[libc][NFC] Switch use of errno in src/unistd and src/sys to libc_errno.

[sivachandra]

clang-format and update bazel.

libc/src/sys/mman/linux/madvise.cpp

 //===---------- Linux implementation of the POSIX madvise function --------===//
 //
 // 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/mman/madvise.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // madvise is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(int, madvise, (void *addr, size_t size, int advice)) {
   long ret_val = __llvm_libc::syscall_impl(
       SYS_madvise, reinterpret_cast<long>(addr), size, advice);
 
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.
   if (ret_val < 0) {
-    errno = -ret_val;
+    libc_errno = -ret_val;
     return -1;
   }
 
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/mman/linux/mmap.cpp

 //===---------- Linux implementation of the POSIX mmap function -----------===//
 //
 // 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/mman/mmap.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <linux/param.h> // For EXEC_PAGESIZE.
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // mmap is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(void *, mmap,
#endif
   // up in case an error code is detected.
   //
   // A point to keep in mind for the fix up is that a negative return value
   // from the syscall can also be an error-free value returned by the syscall.
   // However, since a valid return address cannot be within the last page, a
   // return value corresponding to a location in the last page is an error
   // value.
   if (ret_val < 0 && ret_val > -EXEC_PAGESIZE) {
-    errno = -ret_val;
+    libc_errno = -ret_val;
     return MAP_FAILED;
   }
 
   return reinterpret_cast<void *>(ret_val);
 }
 
 } // namespace __llvm_libc

libc/src/sys/mman/linux/mprotect.cpp

 //===---------- Linux implementation of the POSIX mprotect function -------===//
 //
 // 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/mman/mprotect.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // mprotect is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(int, mprotect, (void *addr, size_t size, int prot)) {
   long ret_val = __llvm_libc::syscall_impl(
       SYS_mprotect, reinterpret_cast<long>(addr), size, prot);
 
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.
   if (ret_val < 0) {
-    errno = -ret_val;
+    libc_errno = -ret_val;
     return -1;
   }
 
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/mman/linux/munmap.cpp

 //===---------- Linux implementation of the POSIX munmap function ---------===//
 //
 // 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/mman/munmap.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h>          // For syscall numbers.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // mmap is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(int, munmap, (void *addr, size_t size)) {
   long ret_val =
       __llvm_libc::syscall_impl(SYS_munmap, reinterpret_cast<long>(addr), size);
 
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.
   if (ret_val < 0) {
-    errno = -ret_val;
+    libc_errno = -ret_val;
     return -1;
   }
 
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/random/linux/getrandom.cpp

 //===-- Linux implementation of getrandom ---------------------------------===//
 //
 // 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/random/getrandom.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, getrandom,
                    (void *buf, size_t buflen, unsigned int flags)) {
   long ret = __llvm_libc::syscall_impl(SYS_getrandom, buf, buflen, flags);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/resource/linux/getrlimit.cpp

 //===-- Linux implementation of getrlimit ---------------------------------===//
 //
 // 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/resource/getrlimit.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/resource.h> // For struct rlimit
 #include <sys/syscall.h>  // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, getrlimit, (int res, struct rlimit *limits)) {
   long ret = __llvm_libc::syscall_impl(SYS_prlimit64, 0, res, nullptr, limits);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/resource/linux/setrlimit.cpp

 //===-- Linux implementation of setrlimit ---------------------------------===//
 //
 // 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/resource/setrlimit.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/resource.h> // For struct rlimit
 #include <sys/syscall.h>  // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, setrlimit, (int res, const struct rlimit *limits)) {
   long ret = __llvm_libc::syscall_impl(SYS_prlimit64, 0, res, limits, nullptr);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/select/linux/select.cpp

 //===-- Linux implementation of select ------------------------------------===//
 //
 // 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/select/select.h"
 
 #include "src/__support/CPP/limits.h"
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <signal.h>
 #include <stddef.h> // For size_t
 #include <sys/select.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 struct pselect6_sigset_t {
if ((TIME_MAX - timeout->tv_sec) < (timeout->tv_usec / 1000000)) {
       ts.tv_sec = timeout->tv_sec + timeout->tv_usec / 1000000;
       ts.tv_nsec = timeout->tv_usec * 1000;
     }
   }
   pselect6_sigset_t pss{nullptr, sizeof(sigset_t)};
   long ret = __llvm_libc::syscall_impl(SYS_pselect6, nfds, read_set, write_set,
                                        error_set, &ts, &pss);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/sys/sendfile/linux/sendfile.cpp

