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Date: Wed, 16 Jul 2008 14:35:57 +0200
From: Jan Kiszka <jan.kiszka@web.de>
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Subject: [Qemu-devel] Re: [4875] Remove unintended dereference,
 kills a warning (Jan Kiszka).
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To: qemu-devel@nongnu.org

Laurent Desnogues wrote:
> On Wed, Jul 16, 2008 at 2:04 PM, Andreas Schwab <schwab@suse.de> wrote:
>> Andrzej Zaborowski <balrogg@gmail.com> writes:
>>
>>>  void OPPROTO op_tasb_rN(void)
>>>  {
>>> -    cond_t(*(int8_t *) env->gregs[PARAM1] == 0);
>>> -    *(int8_t *) env->gregs[PARAM1] |= 0x80;
>>> +    cond_t((env->gregs[PARAM1] && 0xff) == 0);
>>> +    *(int8_t *) &env->gregs[PARAM1] |= 0x80;
>> That does not make any sense at all.  The TAS insn operates on memory,
>> not on a register (atomic operations only make sense on memory anyway).
> 
> SH4 documentation says this:
> 
> TAS.B @Rn
>           If (Rn) = 0, 1 → T, else 0 → T
>           1 → MSB of (Rn)
> 
> So indeed it looks like Jan and Andrzej patch is wrong.

At least the audience is finally listening. ;)

Is this one better?

Index: qemu/target-sh4/op.c
===================================================================
--- qemu.orig/target-sh4/op.c
+++ qemu/target-sh4/op.c
@@ -594,8 +594,9 @@ void OPPROTO op_shlr16_Rn(void)
 
 void OPPROTO op_tasb_rN(void)
 {
-    cond_t(*(int8_t *) env->gregs[PARAM1] == 0);
-    *(int8_t *) env->gregs[PARAM1] |= 0x80;
+    uint8_t val = ldub(env->gregs[PARAM1]);
+    cond_t(val == 0);
+    stb(env->gregs[PARAM1], val | 0x80);
     RETURN();
 }