Re: [PATCH 1/1] checkpatch.pl: thou shalt not use () or (...) infunction declarations

From: Nick Bowler
Date: Thu Mar 22 2012 - 13:19:53 EST


On 2012-03-22 13:17 -0400, Nick Bowler wrote:
> On 2012-03-22 17:22 +0100, Jiri Slaby wrote:
> > On 03/22/2012 04:27 PM, Phil Carmody wrote:
> [...]
> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > > index a3b9782..3993011 100755
> > > --- a/scripts/checkpatch.pl
> > > +++ b/scripts/checkpatch.pl
> > > @@ -1881,6 +1881,10 @@ sub process {
> > > substr($ctx, 0, $name_len + 1, '');
> > > $ctx =~ s/\)[^\)]*$//;
> > >
> > > + if ($ctx =~ /^\s*(?:\.\.\.)?\s*$/) {
> > > + # HPA explains why: http://lwn.net/Articles/487493/
> > > + ERROR("(...) and () are not sufficiently informative function declarations\n$hereline");
> > > + }
> >
> > That explanation is not fully correct. C99 explicitly says (6.7.5.3.14):
> > An identifier list declares only the identifiers of the parameters of
> > the function. An empty list in a function declarator that is part of a
> > definition of that function specifies that the function has no
> > parameters.
>
> Nevertheless, an empty identifier list in a declaration is still not the
^^^^^^^^^^^
That should obviously have said "definition". Sigh.

> same as a parameter type list with (void). In particular, the empty
> identifier list *is not a prototype declaration for the function*. That
> means that arguments passed to the function are not subject to the usual
> checks/conversions implied by a prototype.
>
> Consider:
>
> int foo()
> {
> return 0;
> }
>
> int main(void)
> {
> return foo(1, 2, 3, 4, 5); /* this is syntactically OK; undefined
> behaviour at runtime. */
> }
>
> GCC will not normally warn about the above (unless you pass
> -Wold-style-definition) which warns for all function definitions that
> lack a prototype. On the other hand, changing it to int foo(void)
> provides the required prototype for the arguments to be checked, and the
> above becomes a proper error.
>
> > So what you are trying to force here holds only for (forward)
> > declarations. Not for functions with definitions (bodies). Is
> > checkpatch capable to differ between those?
>
> For the above reasons, non-prototype declarations of any sort should be
> avoided. No need for checkpatch to distinguish between whether or not
> there's a function body.
>
> Cheers,
--
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

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