Re: [Qemu-devel] [PATCH] tcg/i386: 'nop' instruction with 'lock' prefix is illegal

[Pranith Kumar]

On Sun, May 14, 2017 at 5:12 PM, Richard Henderson <address@hidden> wrote:
>>
> Surely you'd also want to make this change for 0x11a and 0x11b.  Which would
> also simplify that code a bit.
>
> That said, there's *lots* of missing LOCK prefix checks.  What brings this
> one in particular to your attention?
>

The motivation for this change is here:
https://github.com/aquynh/capstone/issues/915

Apparently LLVM generates it in certain scenarios when padding with
multi-byte nop (it shouldn't).

>From what I understand, a proper instruction like "lock; <valid inst>"
is converted to "lock; multi-byte nop; <valid inst>" due to code
alignment.

There were bugs reported regarding this:
https://bugs.chromium.org/p/nativeclient/issues/detail?id=3929

I am not sure we want to fix this, but I thought it would be easy
enough to cover this case.

Thanks,
-- 
Pranith