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

[Richard Henderson <rth@twiddle.net>]

On 05/13/2017 08:58 AM, Pranith Kumar wrote:
> The instruction "lock nopl (%rax)" should raise an exception. However,
> we don't do that since we do not check for lock prefix for nop
> instructions. The following patch adds this check and makes the
> behavior similar to hardware.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> ---
>   target/i386/translate.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/target/i386/translate.c b/target/i386/translate.c
> index 1d1372fb43..76f4ccd3b4 100644
> --- a/target/i386/translate.c
> +++ b/target/i386/translate.c
> @@ -7881,6 +7881,9 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
>           gen_nop_modrm(env, s, modrm);
>           break;
>       case 0x119: case 0x11c ... 0x11f: /* nop (multi byte) */
> +        if (prefixes & PREFIX_LOCK) {
> +            goto illegal_op;
> +        }
>           modrm = cpu_ldub_code(env, s->pc++);
>           gen_nop_modrm(env, s, modrm);
>           break;
> 
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?


r~