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

[Daniel Golle]

On 7 March 2024 09:17:45 UTC, Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>> > ---
>> > 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@xxxxxxxxxxxxxx/

>
>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

> It's fine if you're
>able to manually create your own .configs to work around build breakage.
>But if you're doing automated testing at scale then it's a show stopper.
>Could we please fix it.
>
>regards,
>dan carpenter
>
>
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