Re: [PATCH] sched/fair: Replace zero-length array with flexible-array member

[Joe Perches]

On Fri, 2020-02-14 at 00:25 +0000, Valentin Schneider wrote:
> On 13/02/2020 22:02, Joe Perches wrote:
> > That might be a somewhat difficult thing to add to checkpatch
> > as it is effectively a per-line scanner:
> > 
> > Try something like:
> > 
> > $ git grep -P -A1 '^\s*(?!return)(\w+\s+){1,3}\w+\[0\];' -- '*.[ch]'
> > 
> > and look at the results.
> > 
> > In checkpatch that could be something like:
> > 
> > 	if ($line =~ /^.\s*$Type\s+$Ident\s*\[\s*0\s*\]\s*;/) {
> > 		warn...
> > 	}
> > 
> 
> So FWIW I felt like doing some coccinelle and ended up with this:
> 
> This patches up valid ZLAs:
>   $ spatch -D patch zero_length_array.cocci kernel/sched/fair.c
> 
> This prints out the location of invalid ZLAs:
>   $ spatch -D report zero_length_array.cocci kernel/sched/fair.c
> 
> ---
> virtual patch
> virtual report
> 
> @valid_zla depends on patch@
> identifier struct_name;
> type T;
> identifier zla;
> position pos;
> @@
> struct struct_name {
>        ...
>        T zla@pos
> - [0];
> + [];
> };
> 
> @invalid_zla depends on report@
> identifier struct_name;
> type T1;
> identifier zla;
> type T2;
> identifier tail;
> position pos;
> @@
> struct struct_name {
>        ...
>        T1 zla[0]@pos;
>        T2 tail;
>        ...
> };
> 
> @script:python depends on invalid_zla@
> pos << invalid_zla.pos;
> @@
> coccilib.report.print_report(pos[0], "Invalid ZLA!");
> ---

Nice.
It would miss a few forms like:

	typedef struct tagfoo {
		...
		type t[0];
	} foo;

and

	struct {
		...
		type t[0];
	} foo;

and

	struct foo {
		...
		type t[0];
	} *foo;

etc...