[Linux-kernel-mentees] [PATCH RFC] checkpatch: fix multi-statement macro checks

[Dwaipayan Ray]

On Thu, Oct 1, 2020 at 7:12 PM Joe Perches <joe at perches.com> wrote:
>
> On Thu, 2020-10-01 at 18:57 +0530, Dwaipayan Ray wrote:
> > On Thu, Oct 1, 2020 at 6:47 PM Joe Perches <joe at perches.com> wrote:
> > > On Thu, 2020-10-01 at 16:03 +0530, Dwaipayan Ray wrote:
> > > > Checkpatch.pl doesn't have a check for excluding while (...) {...}
> > > > blocks from MULTISTATEMENT_MACRO_USE_DO_WHILE error.
> > > >
> > > > For example, running checkpatch.pl on the file mm/access.c in the
> > > > kernel generates the following error:
> > > >
> > > > ERROR: Macros with complex values should be enclosed in parentheses
> > > > +#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label)        \
> > > > +     while (len >= sizeof(type)) {                                   \
> > > > +             __get_kernel_nofault(dst, src, type, err_label);        \
> > > > +             dst += sizeof(type);                                    \
> > > > +             src += sizeof(type);                                    \
> > > > +             len -= sizeof(type);                                    \
> > > > +     }
> > > >
> > > > The error is misleading for this case. Enclosing it in parantheses
> > > > doesn't make any sense.
> > >
> > > OK
> > >
> > > > Checkpatch already has an exception list for such common macro types.
> > > > Added a new exception for while (...) {...} style blocks to the same.
> > > > This effectively fixed the wrong error message.
> > > []
> > > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > > []
> > > > @@ -5342,6 +5342,7 @@ sub process {
> > > >                           $dstat !~ /^\.$Ident\s*=/ &&                                # .foo =
> > > >                           $dstat !~ /^(?:\#\s*$Ident|\#\s*$Constant)\s*$/ &&          # stringification #foo
> > > >                           $dstat !~ /^do\s*$Constant\s*while\s*$Constant;?$/ &&       # do {...} while (...); // do {...} while (...)
> > > > +                         $dstat !~ /^while\s*$Constant\s*$Constant\s*$/ &&           # while (...) {...}
>
> Note the \s*
>                                                               ^
>
> > > Did you try to output $dstat for some matching cases?
> > > What was the $dstat value for the cases you tried?
> > >
> > >
> > Hi,
> > I did check $dstat values.
> >
> > For example on file mm/maccess.c, there were two such macros:
> >
> > Case 1:
> >
> > $ctx:
> > +#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
> > + while (len >= sizeof(type)) { \
> > + __get_kernel_nofault(dst, src, type, err_label); \
> > + dst += sizeof(type); \
> > + src += sizeof(type); \
> > + len -= sizeof(type); \
> > + }
> >
> > $dstat:
> > while 1 1
>
> And perhaps this test should use \s+ instead.
> What is $dstat with a #define like:
>
> #define foo(bar,baz)while(bar){bar--;baz++;}
>
> (no spaces anywhere bot the required one after define
>

In this case, $dstat is: while11

So, if \s+ is used, it won't match with this. I ran checkpatch
on it and some other condition seems to match, so it is
excluded from the error.

However, if the macro is like:

#define foo(bar,baz)while(bar) {bar--;baz++;}
(one space after condition)

$dstat is: while1 1
(space after first 1)
and the same error is again emitted.

So I think \s* works better since there can be
0 or more whitespaces between them.

Thanks,
Dwaipayan.