Re: [PATCH 0/2] nptl: Update struct pthread_unwind_buf

[Florian Weimer <fw at deneb dot enyo dot de>]

* H. J. Lu:

> PLEASE take a closer look:
>
> Yes, there are
>
> void *__pad[4];
>
> But the name is misleading.   It isn't real padding.  This is
> an opaque array:
>
> /* Private data in the cleanup buffer.  */
> union pthread_unwind_buf_data
> {
>   /* This is the placeholder of the public version.  */
>   void *pad[4];
>
>   struct
>   {
>     /* Pointer to the previous cleanup buffer.  */
>     struct pthread_unwind_buf *prev;
>
>     /* Backward compatibility: state of the old-style cleanup
>        handler at the time of the previous new-style cleanup handler
>        installment.  */
>     struct _pthread_cleanup_buffer *cleanup;
>
>     /* Cancellation type before the push call.  */
>     int canceltype;
>   } data;
> };
>
> Only the last element in __pad[4] is unused.  There is

The entire __pad array is unused until the handler is registered,
which happens *after* the call to __sigsetjmp, in the
__pthread_register_cancel function.  This means that __sigsetjmp may
clobber it.