Re: Minimal GCC/Linux shared lib + EH bug example

[martin at v dot loewis dot de (Martin v. Loewis)]

"David Abrahams" <david.abrahams@rcn.com> writes:

> > No. For template static data, it *only* emits them as .comm, not as
> > .weak. For initialized data that need to be merged at run-time (such
> > as vtables), it emits them as weak.
> 
> Hmm; don't initialized instances of a template static data member need to
> be merged at run-time?

Yes. It turns out that weak symbols only contribute lightly to
run-time semantics of symbol resolution: Even if a symbol is strong,
the dynamic linker will deal with multiple definitions gracefully, and
take the first one it finds. Weak symbols matter in that case only if
the first one it finds is weak: a later strong symbol may then
override the resolution.

.comm is only relevant for object files (relocatable objects): the
(static) linker will eliminate duplicates of .comm (common data).  It
will do so by finding the definition of the symbol that is largest (so
they even might have different sizes), and then allocate a global
symbol in the .bss section.

Regards,
Martin