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

[Jonathan Wakely]

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.