Re: [PATCH v2 1/2] setjmp: Use BSD sematic as default for setjmp

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 04/08/23 05:43, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> 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.
> 
> I still think we shouldn't do this due to the performance implications.

By not changing it and with the abort AS-safe fix, the following code
will always abort the program:

--
 static jmp_buf jb;

 static void
 sigabrt_handler (int sig)
 {
   longjmp (jb, 1);
 }

 struct sigaction sa = { .sa_handler = sigabrt_handler, .sa_flags = 0 };
 sigemptyset (&sa.sa_mask);
 assert (sigaction (SIGABRT, &sa, 0) == 0);

 if (setjmp (jb) == 0)
   abort ();

 if (setjmp (jb) == 0)
   abort ();

 // No reached.
--

Callers will need to change to sigsetjmp (..., 1) to have the same semantic.
That's the main reason I am suggesting this patch.