Date: Sat, 23 Aug 2014 19:52:44 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: Konstantin Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Roger Pau Monn? <royger@FreeBSD.org>, src-committers@freebsd.org, Bryan Drewery <bdrewery@FreeBSD.org> Subject: Re: svn commit: r265003 - head/secure/usr.sbin/sshd Message-ID: <20140823175244.GA29648@stack.nl> In-Reply-To: <20140822153139.GN2737@kib.kiev.ua> References: <53F4B381.5010205@FreeBSD.org> <20140820151310.GB2737@kib.kiev.ua> <53F4BC9B.3090405@FreeBSD.org> <53F4BEB1.6070000@FreeBSD.org> <53F4C022.5050804@FreeBSD.org> <20140821080541.GE2737@kib.kiev.ua> <53F5D42E.9080908@FreeBSD.org> <20140821123246.GH2737@kib.kiev.ua> <20140822134353.GA21891@stack.nl> <20140822153139.GN2737@kib.kiev.ua>
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On Fri, Aug 22, 2014 at 06:31:39PM +0300, Konstantin Belousov wrote: > On Fri, Aug 22, 2014 at 03:43:53PM +0200, Jilles Tjoelker wrote: > > This is good and necessary for SA_SIGINFO (because of the type of the > > SIG_DFL and SIG_IGN constants, and because POSIX says so in the > > description of SA_RESETHAND in the sigaction() page). However, there > > seems no reason to clear the other flags, which have no effect when the > > disposition is SIG_DFL or SIG_IGN but have historically always been > > preserved. (Slight exception: if kernel code erroneously loops on > > ERESTART, it will eat CPU time iff SA_RESTART is set, independent of the > > signal's disposition.) > Well, I already committed the patch with several bugs fixed comparing > with what was mailed, before your feedback arrived. > Do you consider it is important enough to revert the resetting of other > flags ? In particular, your note about the traditional historic > behaviour makes me wonder. I consider it important enough. Clearing the other flags is not POSIX-compliant and might break applications. For example, I can imagine an application modifying a struct sigaction with sa_handler == SIG_DFL from a sigaction() call. > I do not see why SA_SIGINFO is so special that it must be reset, > while other flags are not. The absence of the cases where the > default/ignored disposition is affected by the flags seems rather > arbitrary. The difference is that SA_SIGINFO changes the disposition field from sa_handler to sa_sigaction, and it is not unambiguously clear how SIG_DFL and SIG_IGN are represented in sa_sigaction. Note that sa_handler and sa_sigaction may or may not share storage, and implementations may or may not support (void (*)(int, siginfo_t *, void *))SIG_DFL. For example, when I wrote system() using posix_spawn() in https://lists.freebsd.org/pipermail/freebsd-hackers/2012-July/040065.html I needed to know whether SIGINT and SIGQUIT were ignored or not. I wrote ] if ((intact.sa_flags & SA_SIGINFO) != 0 || ] intact.sa_handler != SIG_IGN) ] (void)sigaddset(&defmask, SIGINT); ] if ((quitact.sa_flags & SA_SIGINFO) != 0 || ] quitact.sa_handler != SIG_IGN) ] (void)sigaddset(&defmask, SIGQUIT); in the assumption that there is always an actual handler if SA_SIGINFO is set. I did not really like this code and eventually system() was changed to use vfork() directly instead of posix_spawn(), but I think it is correct. Note that this means that it is sometimes necessary to install a handler function that will never be called. Per POSIX, SA_SIGINFO must be set for sigwaitinfo() to be guaranteed to return siginfo_t data, and the only way to do this is to specify a handler function, even though it will never be called because the signal is masked. (A never-called handler function also needs to be specified when using sigwait-like functions with signals that default to ignore.) The other flags do not affect the representation of the disposition, and can therefore remain set without problem. -- Jilles Tjoelker
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