dlopen() and symbols and none shared libraries

Aurel Balmosan

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Mar 3, 1998, 3:00:00 AM3/3/98

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Hi all,

I have a major problem with dynamic loaded shared objects. dlopen() fails
because it can not resolve symboles defined in normal ".a" libraries linked with
the program.

Here an example:

C-Source: x.c
Compiled with: gcc -o x x.c -ldl
-------------------------
#include <dlfcn.h>

void MyMainFunction()
{ printf("My main function\n");
}

void main()
{ void *hdl=dlopen("./y.so", RTLD_NOW);
void (*fnc)();
if (!hdl) { printf("dlopen(%s)\n", dlerror()); exit(1); }
printf("My first main\n");
fnc=dlsym(hdl, "MySharedFunction");
if (!fnc) { printf("dlsym(%s)\n", dlerror()); exit(1); }
fnc();
printf("My second main\n");
exit(0);
}
--------------------------

C-Source:y.c
Compiled with: gcc -fPIC -shared -o y.so y.c
---------------------------------
#include <stdio.h>
void MySharedFunction()
{ printf("My first shared\n");
MyMainFunction();
printf("My second shared\n");
}
----------------------------------

Running x give following output:
x: can't resolve symbol 'MyMainFunction'
dlopen(Unable to resolve symbol)

The same happens if the symbol is from a static linked library ("libxyz.a") It
happens also when the x.o is generated as shared as follows:

gcc -fPIC -shared -c x.c; gcc -o x x.o -ldl

In case the function MyMainFunction is in another shared object xx.so only
containing that function. And the dlopen() flags are RTLD_NOW|RTLD_GLOBAL every
thing is ok.

The same code runs on Solaris-2.5.1, Solaris-2.6, DEC-Unix-3.2, DEC-Unix-4.0 and
other UNIX. It looks like that the local symbols are not known to the dynamic
loader. Why? I think that this is a bug. Who can help me?

Bye,
Aurel.

--
=========================================================
Aurel Balmosan | a...@orga.com, au...@orga.com
=========================================================

Richard Jones

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Mar 3, 1998, 3:00:00 AM3/3/98

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Aurel Balmosan <a...@orga.com> wrote:
> Hi all,

> I have a major problem with dynamic loaded shared objects. dlopen() fails
> because it can not resolve symboles defined in normal ".a" libraries linked with
> the program.

Does compiling the main program with -rdynamic make it
work?

Rich.

--
Richard Jones rjo...@orchestream.com Tel: +44 171 460 6141 Fax: .. 4461
Orchestream Ltd. 262a Fulham Rd. London SW10 9EL. "you'll write in
PGP: www.four11.com telegraphic, or you won't write at all" [Céline]
Copyright © 1998 Richard W.M. Jones

Aurel Balmosan

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Mar 3, 1998, 3:00:00 AM3/3/98

to

Aurel Balmosan wrote:

> I have a major problem with dynamic loaded shared objects. dlopen() fails
> because it can not resolve symboles defined in normal ".a" libraries linked with
> the program.

Thank you all for responding via e-mail.Now i use -Wl,-export-dynamic when linking
and it works fine.

Bye,
Aurel.

--
================================================================
Aurel Balmosan | au...@xylo.owl.de, a...@orga.com
http://gaia.owl.de/~aurel/ |
================================================================

Paul Flinders

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Mar 4, 1998, 3:00:00 AM3/4/98

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Richard Jones <rjo...@orchestream.com> writes:

> Aurel Balmosan <a...@orga.com> wrote:
> > Hi all,
>

> > I have a major problem with dynamic loaded shared objects. dlopen() fails
> > because it can not resolve symboles defined in normal ".a" libraries linked with
> > the program.
>

> Does compiling the main program with -rdynamic make it
> work?

Not with a recent ld - the dlopen man page is out of sync.

You want --export-dynamic as a linker flag. Aurel's code works OK then

--
Paul