[PATCH v2] mtd: ubi: fix NVMEM over UBI volumes on 32-bit systems

[Dan Carpenter]

On Thu, Mar 07, 2024 at 11:42:12AM +0000, Daniel Golle wrote:
> 
> 
> On 7 March 2024 09:17:45 UTC, Dan Carpenter <dan.carpenter at linaro.org> wrote:
> >On Wed, Feb 28, 2024 at 09:45:13AM +0800, Zhihao Cheng wrote:
> >> 在 2024/2/28 8:46, Daniel Golle 写道:
> >> > A compiler warning related to sizeof(int) != 8 when calling do_div()
> >> > is triggered when building on 32-bit platforms.
> >> > Address this by using integer types having a well-defined size.
> >> > 
> >> > Fixes: 3ce485803da1 ("mtd: ubi: provide NVMEM layer over UBI volumes")
> >> > Signed-off-by: Daniel Golle <daniel at makrotopia.org>
> >> > ---
> >> > v2: use size_t for 'bytes_left' variable to match parameter type
> >> > 
> >> >   drivers/mtd/ubi/nvmem.c | 5 ++++-
> >> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >> > 
> >> > diff --git a/drivers/mtd/ubi/nvmem.c b/drivers/mtd/ubi/nvmem.c
> >> > index b7a93c495d172..e68b8589c4279 100644
> >> > --- a/drivers/mtd/ubi/nvmem.c
> >> > +++ b/drivers/mtd/ubi/nvmem.c
> >> > @@ -23,9 +23,12 @@ struct ubi_nvmem {
> >> >   static int ubi_nvmem_reg_read(void *priv, unsigned int from,
> >> >   			      void *val, size_t bytes)
> >> >   {
> >> > -	int err = 0, lnum = from, offs, bytes_left = bytes, to_read;
> >> >   	struct ubi_nvmem *unv = priv;
> >> >   	struct ubi_volume_desc *desc;
> >> > +	size_t bytes_left = bytes;
> >> > +	uint32_t offs, to_read;
> >> There still exist a type truncation assignment 'to_read = bytes_left' below,
> >> although it's safe in logic.
> >
> >Yeah.  As you say, from looking at the logic we know it's safe.
> >
> >    41                  if (to_read > bytes_left)
> >    42                          to_read = bytes_left;
> >
> >Obviously the new value is smaller than the original, so it must fit
> >within a u32 range...
> 
> 
> I've sent v3 of this fix which should be finally be warning free now.
> 
> https://patchwork.ozlabs.org/project/linux-mtd/patch/ff29447dcee834c17e4e1e99725b9454c90136ca.1709178325.git.daniel@makrotopia.org/
> 

Thanks!

> >
> >This bug has been breaking the build since Dec 19.  
> 
> I have a hard time believing that as the offending commit was only applied on Feb 25.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=3ce485803da1b79b2692b6d0c2792829292ad838
> 

Ah...  Okay.  I was looking at the author date.  Not the merge date.  My
bad.

regards,
dan carpenter