[PATCH 0/2] nptl: Update struct pthread_unwind_buf

[Florian Weimer]

* Carlos O'Donell:

> I would like to see an argument made for CET markup against versioning
> __pthread_register_cleanup.

I don't think __pthread_register_cleanup.  It's __sigsetjmp.  We would
have to version __sigsetjmp.  Changing the name would be ideal, but
this will be difficult because of its returns-twice nature.

I also don't have a problem with requiring -fexceptions for
cancellation handlers with CET support.  For additional safety, we
could change sigsetjmp to write the shadow stack pointer before the
kernel signal mask, so that it will still be in bounds for legacy
cancellation handler allocation.  __pthread_register_cleanup will
overwrite it, but I don't think we ever need to restore it, so that
shouldn't be a problem.