[PATCH] elf: Add back support for programs that do not load libc.so

[Florian Weimer]

* Cristian Rodríguez:

> On Fri, Nov 8, 2024 at 10:51 AM Florian Weimer <fweimer@redhat.com> wrote:
>
>  Commit 8f8dd904c4a2207699bb666f30acceb5209c8d3f (“elf:
>  rtld_multiple_ref is always true”) removed some code that happened
>  to enable compatibility with programs that do not link against
>  libc.so.  Such programs cannot call dlopen or any dynamic linker
>  functions (except __tls_get_addr), so this is not really useful.
>  Still ld.so should not crash with a null-pointer dereference
>  or undefined symbol reference in these cases.
>
> Perhaps adding a warning that this does not make sense somewhere.?

It's sort if implied in our dynamic linker hardening guidelines.  Maybe
we have to mention explicitly there that the glibc-provided startup
files and the libc.so linker script should be used for linking.  With te
official startup files, this can't happen due to the __libc_start_main
symbol dependency.

Thanks,
Florian