dlopen and shared objects using pthreads.

[Adam Dickmeiss]

Hi,

it is a well known rule for Apache admins that if they plan
to use loadable modules that uses pthreads they have to recompile
Apache and add the flag -lpthread for the Linker in order to
prevent a crash.

I think the bug is related to glibc, so I decided to spent some
time creating a small test case that illustrates this. See the
Makefile and the two C sources below.

[snip] sub.c:
int sub(void) { return 1; }

[snip] main.c:

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

int main(int argc, char **argv)
{
        int r;
        void *h;

        h = dlopen ("./sub.so", RTLD_NOW|RTLD_GLOBAL);
        if (!h)
        {
                printf ("dlopen failed\n");
                exit (1);
        }
        gethostbyname("slashdot.org");
        dlclose (h);

        exit (0);
}

[snip] Makefile
all: sub.so main-wt main-wot 

sub.so: sub.c
        gcc -D_REENTRANT -shared sub.c -o sub.so -lpthread

main-wt: main.c
        gcc main.c -o main-wt -ldl -lpthread

main-wot: main.c
        gcc main.c -o main-wot -ldl

clean:
        rm -f main-wt main-wot sub.so core


[end]

The program main-wt works. The other main-wot dies with a SEGV
in dlclose or gethostbyname.

I see this behaviour on a Debian GNU/Linux using ldd version 1.9.11 and
on Redhat Fisher using ldd 1.2.1.

Cheers,
  Adam

-- 
Adam Dickmeiss  mailto:address@hidden  http://www.indexdata.dk
Index Data      T: +45 33410100           Mob.: 212 212 66