Help needed to identify golang fork / memory corruption issue on FreeBSD

[Steven Hartland]

Ok I think I've identified the cause.

If an alternative signal stack is applied to a non-main thread and that 
thread calls execve then the signal stack is not cleared.

This results in all sorts of badness.

Full details, including a small C reproduction case can be found here:
https://github.com/golang/go/issues/15658#issuecomment-287276856

So looks like its kernel bug. If anyone has an ideas about that before I 
look tomorrow that would be appreciated.

     Regards
     Steve