1 files changed, 54 insertions, 0 deletions
diff --git a/src/runtime/sys_x86.go b/src/runtime/sys_x86.go
new file mode 100644
index 000000000..086af8ff1
--- /dev/null
+++ b/src/runtime/sys_x86.go
@@ -0,0 +1,54 @@
+// Copyright 2013 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.
+
+// +build amd64 amd64p32 386
+
+package runtime
+
+import "unsafe"
+
+// adjust Gobuf as it if executed a call to fn with context ctxt
+// and then did an immediate gosave.
+func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
+	sp := buf.sp
+	if regSize > ptrSize {
+		sp -= ptrSize
+		*(*uintptr)(unsafe.Pointer(sp)) = 0
+	}
+	sp -= ptrSize
+	*(*uintptr)(unsafe.Pointer(sp)) = buf.pc
+	buf.sp = sp
+	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) {
+	pc := (*[8]byte)(unsafe.Pointer(buf.pc))
+	if pc[0] == 0xe9 { // jmp 4-byte offset
+		buf.pc = buf.pc + 5 + uintptr(int64(*(*int32)(unsafe.Pointer(&pc[1]))))
+		return
+	}
+	if pc[0] == 0xeb { // jmp 1-byte offset
+		buf.pc = buf.pc + 2 + uintptr(int64(*(*int8)(unsafe.Pointer(&pc[1]))))
+		return
+	}
+	if pc[0] == 0xcc {
+		// This is a breakpoint inserted by gdb.  We could use
+		// runtime·findfunc to find the function.  But if we
+		// do that, then we will continue execution at the
+		// function entry point, and we will not hit the gdb
+		// breakpoint.  So for this case we don't change
+		// buf.pc, so that when we return we will execute
+		// the jump instruction and carry on.  This means that
+		// stack unwinding may not work entirely correctly
+		// (http://golang.org/issue/5723) but the user is
+		// running under gdb anyhow.
+		return
+	}
+	print("runtime: pc=", pc, " ", hex(pc[0]), " ", hex(pc[1]), " ", hex(pc[2]), " ", hex(pc[3]), " ", hex(pc[4]), "\n")
+	gothrow("runtime: misuse of rewindmorestack")
+}