Re: relocation of shared libs not based at 0

[Paul Koning <pkoning at equallogic dot com>]

>>>>> "Kevin" == Kevin Buettner <kevinb@redhat.com> writes:

 Kevin> ...
 Kevin> So, as I understand it, the "base address" is *not* an
 Kevin> absolute location, but is actually the difference between
 Kevin> where the segment ended up and the location assigned to it in
 Kevin> the executable file.  Thus the "base address" is the proper
 Kevin> value to use to relocate the segment's start and end
 Kevin> addresses.

That interpretation certainly matches the code.  The document you
quoted is not all that clearly worded, but it seems to take the same
view of things.

On the other hand, the shared library loader in NetBSD doesn't.  It
sets the "base address" in the link_map to the load address of the
section, not the bias from the link address to the load address.
That's why I changed solib-svr4.c in my copy of gdb.

Perhaps a better fix is to change the loader in NetBSD to set "base
address" to match gdb's expectations.  

 Kevin> Now, it's possible that my understanding is flawed.  If so, I
 Kevin> await enlightenment.  I think it's also possible that the
 Kevin> shared library implementation that you're using might not
 Kevin> conform to the above definition of "base address".  If that's
 Kevin> the case, then you can either attempt to get it fixed in the
 Kevin> code which implements the dynamic loader, or, if that's not
 Kevin> possible, create a new solib backend for gdb which implements
 Kevin> support for your shared library machinery.  I suspect it would
 Kevin> be very similar to solib-svr4.c.

 Kevin> With regard to the two patches that have been posted for
 Kevin> fixing this problem, I don't think that either one is correct
 Kevin> in light of the above definition of "base address".

It would be interesting to hear from a NetBSD wizard.  I'd be happy
with any fix that makes shared libs work in gdb for my platform.

Part of the reason why I patched gdb rather than ldd.elf_so is so I
could process coredumps from already shipped systems.  Then again,
there are few enough of those that this isn't a big consideration.

      paul