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Re: [PATCH] Look for FIR in the last FreeBSD/mips floating-point register.
- From: "Maciej W. Rozycki" <macro at imgtec dot com>
- To: John Baldwin <jhb at freebsd dot org>
- Cc: <gdb-patches at sourceware dot org>
- Date: Mon, 12 Jun 2017 21:23:22 +0100
- Subject: Re: [PATCH] Look for FIR in the last FreeBSD/mips floating-point register.
- Authentication-results: sourceware.org; auth=none
- References: <20170531165803.50633-1-jhb@FreeBSD.org> <alpine.DEB.2.00.1706080744320.21750@tp.orcam.me.uk> <1648023.dfXdf8hDrr@ralph.baldwin.cx>
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