[libc] Add implementation of POSIX function "access".

[sivachandra]

• Fix typo in a comment.
• Enable for aarch64 also.

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     # sys/stat.h entrypoints
     libc.src.sys.stat.chmod
     libc.src.sys.stat.fchmod
     libc.src.sys.stat.fchmodat
     libc.src.sys.stat.mkdir
     libc.src.sys.stat.mkdirat
 
     # unistd.h entrypoints
+    libc.src.unistd.access
     libc.src.unistd.chdir
     libc.src.unistd.close
     libc.src.unistd.dup
     libc.src.unistd.dup2
     libc.src.unistd.dup3
     libc.src.unistd.fchdir
     libc.src.unistd.fsync
     libc.src.unistd.ftruncate

libc/include/CMakeLists.txt

 
 add_gen_header(
   unistd
   DEF_FILE unistd.h.def
   GEN_HDR unistd.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.file_seek_macros
+    .llvm-libc-macros.unistd_macros
     .llvm-libc-types.size_t
     .llvm-libc-types.ssize_t
 )
 
 add_gen_header(
   pthread
   DEF_FILE pthread.h.def
   GEN_HDR pthread.h

libc/include/llvm-libc-macros/CMakeLists.txt

 
 add_header(
   sys_stat_macros
   HDR
     sys-stat-macros.h
   DEPENDS
     .linux.sys_stat_macros
 )
+
+add_header(
+  unistd_macros
+  HDR
+    unistd-macros.h
+  DEPENDS
+    .linux.unistd_macros
+)

libc/include/llvm-libc-macros/linux/CMakeLists.txt

 add_header(
   fcntl_macros
   HDR
     fcntl-macros.h
 )
 
 add_header(
   sys_stat_macros
   HDR
     sys-stat-macros.h
 )
+
+add_header(
+  unistd_macros
+  HDR
+    unistd-macros.h
+)

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

+//===-- Definition of macros from unistd.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_UNISTD_MACROS_H
+#define __LLVM_LIBC_MACROS_LINUX_UNISTD_MACROS_H
+
+// Values for mode argument to the access(...) function.
+#define F_OK 0
+#define X_OK 1
+#define W_OK 2
+#define R_OK 4
+
+#endif // __LLVM_LIBC_MACROS_LINUX_UNISTD_MACROS_H

libc/include/llvm-libc-macros/unistd-macros.h

+#ifndef __LLVM_LIBC_MACROS_UNISTD_MACROS_H
+#define __LLVM_LIBC_MACROS_UNISTD_MACROS_H
+
+#ifdef __unix__
+#include "linux/unistd-macros.h"
+#endif
+
+#endif // __LLVM_LIBC_MACROS_UNISTD_MACROS_H

libc/include/unistd.h.def

 //===-- C standard library header unistd.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_UNISTD_H
 #define LLVM_LIBC_UNISTD_H
 
 #include <__llvm-libc-common.h>
 #include <llvm-libc-macros/file-seek-macros.h>
+#include <llvm-libc-macros/unistd-macros.h>
 
 %%public_api()
 
 #endif // LLVM_LIBC_UNISTD_H

libc/spec/posix.td

HeaderSpec UniStd = HeaderSpec<
     [
       OffTType,
       SSizeTType,
       SizeTType,
     ],
     [], // Enumerations
     [
         FunctionSpec<
+          "access",
+          RetValSpec<IntType>,
+          [ArgSpec<ConstCharPtr>, ArgSpec<IntType>]
+        >,
+        FunctionSpec<
           "chdir",
           RetValSpec<IntType>,
           [ArgSpec<ConstCharPtr>]
         >,
         FunctionSpec<
           "dup",
           RetValSpec<IntType>,
           [ArgSpec<IntType>]

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(
+  access
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.access
+)
+
+add_entrypoint_object(
   chdir
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.chdir
 )
 
 add_entrypoint_object(
   close

libc/src/unistd/access.h

-//===-- C standard library header unistd.h --------------------------------===//
+//===-- Implementation header for access ------------------------*- 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_UNISTD_H
-#define LLVM_LIBC_UNISTD_H
+#ifndef LLVM_LIBC_SRC_UNISTD_ACCESS_H
+#define LLVM_LIBC_SRC_UNISTD_ACCESS_H
 
-#include <__llvm-libc-common.h>
-#include <llvm-libc-macros/file-seek-macros.h>
+namespace __llvm_libc {
 
-%%public_api()
+int access(const char *path, int mode);
 
-#endif // LLVM_LIBC_UNISTD_H
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_ACCESS_H

libc/src/unistd/linux/CMakeLists.txt

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

libc/src/unistd/linux/access.cpp

+//===-- Linux implementation of access ------------------------------------===//
+//
+// 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/access.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, access, (const char *path, int mode)) {
+#ifdef SYS_access
+  long ret = __llvm_libc::syscall(SYS_access, path, mode);
+#elif defined(SYS_accessat)
+  long ret = __llvm_libc::syscall(SYS_accessat, AT_FDCWD, path, mode);
+#else
+#error "access syscalls not available."
+#endif
+
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/test/src/unistd/CMakeLists.txt

 add_libc_testsuite(libc_unistd_unittests)
 
 add_subdirectory(testdata)
 
 add_libc_unittest(
+  access_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    access_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.unistd
+    libc.src.fcntl.open
+    libc.src.unistd.access
+    libc.src.unistd.close
+    libc.src.unistd.unlink
+)
+
+add_libc_unittest(
   chdir_test
   SUITE
     libc_unistd_unittests
   SRCS
     chdir_test.cpp
   DEPENDS
     libc.include.errno
     libc.include.unistd

libc/test/src/unistd/access_test.cpp

+//===-- Unittests for access ----------------------------------------------===//
+//
+// 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/access.h"
+#include "src/unistd/close.h"
+#include "src/unistd/unlink.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+TEST(LlvmLibcAccessTest, CreateAndTest) {
+  // The test strategy is to repeated create a file in different modes and test
+  // that it is accessable in those modes but not in others.
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_FILE = "testdata/access.test";
+  int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, F_OK), 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, X_OK | W_OK | R_OK), 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IXUSR);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, F_OK), 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, X_OK), 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, R_OK), -1);
+  ASSERT_EQ(errno, EACCES);
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::access(TEST_FILE, W_OK), -1);
+  ASSERT_EQ(errno, EACCES);
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcAccessTest, AccessNonExistentFile) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::access("testdata/non-existent-file", F_OK),
+              Fails(ENOENT));
+}