[Ksummit-discuss] [TECH TOPIC] How to encourage driver authors to annotate integer endianness properly

Leon Romanovsky leon at kernel.org
Wed Oct 25 10:18:13 UTC 2017

On Wed, Oct 25, 2017 at 10:06:59AM +0000, Bart Van Assche wrote:
> On Wed, 2017-10-25 at 11:54 +0200, Greg KH wrote:
> > On Wed, Oct 25, 2017 at 09:47:25AM +0000, Bart Van Assche wrote:
> > > Hello Ted,
> > >
> > > As you most likely know endianness annotations like __be32 can be verified
> > > by the static source code analyzer called sparse. These annotations are a
> > > big help to verify whether endianness conversions in drivers are correct
> > > (e.g. be32_to_cpu()). However, many driver authors either are not familiar
> > > with sparse or do not use it to verify their work. I think we need a way
> > > to encourage driver authors to pay attention to endianness annotations,
> > > e.g. by letting the zero-day kernel test infrastructure verify endianness
> > > annotations. Please consider to add this topic to the kernel summit agenda.
> >
> > Driver subsystem maintainers should know this, and sparse reports should
> > be simple to run and notice these issues.  If you know of a subsystem
> > that is not paying attention to this, please let those maintainers know
> > and send patches to resolve the issues :)
> Hi Greg,
> A significant challenge is that for several drivers (e.g. drivers/scsi/qla2xxx
> and drivers/infiniband/hw/nes) fixing the endianness annotations is so hard
> that only the driver authors can make these drivers endianness clean. Three
> challenges that have been encountered while trying to make drivers endianness
> clean are:
> - Some driver authors use a single variable to store both cpu-endian and big
>   endian data.
> - Endianness bugs - using a big endian integer where a cpu endian number
>   should have been used or vice versa.
> - The definitive resource for the endianness format is the firmware
>   documentation. For many kernel drivers the firmware documentation is either
>   not available or only available under NDA.

It is e very appealing to fix the driver endianness issues without involving
driver authors, but it is not feasible without their cooperation and it is not
always possible especially for not-active drivers.


> Bart.
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