> From: "Todd C. Miller" <todd.mil...@courtesan.com> > Date: Tue, 14 Apr 2015 10:52:47 -0600 > > The situation is a little complicated. POSIX defines the third > argument to the sa_sigaction handler as void * and says it may be > cast to ucontext_t. On OpenBSD, it is really a pointer to struct > sigcontext but this is really an implementation detail. > > - todd > > Index: lib/libc/sys/sigaction.2 > =================================================================== > RCS file: /cvs/src/lib/libc/sys/sigaction.2,v > retrieving revision 1.68 > diff -u -p -u -r1.68 sigaction.2 > --- lib/libc/sys/sigaction.2 14 Dec 2014 07:42:50 -0000 1.68 > +++ lib/libc/sys/sigaction.2 14 Apr 2015 16:49:48 -0000 > @@ -352,7 +352,7 @@ If the > option is enabled, the canonical way to declare it is: > .Bd -literal -offset indent > void > -handler(int sig, siginfo_t *sip, struct sigcontext *scp) > +handler(int sig, siginfo_t *sip, void *ctx) > .Ed > .Pp > Here > @@ -375,13 +375,19 @@ The function specified in > .Fa sa_sigaction > will be called instead of the function specified by > .Fa sa_handler > -(Note that in some implementations these are in fact the same). > -.Fa scp > -is a pointer to the > +(note that in some implementations these are in fact the same). > +.Fa ctx > +may be cast to a pointer to > +.Fa ucontext_t > +which can be used to restore the thread's context from before the signal. > +On > +.Ox , > +.Fa ucontext_t > +is an alias for the > .Fa sigcontext > -structure (defined in > -.In signal.h ) , > -used to restore the context from before the signal. > +structure defined in > +.In signal.h . > +The contents of this structure are machine-dependent. > .Sh ERRORS > .Fn sigaction > will fail and no new signal handler will be installed if one
Not sure if mentioning ucontext_t is such a good idea. While POSIX does contain similar text. it doesn't actually tell you which header provides ucontext_t. There used to be a <ucontext.h> header file, but that one is gone now. Personally I'd just state that on OpenBSD (and other BSD-derived systems) the third argument is a pointer to a struct sigcontext. But meh.
