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

[unlvsur at live dot com]

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

cqwrteur <unlvsur at live dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---

--- Comment #17 from cqwrteur <unlvsur at live dot com> ---
(In reply to Arsen Arsenović from comment #15)
> (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.

Then why? Why does it define _ISOC2X_SOURCE? C++ is not even C.