 //===-- Linux implementation of sendfile ----------------------------------===//
 //
 // 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/sendfile/sendfile.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/sendfile.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, sendfile,
                    (int out_fd, int in_fd, off_t *offset, size_t count)) {
   long ret =
       __llvm_libc::syscall_impl(SYS_sendfile, in_fd, out_fd, offset, count);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

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 "src/errno/libc_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_impl(SYS_chmod, path, mode);
 #elif defined(SYS_fchmodat)
   long ret = __llvm_libc::syscall_impl(SYS_fchmodat, AT_FDCWD, path, mode);
 #else
 #error "chmod and chmodat syscalls not available."
 #endif
 
   if (ret < 0) {
-    errno = -ret;
+    libc_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 "src/errno/libc_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_impl(SYS_fchmod, fd, mode);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

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

 //===-- Linux implementation of fchmodat ----------------------------------===//
 //
 // 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/fchmodat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/stat.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, fchmodat,
                    (int dirfd, const char *path, mode_t mode, int flags)) {
   long ret = __llvm_libc::syscall_impl(SYS_fchmodat, dirfd, path, mode, flags);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

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

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

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

 //===-- Linux implementation of mkdirat -----------------------------------===//
 //
 // 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/mkdirat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/stat.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, mkdirat, (int dfd, const char *path, mode_t mode)) {
 #ifdef SYS_mkdirat
   long ret = __llvm_libc::syscall_impl(SYS_mkdirat, dfd, path, mode);
 #else
 #error "mkdirat syscalls not available."
 #endif
 
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/sys/utsname/linux/uname.cpp

 //===-- Linux implementation of uname -------------------------------------===//
 //
 // 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/utsname/uname.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 #include <sys/utsname.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, uname, (struct utsname * name)) {
   long ret = __llvm_libc::syscall_impl(SYS_uname, name);
 
   if (ret >= 0)
     return 1;
-  errno = -ret;
+  libc_errno = -ret;
   return -1;
 }
 
 } // namespace __llvm_libc

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

 add_entrypoint_object(
   wait
   SRCS
     wait.cpp
   HDRS
     ../wait.h
   DEPENDS
-    libc.include.errno
     libc.include.sys_wait
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   wait4
   SRCS
     wait4.cpp
   HDRS
     ../wait4.h
   DEPENDS
-    libc.include.errno
     libc.include.sys_wait
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   waitpid
   SRCS
     waitpid.cpp
   HDRS
     ../waitpid.h
   DEPENDS
-    libc.include.errno
     libc.include.sys_wait
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )

libc/src/sys/wait/linux/wait.cpp

 //===-- Linux implementation of wait --------------------------------------===//
 //
 // 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/wait/wait.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 #include <sys/wait.h>
 
 namespace __llvm_libc {
 
 // The implementation of wait here is very minimal. We will add more
 // functionality and standard compliance in future.
 
 LLVM_LIBC_FUNCTION(pid_t, wait, (int *wait_status)) {
   pid_t pid = __llvm_libc::syscall_impl(SYS_wait4, -1, wait_status, 0, 0);
   if (pid < 0) {
     // Error case, a child process was not created.
-    errno = -pid;
+    libc_errno = -pid;
     return -1;
   }
 
   return pid;
 }
 
 } // namespace __llvm_libc

libc/src/sys/wait/linux/wait4.cpp

 //===-- Linux implementation of wait4 -------------------------------------===//
 //
 // 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/wait/wait4.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 #include <sys/wait.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(pid_t, wait4,
                    (pid_t pid, int *wait_status, int options,
                     struct rusage *usage)) {
   pid = __llvm_libc::syscall_impl(SYS_wait4, pid, wait_status, options, usage);
   if (pid < 0) {
-    errno = -pid;
+    libc_errno = -pid;
     return -1;
   }
   return pid;
 }
 
