Re: [PATCH] ASoC: wcd934x: Remove some unnecessary NULL checks

[Nathan Chancellor <natechancellor@gmail.com>]

On Tue, Feb 04, 2020 at 10:00:39AM +0000, Mark Brown wrote:
> On Mon, Feb 03, 2020 at 11:01:44PM -0700, Nathan Chancellor wrote:
> > Clang warns:
> > 
> > ../sound/soc/codecs/wcd934x.c:1886:11: warning: address of array
> > 'wcd->rx_chs' will always evaluate to 'true' [-Wpointer-bool-conversion]
> >         if (wcd->rx_chs) {
> >         ~~  ~~~~~^~~~~~
> > ../sound/soc/codecs/wcd934x.c:1894:11: warning: address of array
> > 'wcd->tx_chs' will always evaluate to 'true' [-Wpointer-bool-conversion]
> >         if (wcd->tx_chs) {
> >         ~~  ~~~~~^~~~~~
> > 2 warnings generated.
> > 
> > Arrays that are in the middle of a struct are never NULL so they don't
> > need a check like this.
> 
> I'm not convincd this is a sensible warning, at the use site a
> pointer to an array in a struct looks identical to an array
> embedded in the struct so it's not such a bad idea to check and
> refactoring of the struct could easily introduce problems.

There have been a few other bugs found with this warning:

9fcf2b3c1c02 ("drm/atmel-hlcdc: check stride values in the first plane")
44d7f1a77d8c ("media: pxa_camera: Fix check for pdev->dev.of_node")
8a72b81e6df5 ("isdn: isdnloop: fix pointer dereference bug")

Other static checkers like smatch will warn about this as well (since I
am sure that is how Dan Carpenter found the same issue in the wcd9335
driver). Isn't an antipattern in the kernel to do things "just in
case we do something later"? There are plenty of NULL checks removed
from the kernel because they do not do anything now.

I'd be fine with changing the check to something else that keeps the
same logic but doesn't create a warning; I am not exactly sure what that
would be because that is more of a specific driver logic thing, which I
am not familiar with.

Cheers,
Nathan