linux-kernel - Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &

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Date:	Tue, 4 Mar 2008 22:49:47 -0800
From:	"Christopher Li" <sparse@...isli.org>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Julia Lawall" <julia@...u.dk>, yi.zhu@...el.com,
	linux-wireless@...r.kernel.org,
	ipw3945-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	"Harvey Harrison" <harvey.harrison@...il.com>,
	"Alexander Viro" <viro@....linux.org.uk>,
	linux-sparse@...r.kernel.org,
	"Josh Triplett" <josh@...edesktop.org>
Subject: Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &

I think Al Viro has sent a patch to linux-sparse with subject
"[PATCH 3/3] catch !x & y brainos" does exactly that.

Chris



On Tue, Mar 4, 2008 at 10:38 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
>  * Julia Lawall <julia@...u.dk> wrote:
>
>  > From: Julia Lawall <julia@...u.dk>
>  >
>  > In commit e6bafba5b4765a5a252f1b8d31cbf6d2459da337, a bug was fixed
>  > that involved converting !x & y to !(x & y).  The code below shows the
>  > same pattern, and thus should perhaps be fixed in the same way.
>
>
> >       if (sta_ht_inf) {
>  >               if ((!sta_ht_inf->ht_supported) ||
>  > -                (!sta_ht_inf->cap & IEEE80211_HT_CAP_SUP_WIDTH))
>  > +                (!(sta_ht_inf->cap & IEEE80211_HT_CAP_SUP_WIDTH)))
>  >                       return 0;
>
>  i'm wondering, could Sparse be extended to check for such patterns?
>
>  People are regularly running "make C=1" and are sending fixes to make
>  entire subsystems sparse-warning-free, so Sparse is a nice mechanism
>  that works and it keeps code clean in the long run.
>
>  I dont think the "!X & Y" pattern is ever used legitimately [and even if
>  it were used legitimately, it's easy to avoid the sparse false positive
>  - while in the buggy case we have a clear bug].
>
>         Ingo
>  --
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