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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory
Subject: Re: DD emulated by HHH cannot possibly terminate normally --- x86
 code
Date: Fri, 28 Feb 2025 20:05:30 -0600
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On 2/28/2025 7:00 PM, dbush wrote:
> On 2/28/2025 7:47 PM, olcott wrote:
>> _DD()
>> [00002133] 55         push ebp      ; housekeeping
>> [00002134] 8bec       mov ebp,esp   ; housekeeping
>> [00002136] 51         push ecx      ; make space for local
>> [00002137] 6833210000 push 00002133 ; push DD
>> [0000213c] e882f4ffff call 000015c3 ; call HHH(DD)
>> [00002141] 83c404     add esp,+04
>> [00002144] 8945fc     mov [ebp-04],eax
>> [00002147] 837dfc00   cmp dword [ebp-04],+00
>> [0000214b] 7402       jz 0000214f
>> [0000214d] ebfe       jmp 0000214d
>> [0000214f] 8b45fc     mov eax,[ebp-04]
>> [00002152] 8be5       mov esp,ebp
>> [00002154] 5d         pop ebp
>> [00002155] c3         ret
>> Size in bytes:(0035) [00002155]
>>
>> When we hypothesize that the code at machine address
>> 0000213c is an x86 emulator then we know that DD
>> remains stuck in recursive emulation and cannot possibly
>> reach its own "ret" instruction and terminate normally.
>>
>> When we add the additional complexity that HHH also
>> aborts this sequence at some point then every level
>> of recursive emulation immediately stops. This does
>> not enable any DD to ever reach its "ret" instruction.
>>
> 
> Likewise:
> 
> 0000000000400534 <no_numbers_greater_than_10>:
>    400534:    55                       push   rbp
>    400535:    48 89 e5                 mov    rbp,rsp
>    400538:    b8 34 05 40 00           mov    eax,0x400534 ; push 
> no_numbers_greater_than_10
>    40053d:    48 89 c7                 mov    rdi,rax
>    400540:    e8 a8 ff ff ff           call   4004ed <F>   ; call F
>    400545:    5d                       pop    rbp
>    400546:    c3                       ret
> 
> When we hypothesize that the code at machine address
> 4004ed is an x86 emulator then we know that no_numbers_greater_than_10
> remains stuck in recursive emulation and cannot possibly
> reach its own "ret" instruction and terminate normally.
> 
> When we add the additional complexity that F also
> aborts this sequence at some point then every level
> of recursive emulation immediately stops. This does
> not enable any no_numbers_greater_than_10 to ever reach its "ret" 
> instruction.
> 

So you and your code agrees with me.

-- 
Copyright 2025 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer