linux-kernel - Re: [PATCH] coccinelle: misc: add swap script

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Message-ID: <alpine.DEB.2.22.394.2102181114380.2748@hadrien>
Date:   Thu, 18 Feb 2021 11:17:02 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Denis Efremov <efremov@...ux.com>
cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coccinelle: misc: add swap script



On Thu, 18 Feb 2021, Denis Efremov wrote:

>
>
> On 2/18/21 12:31 AM, Julia Lawall wrote:
> >> +@...ends on patch@
> >> +identifier tmp;
> >> +expression a, b;
> >> +type T;
> >> +@@
> >> +
> >> +(
> >> +- T tmp;
> >> +|
> >> +- T tmp = 0;
> >> +|
> >> +- T *tmp = NULL;
> >> +)
> >> +... when != tmp
> >> +- tmp = a;
> >> +- a = b;
> >> +- b = tmp;
> >> ++ swap(a, b);
> >> +... when != tmp
> >
> > In this rule and the next one, if you remove the final ; from the b = tmp
> > line and from the swap line, and put it into context code afterwards, them
> > the generated code looks better on cases like fs/xfs/xfs_inode.c in the
> > function xfs_lock_two_inodes where two successive swap calls are
> > generated.
> >
> > There are also some cases such as drivers/net/wireless/ath/ath5k/phy.c in
> > the function ath5k_hw_get_median_noise_floor where the swap code makes up
> > a whole if branch.
>
> > In this cases it would be good to remove the {}.
>
> How this can be handled?
>
> If I use this pattern:
> @depends on patch@
> identifier tmp;
> expression a, b;
> @@
>
> (
>   if (...)
> - {
> -       tmp = a;
> -       a = b;
> -       b = tmp
> +       swap(a, b)
>         ;
> - }
> |
> -       tmp = a;
> -       a = b;
> -       b = tmp
> +       swap(a, b)
>         ;
> )
>
> The tool fails with error:
>
> EXN: Failure("rule starting on line 58: already tagged token:\nC code
> context\nFile \"drivers/net/wireless/ath/ath5k/phy.c\", line 1574,
> column 4, charpos = 41650\n around = 'sort',\n whole content =
> \t\t\t\tsort[j - 1] = tmp;") in drivers/net/wireless/ath/ath5k/phy.c

A disjunction basically says "at this node in the cfg, can I match the
first patter, or can I match the second pattern, etc."  Unfortunately in
this case the two branches start matching at different nodes, so the short
circuit aspect of a disjunction isn't used, and it matches both patterns.

The solution is to just make two rules.  The first for the if case and the
second for everything else.

julia