[9fans] Plan9 C conversion to unnamed member drops qualifiers

[9fans] Plan9 C conversion to unnamed member drops qualifiers

[Alejandro Colomar via 9fans]

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Hi!

GCC implements Plan9 C extensions, and has a bug by which it allows
discarding qualifiers without a cast.  I'm wondering if this is a bug
only in GCC, or if it's a bug also in Plan9.  Anyone using a Plan9
compiler can check this code and let me know if it diagnoses about the
qualifier drop?

	alx@devuan:~/tmp$ cat q.c
	struct foo {
		int a;
	};

	struct bar {
		struct foo;
	};

	void f(struct foo *);

	int
	main(void)
	{
		const struct bar  b;

		f(&b);
	}
	alx@devuan:~/tmp$ gcc -Wall -Wextra -fplan9-extensions -S q.c
	alx@devuan:~/tmp$ 

Thanks!

Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>

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Re: [9fans] Plan9 C conversion to unnamed member drops qualifiers

[Paul Lalonde]

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The plan9 C compilers ignore the qualifier drop (and I just compiled the
example to make sure).
Quoting Ken Thompson from "A New C Compiler"
<https://c9x.me/compile/bib/new-c.pdf>:

3.1. Register, volatile, const The keywords register, volatile, and const,
are recognised syntactically but are semantically ignored. Volatile seems
to have no meaning, so it is hard to tell if ignoring it is a departure
from the standard. Const only confuses library interfaces with the hope of
catching some rare errors.


Paul

On Tue, Mar 25, 2025 at 6:44 AM Alejandro Colomar via 9fans <9fans@9fans.net>
wrote:

> Hi!
> 
> GCC implements Plan9 C extensions, and has a bug by which it allows
> discarding qualifiers without a cast.  I'm wondering if this is a bug
> only in GCC, or if it's a bug also in Plan9.  Anyone using a Plan9
> compiler can check this code and let me know if it diagnoses about the
> qualifier drop?
> 
> alx@devuan:~/tmp$ cat q.c
> struct foo {
>         int a;
> };
> 
> struct bar {
>         struct foo;
> };
> 
> void f(struct foo *);
> 
> int
> main(void)
> {
>         const struct bar  b;
> 
> f(&b);
> }
> alx@devuan:~/tmp$ gcc -Wall -Wextra -fplan9-extensions -S q.c
> alx@devuan:~/tmp$
> 
> Thanks!
> 
> Have a lovely day!
> Alex
> 
> --
> <https://www.alejandro-colomar.es/>

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