sysdeps/unix/sysv/linux/getcwd.c

   1 /* Determine current working directory.  Linux version.
   2    Copyright (C) 1997-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <stdlib.h>
  23 #include <unistd.h>
  24 #include <sys/param.h>
  25
  26 #include <sysdep.h>
  27 #include <sys/syscall.h>
  28
  29
  30 /* If we compile the file for use in ld.so we don't need the feature
  31    that getcwd() allocates the buffers itself.  */
  32 #if IS_IN (rtld)
  33 # define NO_ALLOCATION  1
  34 #endif
  35
  36
  37 /* The "proc" filesystem provides an easy method to retrieve the value.
  38    For each process, the corresponding directory contains a symbolic link
  39    named `cwd'.  Reading the content of this link immediate gives us the
  40    information.  But we have to take care for systems which do not have
  41    the proc filesystem mounted.  Use the POSIX implementation in this case.  */
  42
  43 /* Get the code for the generic version.  */
  44 #define GETCWD_RETURN_TYPE      static char *
  45 #include <sysdeps/posix/getcwd.c>
  46
  47 char *
  48 __getcwd (char *buf, size_t size)
  49 {
  50   char *path;
  51   char *result;
  52
  53 #ifndef NO_ALLOCATION
  54   size_t alloc_size = size;
  55   if (size == 0)
  56     {
  57       if (buf != NULL)
  58         {
  59           __set_errno (EINVAL);
  60           return NULL;
  61         }
  62
  63       alloc_size = MAX (PATH_MAX, __getpagesize ());
  64     }
  65
  66   if (buf == NULL)
  67     {
  68       path = malloc (alloc_size);
  69       if (path == NULL)
  70         return NULL;
  71     }
  72   else
  73 #else
  74 # define alloc_size size
  75 #endif
  76     path = buf;
  77
  78   int retval;
  79
  80   retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
  81   if (retval > 0 && path[0] == '/')
  82     {
  83 #ifndef NO_ALLOCATION
  84       if (buf == NULL && size == 0)
  85         /* Ensure that the buffer is only as large as necessary.  */
  86         buf = realloc (path, (size_t) retval);
  87
  88       if (buf == NULL)
  89         /* Either buf was NULL all along, or `realloc' failed but
  90            we still have the original string.  */
  91         buf = path;
  92 #endif
  93
  94       return buf;
  95     }
  96
  97   /* The system call either cannot handle paths longer than a page
  98      or can succeed without returning an absolute path.  Just use the
  99      generic implementation right away.  */
 100   if (retval >= 0 || errno == ENAMETOOLONG)
 101     {
 102 #ifndef NO_ALLOCATION
 103       if (buf == NULL && size == 0)
 104         {
 105           free (path);
 106           path = NULL;
 107         }
 108 #endif
 109
 110       result = __getcwd_generic (path, size);
 111
 112 #ifndef NO_ALLOCATION
 113       if (result == NULL && buf == NULL && size != 0)
 114         free (path);
 115 #endif
 116
 117       return result;
 118     }
 119
 120   /* It should never happen that the `getcwd' syscall failed because
 121      the buffer is too small if we allocated the buffer ourselves
 122      large enough.  */
 123   assert (errno != ERANGE || buf != NULL || size != 0);
 124
 125 #ifndef NO_ALLOCATION
 126   if (buf == NULL)
 127     free (path);
 128 #endif
 129
 130   return NULL;
 131 }
 132 libc_hidden_def (__getcwd)
 133 weak_alias (__getcwd, getcwd)