[Openquicktime-devel] fix for dlsym() on OS X

[Jean-Francois P. <pan...@co...>]

In acinclude.m4, there is code to figure out if dlsym() automatically 
adds an underscore in front
of a symbol name on systems where symbols have an underscore prepended 
to them when an
object file is generated. Here is what the code says:

dnl *********************
dnl dlsym and Underscores
dnl *********************

dnl Check checks whether dlsym (if present) requires a leading underscore.
dnl Written by Dan Hagerty <ha...@ai...> for scsh-0.5.0.


Unfortunately, this code doesn't work, since it depends on having 
previously tested
for the presence of dlopen and/or whether dlopen lives in libdl, which 
is not done
in configure.in. Thus on OS X, which adds underscores to names in 
objects but
compensates for this in dlsym(), you end up with:

/* #undef DLSYM_ADDS_USCORE */

but:

#define USCORE 1

in include/openquicktime/config.h when you run ./configure (I know that 
there's a special
macconfig.h in macos, but on OS X 10.3.x, it looks like the generic 
bootstrap/configure mechanism
mostly works without needing special magic).

The solution is to add the following tests to configure.in:

*** configure.in.orig   2004-07-06 00:40:59.000000000 -0700
--- configure.in        2004-07-06 00:42:31.000000000 -0700
***************
*** 180,185 ****
--- 180,187 ----
  CFLAGS="$CFLAGS $my_cv_comment"
 
  dnl Check to see if dlsym adds an underscore
+ AC_CHECK_LIB(dl, dlopen)
+ AC_HAVE_FUNCS(dlopen)
  MY_DLSYM_USCORE
  AH_TEMPLATE([USCORE], [Define if symbol tables on this system use 
leading underscores.])
  AH_TEMPLATE([DLSYM_ADDS_USCORE], [Define if dlsym automatically 
supplies a leading underscore.])

These tests will set the variables ac_cv_func_dlopen and 
ac_cv_lib_dl_dlopen to the correct
values for the platform, and will make the code in MY_DLSYM_USCORE 
correctly generate
the DLSYM_ADDS_USCORE define in config.h

With this fix, OpenQuicktime can correctly load codec plugins on OS X 
10.3.4.

JF