[PATCH 1/2] setjmp: Use BSD sematic as default for setjmp

[Florian Weimer]

* Adhemerval Zanella Netto:

> On 01/08/23 05:35, Florian Weimer wrote:
>> * Adhemerval Zanella via Libc-alpha:
>> 
>>> POSIX relaxed the relation of setjmp/longjmp and the signal mask
>>> save/restore, meaning that setjmp does not require to be routed to
>>> _setjmp to be standard compliant.
>>>
>>> This is done to avoid breakage of SIGABRT handlers, since to fully
>>> make abort AS-safe, it is required to remove the recurisve lock
>>> used to unblock SIGABRT prior raised the signal.
>>>
>>> Also, it allows caller to actually use setjmp, since from
>>> 7011c2622fe3e10a29dbe74f06aaebd07710127d the symbol is unconditionally
>>> routed to _setjmp.
>> 
>> Doesn't this have non-trivial performance impact?
>
> Yes, it is two extra sigprocmask to get/set the signal mask.  This is
> not *strictly* required, but the SIGABRT on abort generates racy
> conditions on process creation and.  This patch can be dropped, but it
> would mean that to get expected semantic for abort handlers will need
> to use sigsetjmp (..., 1) instead of setjmp.

Sorry, I don't understand?  With the current locking, this change should
really not be required because the user SIGABRT handler does not run
with the signal mask changed.

Thanks,
Florian