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@

3 files changed, 22 insertions, 3 deletions

diff --git a/sys/arch/amd64/conf/GENERIC b/sys/arch/amd64/conf/GENERIC
index d07eb346fce..d3b593f71f4 100644
--- a/sys/arch/amd64/conf/GENERIC
+++ b/sys/arch/amd64/conf/GENERIC
@@ -1,4 +1,4 @@
-#	$OpenBSD: GENERIC,v 1.457 2018/08/03 01:50:14 kevlo Exp $
+#	$OpenBSD: GENERIC,v 1.458 2018/08/19 11:42:33 anton Exp $
 #
 # For further information on compiling OpenBSD kernels, see the config(8)
 # man page.
@@ -658,6 +658,9 @@ pseudo-device	hotplug		1	# devices hot plugging
 # mouse & keyboard multiplexor pseudo-devices
 pseudo-device	wsmux		2
 
+# kernel code coverage
+pseudo-device	kcov		1
+
 # Virtio devices
 virtio*		at pci?		# Virtio PCI device
 vioblk*		at virtio?	# Virtio block device
diff --git a/sys/arch/amd64/conf/Makefile.amd64 b/sys/arch/amd64/conf/Makefile.amd64
index 3950ac592dc..f6f6f286aa9 100644
--- a/sys/arch/amd64/conf/Makefile.amd64
+++ b/sys/arch/amd64/conf/Makefile.amd64
@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile.amd64,v 1.98 2018/07/13 08:10:56 deraadt Exp $
+#	$OpenBSD: Makefile.amd64,v 1.99 2018/08/19 11:42:33 anton Exp $
 
 # For instructions on building kernels consult the config(8) and options(4)
 # manual pages.
@@ -43,6 +43,10 @@ SORTR=		cat
 .else
 CMACHFLAGS+=	-mretpoline
 .endif
+.if ${IDENT:M-DKCOV} && ${COMPILER_VERSION:Mclang}
+CMACHFLAGS+=	-fno-ret-protector
+PROF=		-fsanitize-coverage=trace-pc
+.endif
 .if ${COMPILER_VERSION:Mclang}
 NO_INTEGR_AS=	-no-integrated-as
 .endif
@@ -135,6 +139,12 @@ vers.o: ${SYSTEM_DEP:Ngap.o}
 	sh $S/conf/newvers.sh
 	${CC} ${CFLAGS} ${CPPFLAGS} ${PROF} -c vers.c
 
+.if ${IDENT:M-DKCOV} && ${COMPILER_VERSION:Mclang}
+kcov.o: $S/dev/kcov.c
+	${NORMAL_C} -fno-sanitize-coverage=trace-pc
+.endif
+
+
 clean:
 	rm -f *bsd *bsd.gdb *.[dio] [a-z]*.s assym.* \
 	    gap.link ld.script lorder makegap.sh param.c
diff --git a/sys/arch/amd64/conf/files.amd64 b/sys/arch/amd64/conf/files.amd64
index 6da1a7b0aa6..a4b89dde769 100644
--- a/sys/arch/amd64/conf/files.amd64
+++ b/sys/arch/amd64/conf/files.amd64
@@ -1,4 +1,4 @@
-#	$OpenBSD: files.amd64,v 1.97 2018/07/12 12:46:00 fcambus Exp $
+#	$OpenBSD: files.amd64,v 1.98 2018/08/19 11:42:33 anton Exp $
 
 maxpartitions 16
 maxusers 2 16 128
@@ -245,6 +245,12 @@ file	arch/amd64/amd64/vmm.c			vmm		needs-flag
 file	arch/amd64/amd64/vmm_support.S		vmm
 
 #
+# KCOV
+#
+pseudo-device kcov
+file	dev/kcov.c				kcov
+
+#
 # Machine-independent SD/MMC drivers
 #
 include "dev/sdmmc/files.sdmmc"