Re: DD emulated by HHH cannot possibly terminate normally --- x86 code

On Fri, 2025-02-28 at 20:05 -0600, olcott wrote:

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.

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