Re: [PATCH] target: i386: Check float overflow about register stack

[Chen Gang]

On 2020/2/22 上午12:18, Paolo Bonzini wrote:
> On 21/02/20 15:09, Chen Gang wrote:
>>> -    /* XXX: test fptags too */
>>> +    if (env->fptags[env->fpstt]) {
>>> +        env->fpus |= 0x4100; /* Empty */
>>> +        return;
>>> +    }
>>> +
>> For fpop overflow, this fix is enough, but for me, we still need
>> foverflow to check fpush/fld*_ST0 overflow.
>>
>> Don't you think we need check fpush/f[i]ld*_ST0 overflow?
> 
> After fld/fild or any other push, FXAM ST0 should not return empty in my
> opinion.
> 

OK, it sounds reasonable.

After check the intel document for f[i]ld* instructions, it says:

  "Set C1 to 1 if stack overflow occurred; set to 0 otherwise".

In helper_fxam_ST0, I guess, we need "env->fpus |= 0x200" (but I don't
know wheter it will be conflict with SIGND(temp)). And we have to still
need foverflow, because all env->fptags being 0 doesn't mean overflow.

Thanks.