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From: Richard Damon <richard@damon-family.org>
Newsgroups: comp.theory
Subject: Re: A state transition diagram proves ...
Date: Fri, 18 Oct 2024 07:17:21 -0400
Organization: i2pn2 (i2pn.org)
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On 10/17/24 11:47 PM, olcott wrote:
> On 10/17/2024 10:27 PM, Richard Damon wrote:
>> On 10/17/24 9:47 PM, olcott wrote:
>>> On 10/17/2024 8:13 PM, Richard Damon wrote:
>>>> On 10/17/24 7:31 PM, olcott wrote:
>>>>> _DDD()
>>>>> [00002172] 55         push ebp      ; housekeeping
>>>>> [00002173] 8bec       mov ebp,esp   ; housekeeping
>>>>> [00002175] 6872210000 push 00002172 ; push DDD
>>>>> [0000217a] e853f4ffff call 000015d2 ; call HHH(DDD)
>>>>> [0000217f] 83c404     add esp,+04
>>>>> [00002182] 5d         pop ebp
>>>>> [00002183] c3         ret
>>>>> Size in bytes:(0018) [00002183]
>>>>>
>>>>> When DDD is correctly emulated by HHH according
>>>>> to the semantics of the x86 language DDD cannot
>>>>> possibly reach its own machine address [00002183]
>>>>> no matter what HHH does.
>>>>>
>>>>> +-->[00002172]-->[00002173]-->[00002175]-->[0000217a]--+
>>>>> +------------------------------------------------------+
>>>>>
>>>>> That may not line up that same way when view
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> https://en.wikipedia.org/wiki/State_diagram
>>>>>
>>>>
>>>>
>>>> Except that 0000217a doesn't go to 00002172, but to 000015d2
>>>>
>>>
>>> IS THIS OVER YOUR HEAD?
>>> What is the first machine address of DDD that HHH
>>> emulating itself emulating DDD would reach?
>>>
>>
>> Yes, HHH EMULATES the code at that address, 
> 
> Which HHH emulates what code at which address?
> 

Everyone, just once, which you should know, but ignore.

The Emulating HHH sees those addresses at its begining and then never again.

Then the HHH that it is emulating will see those addresses, but not the 
outer one that is doing that emulation of HHH.

Then the HHH that the second HHH is emulating will, but neither of the 
outer 2 HHH.

And so on.

Which HHH do you think EVER gets back to 00002172?

What instruction do you think that it emulates that would tell it to do so?

It isn't the call instruction at 0000217a, as that tells it to go into HHH.

At best the trace is:

00002172
00002173
00002175
0000217a
conditional emulation of 00002172
conditional emulation of 00002173
conditional emulation of 00002175
conditional emulation of 0000217a
CE of CE of 00002172
....

The "state" never repeats, it is alway a new state, and if HHH decides 
to abort its emulation, it also should know that every level of 
condition emulation it say will also do the same thing, and thus the 
call HHH at 0000217a will be returned from, and HHH has no idea what 
will happen after that, so it KNOWS it is ignorant of the answer.