[PATCH] Look for FIR in the last FreeBSD/mips floating-point register.
Maciej W. Rozycki
macro@imgtec.com
Mon Jun 12 20:23:00 GMT 2017
On Mon, 12 Jun 2017, John Baldwin wrote:
> > Well, CP1.FIR is generally expected to hold non zero; in particular in
> > legacy MIPS processors (before CP0.Config1.FP was defined) checking for a
> > non-zero value in CP1.FIR (bits 15:8 specifically) was the recommended way
> > to detect the presence of FPU hardware[1]. And from MIPSr1 on there have
> > to be floating-point formats supported reported in CP1.FIR, with D and S
> > being mandatory, so you'll see non-zero bits at least in their positions
> > (the W bit was only added with MIPSr2).
>
> Ah, I had been going off of my (probably stale) copy of See Mips Run which
> only talks about comparing FIR with 0. FreeBSD requires MIPSr3, so it should
> always see a non-zero FIR then.
FAOD MIPSr3 (as in MIPS32r3/MIPS64r3) or MIPS III?
I'm asking as I find it odd for anything to require MIPSr3 and not to
handle MIPSr2 given that the main difference between the two is microMIPS
and 2008-NaN support, both optional.
Maciej
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