static binary, dlopen, and ifunc

[Florian Weimer]

* Samuel Thibault via Libc-alpha:

> Samuel Thibault, le ven. 13 nov. 2020 01:00:51 +0100, a ecrit:
>> It happens that the output of the program is
>> 
>> info: C locale tests
>> info: en_US.ISO-8859-1 locale tests
>> tst-idna_name_classify: Relink `/usr/src/glibc-upstream/build/mach/libmachuser.so.1' with `/usr/src/glibc-upstream/build/libc.so.0.3' for IFUNC symbol `__stpncpy'
>> Segmentation fault
>> 
>> Is that perhaps what triggers the ifunc selection unexpectedly early?
>
> I realize something: libc.so "NEED"s libmachuser.so for the RPC stubs.
> So I guess the linker is here relocating libmachuser.so first, and here
> trying to select for __stpncpy before libc.so is relocated. I guess I
> need a way to make libmachuser.so only use non-ifunc functions so its
> relocation can proceed before that of libc.so.

Yes, this what I worried about when we discussed storing CPU features in
_rtld_global_ro.  I still think it's the wrong approach, but I haven't
had the time yet to clean it up.

Thanks,
Florian
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