[14] Backdating the ABI

[Florian Weimer]

* Andreas K. Huettel:

> Am Samstag, 14. September 2024, 14:26:00 MESZ schrieb Florian Weimer:
>> * Add a way to link applications with an earlier glibc ABI.
>> * May need GCC and binutils changes.
>> * Unchanged system library dependencies?
>> * Is blaming glibc technically accurate?
>> 
> [snip]
>
> Isn't this basically a complaint about
> "It's too hard to build against a non-system older glibc branch"
> ?
>
> Maybe adressing this would be easier.

The linker performs symbol checks across the entire link.  If the shared
objects for glibc are actually downgraded, you must downgrade the system
libraries as well, even if the application does not use any recent
versions from them.  This effect is amplified by DT_RELR if the
downgraded glibc does not define GLIBC_ABI_DT_RELR.

I don't know if the answer is to relax that linker check.  But
cross-tools that only build the core run-time libraries do not solve
this issue today.

Thanks,
Florian