Add kcov(4), a kernel code coverage tracing driver. It's used in conjunction

with the syzkaller kernel fuzzer. So far, 8 distinct panics have been found and
fixed. This effort will continue.
kcov is limited to architectures using Clang as their default compiler and is
not enabled by default.
With help from mpi@, thanks!
ok kettenis@ mpi@ visa@

src/etc/MAKEDEV.common

@@ -1,4 +1,4 @@
-vers(a, {-$OpenBSD: MAKEDEV.common,v 1.99 2018/07/28 08:09:50 ratchov Exp $-})dnl
+vers(a, {-$OpenBSD: MAKEDEV.common,v 1.100 2018/08/19 11:42:33 anton Exp $-})dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
 dnl
@@ -167,6 +167,7 @@ target(all, fuse)dnl
 target(all, vmm)dnl
 target(all, pvbus, 0, 1)dnl
 target(all, bpf)dnl
+target(all, kcov)dnl
 dnl
 _mkdev(all, {-all-}, {-dnl
 show_target(all)dnl
@@ -521,3 +522,5 @@ _mkdev(vmm, vmm, {-M vmm c major_vmm_c 0 600-})dnl
 __devitem(pvbus, pvbus*, paravirtual device tree root)dnl
 _mkdev(pvbus, {-pvbus*-}, {-M pvbus$U c major_pvbus_c $U 640-}, 640)dnl
 _mkdev(local, local, {-test -s $T.local && sh $T.local-})dnl
+__devitem(kcov, kcov, Kernel code coverage tracing)dnl
+_mkdev(kcov, kcov, {-M kcov c major_kcov_c 0 600-})dnl

src/etc/etc.amd64/MAKEDEV.md

@@ -1,6 +1,6 @@
 define(MACHINE,amd64)dnl
 vers(__file__,
-	{-$OpenBSD: MAKEDEV.md,v 1.69 2016/09/11 19:59:53 deraadt Exp $-},
+	{-$OpenBSD: MAKEDEV.md,v 1.70 2018/08/19 11:42:33 anton Exp $-},
 etc.MACHINE)dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
@@ -77,6 +77,7 @@ _DEV(hotplug, 82)
 _DEV(ipmi, 96)
 dnl _DEV(joy, 26)
 _DEV(nvram, 85)
+_DEV(kcov, 19)
 _DEV(pci, 72)
 _DEV(pctr, 46)
 _DEV(pf, 73)

src/etc/etc.i386/MAKEDEV.md

@@ -1,6 +1,6 @@
 define(MACHINE,i386)dnl
 vers(__file__,
-	{-$OpenBSD: MAKEDEV.md,v 1.83 2016/09/11 19:59:53 deraadt Exp $-},
+	{-$OpenBSD: MAKEDEV.md,v 1.84 2018/08/19 11:42:33 anton Exp $-},
 etc.MACHINE)dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
@@ -78,6 +78,7 @@ _DEV(gpr, 80)
 _DEV(hotplug, 82)
 _DEV(ipmi, 96)
 _DEV(joy, 26)
+_DEV(kcov, 19)
 _DEV(nvram, 84)
 _DEV(pci, 72)
 _DEV(pctr, 46)