linux-kernel - Re: [PATCH v2] smp: kernel/panic.c

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Message-ID: <YFI+YMo7zml+spKc@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Mar 2021 18:37:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Ingo Molnar <mingo@...nel.org>, He Ying <heying24@...wei.com>,
        frederic@...nel.org, paulmck@...nel.org, clg@...d.org,
        qais.yousef@....com, johnny.chenyi@...wei.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] smp: kernel/panic.c - silence warnings

On Wed, Mar 17, 2021 at 06:17:26PM +0100, Christophe Leroy wrote:
> 
> 
> Le 17/03/2021 à 13:23, Peter Zijlstra a écrit :
> > On Wed, Mar 17, 2021 at 12:00:29PM +0100, Christophe Leroy wrote:
> > > What do you mean ? 'extern' prototype is pointless for function prototypes
> > > and deprecated, no new function prototypes should be added with the 'extern'
> > > keyword.
> > > 
> > > checkpatch.pl tells you: "extern prototypes should be avoided in .h files"
> > 
> > I have a very strong preference for extern on function decls, to match
> > the extern on variable decl.
> 
> You mean you also do 'static inline' variable declarations ?

That's a func definition, not a declaration. And you _can_ do static
variable definitions in a header file just fine, although that's
typically not what you'd want. Although sometimes I've seen people do:

static const int my_var = 10;

inline is an attribute that obviously doesn't work on variables.

> Using the extern keyword on function prototypes is superfluous visual
> noise so suggest removing it.

I don't agree; and I think the C spec is actually wrong there (too).

The thing is that it distinguishes between a forward declaration of a
function in the same TU and an external declaration for a function in
another TU.

That is; if I see:

void ponies(int legs);

I expect that function to be defined later in the same TU. IOW it's a
forward declaration. OTOH if I see:

extern void ponies(int legs);

I know I won't find it in this TU and the linker will end up involved.

Now, the C people figured that distinction was useless and allowed
sloppiness. But I still think there's merrit to that. And as mentioned
earlier, it is consistent with variable declarations.