Re: [musl] Shared library loading

[Rich Felker <dalias@libc.org>]

On Thu, May 28, 2020 at 03:20:46PM -0400, Jeffrey Walton wrote:
> On Wed, May 27, 2020 at 2:10 PM Dmitry Samersoff <dms@samersoff.net> wrote:
> >
> > > The "b" library loading works on my Ubuntu 19.10 and
> > > fails on Alpine 3.11.6 with message: > dlopen failed: Error loading shared library liba.so: No such file or
> > > directory (needed by /root/load-lib-sample/bin/b/libb.so)
> > > Should it work on Alpine with musl libc as well?
> >
> > 1. You explicitly load library with a path (.../liba.so)
> >
> > 2. You are explicitly loading another library (.../libb.so)
> >
> > 3. Linker find liba.so in the appropriate section of libb.so and
> > attempts to load it from syspath (LD_LIBRARY_PATH etc)
> >
> > 4. Linker doesn't find it. Musl return error on this step but glibc and
> > BSD go further.
> >
> > 5. Linker compares short names of already loaded library and the
> > required one
> >
> > 6. It matches, so Linker decides to resolve
> >
> > I didn't find any specification that dictates one or other behavior, so
> > it could not be considered as a bug.
> 
> I believe Drepper's DSO HowTo specifies the behavior for Linux.
> 
> Also see https://www.akkadia.org/drepper/dsohowto.pdf.

I'm not sure if the further search of already loaded libraries is
harmful or not, but Drepper's spec is not a standard we implement in
musl. It's certainly open to discussion but it's the type of behavior
that can easily have unforseen and bad consequences, and I would not
want to be hasty/sloppy about adopting it.

Rich