Re: [PATCH 3/3] objtool/x86: Fix NOP decode

Andrew Cooper
2025-09-25T11:29:21Z

> I've made that:
>
> case 0x90:
> if (rex_b) /* XCHG %r8, %rax */
> break;
>
> if (prefix == 0xf3) /* REP NOP := PAUSE */
> break;
>
> insn->type = INSN_NOP;
> break;

Legacy prefixes can come in any order.  What is F3 66 90 ?

Also, VEX/EVEX/REX2 want excluding too, all of which can encode rex_b
differently.

Is it really only rex_b which prevents NOP becoming a pause, or is it
any REX prefix?  I would have thought it was any REX prefix.

~Andrew