1 files changed, 40 insertions, 6 deletions
diff --git a/src/pkg/runtime/mkasmh.sh b/src/pkg/runtime/mkasmh.sh
index aae773cfe..3ed5f74c9 100755
--- a/src/pkg/runtime/mkasmh.sh
+++ b/src/pkg/runtime/mkasmh.sh
@@ -16,14 +16,44 @@ case "$GOARCH" in
 	# The offsets 0 and 4 are also known to:
 	#	nacl/thread.c:/^newosproc
 	#	../../cmd/8l/pass.c:/D_GS
-	#	../../libcgo/linux_386.c:/^start
-	#	../../libcgo/darwin_386.c:/^start
+	#	../../libcgo/linux_386.c:/^threadentry
+	#	../../libcgo/darwin_386.c:/^threadentry
 	case "$GOOS" in
 	windows)
 		echo '#define	get_tls(r)	MOVL 0x2c(FS), r'
 		echo '#define	g(r)	0(r)'
 		echo '#define	m(r)	4(r)'
 		;;
+	plan9)
+		echo '#define	get_tls(r)'
+		echo '#define	g(r)	0xdfffefc0'
+		echo '#define	m(r)	0xdfffefc4'
+		;;
+	linux)
+		# On Linux systems, what we call 0(GS) and 4(GS) for g and m
+		# turn into %gs:-8 and %gs:-4 (using gcc syntax to denote
+		# what the machine sees as opposed to 8l input).
+		# 8l rewrites 0(GS) and 4(GS) into these.
+		#
+		# On Linux Xen, it is not allowed to use %gs:-8 and %gs:-4
+		# directly.  Instead, we have to store %gs:0 into a temporary
+		# register and then use -8(%reg) and -4(%reg).  This kind
+		# of addressing is correct even when not running Xen.
+		#
+		# 8l can rewrite MOVL 0(GS), CX into the appropriate pair
+		# of mov instructions, using CX as the intermediate register
+		# (safe because CX is about to be written to anyway).
+		# But 8l cannot handle other instructions, like storing into 0(GS),
+		# which is where these macros come into play.
+		# get_tls sets up the temporary and then g and r use it.
+		#
+		# The final wrinkle is that get_tls needs to read from %gs:0,
+		# but in 8l input it's called 8(GS), because 8l is going to
+		# subtract 8 from all the offsets, as described above.
+		echo '#define	get_tls(r)	MOVL 8(GS), r'
+		echo '#define	g(r)	-8(r)'
+		echo '#define	m(r)	-4(r)'
+		;;
 	*)
 		echo '#define	get_tls(r)'
 		echo '#define	g(r)	0(GS)'
@@ -32,10 +62,14 @@ case "$GOARCH" in
 	esac
 	;;
 amd64)
-	# These registers are also known to:
-	#	../../libcgo/linux_amd64.c:/^start
-	echo '#define	g	R15'
-	echo '#define	m	R14'
+	# The offsets 0 and 8 are known to:
+	#	../../cmd/6l/pass.c:/D_GS
+	#	../../libcgo/linux_amd64.c:/^threadentry
+	#	../../libcgo/darwin_amd64.c:/^threadentry
+	#
+	echo '#define	get_tls(r)'
+	echo '#define	g(r) 0(GS)'
+	echo '#define	m(r) 8(GS)'
 	;;
 arm)
 	echo '#define	g	R10'