 } // namespace __llvm_libc

libc/src/sys/wait/linux/waitpid.cpp

 //===-- Linux implementation of waitpid -----------------------------------===//
 //
 // 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/wait/waitpid.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include "src/errno/libc_errno.h"
 #include <sys/syscall.h> // For syscall numbers.
 #include <sys/wait.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(pid_t, waitpid, (pid_t pid, int *wait_status, int options)) {
   pid = __llvm_libc::syscall_impl(SYS_wait4, pid, wait_status, options, 0);
   if (pid < 0) {
-    errno = -pid;
+    libc_errno = -pid;
     return -1;
   }
   return pid;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/CMakeLists.txt

 
 add_entrypoint_object(
   fork
   SRCS
     fork.cpp
   HDRS
     ../fork.h
   DEPENDS
-    libc.include.errno
     libc.include.unistd
     libc.include.sys_syscall
     libc.src.__support.threads.fork_callbacks
     libc.src.__support.OSUtil.osutil
     libc.src.__support.threads.thread
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   execv
   SRCS
     execv.cpp
   HDRS
     ../execv.h
   DEPENDS
-    libc.include.errno
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
     libc.src.unistd.environ
 )
 
 add_entrypoint_object(
   execve
   SRCS
     execve.cpp
   HDRS
     ../execve.h
   DEPENDS
-    libc.include.errno
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   fsync
   SRCS

 
 add_entrypoint_object(
   getcwd
   SRCS
     getcwd.cpp
   HDRS
     ../getcwd.h
   DEPENDS
-    libc.include.errno
     libc.include.stdlib
     libc.include.unistd
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(

 add_entrypoint_object(
   isatty
   SRCS
     isatty.cpp
   HDRS
     ../isatty.h
   DEPENDS
     libc.include.unistd
-    libc.include.errno
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   link
   SRCS

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 <src/errno/libc_errno.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_impl(SYS_access, path, mode);
 #elif defined(SYS_faccessat)
   long ret = __llvm_libc::syscall_impl(SYS_faccessat, AT_FDCWD, path, mode, 0);
 #else
 #error "access syscalls not available."
 #endif
 
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

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 <src/errno/libc_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_impl(SYS_chdir, path);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/close.cpp

 //===-- Linux implementation of close -------------------------------------===//
 //
 // 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/close.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, close, (int fd)) {
   long ret = __llvm_libc::syscall_impl(SYS_close, fd);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/dup.cpp

 //===-- Linux implementation of dup ---------------------------------------===//
 //
 // 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/dup.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, dup, (int fd)) {
   long ret = __llvm_libc::syscall_impl(SYS_dup, fd);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/dup2.cpp

 //===-- Linux implementation of dup2 --------------------------------------===//
 //
 // 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/dup2.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <fcntl.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, dup2, (int oldfd, int newfd)) {
 #ifdef SYS_dup2
   // If dup2 syscall is available, we make use of directly.
   long ret = __llvm_libc::syscall_impl(SYS_dup2, oldfd, newfd);
 #elif defined(SYS_dup3)
   // If dup2 syscall is not available, we try using the dup3 syscall. However,
   // dup3 fails if oldfd is the same as newfd. So, we handle that case
   // separately before making the dup3 syscall.
   if (oldfd == newfd) {
     // Check if oldfd is actually a valid file descriptor.
     long ret = __llvm_libc::syscall_impl(SYS_fcntl, oldfd, F_GETFD);
     if (ret >= 0)
       return oldfd;
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   long ret = __llvm_libc::syscall_impl(SYS_dup3, oldfd, newfd, 0);
 #else
 #error "SYS_dup2 and SYS_dup3 not available for the target."
 #endif
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/dup3.cpp

 //===-- Linux implementation of dup3 --------------------------------------===//
 //
 // 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/dup3.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, dup3, (int oldfd, int newfd, int flags)) {
   // If dup2 syscall is available, we make use of directly.
   long ret = __llvm_libc::syscall_impl(SYS_dup3, oldfd, newfd, flags);
   if (ret >= 0)
     return ret;
-  errno = -ret;
+  libc_errno = -ret;
   return -1;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/execv.cpp

 //===-- Linux implementation of execv -------------------------------------===//
 //
 // 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/execv.h"
 #include "src/unistd/environ.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, execv, (const char *path, char *const argv[])) {
   long ret =
       __llvm_libc::syscall_impl(SYS_execve, path, argv, __llvm_libc::environ);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
 
   // Control will not reach here on success but have a return statement will
   // keep the compilers happy.
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/execve.cpp

 //===-- Linux implementation of execve ------------------------------------===//
 //
 // 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/execve.h"
 #include "src/unistd/environ.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, execve,
                    (const char *path, char *const argv[], char *const envp[])) {
   long ret = __llvm_libc::syscall_impl(SYS_execve, path, argv, envp);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
 
   // Control will not reach here on success but have a return statement will
   // keep the compilers happy.
   return ret;
 }
 
 } // 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 <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, fchdir, (int fd)) {
   long ret = __llvm_libc::syscall_impl(SYS_fchdir, fd);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/fork.cpp

 //===-- Linux implementation of fork --------------------------------------===//
 //
 // 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/fork.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 #include "src/__support/threads/fork_callbacks.h"
 #include "src/__support/threads/thread.h" // For thread self object
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 // The implementation of fork here is very minimal. We will add more
 // functionality and standard compliance in future.
 
 LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
if (ret == 0) {
     // the child process' self object with the new process' tid.
     self.attrib->tid = __llvm_libc::syscall_impl(SYS_gettid);
     invoke_child_callbacks();
     return 0;
   }
 
   if (ret < 0) {
     // Error case, a child process was not created.
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
 
   invoke_parent_callbacks();
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/fsync.cpp

 //===-- Linux implementation of fsync -------------------------------------===//
 //
 // 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/fsync.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, fsync, (int fd)) {
   long ret = __llvm_libc::syscall_impl(SYS_fsync, fd);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/ftruncate.cpp

 //===-- Linux implementation of ftruncate ---------------------------------===//
 //
 // 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/ftruncate.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 #include <unistd.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, ftruncate, (int fd, off_t len)) {
   int ret = __llvm_libc::syscall_impl(SYS_ftruncate, fd, len);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/getcwd.cpp

 //===-- Linux implementation of getcwd ------------------------------------===//
 //
 // 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/getcwd.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 #include "src/string/allocating_string_utils.h" // For strdup.
 
-#include <errno.h>
 #include <linux/limits.h> // This is safe to include without any name pollution.
+#include <src/errno/libc_errno.h>
 #include <stdlib.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 namespace {
 
 bool getcwd_syscall(char *buf, size_t size) {
   int ret = __llvm_libc::syscall_impl(SYS_getcwd, buf, size);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return false;
   } else if (ret == 0 || buf[0] != '/') {
-    errno = ENOENT;
+    libc_errno = ENOENT;
     return false;
   }
   return true;
 }
 
 } // anonymous namespace
 
 LLVM_LIBC_FUNCTION(char *, getcwd, (char *buf, size_t size)) {
   if (buf == nullptr) {
     // We match glibc's behavior here and return the cwd in a malloc-ed buffer.
     // We will allocate a static buffer of size PATH_MAX first and fetch the cwd
     // into it. This way, if the syscall fails, we avoid unnecessary malloc
     // and free.
     char pathbuf[PATH_MAX];
     if (!getcwd_syscall(pathbuf, PATH_MAX))
       return nullptr;
     auto cwd = internal::strdup(pathbuf);
     if (!cwd) {
-      errno = ENOMEM;
+      libc_errno = ENOMEM;
       return nullptr;
     }
     return *cwd;
   } else if (size == 0) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return nullptr;
   }
 
   // TODO: When buf is not sufficient, evaluate the full cwd path using
   // alternate approaches.
 
   if (!getcwd_syscall(buf, size))
     return nullptr;
   return buf;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/isatty.cpp

 //===-- Linux implementation of isatty ------------------------------------===//
 //
 // 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/isatty.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/ioctl.h>   // For ioctl numbers.
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, isatty, (int fd)) {
   constexpr int INIT_VAL = 0x1234abcd;
   int line_d_val = INIT_VAL;
   // This gets the line dicipline of the terminal. When called on something that
   // isn't a terminal it doesn't change line_d_val and returns -1.
   int result = __llvm_libc::syscall_impl(SYS_ioctl, fd, TIOCGETD, &line_d_val);
   if (result == 0)
     return 1;
 
-  errno = -result;
+  libc_errno = -result;
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/link.cpp

 //===-- Linux implementation of link --------------------------------------===//
 //
 // 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/link.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <fcntl.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, link, (const char *path1, const char *path2)) {
 #ifdef SYS_link
   long ret = __llvm_libc::syscall_impl(SYS_link, path1, path2);
 #elif defined(SYS_linkat)
   long ret = __llvm_libc::syscall_impl(SYS_linkat, AT_FDCWD, path1, AT_FDCWD,
                                        path2, 0);
 #else
 #error "SYS_link or SYS_linkat not available."
 #endif
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/linkat.cpp

 //===-- Linux implementation of linkat ------------------------------------===//
 //
 // 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/linkat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <fcntl.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, linkat,
                    (int fd1, const char *path1, int fd2, const char *path2,
                     int flags)) {
   long ret =
       __llvm_libc::syscall_impl(SYS_linkat, fd1, path1, fd2, path2, flags);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/lseek.cpp

