libc/src/unistd/linux/getcwd.cpp

   1 //===-- Linux implementation of getcwd ------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/unistd/getcwd.h"
  10
  11 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
  12 #include "src/__support/common.h"
  13 #include "src/string/allocating_string_utils.h" // For strdup.
  14
  15 #include "src/errno/libc_errno.h"
  16 #include <linux/limits.h> // This is safe to include without any name pollution.
  17 #include <stdlib.h>
  18 #include <sys/syscall.h> // For syscall numbers.
  19
  20 namespace LIBC_NAMESPACE {
  21
  22 namespace {
  23
  24 bool getcwd_syscall(char *buf, size_t size) {
  25   int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_getcwd, buf, size);
  26   if (ret < 0) {
  27     libc_errno = -ret;
  28     return false;
  29   } else if (ret == 0 || buf[0] != '/') {
  30     libc_errno = ENOENT;
  31     return false;
  32   }
  33   return true;
  34 }
  35
  36 } // anonymous namespace
  37
  38 LLVM_LIBC_FUNCTION(char *, getcwd, (char *buf, size_t size)) {
  39   if (buf == nullptr) {
  40     // We match glibc's behavior here and return the cwd in a malloc-ed buffer.
  41     // We will allocate a static buffer of size PATH_MAX first and fetch the cwd
  42     // into it. This way, if the syscall fails, we avoid unnecessary malloc
  43     // and free.
  44     char pathbuf[PATH_MAX];
  45     if (!getcwd_syscall(pathbuf, PATH_MAX))
  46       return nullptr;
  47     auto cwd = internal::strdup(pathbuf);
  48     if (!cwd) {
  49       libc_errno = ENOMEM;
  50       return nullptr;
  51     }
  52     return *cwd;
  53   } else if (size == 0) {
  54     libc_errno = EINVAL;
  55     return nullptr;
  56   }
  57
  58   // TODO: When buf is not sufficient, evaluate the full cwd path using
  59   // alternate approaches.
  60
  61   if (!getcwd_syscall(buf, size))
  62     return nullptr;
  63   return buf;
  64 }
  65
  66 } // namespace LIBC_NAMESPACE