Re: [PATCH] c++/58796 Make nullptr match exception handlers of pointer type

[Jonathan Wakely <jwakely at redhat dot com>]

On 15/07/16 22:53 +0100, Jonathan Wakely wrote:
> On 15/07/16 23:36 +0200, Jakub Jelinek wrote:
> > On Fri, Jul 15, 2016 at 10:07:03PM +0100, Jonathan Wakely wrote:
> > > > +      if (typeid (*this) == typeid(__pointer_type_info))
> > > > +        {
> > > > +          *thr_obj = nullptr;
> > > > +          return true;
> >
> > But you have the above store too.
>
> That doesn't write to the exception object, it only does a single
> dereference (compared to the double dereference of the racy write), so
> it writes to the local variable in the PERSONALITY_FUNCTION in
> eh_personality.cc
>
> So that shouldn't race with other threads. I think.

TSan agrees. When I compile my test and yours (and include
libsupc++/pbase_type_info.cc in the executable, so the writes are also
instrumented by tsan) then I see races for the *(ptrdiff_t*)*thr_obj
writes but not the *thr_obj ones.

It's only the ptr-to-data-member case that scribbles in the actual
exception object.