Re: Bug#111581: more information needed on your bug report
On Mon, Aug 19, 2002 at 03:11:25PM -0500, Branden Robinson wrote:
> On Mon, Aug 19, 2002 at 07:22:14PM +0100, Philip Blundell wrote:
> > The kernel does have some support for emulating umul in software; see
> > arch/sparc/kernel/traps.c::do_illegal_instruction. This code seems to
> > only be enabled for sun4c and sun4, whereas the original poster
> > mentioned he is using sun4m.
>
> Thanks, Phil!
>
> SPARC folks: is there such a thing as a 4m that doesn't implement the
> umul instruction?
Sounds pretty odd but i guess it is possible. I always thought that v8
defined umul, and sun4m is supposed to be v8 (and sometimes v8plus)
complaint.
> > It looks like the umul in X is actually coming from a piece of
> > handwritten assembler in hw/xfree86/loader/SparcMulDiv.S. This could
> > presumably be replaced by an implementation that doesn't use umul
> > without too much trouble, but I guess the performance hit for other
> > users wouldn't be justified.
>
> Any suggestions for how run-time checking could be done?
I'm not sure how to runtime check this. You could presumably get the cpu
capabilities, but that may be just as expensive as using umul in ASM
unconditionally. The fix seems to be in the kernel itself. I'd leave
XFree86 alone, and see what we can do for this special case in the
kernel.
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