s390 port

[Paul Edwards]

Hi Ulrich.

Thanks a lot for your reply.

Could you give me an example of an instruction
generated by –m31 that is not expected to work
on an AM64 system?

E.g. the 32-bit

LR R2,R3

will definitely work on AM64.

So what specifically won’t work? How many different
things won’t work?

Thanks. Paul.




From: Ulrich Weigand 
Sent: Friday, September 3, 2021 12:34 AM
To: Paul Edwards 
Cc: gcc@gcc.gnu.org ; Ulrich Weigand 
Subject: Re: s390 port

Hi Paul,

"Paul Edwards" <mutazilah@gmail.com> wrote on 02.09.2021 10:15:44:

> We got the IPL process in place on ESA/390, and then
> I decided that the next thing to do would be to switch
> to z/Arch so that we could get rid of the AMODE 31
> architectural limit on 32-bit programs.
> 
> It all worked fine, and we were able to use GCC 11 to
> target S/390 and use the -m31 to generate 32-bit code,
> run it under z/Arch as AM64, sort of making it the
> equivalent of AM32. Really it is the equivalent of
> AM-infinity, and there's the rub - GCC 11 is generating
> negative indexes, which cause memory above 4 GiB
> to be accessed (instead of wrapping at 2/4 GiB), which
> of course fails.

Can you elaborate what exactly your goals are?  The point
of the -m31 vs. -m64 option is exactly to match the
AMODE 31 vs. AMODE 64 hardware distinction, so trying to
run -m31 code in AMODE 64 is not supposed to work.

Bye,
Ulrich