 //===-- Linux implementation of lseek -------------------------------------===//
 //
 // 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/lseek.h"
+#include "src/errno/libc_errno.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.
 #include <unistd.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(off_t, lseek, (int fd, off_t offset, int whence)) {
   off_t result;
 #ifdef SYS_lseek
   long ret = __llvm_libc::syscall_impl(SYS_lseek, fd, offset, whence);
   result = ret;
 #elif defined(SYS__llseek)
   long ret = __llvm_libc::syscall_impl(SYS__llseek, fd, offset >> 32, offset,
                                        &result, whence);
 #else
 #error "lseek and _llseek syscalls not available."
 #endif
 
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return result;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/pread.cpp

 //===-- Linux implementation of pread -------------------------------------===//
 //
 // 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/pread.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, pread,
                    (int fd, void *buf, size_t count, off_t offset)) {
   long ret = __llvm_libc::syscall_impl(SYS_pread64, fd, buf, count, offset);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/pwrite.cpp

 //===-- Linux implementation of pwrite ------------------------------------===//
 //
 // 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/pwrite.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, pwrite,
                    (int fd, const void *buf, size_t count, off_t offset)) {
   long ret = __llvm_libc::syscall_impl(SYS_pwrite64, fd, buf, count, offset);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/read.cpp

 //===-- Linux implementation of read --------------------------------------===//
 //
 // 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/read.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, read, (int fd, void *buf, size_t count)) {
   long ret = __llvm_libc::syscall_impl(SYS_read, fd, buf, count);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/readlink.cpp

 //===-- Linux implementation of readlink ----------------------------------===//
 //
 // 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/readlink.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <fcntl.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, readlink,
                    (const char *__restrict path, char *__restrict buf,
                     size_t bufsize)) {
 #ifdef SYS_readlink
   ssize_t ret = __llvm_libc::syscall_impl(SYS_readlink, path, buf, bufsize);
 #elif defined(SYS_readlinkat)
   ssize_t ret =
       __llvm_libc::syscall_impl(SYS_readlinkat, AT_FDCWD, path, buf, bufsize);
 #else
 #error "SYS_readlink or SYS_readlinkat not available."
 #endif
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/readlinkat.cpp

 //===-- Linux implementation of readlinkat --------------------------------===//
 //
 // 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/readlinkat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <fcntl.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, readlinkat,
                    (int fd, const char *__restrict path, char *__restrict buf,
                     size_t bufsize)) {
   ssize_t ret =
       __llvm_libc::syscall_impl(SYS_readlinkat, fd, path, buf, bufsize);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/rmdir.cpp

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

libc/src/unistd/linux/symlink.cpp

 //===-- Linux implementation of symlink -----------------------------------===//
 //
 // 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/symlink.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <fcntl.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, symlink, (const char *path1, const char *path2)) {
 #ifdef SYS_symlink
   long ret = __llvm_libc::syscall_impl(SYS_symlink, path1, path2);
 #elif defined(SYS_symlinkat)
   long ret = __llvm_libc::syscall_impl(SYS_symlinkat, path1, AT_FDCWD, path2);
 #else
 #error "SYS_symlink or SYS_symlinkat not available."
 #endif
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/symlinkat.cpp

 //===-- Linux implementation of symlinkat ---------------------------------===//
 //
 // 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/symlinkat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <fcntl.h>
+#include <src/errno/libc_errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, symlinkat,
                    (const char *path1, int fd, const char *path2)) {
   long ret = __llvm_libc::syscall_impl(SYS_symlinkat, path1, fd, path2);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/syscall.cpp

 //===-- Linux implementation of syscall -----------------------------------===//
 //
 // 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/syscall.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <errno.h>
+#include <src/errno/libc_errno.h>
 #include <stdarg.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(long, __llvm_libc_syscall,
                    (long number, long arg1, long arg2, long arg3, long arg4,
                     long arg5, long arg6)) {
   long ret =
       __llvm_libc::syscall_impl(number, arg1, arg2, arg3, arg4, arg5, arg6);
   // Syscalls may return large positive values that overflow, but will never
   // return values between -4096 and -1
   if (static_cast<unsigned long>(ret) > -4096UL) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/sysconf.cpp

 //===-- Linux implementation of sysconf -----------------------------------===//
 //
 // 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/sysconf.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <linux/param.h> // For EXEC_PAGESIZE.
+#include <src/errno/libc_errno.h>
 #include <unistd.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(long, sysconf, (int name)) {
   long ret = 0;
   if (name == _SC_PAGESIZE) {
     // TODO: get this information from the auxvector.
     return EXEC_PAGESIZE;
   }
   // TODO: Complete the rest of the sysconf options.
   if (ret < 0) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/truncate.cpp

