[src/trunk]: src/lib/libc/sys mention what we are allowed to do.

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/3ec38170c836
branches:  trunk
changeset: 341341:3ec38170c836
user:      christos <christos%NetBSD.org@localhost>
date:      Sat Oct 31 17:45:32 2015 +0000

description:
mention what we are allowed to do.

diffstat:

 lib/libc/sys/sigaction.2 |  20 ++++++++++++++++++--
 1 files changed, 18 insertions(+), 2 deletions(-)

diffs (41 lines):

diff -r deec98476956 -r 3ec38170c836 lib/libc/sys/sigaction.2
--- a/lib/libc/sys/sigaction.2  Sat Oct 31 17:04:39 2015 +0000
+++ b/lib/libc/sys/sigaction.2  Sat Oct 31 17:45:32 2015 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: sigaction.2,v 1.45 2014/01/04 15:54:27 wiz Exp $
+.\"    $NetBSD: sigaction.2,v 1.46 2015/10/31 17:45:32 christos Exp $
 .\"
 .\" Copyright (c) 1980, 1990, 1993
 .\"    The Regents of the University of California.  All rights reserved.
@@ -29,7 +29,7 @@
 .\"
 .\"    @(#)sigaction.2 8.2 (Berkeley) 4/3/94
 .\"
-.Dd June 3, 2006
+.Dd October 31, 2015
 .Dt SIGACTION 2
 .Os
 .Sh NAME
@@ -287,6 +287,22 @@
 .Xr termios 4 .
 .El
 .Pp
+If the signal handler is called due to signal delively resulting from reasons
+other than direct calls to
+.Xr kill 2 
+or 
+.Xr _lwp_kill 2
+or indirect calls to
+.Xr _lwp_kill 2
+via
+.Xr abort 3
+or
+.Xr raise 3
+any activity (such as calling functions or assigning variables in the global
+or static scopes) other than setting a variable of the type
+.Dt volatile sig_atomic_t
+is undefined.
+.Pp
 Only functions that are async-signal-safe can safely be used in signal
 handlers; see
 .Xr signal 7