[PATCH] libgcc, libstdc++: Make more entities no longer TU-local [PR115126]

[Nathaniel Shead]

On Wed, Sep 25, 2024 at 01:30:55PM +0200, Jakub Jelinek wrote:
> On Wed, Sep 25, 2024 at 12:18:07PM +0100, Jonathan Wakely wrote:
> > > >  And whether similarly we couldn't use
> > > > __attribute__((__visibility__ ("hidden"))) on the static block scope
> > > > vars for C++ (again, if compiler supports that), so that the changes
> > > > don't affect ABI of C++ libraries.
> > >
> > > That sounds good too.
> > 
> > Can you use visibility attributes on a local static? I get a warning
> > that it's ignored.
> 
> Indeed :(
> 
> And #pragma GCC visibility push(hidden)/#pragma GCC visibility pop around
> just the static block scope var definition does nothing.
> If it is around the whole inline function though, then it seems to work.
> Though, unsure if we want that around the whole header; wonder what it would
> do with the weakrefs.
> 
> 	Jakub
> 

Thanks for the thoughts.  WRT visibility, it looks like the main gthr.h
surrounds the whole function in a

  #ifndef HIDE_EXPORTS
  #pragma GCC visibility push(default)
  #endif

block, though I can't quite work out what the purpose of that is here
(since everything is currently internal linkage to start with).

But it sounds like doing something like

  #ifdef __has_attribute
  # if __has_attribute(__always_inline__)
  #  define __GTHREAD_ALWAYS_INLINE __attribute__((__always_inline__))
  # endif
  #endif
  #ifndef __GTHREAD_ALWAYS_INLINE
  # define __GTHREAD_ALWAYS_INLINE
  #endif

  #ifdef __cplusplus
  # define __GTHREAD_INLINE inline __GTHREAD_ALWAYS_INLINE
  #else
  # define __GTHREAD_INLINE static inline
  #endif

and then marking maybe even just the new inline functions with
visibility hidden should be OK?

Nathaniel