1 files changed, 45 insertions, 0 deletions
diff --git a/libgo/go/runtime/sys_s390x.go b/libgo/go/runtime/sys_s390x.go
new file mode 100644
index 00000000000..2aa81e75c06
--- /dev/null
+++ b/libgo/go/runtime/sys_s390x.go
@@ -0,0 +1,45 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "unsafe"
+
+// adjust Gobuf as if it executed a call to fn with context ctxt
+// and then did an immediate Gosave.
+func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
+	if buf.lr != 0 {
+		throw("invalid use of gostartcall")
+	}
+	buf.lr = buf.pc
+	buf.pc = uintptr(fn)
+	buf.ctxt = ctxt
+}
+
+// Called to rewind context saved during morestack back to beginning of function.
+// To help us, the linker emits a jmp back to the beginning right after the
+// call to morestack. We just have to decode and apply that jump.
+func rewindmorestack(buf *gobuf) {
+	var inst uint64
+	if buf.pc&1 == 0 && buf.pc != 0 {
+		inst = *(*uint64)(unsafe.Pointer(buf.pc))
+		switch inst >> 48 {
+		case 0xa7f4: // BRC (branch relative on condition) instruction.
+			inst >>= 32
+			inst &= 0xFFFF
+			offset := int64(int16(inst))
+			offset <<= 1
+			buf.pc += uintptr(offset)
+			return
+		case 0xc0f4: // BRCL (branch relative on condition long) instruction.
+			inst >>= 16
+			inst = inst & 0xFFFFFFFF
+			inst = (inst << 1) & 0xFFFFFFFF
+			buf.pc += uintptr(int32(inst))
+			return
+		}
+	}
+	print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
+	throw("runtime: misuse of rewindmorestack")
+}