On Thu, Feb 23, 2017 at 03:09:29PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 23, 2017 at 02:28:13PM +0100, Peter Zijlstra wrote:
> > + * Since various instruction decoders disagree on the length of UD1,
> > + * we cannot use it either. So use UD0 for WARN.
> > + *
> > + * (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
> > + * our kernel decoder thinks it takes a ModRM byte, which seems consistent
> > + * with various things like the Intel SDM instruction encoding rules)
> > + */
> > +
> > +#define ASM_UD0 ".byte 0x0f, 0xff"
> > +#define ASM_UD1 ".byte 0x0f, 0xb9" /* + ModRM */
> > +#define ASM_UD2 ".byte 0x0f, 0x0b"
>
> http://repo.or.cz/nasm.git/blob/HEAD:/x86/insns.dat
>
> has:
>
> 1378 UD0 void [ 0f ff]
> 186,UNDOC
> 1379 UD1 void [ 0f b9]
> 186,UNDOC
> 1380 UD2B void [ 0f b9]
> 186,UNDOC,ND
> 1381 UD2 void [ 0f 0b]
> 186
> 1382 UD2A void [ 0f 0b]
> 186,ND
>
> which seems to use the 2 byte version of UD1.
>
> hpa, any input?
N/m, as Josh said, they're listed in the latest SDM (Dec 2016) and that
lists UD1 /r, so 3 bytes.
This means binutils decodes it wrong.
