code review 139930043: runtime: convert lock*.c to Go

src/pkg/runtime/os_plan9.go

 // Copyright 2014 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"
 
 func pread(fd int32, buf unsafe.Pointer, nbytes int32, offset int64) int32
 func pwrite(fd int32, buf unsafe.Pointer, nbytes int32, offset int64) int32
 func seek(fd int32, offset int64, whence int32) int64
 func exits(msg *byte)
 func brk_(addr unsafe.Pointer) uintptr
 func sleep(ms int32) int32
 func rfork(flags int32, stk, mm, gg, fn unsafe.Pointer) int32
 func plan9_semacquire(addr *uint32, block int32) int32
 func plan9_tsemacquire(addr *uint32, ms int32) int32
 func plan9_semrelease(addr *uint32, count int32) int32
 func notify(fn unsafe.Pointer) int32
 func noted(mode int32) int32
 func nsec(*int64) int64
 func sigtramp(ureg, msg unsafe.Pointer)
 func setfpmasks()
 func errstr() string
+
+// The size of the note handler frame varies among architectures,
+// but 512 bytes should be enough for every implementation.
+const stackSystem = 512