windows/svc: do not pass theService to windows.RegisterServiceCtrlHan…

…dlerEx

windows.RegisterServiceCtrlHandlerEx context parameter is uintptr, so it
is unsafe to pass pointers in that parameter. Use theService global
variable in ctlHandler function instead.

Fixes golang/go#67437

Change-Id: I84c910eaa354603c2a5114421cd61788cb40b86f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/591475
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: David Chase <drchase@google.com>

windows/svc/service.go

@@ -199,9 +199,8 @@ var (
 )
 
 func ctlHandler(ctl, evtype, evdata, context uintptr) uintptr {
-	s := (*service)(unsafe.Pointer(context))
 	e := ctlEvent{cmd: Cmd(ctl), eventType: uint32(evtype), eventData: evdata, context: 123456} // Set context to 123456 to test issue #25660.
-	s.c <- e
+	theService.c <- e
 	return 0
 }
 
@@ -210,7 +209,7 @@ var theService service // This is, unfortunately, a global, which means only one
 // serviceMain is the entry point called by the service manager, registered earlier by
 // the call to StartServiceCtrlDispatcher.
 func serviceMain(argc uint32, argv **uint16) uintptr {
-	handle, err := windows.RegisterServiceCtrlHandlerEx(windows.StringToUTF16Ptr(theService.name), ctlHandlerCallback, uintptr(unsafe.Pointer(&theService)))
+	handle, err := windows.RegisterServiceCtrlHandlerEx(windows.StringToUTF16Ptr(theService.name), ctlHandlerCallback, 0)
 	if sysErr, ok := err.(windows.Errno); ok {
 		return uintptr(sysErr)
 	} else if err != nil {