Re: [PATCH] mtd: sm_ftl: fix NULL pointer warning

[Arnd Bergmann]

On Wed, Jan 8, 2020 at 9:15 AM Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote:
>
> Hi Arnd,
>
> Arnd Bergmann <arnd@xxxxxxxx> wrote on Tue,  7 Jan 2020 22:24:52 +0100:
>
> > With gcc -O3, we get a new warning:
> >
> > In file included from arch/arm64/include/asm/processor.h:28,
> >                  from drivers/mtd/sm_ftl.c:8:
> > In function 'memset',
> >     inlined from 'sm_read_sector.constprop' at drivers/mtd/sm_ftl.c:250:3:
> > include/linux/string.h:411:9: error: argument 1 null where non-null expected [-Werror=nonnull]
> >   return __builtin_memset(p, c, size);
> >
> > From all I can tell, this cannot happen (the function is called
> > either with a NULL buffer or with a -1 block number but not both),
> > but adding a check makes it more robust and avoids the warning.
> >
> > Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> >  drivers/mtd/sm_ftl.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mtd/sm_ftl.c b/drivers/mtd/sm_ftl.c
> > index 4744bf94ad9a..b9f272408c4d 100644
> > --- a/drivers/mtd/sm_ftl.c
> > +++ b/drivers/mtd/sm_ftl.c
> > @@ -247,7 +247,8 @@ static int sm_read_sector(struct sm_ftl *ftl,
> >
> >       /* FTL can contain -1 entries that are by default filled with bits */
> >       if (block == -1) {
> > -             memset(buffer, 0xFF, SM_SECTOR_SIZE);
> > +             if (buffer)
> > +                     memset(buffer, 0xFF, SM_SECTOR_SIZE);
> >               return 0;
> >       }
> >
>
> What about a simpler form:
>
>         if (buffer && block == -1) { ...
>
> Instead of an additional indentation level?

That would fail to return early from the function if we ever get block==-1
and buffer==NULL, probably resulting is worse problems later.

       Arnd