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


From: Richard Henderson
Subject: Re: [PATCH v2 12/25] target/m68k: Reject immediate as destination in gen_ea_mode
Date: Thu, 9 Mar 2023 08:27:46 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1

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~



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