linux-kernel - Re: endian bitshift defects [ was: staging: fusb302: don't bitshift _

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Message-ID: <alpine.DEB.2.20.1706170722550.2045@hadrien>
Date:   Sat, 17 Jun 2017 07:23:38 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Joe Perches <joe@...ches.com>
cc:     Frans Klaver <fransklaver@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Yueyao Zhu <yueyao.zhu@...il.com>,
        Rui Miguel Silva <rmfrfs@...il.com>,
        Guru Das Srinagesh <gurooodas@...il.com>,
        Javier Martinez Canillas <javier@...hile0.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: endian bitshift defects [ was: staging: fusb302: don't bitshift
 __le16 type ]



On Fri, 16 Jun 2017, Joe Perches wrote:

> On Fri, 2017-06-16 at 19:45 +0200, Frans Klaver wrote:
> > The header field in struct pd_message is declared as an __le16 type. The
> > data in the message is supposed to be little endian. This means we don't
> > have to go and shift the individual bytes into position when we're
> > filling the buffer, we can just copy the contents right away. As an
> > added benefit we don't get fishy results on big endian systems anymore.
>
> Thanks for pointing this out.
>
> There are several instances of this class of error.
>
> Here's a cocci script to find them.
>
> This is best used with cocci's --all-includes option like:
>
> $ spatch --all-includes --very-quiet --sp-file lebe_bitshifts.cocci .
> [ many defects...]
>
> $ cat lebe_bitshifts.cocci
> @@
> typedef __le16, __le32, __le64,  __be16, __be32, __be64;
> { __le16, __le32, __le64,  __be16, __be32, __be64 } a;
> expression b;
> @@
>
> *	a << b
>
> @@
> { __le16, __le32, __le64,  __be16, __be32, __be64 } a;
> expression b;
> @@
>
> *	a <<= b
>
> @@
> { __le16, __le32, __le64,  __be16, __be32, __be64 } a;
> expression b;
> @@
>
> *	a >> b
>
> @@
> { __le16, __le32, __le64,  __be16, __be32, __be64 } a;
> expression b;
> @@
>
> *	a >>= b

Is this always a problem?  Would it be useful to add this to the scripts
in the kernel?

julia