Re: PowerBook 540c
On Fri, 29 Oct 2004, John Klos wrote:
> >> Question for the lists: does it make sense to pursue a software
> >> floating point solution as opposed to trapping floating point
> >> instructions? My guess to the answer would be no, as I suspect that
> >> 99.9%+ of the code that runs in Linux (both in the kernel and in
> >> userland) does not use floating point, but if that's wrong, I'd be
> >> interested in hearing opposing viewpoints.
> >
> > Fixing the handling of real FPU instructions would be better.
I wonder if there is a performance benefit to either solution. My
suspicion is there is not, assuming the emulation code is equal. (Though
the linux kernel FPU emulation does offer a choice of precision/speed
tradeoff.)
> > That way you don't crash stuff if you accidentally run a regular 68k
> > binary on your box. Although it's not like it kills the whole kernel
> > anyway.
>
> This is a nice idea, but a majority of the LC040s out there are the ones
> with the more extreme bug where the process' state isn't properly saved.
> Nothing short of something which generates tons of overhead is going to
> fix that.
There are two bugs? As Brad pointed out, apple fixed a bug that broke
A-trap exceptions without significant overhead. (You aren't referring to
that bug I gather). I guess it is also possible that Motorola gave Apple
information about the bug(s) that we don't have, that permitted a simple
solution.
> > I think you're drastically underestimating where floating point shows
> > up in regular software. I know things like perl have a tendency to
> > trigger this bug. X is pretty heavy on the FPU as well. While it would
> > be possible to recompile everything, it takes long enough to compile
> > just once. The 68k build boxes for Debian barely keep up as it is.
>
> Floating point is used everywhere. Even common stuff like top uses it.
Yes. The linux 2.6.8.1 kernel will not boot my LC040 at all unless FPU
emulation is configured in. Could I fix it simply building the kernel with
a softfloat-enabled gcc?
> With NetBSD, we've added softfloat to gcc (thanks, Bruce O'neel),
Which gcc releases are supported?
-F
> created softfloat OS snapshots for download, plus I have two dedicated
> m68060 machines doing softfloat binary packages. I am only doing non-X
> apps at the moment since I can't imagine that people with LC040 systems
> are going to expect to have a GUI, but the X apps will come soon.
>
> While Debian's resources should obviously stay with the regular m68k
> builds, I can definitely see that making a kernel and OS snapshot
> available for broken LC040 systems every now and again would not be
> hard.
>
> John Klos
>
>
>
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