Re: Dynamic module loading problem

[Philipp Janda <siffiejoe@...>]

Am 19.09.2013 18:19 schröbte Philipp Janda:
> Am 19.09.2013 17:10 schröbte Francesco Santini:
> > I guess linking lua with the module would help, but I would like to
> > avoid that if possible.
>
> There is a glibc-specific dlopen-flag (man 3 dlopen):

This is not only for glibc. FreeBSD has it too.

> RTLD_NOLOAD (since glibc 2.2)
>      Don't load the library. This can be used to test if the library is
> already resident (dlopen() returns NULL if it is not, or the library's
> handle if it is resident). This flag can also be used to promote the
> flags on a library that is already loaded. For example, a library that
> was previously loaded with RTLD_LOCAL can be reopened with RTLD_NOLOAD |
> RTLD_GLOBAL. This flag is not specified in POSIX.1-2001.
>
> I don't know if this also works from within the dynamically loaded
> library, but you can try (and tell us how it went) ...

I got curious ...
So for the record, this actually seems to work! I've attached the code I 
used (which I hereby place in the public domain), maybe it is useful for 
someone else ...

Tested on:
- Ubuntu 12.04.3, x86, Lua 5.1
- Ubuntu 13.04, amd64, Lua 5.1 + Lua 5.2
- FreeBSD 9.1, amd64, Lua 5.1

Philipp

#ifndef FIXLUASO_H_
#define FIXLUASO_H_

/* Provides a C function macro that tries to reopen the Lua library
 * in global mode, so that C extension modules do not have to be
 * relinked for Lua VMs in shared libraries.
 */

/* detect some form of UNIX, so that unistd.h can be included to
 * use other feature macros */
#if defined( unix ) || defined( __unix ) || defined( __unix__ ) || \
    defined( __TOS_AIX__ ) || defined( _SYSTYPE_BSD ) || \
    defined( HAVE_UNISTD_H )

#include <unistd.h>
/* check for minimum POSIX version that specifies dlopen etc. */
#if (defined( _POSIX_VERSION ) && _POSIX_VERSION >= 200112L) || \
    defined( HAVE_DLFCN_H )

#include <dlfcn.h>
/* check for the existence of the RTLD_NOLOAD flag
 * - GLIBC has it (since 2.2)
 * - FreeBSD has it
 */
#ifdef RTLD_NOLOAD

/* Lua VM library names to try
 * Most of them require the dev-package to be installed,
 * but guessing the real library names for multiple distros
 * is pretty difficult ...
 * If the library is not in the default search path you can
 * set LD_LIBRARY_PATH, or use FIXLUASO_LIBNAME to specify
 * an absolute path to the library.
 */
static char const* fixluaso_lib_names[] = {
/* you can define your own custom name via compiler define: */
#ifdef FIXLUASO_LIBNAME
  FIXLUASO_LIBNAME,
#endif /* custom Lua library name */
  "liblua5.2.so",       /* Lua 5.2, Debian/Ubuntu naming */
  "liblua52.so",
  "liblua.so",          /* default name from Lua's makefile */
  "liblua5.1.so",       /* Lua 5.1, Debian/Ubuntu naming */
  "liblua51.so",
  "libluajit-5.1.so",   /* LuaJIT default name */
};

#define FIX_LUA_SO() \
  do { \
    unsigned i = 0; \
    for( ; i < sizeof( fixluaso_lib_names )/sizeof( *fixluaso_lib_names ); ++i ) { \
      if( dlopen( fixluaso_lib_names[ i ], RTLD_LAZY|RTLD_GLOBAL|RTLD_NOLOAD ) ) \
        break; \
    } \
  } while( 0 )

#endif /* has RTLD_NOLOAD */
#endif /* has dlfcn.h */
#endif /* has unistd.h */

/* define fallback */
#ifndef FIX_LUA_SO
#define FIX_LUA_SO()
#endif

#endif /* FIXLUASO_H_ */