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

   1 /* Find path of executable.
   2    Copyright (C) 1998-2024 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 <dl-dst.h>
  21 #include <fcntl.h>
  22 #include <ldsodefs.h>
  23 #include <sysdep.h>
  24
  25 /* On Linux >= 2.1 systems which have the dcache implementation we can get
  26    the path of the application from the /proc/self/exe symlink.  Try this
  27    first and fall back on the generic method if necessary.  */
  28
  29 const char *
  30 _dl_get_origin (void)
  31 {
  32   char linkval[PATH_MAX];
  33   char *result;
  34   int len;
  35
  36   len = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, "/proc/self/exe",
  37                                linkval, sizeof (linkval));
  38   if (len > 0 && linkval[0] != '[')
  39     {
  40       /* We can use this value.  */
  41       assert (linkval[0] == '/');
  42       while (len > 1 && linkval[len - 1] != '/')
  43         --len;
  44       result = (char *) malloc (len + 1);
  45       if (result == NULL)
  46         result = (char *) -1;
  47       else if (len == 1)
  48         memcpy (result, "/", 2);
  49       else
  50         *((char *) __mempcpy (result, linkval, len - 1)) = '\0';
  51     }
  52   else
  53     {
  54       result = (char *) -1;
  55       /* We use the environment variable LD_ORIGIN_PATH.  If it is set make
  56          a copy and strip out trailing slashes.  */
  57       if (GLRO(dl_origin_path) != NULL)
  58         {
  59           size_t len = strlen (GLRO(dl_origin_path));
  60           result = (char *) malloc (len + 1);
  61           if (result == NULL)
  62             result = (char *) -1;
  63           else
  64             {
  65               char *cp = __mempcpy (result, GLRO(dl_origin_path), len);
  66               while (cp > result + 1 && cp[-1] == '/')
  67                 --cp;
  68               *cp = '\0';
  69             }
  70         }
  71     }
  72
  73   return result;
  74 }