Re: dlopen question...

[Miod Vallat <miod@online.fr>]

> This has nothing whatsoever to do with the additional leading
> underscore in symbol names for a.out.  Please don't confuse the
> issue any further.

For what it's worth, I wrote this snippet of autoconf script some time
ago (actually, the full code also checks for HP-UX style libraries and
provides a dlfcn wrapper, but this is outside the scope of this topic).

Miod

myapp_dynload=no
myapp_dynload_underscores=no
myapp_dllib=

# Check for SunOS-style shared libraries
AC_CHECK_HEADERS(dlfcn.h)
if test $ac_cv_header_dlfcn_h = yes
then
	AC_CHECK_LIB(c,dlopen,myapp_dynload=yes,
             [AC_CHECK_LIB(dl,dlopen,[myapp_dynload=sun
                                      myapp_dllib="-ldl"],myapp_dynload=no)])
fi

if test $myapp_dynload = yes
then
	AC_CACHE_CHECK(
		[wherever dynamically loaded symbols need underscores],
		myapp_cv_dynload_underscores,
		myapp_oldlibs=$LIBS
		LIBS="$LIBS $myapp_dllib"
		AC_LANG_SAVE
		AC_LANG_C
		AC_TRY_RUN([#include <dlfcn.h>
#ifndef	RTLD_GLOBAL
#define	RTLD_GLOBAL 0
#endif

int main(void)
{
	void *libc, *printfptr;
	libc = dlopen("libc.so", RTLD_LAZY | RTLD_GLOBAL);
	if (!libc)
		exit(1);
	
	printfptr = dlsym(libc, "_printf");
	dlclose(libc);
	exit(!printfptr);
}],
			myapp_cv_dynload_underscores=yes,
			myapp_cv_dynload_underscores=no,
			myapp_cv_dynload_underscores=no)
		AC_LANG_RESTORE
		LIBS=$myapp_oldlibs
	)
	if test $myapp_cv_dynload_underscores = yes
	then
		AC_DEFINE(DLSYM_NEEDS_UNDERSCORE)
	fi
fi