Re: Moving forward with sh2/nommu

[Yoshinori Sato <ysato@users.sourceforge.jp>]

On Fri, 12 Jun 2015 13:28:21 +0900,
Rich Felker wrote:
> 
> On Fri, Jun 12, 2015 at 01:08:05PM +0900, Yoshinori Sato wrote:
> > > > >> 4. Syscall trap numbers differ on SH2 vs SH3/4. Presumably the reason
> > > > >>    is that these two SH2A hardware traps overlap with the syscall
> > > > >>    range used by SH3/4 ABI:
> > > > > 
> > > > > I haven't patched this yet. I'd like to use 31 (0x1f) as the new
> > > > > universal SH syscall trap number, instead of 22. More details on the
> > > > > reasons later.
> > > > 
> > > > I've cc'd Yoshinori Sato (who did most of the historical sh2 work) and
> > > > Shumpei Kawasaki (the original superh architect). They'll probably have
> > > > an opinion on your "more reasons" for changing sh2 system call numbers
> > > > to match sh4.
> > 
> > It histrical reason.
> > SH3/4 is assigned #0x10 to #0x17 for system call entry.
> > But SH2A system using this vector.
> > So we moved to #0x20 to #0x27 for SH2A.
> > (SH2A specification is #0x20 to #0x3f allocated for user application.)
> > 
> > And SH2 port is based on SH2A port.
> > It have same systemcall interface.
> > 
> > > Thank you. I'd really like to make progress at least on the matter of
> > > determining if this is feasible. I now have a new musl/sh2 patch that
> > > simply uses "trapa #31" unconditionally, and it's a lot
> > > simpler/cleaner and working on my patched kernel. The big question is
> > > just whether this is an unacceptable constraint on hardware.
> > 
> > SH2A reserved system for vector 31.
> > But not assigned now.
> > I think no problem.
> 
> Thank you for the feedback. This sounds promising.
> 
> We still need whoever ends up being the new kernel maintainer for SH
> to be okay with adding trap 31 syscall support for sh2 and declaring
> it supported/stable for sh3/4 too, but at least it looks like there
> arent technical problems for doing this.
> 
> Rich

Yes.
I think test necessary by SH2A, but there would be no problems.

-- 
Yoshinori Sato
<ysato@users.sourceforge.jp>