[Bug libstdc++/115907] Libstdc++ and GCC itself should avoid glibc above 2.34 dependency

[arsen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115907

Arsen Arsenović <arsen at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---
                 CC|                            |arsen at gcc dot gnu.org

--- Comment #15 from Arsen Arsenović <arsen at gcc dot gnu.org> ---
(In reply to cqwrteur from comment #12)
> (In reply to Andrew Pinski from comment #6)
> > There is NO fix inside gcc/libstdc++.
> > THe only fix is your build of GCC (which includes the target libraries)
> > needs to be build against the oldest version of glibc you support. This is
> > something which GCC cannot control.
> > THIS IS HOW linking and backwards compatibility works.
> 
> Also if you don't think this is a bug. Explain this to me. Why C++ will use
> __isoc23_sscanf but C does not?

cc1plus defines _GNU_SOURCE which enables _ISOC2X_SOURCE in glibc features.h.

downgrading libraries at runtime is _never_ supported.  just downgrade the
build sysroot, as I told you already.

this is indeed not a bug, in any component.  LLVM will not fix it either.