sysdeps/unix/sysv/linux/getcwd.c

   1 /* Determine current working directory.  Linux version.
   2    Copyright (C) 1997-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <limits.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <sys/param.h>
  26
  27 #include <sysdep.h>
  28 #include <sys/syscall.h>
  29
  30
  31 /* If we compile the file for use in ld.so we don't need the feature
  32    that getcwd() allocates the buffers itself.  */
  33 #if IS_IN (rtld)
  34 # define NO_ALLOCATION  1
  35 #endif
  36
  37
  38 /* The "proc" filesystem provides an easy method to retrieve the value.
  39    For each process, the corresponding directory contains a symbolic link
  40    named `cwd'.  Reading the content of this link immediate gives us the
  41    information.  But we have to take care for systems which do not have
  42    the proc filesystem mounted.  Use the POSIX implementation in this case.  */
  43
  44 /* Get the code for the generic version.  */
  45 #define GETCWD_RETURN_TYPE      static char *
  46 #include <sysdeps/posix/getcwd.c>
  47
  48 char *
  49 __getcwd (char *buf, size_t size)
  50 {
  51   char *path;
  52   char *result;
  53
  54 #ifndef NO_ALLOCATION
  55   size_t alloc_size = size;
  56   if (size == 0)
  57     {
  58       if (buf != NULL)
  59         {
  60           __set_errno (EINVAL);
  61           return NULL;
  62         }
  63
  64       alloc_size = MAX (PATH_MAX, __getpagesize ());
  65     }
  66
  67   if (buf == NULL)
  68     {
  69       path = malloc (alloc_size);
  70       if (path == NULL)
  71         return NULL;
  72     }
  73   else
  74 #else
  75 # define alloc_size size
  76 #endif
  77     path = buf;
  78
  79   int retval;
  80
  81   retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
  82   if (retval > 0 && path[0] == '/')
  83     {
  84 #ifndef NO_ALLOCATION
  85       if (buf == NULL && size == 0)
  86         /* Ensure that the buffer is only as large as necessary.  */
  87         buf = realloc (path, (size_t) retval);
  88
  89       if (buf == NULL)
  90         /* Either buf was NULL all along, or `realloc' failed but
  91            we still have the original string.  */
  92         buf = path;
  93 #endif
  94
  95       return buf;
  96     }
  97
  98   /* The system call either cannot handle paths longer than a page
  99      or can succeed without returning an absolute path.  Just use the
 100      generic implementation right away.  */
 101   if (retval >= 0 || errno == ENAMETOOLONG)
 102     {
 103 #ifndef NO_ALLOCATION
 104       if (buf == NULL && size == 0)
 105         {
 106           free (path);
 107           path = NULL;
 108         }
 109 #endif
 110
 111       result = __getcwd_generic (path, size);
 112
 113 #ifndef NO_ALLOCATION
 114       if (result == NULL && buf == NULL && size != 0)
 115         free (path);
 116 #endif
 117
 118       return result;
 119     }
 120
 121   /* It should never happen that the `getcwd' syscall failed because
 122      the buffer is too small if we allocated the buffer ourselves
 123      large enough.  */
 124   assert (errno != ERANGE || buf != NULL || size != 0);
 125
 126 #ifndef NO_ALLOCATION
 127   if (buf == NULL)
 128     free (path);
 129 #endif
 130
 131   return NULL;
 132 }
 133 libc_hidden_def (__getcwd)
 134 weak_alias (__getcwd, getcwd)