[PATCH] sigalstack.2: Mention the need for separate signal stacks for threads

[Florian Weimer <fweimer@redhat.com>]

Signed-off-by: Florian Weimer <fweimer@redhat.com>

---
 man2/sigaltstack.2 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/man2/sigaltstack.2 b/man2/sigaltstack.2
index 53268ccbe..1510a98ab 100644
--- a/man2/sigaltstack.2
+++ b/man2/sigaltstack.2
@@ -54,7 +54,10 @@ alternate signal stack.
 An alternate signal stack is used during the
 execution of a signal handler if the establishment of that handler (see
 .BR sigaction (2))
-requested it.
+requested it using the
+.B SA_ONSTACK
+flag.  Each thread that can execute such signal handlers needs its own
+separate alternate signal stack.
 .PP
 The normal sequence of events for using an alternate signal stack
 is the following:
@@ -67,7 +70,7 @@ signal stack.
 Use
 .BR sigaltstack ()
 to inform the system of the existence and
-location of the alternate signal stack.
+location of the alternate signal stack for the current thread.
 .TP
 3.
 When establishing a signal handler using