Re: [PATCH] ARM: vfp: fix fpsid register subarchitecture field maskwidth
From: Stephen Boyd
Date: Tue Feb 26 2013 - 20:37:39 EST
On 02/25/13 12:02, Russell King - ARM Linux wrote:
> This can of worms is getting bigger. We have more problems with our
> handling of the different VFP versions, specifically the handling of
> the EX=0 DEX=0 case.
> VFP common subarch 3 defines the EX=0, DEX=0 encoding to mean one of
> the following conditions have been met:
> 1. an unallocated VFP instruction was encountered.
> In other words, the VFP was the target of the co-processor instruction,
> but the instruction is not a known VFP instruction encoding. This
> should raise an undefined instruction exception.
> 2. an allocated VFP instruction was encountered, but not handled in
> In other words, the instruction is a valid VFP instruction, but the
> hardware has opted not to implement this instruction and wants
> software to emulate it instead.
> (Note: this can also be raised as EX=0, DEX=1 - implementation
> So, if EX or DEX is set, _or_ IXE is set, we pass control to VFP_bounce.
> This is problematical.
> (a) condition (2) above isn't correctly handled for common subarch v3 - it
> is always treated as an undefined instruction, and will result in a
> SIGILL being delivered.
> Now, (a) is just bad behaviour - as we haven't had any reports of this
> yet, I suspect that no one has implemented VFP hardware with this
> behaviour yet.
I believe we ran into this a while ago and fixed it for our chips. We
never sent the patch upstream. Sorry.
I'm looking into what our bits correspond to. Hopefully get back to you
in 20 something hours.
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