Question about rtld-elf. Anyone?.. Anyone?

[Daniel Eischen]

On Wed, 30 Apr 2003, Daniel Eischen wrote:

> On Tue, 29 Apr 2003, Peter Wemm wrote:
> > One way I've seen is to have libc and the respective pthreads libraries
> > provide the public access to things like dlopen() etc.  That way, the
> > threads package of your choice does its own serialization of the entry
> > points into the dynamic linker guts/internals.  As John Polstra said
> > earlier, he has some thoughts about how to make the actual lazy symbol
> > lookup be thread-safe.
> 
> I think this would work.  It could even be done in our libc, just
> as malloc, stdio, and friends use locking stubs (overridden by our
> threads libraries).
> 
> > If I recall correctly, our old a.out based shared lib implementation did it
> > precicely this way.  dlopen() was a function in libc, that called through
> > a vector into the guts of ld.so.1.  The dynamic linker itself never provided
> > direct call access to this stuff.  Some systems put these public functions
> > in a seperate library, -ldl.  The ELF implemetation that we use does, and
> > doesn't give the threads library a chance to wrap them.
> > 
> > (And no, this is not an invitation for getting sidetracked on making
> > ld-elf.so.1 into libdl.so.1 as a service library, etc etc)
> > 
> > How would things go if we renamed the ld-elf.so functions to __rtld_dlopen()
> > etc and then had libc provide a weak dlopen() function that redirected to
> > __rtld_dlopen(), and give libpthread a chance to provide a replacement?
> > And of course, deal with making the runtime symbol resolution as John
> > suggested in the commit logs.
> 
> Or just have libc provide the necessary locking so that we don't need
> to repeat it in libc_r, libthr, and libpthread.
> 
> Is a simple mutex around dlopen, dlsym, etc, sufficient?  We don't need
> to handle recursive calls, right?

As an experiment, I made the dlfoo calls in rtld-elf weak
(__dlfoo -> dlfoo) and then overrode them in libpthread
and protected them with mutexes.

I can get mozilla to work about 1/2 of the time now, but
it still gets stuck in the same state the other 1/2 of
the time.  This is a bit of an improvement, and seems to
indicate (at least to me) that rtld-elf is the culprit.

-- 
Dan Eischen