sysdeps/unix/sysv/linux/generic/dl-origin.c

   1 /* Find path of executable.
   2    Copyright (C) 1998-2021 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 <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <fcntl.h>
  24 #include <sys/param.h>
  25 #include <ldsodefs.h>
  26 #include <sysdep.h>
  27
  28 #include <dl-dst.h>
  29
  30 /* On Linux >= 2.1 systems which have the dcache implementation we can get
  31    the path of the application from the /proc/self/exe symlink.  Try this
  32    first and fall back on the generic method if necessary.  */
  33
  34 const char *
  35 _dl_get_origin (void)
  36 {
  37   char linkval[PATH_MAX];
  38   char *result;
  39   int len;
  40
  41   len = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, "/proc/self/exe",
  42                                linkval, sizeof (linkval));
  43   if (! INTERNAL_SYSCALL_ERROR_P (len) && len > 0 && linkval[0] != '[')
  44     {
  45       /* We can use this value.  */
  46       assert (linkval[0] == '/');
  47       while (len > 1 && linkval[len - 1] != '/')
  48         --len;
  49       result = (char *) malloc (len + 1);
  50       if (result == NULL)
  51         result = (char *) -1;
  52       else if (len == 1)
  53         memcpy (result, "/", 2);
  54       else
  55         *((char *) __mempcpy (result, linkval, len - 1)) = '\0';
  56     }
  57   else
  58     {
  59       result = (char *) -1;
  60       /* We use the environment variable LD_ORIGIN_PATH.  If it is set make
  61          a copy and strip out trailing slashes.  */
  62       if (GLRO(dl_origin_path) != NULL)
  63         {
  64           size_t len = strlen (GLRO(dl_origin_path));
  65           result = (char *) malloc (len + 1);
  66           if (result == NULL)
  67             result = (char *) -1;
  68           else
  69             {
  70               char *cp = __mempcpy (result, GLRO(dl_origin_path), len);
  71               while (cp > result + 1 && cp[-1] == '/')
  72                 --cp;
  73               *cp = '\0';
  74             }
  75         }
  76     }
  77
  78   return result;
  79 }