Date: Mon, 18 Aug 1997 08:27:47 -0700 From: "Jordan K. Hubbard" <jkh@FreeBSD.ORG> To: hackers@FreeBSD.ORG Subject: [Fwd: Re: Please Help Me Understand dlopen()] Message-ID: <33F869F3.446B9B3D@FreeBSD.org>
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Hmmm - any comments, ld hackers?
Jordan
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From: Walter Hafner <hafner@pccog4.forwiss.tu-muenchen.de>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Please Help Me Understand dlopen()
Date: 18 Aug 1997 14:39:35 +0200
Organization: Technische Universitaet Muenchen, Germany
Distribution: world
Message-ID: <s9n90xz1x88.fsf@pccog4.forwiss.tu-muenchen.de>
References: <5stu4v$aio$1@vixen.cso.uiuc.edu> <33F29838.59E2B600@FreeBSD.org>
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guy@netapp.com (Guy Harris) writes:
> Jordan K. Hubbard <jkh@FreeBSD.org> wrote:
> >2. You need to look for _hello rather than hello or you won't be able to
> >find the symbol.
>
> That's a significant deficiency:
>
> 1) not all UNIX C compilers prepend an underscore to symbols (I
> think it was originally done to work around the PDP-11 UNIX
> assembler having symbols with the names of the registers and
> opssibly the opcodes), so if you can't, in some UNIXes, do
>
> dlsym(handle, "hello")
>
> to find a pointer to the function "hello" in a
> dynamically-loaded object, that makes it impossible to use
> "dlsym()" portably - SunOS 5.5.1, which expects C compilers
> not to prepend underscores and which supports "dlopen()",
> will *not* remove the prepended underscore if the lookup
> fails (i.e., the lookup of "_hello" will fail to find a
> function "hello()");
>
> 2) it's somewhat counterintuitive, as indicated by the fact that
> Mr. Murphy didn't know he had to do it;
>
> 3) at least one of the UNIXes whose C compiler *does* prepend an
> underscore and that supports "-ldl", namely SunOS 4.1[.x],
> will, if a "dlsym()" lookup fails, retry the lookup with a
> prepended underscore, it appears.
>
> The run-time linker should be changed to do what the SunOS 4.1[.x]
> run-time linker does, allowing you to look for "hello" to find a
> function "hello()".
Hi!
I bragged about just the same behaviour about 4 weeks ago. :-)
The freeBSD dlsym() is - as far as I know - the only dlsym()
implementation that doesn't search for _funktion() ...
I also complained about dlopen() not searching LD_LIBRARY_PATH.
One answer I got was the suggestion to implement it in the FreeBSD dl
routines myself. Well, I could do it but that would be my first try on
system programming ever. And I think it would significantly lower the
high FreeBSD standards on code quality. :-)
Instead I patched the dl code in our application.
Our application ("HALCON") runs on Solaris, SunOS, HP/UX, IRIX, AIX,
Ultrix, DEC Unix (OSF/1), Linux, FreeBSD, ... you name it. And now there
is a very ugly "#ifdef __FreeBSD__" in the dl code. All other platforms
show the expected behaviour. :-(
-Walter
--
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)
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