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

[Richard Henderson]

On 3/9/23 04:32, Laurent Vivier wrote:
> 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.

Because addrp is *not* unused with SRC_EA.  It is a signal for a read-modify-write operand 
and addrp will be passed to DEST_EA.


r~