Re: [PATCH] target/i386: ignore misplaced REX prefixes

[Richard Henderson <richard.henderson@linaro.org>]

On 5/8/25 02:54, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   target/i386/tcg/decode-new.c.inc | 36 ++++++++++++++++++++++++--------
>   1 file changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
> index cda32ee6784..55216e0d249 100644
> --- a/target/i386/tcg/decode-new.c.inc
> +++ b/target/i386/tcg/decode-new.c.inc
> @@ -2542,7 +2542,13 @@ static void disas_insn(DisasContext *s, CPUState *cpu)
>       s->has_modrm = false;
>       s->prefix = 0;
>   
> - next_byte:
> + next_byte:;
> +#ifdef TARGET_X86_64
> +    /* clear any REX prefix followed by other prefixes.  */
> +    int rex;
> +    rex = -1;
> + next_byte_rex:
> +#endif
>       b = x86_ldub_code(env, s);

I guess this is ok, with -1.  It might be worthwhile rewriting without ifdefs, since we 
already let CODE64(s) and REX_PREFIX(s) expand to false without TARGET_X86_64.

The only irritating part would be actually setting s->rex_* at the end, because those 
members are themselves ifdef'ed over in DisasContext.


Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~