Re: [char-misc:char-misc-linus 3/3] drivers/misc/cardreader/rtsx_usb.c:639:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true

[Shuah Khan]

On 7/1/22 9:52 AM, Shuah Khan wrote:
> On 7/1/22 9:39 AM, Nathan Chancellor wrote:
> > On Fri, Jul 01, 2022 at 08:48:11AM -0600, Shuah Khan wrote:
> > > On 7/1/22 2:59 AM, Greg Kroah-Hartman wrote:

> > > > > All warnings (new ones prefixed by >>):
> > > > >
> > > > > > > drivers/misc/cardreader/rtsx_usb.c:639:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
> > > > >              if (!ucr->rsp_buf)
> > > > >                  ^~~~~~~~~~~~~
> > > > >      drivers/misc/cardreader/rtsx_usb.c:678:9: note: uninitialized use occurs here
> > > > >              return ret;
> > > > >                     ^~~
> > > > >      drivers/misc/cardreader/rtsx_usb.c:639:2: note: remove the 'if' if its condition is always false
> > > > >              if (!ucr->rsp_buf)
> > > > >              ^~~~~~~~~~~~~~~~~~
> > > > >      drivers/misc/cardreader/rtsx_usb.c:622:9: note: initialize the variable 'ret' to silence this warning
> > > > >              int ret;
> > > > >                     ^
> > > > >                      = 0
> > > > >      1 warning generated.
> > > >
> > > > Odd, gcc doesn't show this for me.  Shuah, can you send a follow-on
> > > > patch to fix this?  The warning does look correct.
> > >
> > > gcc didn't complain when I compiled either. I will send a follow-on patch.
> >
> > Unfortunately, GCC won't warn for most uninitialized variables by
> > default after 5.7, which included commit 78a5255ffb6a ("Stop the ad-hoc
> > games with -Wno-maybe-initialized"). They will potentially show up at
> > W=2 or with an explicit KCFLAGS=-Wmaybe-uninitialized (it does in this
> > case):
>
> Thank you.
>
> > | drivers/misc/cardreader/rtsx_usb.c: In function ‘rtsx_usb_probe’:
> > | drivers/misc/cardreader/rtsx_usb.c:678:16: error: ‘ret’ may be used uninitialized [-Werror=maybe-uninitialized]
> > |   678 |         return ret;
> > |       |                ^~~
> > | drivers/misc/cardreader/rtsx_usb.c:622:13: note: ‘ret’ was declared here
> > |   622 |         int ret;
> > |       |             ^~~
> > | cc1: all warnings being treated as errors
>
> This is a bug and a good find. ret should have been set
> in the if (!ucr->rsp_buf) before going to error handling.
>
> I wonder if it would have been flagged if ret were to be
> initialized to 0. Something to experiment.

I had to try. As I suspected initializing ret will mask this bug.

KCFLAGS=-Wmaybe-uninitialized will not flag it even though
the bug still exists. It will return 0 when memory allocation
fails.

Initializing isn't always the right answer for these kinds of
warnings.

thanks,
-- Shuah