[RFC PATCH 3/3] add r_debug multiple namespaces support

[H.J. Lu]

On Mon, Jun 29, 2020 at 2:49 AM Florian Weimer via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> * Carlos O'Donell via Libc-alpha:
>
> >>> I'm not sure it would work to version _r_debug, since the debugger
> >>> is using DT_DEBUG and we only get to put one value in that
> >>> .dynamic entry.
> >>
> >> The symbol version is needed to avoid problems due to copy relocations
> >> if the symbol is referenced directly from the main program.  Without
> >> that, the object could be truncated.  It's not a debugger
> >> compatibility feature.
> >
> > Correct, but this violates *how* you're supposed to use _r_debug.
>
> If it is possible to link against it, we need to add the new symbol
> version, in my opinion.
>
> > In the dynamic case it is different. The symbol should be looked up
> > via DT_DEBUG only which always points to the library-local address
> > of the data object (and the most recent version). In effect this
> > bypasses the COPY relocation?
>
> How is this supposed to work if the dynamic linker does contain
> DT_DEBUG?
>
> I only observe DT_DEBUG in PIE binaries, but since the dynamic loader is
> mapped at a random address even for ET_EXEC main programs, there must be
> some other mechanism to locate it.
>
> Thanks,
> Florian
>

I opened:

https://gitlab.com/x86-psABIs/Linux-ABI/-/issues/2

with a proposal to extend struct r_debug for libraries loaded with
dlmopen,  I'd like to resolve it for the next releases of glibc, binutils
and GDB.

-- 
H.J.