On Tue, 16 Oct 2001, David Edelsohn wrote:

> >>>>> One Without Reason writes:
> 
> Sridhar> That's the problem.  There are a couple of others, as well.  Some user
> Sridhar> software apparently makes use of instructions not present on the earlier
> Sridhar> generation systems too.  I'd rather just make it possible for a single
> Sridhar> kernel to be able to boot any of these machines.  Far in the future, even
> Sridhar> 64-bit support for the zSeries.
> 
> 	Running G4 applications on earlier systems will not be trivial.
> For UP, your goal of a single kernel is possible.  For MP, G4 will be a
> dependency. 

I understand that.  However, the code already exists for modifying the
compiler output to eliminate the "Halfword Immediate and Relative Branch
Feature" requirements.  I am simply integrating this code into GCC.  (It
would be done already if I had more time 8-))

How do older systems differ?  Which is the offending instruction?  I might
be able to think of something to kludge up in its place.  This is really
holding my interest, so I don't mind putting in the work.  With any luck,
it won't be impossible to implement.

> Sridhar> Actually, I am basing my work on the Linux-S/390-Vintage work.  They did
> Sridhar> quite a bit of preliminary stuff looking into recompilation before they
> Sridhar> settled on emulation of the missing stuff.  It would indeed be neat to get
> Sridhar> GCC onto the S/370.  I might take a crack at it after I get the
> Sridhar> older-generation S/390 stuff in.  Unless, that is, you want to do it. 8-)
> 
> 	GCC already does work on S/370 -- on z/OS aka OS/390 aka MVS.
> That is what the "i370" port did.  Dave Pitts added support for MVS Unix
> System Services aka Open Edition (X/Open / Unix branded MVS).  Linas
> Vepstas had some Linux for S/370 changes based on that work.  It would be
> much better to merge the S/370 work in the s390 port instead of keeping
> two ports around.

Hmmm.  I think that to get the NetBSD kernel working on S/370 would be a
completely different project from getting it working on 370-XA, ESA/370,
and ESA/390.  The I/O differences might cause problems.

Peace...  Sridhar