 //===-- Linux implementation of truncate ----------------------------------===//
 //
 // 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/truncate.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 #include <unistd.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, truncate, (const char *path, off_t len)) {
   int ret = __llvm_libc::syscall_impl(SYS_truncate, path, len);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/unlink.cpp

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

libc/src/unistd/linux/unlinkat.cpp

 //===-- Linux implementation of unlinkat ----------------------------------===//
 //
 // 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/unlinkat.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <fcntl.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, unlinkat, (int dfd, const char *path, int flags)) {
 #ifdef SYS_unlinkat
   long ret = __llvm_libc::syscall_impl(SYS_unlinkat, dfd, path, flags);
 #else
 #error "unlinkat syscall not available."
 #endif
 
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/unistd/linux/write.cpp

 //===-- Linux implementation of write -------------------------------------===//
 //
 // 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/write.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(ssize_t, write, (int fd, const void *buf, size_t count)) {
   long ret = __llvm_libc::syscall_impl(SYS_write, fd, buf, count);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

textual_hdrs = [
         "src/__support/OSUtil/linux/aarch64/syscall.h",
         "src/__support/OSUtil/linux/x86_64/syscall.h",
     ],
     deps = [
         ":__support_common",
         ":libc_root",
     ],
 )
+############################### errno targets ################################
+
+libc_function(
+    name = "errno",
+    srcs = ["src/errno/libc_errno.cpp"],
+    hdrs = ["src/errno/libc_errno.h"],
+    deps = [
+        ":__support_common",
+    ],
+)
 
 ################################ fenv targets ################################
 
 libc_function(
     name = "fetestexcept",
     srcs = ["src/fenv/fetestexcept.cpp"],
     hdrs = ["src/fenv/fetestexcept.h"],
     deps = [

 
 libc_function(
     name = "chdir",
     srcs = ["src/unistd/linux/chdir.cpp"],
     hdrs = ["src/unistd/chdir.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "close",
     srcs = ["src/unistd/linux/close.cpp"],
     hdrs = ["src/unistd/close.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "fchdir",
     srcs = ["src/unistd/linux/fchdir.cpp"],
     hdrs = ["src/unistd/fchdir.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "fsync",
     srcs = ["src/unistd/linux/fsync.cpp"],
     hdrs = ["src/unistd/fsync.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "ftruncate",
     srcs = ["src/unistd/linux/ftruncate.cpp"],
     hdrs = ["src/unistd/ftruncate.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "link",
     srcs = ["src/unistd/linux/link.cpp"],
     hdrs = ["src/unistd/link.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "linkat",
     srcs = ["src/unistd/linux/linkat.cpp"],
     hdrs = ["src/unistd/linkat.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "lseek",
     srcs = ["src/unistd/linux/lseek.cpp"],
     hdrs = ["src/unistd/lseek.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "read",
     srcs = ["src/unistd/linux/read.cpp"],
     hdrs = ["src/unistd/read.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "readlink",
     srcs = ["src/unistd/linux/readlink.cpp"],
     hdrs = ["src/unistd/readlink.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "readlinkat",
     srcs = ["src/unistd/linux/readlinkat.cpp"],
     hdrs = ["src/unistd/readlinkat.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "rmdir",
     srcs = ["src/unistd/linux/rmdir.cpp"],
     hdrs = ["src/unistd/rmdir.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "symlink",
     srcs = ["src/unistd/linux/symlink.cpp"],
     hdrs = ["src/unistd/symlink.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "symlinkat",
     srcs = ["src/unistd/linux/symlinkat.cpp"],
     hdrs = ["src/unistd/symlinkat.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "truncate",
     srcs = ["src/unistd/linux/truncate.cpp"],
     hdrs = ["src/unistd/truncate.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "unlink",
     srcs = ["src/unistd/linux/unlink.cpp"],
     hdrs = ["src/unistd/unlink.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "unlinkat",
     srcs = ["src/unistd/linux/unlinkat.cpp"],
     hdrs = ["src/unistd/unlinkat.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )
 
 libc_function(
     name = "write",
     srcs = ["src/unistd/linux/write.cpp"],
     hdrs = ["src/unistd/write.h"],
     deps = [
         ":__support_common",
         ":__support_osutil",
+        ":errno",
     ],
 )