Re: More C type errors by default for GCC 14

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Sun, 14 May 2023, 06:28 Po Lu, <luangruo@yahoo.com> wrote:

> Eli Schwartz <eschwartz93@gmail.com> writes:
>
> > Quoting my previous reply on the topic.
> >
> > Until everyone is on the same page as you about whether these are GNUC
> > extensions, this conversation will go nowhere.
> >
> > You are of the opinion that "GCC currently behaves a certain way when
> > compiling the code" means that the behavior is documented and specified
> > as a "C Extension" for the GNUC language dialect.
>
> Yes, by the definition of ``extension'' used by everyone except you.
>

Wrong. I wouldn't bother replying to you again in this thread, but I feel
that as a gcc maintainer I should confirm that Eli S. is right here; and
nobody else I know agrees with your definition of extension as "every
non-standard aspect of the compiler's behaviour, whether intentional or
accidental". That's just silly.



> > You've provided some excuses like "C++ is a valid language for writing
> > documentation in, and the HTML docs are lacking", but your arguments are
> > not convincing.
> >
> > GCC has formal documentation. It is written in HTML. If it is lacking,
> > then the only valid move is to improve the HTML documentation and then
> > abide by it. In the absence of documentation, all behavior is, well,
> > "undocumented", which ***definitely*** means it isn't a formal GNUC
> > language dialect extension.
>
> GCC documentation is written in HTML? That's news to me.  I always
> thought it was written in Texinfo.
>

Some is in docbook XML, and some is in HTML (namely the release notes).



> > You can stop arguing your opinions based on what running gcc or g++
> > produces in the form of machine code. What gcc or g++ produces in the
> > form of machine code is not guaranteed even across bugfix releases --
> > your only guarantee is that if it is documented in the ISO standards
> > documents or in the GCC html manual, the produced machine code shall be
> > in accordance with what the documentation says it shall do.
>
> Generated machine code, really?  Not long-standing and observable
> behavior of the translator itself, as has been re-iterated over and over
> again?
>
> > Undefined and undocumented behavior is not a language extension. It is
> > undefined and undocumented behavior.
>
> But when it becomes defined by the translator, in a precise way, it
> becomes an extension to the Standard.
>

No, Eli S. is quite right.


> > You may feel free to take an exact GCC release (source or binary),
> > analyze it, reverse-engineer it, or verify that it does what you want
> > it to do, and then trust that those undefined and undocumented
> > behaviors are ***benevolent***, but that doesn't cause it to be
> > defined and documented, and your trust will, if you are wise, depend
> > on you pinning an exact source code commit of the compiler. Do not
> > depend on bugfix releases of GCC to preserve your undocumented
> > semantics. They may or they may not, but if they don't, it's not a GCC
> > bug, because it is ***undocumented***.
>
> GCC does not implement its documentation.  The documentation is supposed
> to describe (_not_ specify) how GCC behaves, and when the documentation
> is wrong or contains omissions, the documentation will have to be fixed.
> Not the compiler itself.
>

And when the compiler is wrong and the documentation is correct, the
compiler is fixed.



> And it's not just GCC.  Almost all programs work this way.
>