm_libc::close(fd), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::chmod(TEST_FILE, S_IRWXU), Succeeds(0));
+}
+
+TEST(LlvmLibcChmodTest, NonExistentFile) {
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::chmod("non-existent-file", S_IRUSR), Fails(ENOENT));
+  errno = 0;
+}

libc/test/src/sys/stat/fchmod_test.cpp

+//===-- Unittests for fchmod ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/sys/stat/fchmod.h"
+#include "src/unistd/close.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+TEST(LlvmLibcChmodTest, ChangeAndOpen) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
+  // The test file is initially writable. We open it for writing and ensure
+  // that it indeed can be opened for writing. Next, we close the file and
+  // make it readonly using chmod. We test that chmod actually succeeded by
+  // trying to open the file for writing and failing.
+  constexpr const char *TEST_FILE = "testdata/fchmod.test";
+  const char WRITE_DATA[] = "test data";
+  constexpr ssize_t WRITE_SIZE = ssize_t(sizeof(WRITE_DATA));
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::write(fd, WRITE_DATA, sizeof(WRITE_DATA)), WRITE_SIZE);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  EXPECT_THAT(__llvm_libc::fchmod(fd, S_IRUSR), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  // Opening for writing should fail.
+  EXPECT_EQ(__llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY), -1);
+  EXPECT_NE(errno, 0);
+  errno = 0;
+  // But opening for reading should succeed.
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_RDONLY);
+  EXPECT_GT(fd, 0);
+  EXPECT_EQ(errno, 0);
+
+  EXPECT_THAT(__llvm_libc::fchmod(fd, S_IRWXU), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::close(fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChmodTest, NonExistentFile) {
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::fchmod(-1, S_IRUSR), -1);
+  ASSERT_NE(errno, 0);
+  errno = 0;
+}

libc/test/src/sys/stat/testdata/CMakeLists.txt

-# This directory will be used to create test files and delete them
-# from tests.
+# This directory will be used to create test files.
+
+file(GENERATE OUTPUT chmod.test CONTENT "chmod test")
+file(GENERATE OUTPUT fchmod.test CONTENT "fchmod test")

libc/test/src/unistd/CMakeLists.txt

 add_libc_testsuite(libc_unistd_unittests)
 
 add_subdirectory(testdata)
 
 add_libc_unittest(
+  chdir_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    chdir_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.unistd
+    libc.src.fcntl.open
+    libc.src.unistd.chdir
+    libc.src.unistd.close
+    libc.test.errno_setter_matcher
+)
+
+add_libc_unittest(
+  fchdir_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    fchdir_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.unistd
+    libc.src.fcntl.open
+    libc.src.unistd.fchdir
+    libc.src.unistd.close
+    libc.test.errno_setter_matcher
+)
+
+add_libc_unittest(
   read_write_test
   SUITE
     libc_unistd_unittests
   SRCS
     read_write_test.cpp
   DEPENDS
     libc.include.errno
     libc.include.unistd

libc/test/src/unistd/chdir_test.cpp

+//===-- Unittests for chdir -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/chdir.h"
+#include "src/unistd/close.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+
+TEST(LlvmLibcChdirTest, ChangeAndOpen) {
+  // The idea of this test is that we will first open an existing test file
+  // without changing the directory to make sure it exists. Next, we change
+  // directory and open the same file to make sure that the "chdir" operation
+  // succeeded.
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_DIR = "testdata";
+  constexpr const char *TEST_FILE = "testdata/chdir.test";
+  constexpr const char *TEST_FILE_BASE = "chdir.test";
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::chdir(TEST_DIR), Succeeds(0));
+  fd = __llvm_libc::open(TEST_FILE_BASE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChdirTest, ChangeToNonExistentDir) {
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::chdir("non-existent-dir"), Fails(ENOENT));
+  errno = 0;
+}

libc/test/src/unistd/fchdir_test.cpp

+//===-- Unittests for fchdir ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/fchdir.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+
+TEST(LlvmLibcChdirTest, ChangeAndOpen) {
+  // The idea of this test is that we will first open an existing test file
+  // without changing the directory to make sure it exists. Next, we change
+  // directory and open the same file to make sure that the "fchdir" operation
+  // succeeded.
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_DIR = "testdata";
+  constexpr const char *TEST_FILE = "testdata/fchdir.test";
+  constexpr const char *TEST_FILE_BASE = "fchdir.test";
+  errno = 0;
+
+  int dir_fd = __llvm_libc::open(TEST_DIR, O_DIRECTORY);
+  ASSERT_GT(dir_fd, 0);
+  ASSERT_EQ(errno, 0);
+  int file_fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(file_fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(file_fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::fchdir(dir_fd), Succeeds(0));
+  file_fd = __llvm_libc::open(TEST_FILE_BASE, O_PATH);
+  ASSERT_GT(file_fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(file_fd), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::close(dir_fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChdirTest, ChangeToNonExistentDir) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::fchdir(0), -1);
+  ASSERT_NE(errno, 0);
+  errno = 0;
+}

libc/test/src/unistd/testdata/CMakeLists.txt

-# This directory will be used to create test files and delete them
-# from tests.
+# This directory will be used to create test files.
 
 file(GENERATE OUTPUT lseek.test CONTENT "lseek test")
+file(GENERATE OUTPUT chdir.test CONTENT "chdir test")
+file(GENERATE OUTPUT fchdir.test CONTENT "fchdir test")