Re: [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f

[Linus Torvalds]

On Wed, Feb 7, 2018 at 10:38 AM, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> On 02/07/2018 10:13 AM, Linus Torvalds wrote:
>>
>> That said, intel only _documents_ UD2 (0f 0b).
>
> Intel Order Number: 325383-064US, October 2017, documents UD0, UD1, and UD2.
> Section A.2.5, Table A-1, says:

Ahh, I had an older version.

Looking at the latest one I can find (325462-065US), it does specify
that it has a modrm byte:

  0F FF /r   UD0 1 r32, r/m32

so I think that our opcode maps are wrong, and it's a bit dangerous to
put random constants right after the UD0.

Maybe we should make our use of UD0 have a third byte: add a harmless
modrm byte before the warning constants?

But yes, at least my objdump just thinks it's a bad 2-byte sequence,
and doesn't look at any modrm bytes at all.

                Linus