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

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Message-ID: <CAH6sp9OCydowraafgmvp_BNe_Riqg3YA_fXm38m17nqFi49Tqw@mail.gmail.com>
Date:   Mon, 26 Jun 2017 10:06:14 +0200
From:   Frans Klaver <fransklaver@...il.com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     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 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,
Frans