Date: 30 Jul 1997 11:15:01 +0200 From: Walter Hafner <hafner@forwiss.tu-muenchen.de> To: freebsd-questions@FreeBSD.ORG, hafner@forwiss.tu-muenchen.de Subject: questions about dlopen() Message-ID: <s9nyb6oyk8a.fsf@pccog4.forwiss.tu-muenchen.de>
next in thread | raw e-mail | index | archive | help
The following message is a courtesy copy of an article
that has been posted as well.
Hi there!
I've got a few questions regarding the 'dlopen()' call. I had a look at
the sources (/usr/src/lib), but didn't find any references to
dlopen(). The manpage is no help either.
Problem: We try to read shared libs into an application at runtime. Our
application supports various framegrabbers on various hardware (HP, Sun,
SGI, PC/Linux, PC/FreeBSD ...) and we have to load wrapper-libs that
provide a consistent user interface at runtime (plus the vendor-specific
libs of course). That's where 'dlopen()' comes in handy. The following
code snipplet works on _all_ hard- and software combinations _except_
FreeBSD 2.2.* (didn't try 2.1.*):
#define RTLD_LAZY 1
[...]
hndl = dlopen(name,RTLD_LAZY);
if (hndl == NULL)
return H_ERR_DLOPEN;
On all platforms except FreeBSD, dlopen() searches LD_LIBRARY_PATH for
the library and returns successfully. On FreeBSD, I get a NULL
pointer. If I query dlerror(), I get a "2 ENOENT No such file or
directory".
dlopen() finds the library only if I cd into the lib-Directory.
If it's a ldconfig problem: I can't use ldconfig, because the wrapper
libs are named after the corresponding framegrabbers. In the current
case: Meteor.so. Ldconfig only looks for files named libXXX.so.XXX.
So what's the deal? If a filename is passed to dlopen(), dlopen() seems
to look only in the exact path the filename specifies. And if a name
without directory information is passed, only the current directory is
searched. I find this behaviour very frustrating. Compare the Solaris
manpage to dlopen():
A path name containing an
embedded '/' is interpreted as an absolute path or relative
to the current directory, otherwise the set of search paths
currently in effect by the run-time linker will be used to
locate the specified file
Linux is similar:
If filename is not an
absolute path (i.e., it does not begin with a "/"), then
the file is searched for in the following locations:
A colon-separated list of directories in the user's
LD_ELF_LIBRARY path environment variable. If and
only if LD_ELF_LIBRARY_PATH is not defined,
LD_LIBRARY_PATH is used in its place.
The FreeBSD manpage gives no informations on the search path. As I said:
FreeBSD seems to be the only system that handles dlopen() arguments that
way.
Or _does_ the FreeBSD dlopen() search the library path, but looks only
for lib*.so like ldconfig does?
Is there any convenient way to circumvent these problems? Currently I
use a
getenv("LD_LIBRARY_PATH");
call and then fiddle with the result to provide dlopen() with all the
paths to look in. Is this _really_ the only solution?
Thanks,
-Walter
PS: The date of dlopen(3) is "24 September 1989" ... maybe time for an
update?
--
Walter Hafner_____________________________ hafner@forwiss.tu-muenchen.de
<A href=http://www.forwiss.tu-muenchen.de/~hafner/>*CLICK*</A>;
The best observation I can make is that the BSD Daemon logo is _much_
cooler than that Penguin :-) (Donald Whiteside)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?s9nyb6oyk8a.fsf>