Re: [PATCH 04/04] sh: prefetch early exception data on sh3/sh4/sh4a

[Paul Mundt <lethal@linux-sh.org>]

On Fri, Feb 27, 2009 at 04:53:00PM +0900, Magnus Damm wrote:
> On Fri, Feb 27, 2009 at 4:22 PM, Paul Mundt <lethal@linux-sh.org> wrote:
> > On Mon, Feb 23, 2009 at 04:19:31PM +0900, Magnus Damm wrote:
> >> From: Magnus Damm <damm@igel.co.jp>
> >>
> >> Prefetch early exception data. There is unused space in our
> >> exception handler cache line anyway, so this is almost free.
> >>
> > Hmm, this won't work, 'pref' doesn't exist on SH-3. The binutils opcode
> > table defines it as arch_sh2a_nofpu_or_sh4_nommu_nofpu_up, which excludes
> > SH-3. mova is ok, though.
> >
> > This does show how often SH-3 gets tested though, as asm/processor_32.h
> > happily defines prefetch() for SH-3 when it shouldn't. I'll tidy this up
> > and drop in a PREF() macro.
> 
> Right, I do recall building for hp6xx at some point. Thanks for fixing it up.
> 
The fact that that didn't blow up on the opcode is likely because the
toolchain you were using had no idea about SH-3 ISA tuning, and so fell
back on an anything-goes tuning policy. If you are building for exotic
combinations, always do a single run with V=1 to make sure that the
CFLAGS are sticking and doing what you think they are doing.

There are far more people building SH-3 targetted kernels with an SH-4+
specific toolchain than there are actual SH-3 users, the latter of which
tend to only provide feedback a few times a year. This unfortunately
means that these sorts of bugs can be long lived and tedious to bisect at
a later point in time, but there is not much that can be done about that.