On Thu, Feb 28, 2019 at 10:51:12AM +0100, Richard Weinberger wrote:
> Am Donnerstag, 28. Februar 2019, 09:50:58 CET schrieb Nathan Chancellor:
> > On Thu, Feb 28, 2019 at 09:35:50AM +0100, Richard Weinberger wrote:
> > > Am Donnerstag, 28. Februar 2019, 06:35:51 CET schrieb Dan Carpenter:
> > > > This condition needs to be fipped around because "err" is uninitialized
> > > > when "force" is set. The Smatch static analysis tool complains and
> > > > UBsan will also complain at runtime.
> > > >
> > > > Fixes: 663586c0a892 ("ubi: Expose the bitrot interface")
> > > > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> >
> > Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> > Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
>
> Did you really test the code or just compile it?
>
Compiled tested. If I shouldn't use that tag in that instance, please
let me know.
> > This fixes a -Wsometimes-uninitialized warning from Clang:
> >
> > drivers/mtd/ubi/wl.c:1514:6: warning: variable 'err' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> > if (!force) {
> > ^~~~~~
> > drivers/mtd/ubi/wl.c:1520:6: note: uninitialized use occurs here
> > if (err == UBI_IO_BITFLIPS || force) {
> > ^~~
> > drivers/mtd/ubi/wl.c:1514:2: note: remove the 'if' if its condition is always true
> > if (!force) {
> > ^~~~~~~~~~~~
> > drivers/mtd/ubi/wl.c:1478:9: note: initialize the variable 'err' to silence this warning
> > int err;
> > ^
> > = 0
> > 1 warning generated.
>
> How much false positives does this trigger?
> Many useful gcc warnings are disabled because they produce too much churn.
>
I haven't gone through them all yet but it doesn't seem to trigger as
often as GCC. I think there are only 22 files with a problem across arm,
arm64, and x86_64 allyesconfig.
> > > > ---
> > > > drivers/mtd/ubi/wl.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
> > > > index 40f838d54b0f..2709dc02fc24 100644
> > > > --- a/drivers/mtd/ubi/wl.c
> > > > +++ b/drivers/mtd/ubi/wl.c
> > > > @@ -1517,7 +1517,7 @@ int ubi_bitflip_check(struct ubi_device *ubi, int pnum, int force)
> > > > mutex_unlock(&ubi->buf_mutex);
> > > > }
> > > >
> > > > - if (err == UBI_IO_BITFLIPS || force) {
> > > > + if (force || err == UBI_IO_BITFLIPS) {
> > > > /*
> > > > * Okay, bit flip happened, let's figure out what we can do.
> > > > */
> > > >
> > >
> > > Good catch, Dan!
> > > I thought gcc is supposed to find such issues too. :-/
> >
> > This isn't the first time GCC hasn't caught something...
> >
> > https://lore.kernel.org/lkml/20190221222123.GC6474@magnolia/
>
> Compilers are not perfect. :-)
Would make everyone's life a lot better if they were :)
Nathan
>
> Thanks,
> //richard
>
>
