Re: [PATCH v2 12/25] target/m68k: Reject immediate as destination in gen_ea_mode

[Laurent Vivier]

Le 07/03/2023 à 19:34, Richard Henderson a écrit :
> In theory this should never happen, as all such instructions
> are illegal.  This is checked in e.g. gen_lea_mode and
> gen_ea_mode_fp but not here.  In case something higher up
> isn't checking modes properly, return NULL_QREG.  This will
> result in an illegal instruction exception being raised.

NULL_QREG generates an address exception, not illegal instruction.

> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> Cc: Laurent Vivier <laurent@vivier.eu>
> ---
>   target/m68k/translate.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/target/m68k/translate.c b/target/m68k/translate.c
> index 44c3ac0bc3..fc65dad190 100644
> --- a/target/m68k/translate.c
> +++ b/target/m68k/translate.c
> @@ -894,6 +894,10 @@ static TCGv gen_ea_mode(CPUM68KState *env, DisasContext 
> *s, int mode, int reg0,
>           case 3: /* pc index+displacement.  */
>               goto do_indirect;
>           case 4: /* Immediate.  */
> +            /* Should never be used for an output or RMW input. */
> +            if (what == EA_STORE || addrp) {

Why do you check addrp?

What happens for an instruction that provides addrp to SRC_EA() when it is used 
with immediate mode?
In this case addrp is unused, but it should not trigger an exception.

Thanks,
Laurent
> +                return NULL_QREG;
> +            }
>               /* Sign extend values for consistency.  */
>               switch (opsize) {
>               case OS_BYTE: