Re: Some Haifa scheduler bugs

["David S. Miller" <davem@jenolan.rutgers.edu>]

   Date: Thu, 04 Sep 1997 12:12:15 -0600
   From: Jeffrey A Law <law@hurl.cygnus.com>

   I'm less familiar with how this works under aix or with
   ultrasparcs/solaris, but I assume they both do something relatively
   reasonable.

On the UltraSparc normal load/store instructions still trap on bogus
pointers like they always have.

The compiler must emit a special load instruction (with an address
space specifier for the "no-fault" address space) when it wants a
speculative load.  The chip will not fault on a NULL pointer if page 0
of the process has the "allow non-faulting load" attribute set, when
you use these special load instructions.  Non-faulting stores do not
exist.

Naturally, this depends upon OS support, and I think Solaris does map
page 0 in this special way, or they check the load instruction which
was executed by the user once the fault handling call chain determines
that the access was in outer space.

I lack the support currently on sparc64-linux, but it will be added
should a native compiler out there begin to emit the instructions ;-)

Later,
David "Sparc" Miller
davem@caip.rutgers.edu