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

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Message-ID: <alpine.DEB.2.20.1706260539460.3113@hadrien>
Date:   Mon, 26 Jun 2017 05:39:56 -0400 (EDT)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Frans Klaver <fransklaver@...il.com>
cc:     Julia Lawall <julia.lawall@...6.fr>, Joe Perches <joe@...ches.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" <linux-kernel@...r.kernel.org>
Subject: Re: endian bitshift defects [ was: staging: fusb302: don't bitshift
 __le16 type ]



On Mon, 26 Jun 2017, Frans Klaver wrote:

> On Sat, Jun 24, 2017 at 1:37 AM, Julia Lawall <julia.lawall@...6.fr> wrote:
> >
> >
> > On Sat, 24 Jun 2017, Frans Klaver wrote:
> >
> >> Hm. For some reason the great mail filtering scheme decided to push
> >> this past my inbox :-/
> >>
> >> On Sat, Jun 17, 2017 at 12:44 AM, Joe Perches <joe@...ches.com> 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.
> >>
> >> There are other smells around __(le|be) types that show up in staging
> >> that might be worth checking in the rest of the kernel as well. e.g.
> >> converting to cpu and storing it back into itself (possibly with its
> >> bytes reversed), direct assignments without conversion and what else
> >> you might have. sparse obviously already flags anything fishy going on
> >> with these types, but cannot distinguish between the classes of
> >> errors. I'll need to acquaint myself with spatch a bit more to be able
> >> to track that down.
> >
> > If you have concrete code examples, even fake ones, illustrating a class
> > of problem, then that would be great.
>
> I'll see if I can produce some somewhere this week.

Thanks.

julia