Re: Non-uniform address spaces

[Michael Eager <eager@eagercon.com>]

Daniel Jacobowitz wrote:
> On Sat, Jun 23, 2007 at 09:31:31AM -0700, Michael Eager wrote:
>> Any suggestions on how to support a target which has
>> a non-uniform address space?  An address is a tuple which
>> includes a processor id, a thread id, and an offset.
>> There is a mapping function which translates the tuple
>> into a physical address.
>>
>> Ideally, it would be nice to replace the current definition
>> of CORE_ADDR with a struct and add functions to to do
>> operations like increment/decrement address.  But the
>> assumption that the address space is flat and that you
>> can do arithmetic on addresses is pervasive.
> 
> How big are each of those objects (processor id, thread id, offset)?

They would all fit in a 128-bit word.

> The conventional way to do this in GDB is to have a mapping from
> CORE_ADDR to target addresses, not to target pointers.  Most of the
> Harvard architecture ports work this way.  However, there may not be
> enough hooks for you to get away with it if they're as dynamic as it
> sounds.

Having a 128-bit CORE_ADDR sounds possible, but there are many
places where there's arithmetic or comparisons done on the values.
These would all be problematic.  Usually correct, occasionally not.

I thought most of the HA systems just increased the address size by
one bit and had the high-order bit specify whether the address
was in D or I address space.

-- 
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077