Re: [PATCH 0/4] tree-wide: fix comparison to bitshift when dealing with a mask

Dan Carpenter
2018-02-06T13:23:35Z

On Tue, Feb 06, 2018 at 02:15:51PM +0100, Julia Lawall wrote:
>
>
> On Tue, 6 Feb 2018, Dan Carpenter wrote:
>
> > On Mon, Feb 05, 2018 at 09:09:57PM +0100, Wolfram Sang wrote:
> > > In one Renesas driver, I found a typo which turned an intended bit shift ('<<')
> > > into a comparison ('<'). Because this is a subtle issue, I looked tree wide for
> > > similar patterns. This small patch series is the outcome.
> > >
> > > Buildbot and checkpatch are happy. Only compile-tested. To be applied
> > > individually per sub-system, I think. I'd think only the net: amd: patch needs
> > > to be conisdered for stable, but I leave this to people who actually know this
> > > driver.
> > >
> > > CCing Dan. Maybe he has an idea how to add a test to smatch? In my setup, only
> > > cppcheck reported a 'coding style' issue with a low prio.
> > >
> >
> > Most of these are inside macros so it makes it complicated for Smatch
> > to warn about them. It might be easier in Coccinelle. Julia the bugs
> > look like this:
> >
> > - reissue_mask |= 0xffff < 4;
> > + reissue_mask |= 0xffff << 4;
>
> Thanks. I'll take a look. Do you have an example of the macro issue
> handy?
>

It's the same:

#define EXYNOS_CIIMGEFF_PAT_CBCR_MASK ((0xff < 13) | (0xff < 0))

Smatch only sees the outside of the macro (where it is used in the code)
and the pre-processed code.

regards,
dan carpenter