address space support

[Doug Evans <dje at sebabeach dot org>]

At Transmeta we had a hack to implement address spaces.   I.e., 
CORE_ADDR isn't enough to fully describe all the bits of "memory" one 
might want to examine.  One could do things like "x/x 
<addr-space-name>:<address>".   Using that we also hacked in support for 
x86 segments, so one could do "x/x fs:1234".

We didn't want to maintain a ton of local mods so we took a minimalist 
route.  Other ways that have been discussed in the past are things like 
turning CORE_ADDR into a struct:

typedef struct { int address_space ; OLD_CORE_ADDR address; } NEW_CORE_ADDR;

or some such (appropriately typed, named, etc.).

But that's a ton of work, and not necessarily a maintainable way to go 
(the common case is addresses are just ints).  Hacking CORE_ADDR by 
putting the address space in the upper bits doesn't necessarily work either.

So I don't have a specific proposal, I'm just taking a survey of where 
things have left off.