Re: standards/51024 (NetBSD misses the mandatory waitid() syscall)

[Joerg Schilling <Joerg.Schilling%fokus.fraunhofer.de@localhost>]

The following reply was made to PR standards/51024; it has been noted by GNATS.

From: Joerg Schilling <Joerg.Schilling%fokus.fraunhofer.de@localhost>
To: <wiz%netbsd.org@localhost>, <standards-manager%netbsd.org@localhost>, <netbsd-bugs%netbsd.org@localhost>,
        <gnats-bugs%netbsd.org@localhost>, <gnats-admin%netbsd.org@localhost>,
        <christos%zoulas.com@localhost>
Cc: 
Subject: Re: standards/51024 (NetBSD misses the mandatory waitid() syscall)
Date: Mon, 4 Apr 2016 17:49:34 +0200

 Christos Zoulas <christos%zoulas.com@localhost> wrote:
 
 > On Apr 4, 10:08am, christos%zoulas.com@localhost (Christos Zoulas) wrote:
 > -- Subject: Re: standards/51024 (NetBSD misses the mandatory waitid() syscall
 >
 > | Do you have the reference where it says it needs to preserve all 32 bits
 > | of exit code? I have not found one.
 >
 > The reason I am asking all this is because although FreeBSD has made the
 > change to pass all 32 bits in this particular instance, they have overloaded
 > the meaning of si_status, so that now the user code needs to understand
 > what context we are in to interpret it properly. I.e.
 >
 > - it could be a full 32 bit exit code
 > - it could be a signal number
 > - it could be a composite 'wait status' (as it is always now with NetBSD,
 >   except in the waitid case...).
 
 Does the last apply to the signal handler for SIGCHLD only?
 It is wrong in any case. Only the first two cases are correct.
 
 > kern_exit.c:                    siginfo->si_status = WTERMSIG(p->p_xsig);
 > kern_exit.c:                    siginfo->si_status = WTERMSIG(p->p_xsig);
 > kern_exit.c:                    siginfo->si_status = p->p_xexit;
 > kern_exit.c:                            siginfo->si_status = p->p_xsig;
 > kern_exit.c:                            siginfo->si_status = p->p_xsig;
 > kern_exit.c:                            siginfo->si_status = SIGCONT;
 > kern_sig.c:             p->p_ksi->ksi_status = status;
 
 Thank you for this hint, it seems that I would need to check FreeBSD. 
 Fortunately I have access to an installation with a recent version.
 
 si_status holds the exit() parameter in case of a normal exit (CLD_EXITED).
 
 It holds the signal number in case the child has been terminated as a result of 
 a signal: CLD_DUMPED, CLD_KILLED, CLD_TRAPPED, CLD_STOPPED. 
 
 In case of CLD_CONTINUED, the status is 0.
 
 So in general: si_status either contains the exit code or a signal number.
 
 See the waitid() emulation in sh/jobs.c. The exit code of course cannot be 
 retrieved from the historical wait() status value as this only holds the low 8 
 bits. What you can see from the emulation code in sh/jobs.c is what is expected 
 to be under what condition in si_code.
 
 If you ever implement more than 255 signals, WTERMSIG() will not work as well.
 
 Jörg
 
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