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Re: Problems with shared library linking and pthreads

On Thu, Aug 08, 2002 at 03:14:21PM +0200, Erland Lewin wrote:
> Hello,
> I have problems with pthread-programs dumping core on thread 
> initialization depending on how linking is done.
>  I would appreciate help on what the correct way for linking libraries is.
>  See the files at the end of this E-mail. If they are compiled as follows:
> cc -g   -c -o testlib.o testlib.c
> ld -shared testlib.o -lpthread -o
> cc -g   -c -o testapp.o testapp.c
> cc -L. testapp.o -ltestlib -lpthread -o testapp
> and testapp is run, it will crash/hang in pthread_create. Why?
>  However, if only one of testlib and testapp are linked with -lpthread, 
> then the resulting program will execute correctly.
>  From what I have previously understood, shared libraries must be 
> linked with the shared libraries that they use in order for libc 
> versioning to work properly (that is, it would be incorrect for testlib 
> not to be linked with -lpthread, because then the knowledge about which 
> version of -lpthread was used is lost. Is this wrong?
>  I'm using gcc 3.0.2, binutils 2.12.1, gnu libc 2.2.2.
>  I'd be most grateful if someone could clarify the situation, and 
> explain the correct way of doing things. And maybe even point me to the 
> relevant docs. Please cc: any replies to the list to me.

You're right; shared libraries must be linked with the shared libraries
that they use.  All shared libraries that they use, which includes libc
and often libgcc_s.  The rule is, don't ever use "ld" to link a shared
library.  You should only be doing that for custom static binaries, if
ever.  Use "cc -shared testlib.o -lpthread -o" (and maybe
-Wl,-soname,") and see if that helps.

Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer

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