The kernel bits for SIGINFO support for the sparc are there.

Two things that I noticed while working on this:

1. The i386 port supports clearing the SS_ONSTACK bit in setmcontext()
   through the use of private flags (UC_SETSTACK/UC_CLRSTACK). The
   vax port appears not to reset SS_ONSTACK at all.

   Would it make sense to move UC_{SET,CLR}STACK to the MI ucontext.h
   header so all ports can use this mechanism; possibly even by doing
   it in kern_sig.c:setucontext().
  

2. In kern_sig.c:kpsendsig(), the `ksi_trap' is used to decide which
   arguments to pass to sa_upcall(). I don't what it is used for,
   but blindly using `ksi_trap' without further inspection of the
   siginfo context seems like a bad idea. `ksi_trap' is only defined
   for certain signal numbers, and its contents is MD even then.
   E.g. it might just be file descriptor 0 in a SIGPOLL delivery, or
   the user id of a process in a SIGCLD.. who knows?


-pk