GCC 12.1 Released

Posted May 10, 2022 3:43 UTC (Tue) by wtarreau (subscriber, #51152)
In reply to: GCC 12.1 Released by NYKevin
Parent article: GCC 12.1 Released

That's exactly the way I see it. Nowadays people using C need it for low-level stuff because someone has to do it, and the places where C is needed want to have a good trust on the code translation to machine code because where it's used, it matters. Usually it's a mix of relying on hardware (e.g. hope the compiler will produce a ROL when using both a left and right shifts), the OS (e.g. cause a segfault when writing at address zero), and the libc (e.g; memcpy() does what the standard says it does).

That's why for me it's important that a C compiler tries less to guess about improbable mistakes that are relevant to absolutely zero use cases for this language, but instead focuses on real mistakes that are easy to solve (e.g; operators precedence, asking for braces, undefined use of self-increment in arguments, etc).

I'm fine with having such unlikely analysis but only on developer's request (e.g. -Wsuspicious). It could then go further and report some uncommon constructs that are inefficient and are suspicious because of that without annoying users when -Wall is used to detect likely incompatibilities on their platforms (because that's why most of us use -Wall -Werror, it's to catch problems at build time on other platforms).

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GCC 12.1 Released

Posted May 10, 2022 15:51 UTC (Tue) by dvdeug (subscriber, #10998) [Link] (3 responses)

If you want all warnings, use Wall. If you want a specific set of warnings, turn just those warnings on. Turning arbitrary warnings on and turning warnings into errors turns the language into an ever-evolving, compiler-specific language, which is your choice, but something terribly silly to complain about.

GCC 12.1 Released

Posted May 10, 2022 17:22 UTC (Tue) by mpr22 (subscriber, #60784) [Link] (2 responses)

GCC's -Wall command-line option does not turn on all warnings, hasn't done for years, and quite possibly has never done so in the quarter-century I've been using GCC.

GCC 12.1 Released

Posted May 10, 2022 18:43 UTC (Tue) by wtarreau (subscriber, #51152) [Link] (1 responses)

Exact. Plus "enabling specific warnings" would only work if there was a portable way to enable (or silence) warnings across all compilers without having to perform a discovery pass first. Enabling a fixed set everywhere is trivial when you use *your* compiler for *your* project. When you distribute your code and it builds on a wide range of compilers that's a totally different story.

GCC 12.1 Released

Posted May 11, 2022 21:42 UTC (Wed) by NYKevin (subscriber, #129325) [Link]

The C standard doesn't really give compilers a whole lot to go on here. For certain issues, it directs the compiler to "emit a diagnostic," and for a superset of those issues, it says "the program is ill-formed," but that's it.

* Warnings vs. errors? Unspecified. The compiler is entirely within its rights to produce a binary even if the program is ill-formed and a diagnostic is required, so long as the compiler at least prints some sort of message diagnosing the issue.
* -Wall vs. -Wextra vs. -Wsome-random-thing? Nope. Most compilers emit all standardized warnings with no flags, so the additional warnings you can enable are all nonstandard, and it's purely an issue of implementation quality how they work, which flags toggle which warnings, and so on.
* Formatting of messages? No. The standard simply directs the compiler to "emit a diagnostic," and compiler writers are responsible for figuring out what that means and how to implement it. This is arguably a good thing, because it makes it possible to display warnings graphically or in an IDE (rather than e.g. requiring the use of stderr and then having the IDE parse the output from a separate process, which might be a good design but should not be mandatory), but it also means that different compilers can print totally different messages for the same problem.

About the best you can do is pick a set of warnings that you think is appropriate for your codebase (e.g. start with -Wall and add/subtract warnings as necessary), fix all of those warnings, and then aggressively WONTFIX any bugs that people file about warnings that are not on the list (unless it looks like the warning may have identified a real bug, in which case you might want to consider adding it to your list). If people don't like that, they can fork it.