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Subject: Re: [PATCH] sched/fair: Replace zero-length array with flexible-array
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To:     Joe Perches <joe@perches.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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From:   Valentin Schneider <valentin.schneider@arm.com>
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Date:   Fri, 14 Feb 2020 00:25:03 +0000
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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!");
---