Re: git: 402dbdd98acc - main - Adjust function definition in arm's mv_common.c to avoid clang 15 warning

=On 15 Aug 2022, at 22:07, Konstantin Belousov <kostikbel@gmail.com> wrote:
> 
> On Mon, Aug 15, 2022 at 06:49:17PM +0000, Dimitry Andric wrote:
>> The branch main has been updated by dim:
>> 
>> URL: https://cgit.FreeBSD.org/src/commit/?id=402dbdd98acc7fa94d1d4cd01903e987d2409336
>> 
>> commit 402dbdd98acc7fa94d1d4cd01903e987d2409336
>> Author:     Dimitry Andric <dim@FreeBSD.org>
>> AuthorDate: 2022-08-15 18:02:13 +0000
>> Commit:     Dimitry Andric <dim@FreeBSD.org>
>> CommitDate: 2022-08-15 18:48:33 +0000
>> 
>>    Adjust function definition in arm's mv_common.c to avoid clang 15 warning
>> 
>>    With clang 15, the following -Werror warning is produced:
>> 
>>        sys/arm/mv/mv_common.c:414:20: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
>>        mv_check_soc_family()
>>                           ^
>>                            void
>> 
>>    This is because mv_check_soc_family() is declared with a (void) argument
>>    list, but defined with an empty argument list. Make the definition match
>>    the declaration.
>> 
>>    MFC after:      3 days
>> ---
>> sys/arm/mv/mv_common.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/sys/arm/mv/mv_common.c b/sys/arm/mv/mv_common.c
>> index 6e1d12f8c7a7..c2e25c686583 100644
>> --- a/sys/arm/mv/mv_common.c
>> +++ b/sys/arm/mv/mv_common.c
>> @@ -411,7 +411,7 @@ static int mv_win_cesa_attr_armadaxp(int eng_sel)
>> }
>> 
>> enum soc_family
>> -mv_check_soc_family()
>> +mv_check_soc_family(void)
>> {
>> 	uint32_t dev, rev;
>> 
> I am actually curious about this and other commits.  From the ISO/IEC 9899:2023
> draft N3047, 6.7.6.3 Function declarators, clause 13:
> 
> For a function declarator without a parameter type list: the effect
> is as if it were declared with a parameter type list consisting of
> the keyword void. A function declarator provides a prototype for the
> function 177).
> 
> Then the note 177:
> This implies that a function definition without a parameter list
> provides a prototype, and that subsequent calls to that function in the
> same translation unit are constrained not to provide any argument to the
> function call. Thus a definition of a function without parameter list
> and one that has such a list consisting of the keyword void are fully
> equivalent.
> 
> And more, in the 6.9.1 Function definitions clause 13, there is an example:
> typedef int F(void);  // type F is "function with no parameters
>                      // returning int"
> int g() { /* ... */ } // RIGHT: g has type compatible with F
> 
> So why does clang enforce the warning?

I’m not sure why this is a warning; an empty parameter list in a
function declaration that is part of a definition has always been the
same as (void) (unless you have K&R-style arguments, which the compiler
can also see). C99 6.11.6 Function declarators does however say:

> 1 The use of function declarators with empty parentheses (not
> prototype-format parameter type declarators) is an obsolescent feature.

So technically warning for pre-C23 is compliant with that, though a bit
annoying in the definition case given the semantics have stayed the
same and been un-deprecated. Regardless, it’s probably best practice to
be consistent and use (void) in the definitions so it matches any
declarations rather than have this be a special case that can differ.

Jess