Re: lib/49791: dlopen(0, and dlopened libraries

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Thu, Mar 26, 2015 at 11:45:00PM +0000, prlw1%cam.ac.uk@localhost wrote:
> that our dlopen() does (cf dlfcn(3))
> 
>      If the first argument is NULL, dlopen() returns a handle on the global
>      symbol object.  This object provides access to all symbols from an
>      ordered set of objects consisting of the original program image and any
>      dependencies loaded during startup.

This is the same behavior documented on glibc

> whereas accoding to posix in
> 
>   http://pubs.opengroup.org/onlinepubs/007904975/functions/dlopen.html
> 
> If the value of file is 0, dlopen() shall provide a handle on a global
> symbol object. This object shall provide access to the symbols from an
> ordered set of objects consisting of the original program image file,
> together with any objects loaded at program start-up as specified by
> that process image file (for example, shared libraries), and the set
> of objects loaded using a dlopen() operation together with the
> RTLD_GLOBAL flag. As the latter set of objects can change during
> execution, the set identified by handle can also change dynamically.

This, frankly, doesn't make sense.

> glib assumes the posix variant, and we have a patch in pkgsrc to detect ours as broken.

How can it? It doesn't seem like glibc provides the same:

  If filename is NULL, then the returned handle is for the main program.

> #include <err.h>
> #include <dlfcn.h>
> #include <stdio.h>
> 
> int main()
> {
>     void *handle;
> 
>     handle = dlopen ("libm.so", RTLD_GLOBAL | RTLD_LAZY);
>     if (handle == NULL)
>         errx(1, "dlopen of libm failed (%s)", dlerror());
> 
>     handle = dlopen (NULL, 0);
>     if (handle == NULL)
>         errx(1, "dlopen of global symbol object failed (%s)", dlerror());
> 
>     handle = dlsym (handle, "sin");
>     if (handle == NULL)
>         errx(1, "sin() not found in libm (%s)", dlerror());

I think the "correct" behavior here is:

dlsym(RTLD_DEFAULT, "sin");

Joerg