Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Richard Heathfield Newsgroups: comp.theory Subject: Re: Incorrect requirements --- Computing the mapping from the input to HHH(DD) Date: Thu, 8 May 2025 21:01:42 +0100 Organization: Fix this later Lines: 169 Message-ID: References:

MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Thu, 08 May 2025 22:01:44 +0200 (CEST) Injection-Info: dont-email.me; posting-host="fc99c878bc8892c2ff7fc287d1c7246a"; logging-data="2212487"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18vZbJ2QOYTcHb0xp8iGAdUhTOizo+pMJ+dcW/96t0low==" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:yHRPZMPrxq/8qqzvxUUrAJq4dvw= Content-Language: en-GB In-Reply-To: On 08/05/2025 20:42, olcott wrote: > On 5/8/2025 2:04 PM, Fred. Zwarts wrote: >> Op 08.mei.2025 om 19:00 schreef olcott: >>> On 5/8/2025 11:14 AM, Mike Terry wrote: >>>> On 08/05/2025 06:33, Richard Heathfield wrote: >>>>> On 08/05/2025 06:22, olcott wrote: >>>>>> On 5/7/2025 11:09 PM, Richard Heathfield wrote: >>>>>>> On 08/05/2025 02:20, olcott wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>>> Does there exist an HHH such that DDD emulated by >>>>>>>> HHH according to the rules of the C programming language >>>>>>> >>>>>>> Let's take a look. >>>>>>> >>>>>>> The file is 1373 lines long, but don't worry, because I >>>>>>> plan to stop at HHH's first departure from the rules of >>>>>>> the C programming language (or at least the first >>>>>>> departure I spot). >>>>>>> >>>>>>> Turn in your songbook if you will to: >>>>>>> >>>>>>> void CopyMachineCode(u8* source, u8** destination) >>>>>>> { >>>>>>> u32 size; >>>>>>> for (size = 0; source[size] != 0xcc; size++) >>>>>>> ; >>>>>>> *destination = (u8*) Allocate(size); >>>>>>> for (u32 N = 0; N < size; N++) >>>>>>> { >>>>>>> Output("source[N]: ", source[N]); >>>>>>> *destination[N] = source[N]; >>>>>>> } >>>>>>> ((u32*)*destination)[-1] = size; >>>>>>> Output("CopyMachineCode destination[-1]: ", >>>>>>> ((u32*)*destination) [-1]); >>>>>>> Output("CopyMachineCode destination[-2]: ", >>>>>>> ((u32*)*destination) [-2]); >>>>>>> }; >>>>>>> >>>>>> >>>>>> deprecated. >>>>> >>>>> It's not just deprecated. It's hopelessly broken. >>>>> >>>>> Everybody makes mistakes, and one slip would be all very >>>>> well, but you make essentially the same mistake --- writing >>>>> to memory that your program doesn't own --- no fewer than >>>>> four times in a single function. >>>>> >>>>>>> I'll ignore the syntax error (a null statement at file >>>>>>> scope is a rookie error). >>>>>>> >>>>>>> Instead, let's jump straight to this line: >>>>>>> >>>>>>> *destination = (u8*) Allocate(size); >>>>>>> >>>>>>> On line 79 of my copy of the code, we find: >>>>>>> >>>>>>> u32* Allocate(u32 size) { return 0; } >>>>>>> >>>>>>> In C, 0 is a null pointer constant, so Allocate returns a >>>>>>> null pointer constant... which is fine as long as you >>>>>>> don't try to deref it. So now *destination is NULL. >>>>>>> >>>>>>> We go on: >>>>>>> >>>>>>> for (u32 N = 0; N < size; N++) >>>>>>> { >>>>>>> Output("source[N]: ", source[N]); >>>>>>> *destination[N] = source[N]; >>>>>>> } >>>>>>> >>>>>>> *destination[N] is our first big problem (we're ignoring >>>>>>> syntax errors, remember). destination is a null pointer, >>>>>>> so destination[N] derefs a null pointer. >>>>>>> >>>>>>> That's a fail. 0/10, D-, go away and write it again. And >>>>>>> you / dare/ to impugn other people's C knowledge! Crack a >>>>>>> book, for pity's sake. >>>>>>> >>>>>> >>>>>> If you can't even understand what is essentially >>>>>> an infinite recursive relationship between two functions >>>>>> except that one function can terminate the other then >>>>>> you don't have a clue about the essence of my system. >>>>> >>>>> If you can't even understand why it's a stupendously bad >>>>> idea to dereference a null pointer, you have no business >>>>> trying to teach anyone anything about C. >>>>> >>>>> Your code is the work of a programmer so hideously >>>>> incompetent that 'programmer' is scarcely a fair word to use. >>>>> >>>>> When you publish code like that, to even *think* about >>>>> denigrating other people's C knowledge is the height of >>>>> arrogant hypocrisy. >>>>> >>>> One problem here is that you don't understand how PO's code >>>> works. That's to be expected, and PO's response ought to be >>>> to explain it so that you understand. Instead he goes off on >>>> one of his rants, so blamewise it's really down to PO. >>>> >>>> PO's halt7.c is compiled (it is not linked), then the obj >>>> file is fed as input to his x87utm.exe which is a kind of x86 >>>> obj code execution environment. x87utm provides a number of >>>> primative calls that halt7.c code can make, such as >>>> Allocate(), used to allocate a block of memory for use in >>>> halt7.c. Within halt7.c code calls an Allocate() function, >>>> and x86utm intercepts that and performs the function >>>> internally, then jumps the calling code in halt7.c over the >>>> Allocate call where it continues as normal. The call never >>>> goes to the implementation of Allocate in halt7.c, so the >>>> null pointer dereferencing does not actually occur. There >>>> are a whole bunch of similar x86utm primitive operations that >>>> work in the same way. >>>> >>>> PO should have said all that, not me, but it seems he's not >>>> interested in genuine communication. >>>> >>>> Mike. >>>> >>>> >>> >>> Thanks for those details, they are correct. >>> I try to stay focused on the key essence gist >>> of the issue and never delve down into the weeds. >>> >>> int DD() >>> { >>> int Halt_Status = HHH(DD); >>> if (Halt_Status) >>> HERE: goto HERE; >>> return Halt_Status; >>> } >>> >>> The key gist of the issue (no weeds involved) >>> is that HHH emulated DD according to the rules >>> of the x86 language >>> >>> >> 10/13/2022> >>> *until H correctly determines that* >>> *its simulated D would never stop running unless aborted* >>> >> 10/13/2022> >> >> And since H does not correctly determine that its simulated D >> would never stop running unless aborted, it is a vacuous >> statement and Sipser's agreement does not tell anything. >> > > That is counter factual as any fully qualified > C programmer will tell you. As any competent C programmer can tell you, your simulation is driven by assembly language, not C. Furthermore, neither halt7.c nor x86utm.cpp is syntactically correct C. Once you fix the syntax errors, that still leaves you with the undefined behaviour. Getting it right is tedious. -- ========== REMAINDER OF ARTICLE TRUNCATED ==========