On Tue, Feb 26, 2013 at 05:37:17PM -0800, Stephen Boyd wrote:

On 02/25/13 12:02, Russell King - ARM Linux wrote:

quoted

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
   hardware.

   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
    defined!)

[snip]

quoted

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.

[snip]

quoted

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.

https://www.codeaurora.org/gitweb/quic/la/?p=kernel/msm.git;a=commitdiff;h=00a13be874f230159a6b7f8cc9d0ff23bc1b7d05

Yes, it looks like you did - because your short vector instructions are
"allocated VFP instruction"s and your hardware response is to raise an
exception with EX=0 DEX=0.

As you've found out, with the VFPv2 exception handling that we have, that
is interpreted as an undefined instruction, rather than an instruction
which needs fixing up.