[PATCH 2/2] libstdc++: Move stream initialization into compiled library [PR44952]

[Patrick Palka]

On Fri, 4 Nov 2022, Florian Weimer wrote:

> * Patrick Palka via Gcc-patches:
> 
> > This patch moves the global object for constructing the standard streams
> > out from <iostream> and into the compiled library on targets that support
> > the init_priority attribute.  This means that <iostream> no longer
> > introduces a separate global constructor in each TU that includes it.
> >
> > We can do this only if the init_priority attribute is supported because
> > we need to force that the stream initialization runs first before any
> > user-defined global initializer in programs that that use a static
> > libstdc++.a.
> 
> I think this breaks initialization of iostreams of shared objects that
> are preloaded with LD_PRELOAD.  With the constructor, they initialize
> iostreams once they are loaded via their own ELF constructors (even
> before libstdc++'s ELF constructors run).  Without the constructor in
> <iostream>, that no longer happens.

IIUC wouldn't that shared object depend on libstdc++.so and hence
libstdc++'s constructors would still run before the shared object's?

> 
> Thanks,
> Florian
> 
>