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Re: RFC: Adding minimal amd64/biarch support for sarge

On Thu, Aug 05, 2004 at 02:29:12PM +0200, Goswin von Brederlow wrote:
> It won't use the extra registers in 32bit mode.

 Yeah, I know there's no CPU mode that does that.  I wish, though...

> It would be
> theoretically possible to build for 64bit (with extra registers) but
> 32bit pointers [The Tru64 cc can do that on alpha] but it would
> require extending the pointers to 64bit on every use and would
> probably void all the speedup.

 Yeah.  What if you mmap a memory pool below 2GB in virtual address space,
so you only have to zero-extend?  Isn't that what AMD64 does when you do a
32bit move from memory to register?  gcc -mcmodel=small still uses 64bit
pointers though, because it doesn't constrain data to be in the low 2GB.

> One thing you could do with gcc to emulate this is to use an array
> index instead of a pointer.

 That's a thought.  There are lots of ways to store trees, and data
structures with 64bit pointers could be avoided to cut down on cache

> >  So, for me (and my ~dozen users) at least, this really would be useful.  If
> > you can't get it into sarge, I don't mind tracking unstable for some
> > packages on the cluster (it's not quite what some would call a "production"
> > system).  It would rock to have it in sarge :)
> The progress looks good. I have made an amd64-libs package with some
> patches from Daniel Jacobowitz and he has made a gcc-3.4 package. Now
> if I get thekernel-image-amd64 build and all of them through new in
> time you have the 32/64 bit support.

 Your work (and all amd64 porters') is much appreciated.  happy hacking :)

#define X(x,y) x##y
Peter Cordes ;  e-mail: X(peter@cor , des.ca)

"The gods confound the man who first found out how to distinguish the hours!
 Confound him, too, who in this place set up a sundial, to cut and hack
 my day so wretchedly into small pieces!" -- Plautus, 200 BC

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