From: ahoward <ahoward@...>
Date: 2002-11-13T04:10:22+09:00
Subject: Re: setting LD_LIBRARY_PATH doesn't seem to work?

On 12 Nov 2002, Eric Schwartz wrote:

> Why is that?

see earlier post.

> In any event, the problem is that when loading C extensions, ruby doesn't
> seem to be respecting the LD_LIBRARY_PATH setting.  Regardless of the
> probity of the idea, it's broken, and needs fixing.

it is not ruby which is broken


  eg/c > cat liba.c
  int a;

  eg/c > cat libb.c
  int b;
  extern int a;

  eg/c > gcc -o liba.so -shared liba.c

  eg/c > gcc -o libb.so -shared libb.c -L ./ -la

  eg/c > ldd liba.so
	  libc.so.6 => /lib/libc.so.6 (0x4000b000)
	  /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x80000000)

  eg/c > ldd libb.so
	  liba.so => not found
	  libc.so.6 => /lib/libc.so.6 (0x4000b000)
	  /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x80000000)


so liba.so has NO depends, and libb.so HAS depends.


now a program to dlopen them :

  eg/c > cat dlopen.c
  #include <stdlib.h>
  #include <stdio.h>
  #include <dlfcn.h>

  int
  main (int argc, char **argv)
  {
    char *ld_library_path;

    /* set LD_LIBRARY_PATH if arg given */
    if (argc > 1)
    {
      printf ("SET LD_LIBRARY_PATH TO : %s\n", argv[1]);
      setenv ("LD_LIBRARY_PATH", argv[1], 0);
    }

    /* print LD_LIBRARY_PATH if env has it */
    if (ld_library_path = getenv ("LD_LIBRARY_PATH"))
    {
      printf ("LD_LIBRARY_PATH : %s\n", ld_library_path);
    }

    /* try to open liba.so */
    if ((dlopen ("liba.so", RTLD_NOW|RTLD_GLOBAL)) == NULL)
    {
      printf ("FAILED TO LOAD 'liba.so'\n");
    }
    else
    {
      printf ("SUCCESSFULLY LOADED 'liba.so'\n");
    }

    /* try to open libb.so - which depends on a*/
    if ((dlopen ("libb.so", RTLD_NOW|RTLD_GLOBAL)) == NULL)
    {
      printf ("FAILED TO LOAD 'libb.so'\n");
    }
    else
    {
      printf ("SUCCESSFULLY LOADED 'libb.so'\n");
    }

    return 0;
  }


now using it

  eg/c > dlopen
  FAILED TO LOAD 'liba.so'
  FAILED TO LOAD 'libb.so'

  eg/c > dlopen ./
  SET LD_LIBRARY_PATH TO : ./
  LD_LIBRARY_PATH : ./
  FAILED TO LOAD 'liba.so'
  FAILED TO LOAD 'libb.so'

  eg/c > env LD_LIBRARY_PATH=./ dlopen
  LD_LIBRARY_PATH : ./
  SUCCESSFULLY LOADED 'liba.so'
  SUCCESSFULLY LOADED 'libb.so'

so you see, setting LD_LIBRARY_PATH using setenv does not affect dlopen?!
there is probably a reason for this - but it's non-obvious.  using LD_RUN_PATH
or compiling with -rpath always works and is easy to understand and maintain.

it seems as if dlopen uses the environment of the parent process... perhaps
for securtiy?  anyone?  all i know is that every time i play with dlopen and
LD_LIBRARY_PATH i've been confused...

moral : stay awasy from LD_LIBRARY_PATH

-a


-- 

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 | Ara Howard
 | NOAA Forecast Systems Laboratory
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 | Data Systems Group
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