MFC r317845-r317846

r317845:
Provide a freebsd32 implementation of sigqueue()

The previous misuse of sys_sigqueue() was sending random register or
stack garbage to 64-bit targets.  The freebsd32 implementation preserves
the sival_int member of value when signaling a 64-bit process.

Document the mixed ABI implementation of union sigval and the
incompability of sival_ptr with pointer integrity schemes.

Reviewed by:	kib, wblock
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D10605

r317846:
Regen post r317845.

MFC with:	r317845
Sponsored by:	DARPA, AFRL

1 files changed, 16 insertions, 2 deletions

diff --git a/lib/libc/sys/sigqueue.2 b/lib/libc/sys/sigqueue.2
index 04e101b..8377c67 100644
--- a/lib/libc/sys/sigqueue.2
+++ b/lib/libc/sys/sigqueue.2
@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 10, 2012
+.Dd May 5, 2017
 .Dt SIGQUEUE 2
 .Os
 .Sh NAME
@@ -129,7 +129,6 @@ does not exist.
 .Xr kill 2 ,
 .Xr sigaction 2 ,
 .Xr sigpending 2 ,
-.Xr sigqueue 2 ,
 .Xr sigsuspend 2 ,
 .Xr sigtimedwait 2 ,
 .Xr sigwait 2 ,
@@ -147,3 +146,18 @@ Support for
 .Tn POSIX
 realtime signal queue first appeared in
 .Fx 7.0 .
+.Sh CAVEATS
+When using
+.Nm
+to send signals to a process which might have a different ABI
+(for instance, one is 32-bit and the other 64-bit),
+the
+.Va sival_int
+member of
+.Fa value
+can be delivered reliably, but the
+.Va sival_ptr
+may be truncated in endian dependent ways and must not be relied on.
+Further, many pointer integrity schemes disallow sending pointers to other
+processes, and this technique should not be used in programs intended to
+be portable.