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From: BGB <cr88192@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: C23 thoughts and opinions
Date: Sat, 15 Jun 2024 20:42:47 -0500
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On 6/15/2024 5:42 PM, Lawrence D'Oliveiro wrote:
> On Fri, 14 Jun 2024 03:13:32 -0500, BGB wrote:
> 
>> On 6/14/2024 1:53 AM, Bonita Montero wrote:
>>>
>>> Am 13.06.2024 um 21:07 schrieb BGB:
>>>>
>>>> One possible justification (albeit a weak one) is that if one
>>>> recompiles the program with optimizations turned on, in many cases
>>>> this may subtly change the behavior of the program (particularly in
>>>> relation to things like the contents of uninitialized variables and
>>>> dangling pointers, etc...). ...
>>>
>>> If you rely on that you're misusing the language anyway.
>>>
>> It is a poor practice, but seemingly does occur in the wild (intentional
>> or not).
> 
> It seems to me that kind of thing does tend to get flushed out of open-
> source code. Because such code is often compiled with different compilers,
> on different architectures, using different tool chains etc. And
> assumptions like these tend not to survive such treatment.

Yeah, true enough.

Given that these are the sort of things that tend to break whenever the 
compiler/architecture/optimization settings/etc is changed, then it 
makes sense that they will get weeded out.


As noted, a lot of the sorts of bugs I had found in this category, was 
when trying to port various MS-DOS era code to my project.


Though, not too long ago, ran into a similar sort of bug, where the code 
had "just so happened" to be working because a stack-based array 
happened to be in the same spot between two functions and just so 
happened (in the latter call) to contain the data needed from the former 
function (in this case, perturbing this coincidence would cause the 
PE/COFF loader to fail to locate binaries; trying to access "some random 
garbage" rather than the path to the EXE).

I fairly promptly fixed this bug once discovered, and am then just left 
to wonder how exactly it managed to work in the first place (or didn't 
break already).

Though, I suspect it may had actually have broken in the past (when 
poking around at the code generation in BGBCC), but at the time I had 
thought it was due to "some unknown compiler bug" (and didn't look 
around enough to realize that it was instead an "uninitialized array 
contents" bug in the code being compiled).


....