Re: [v8] misc: pci_endpoint_test: Fix overflow of bar_size

[Hans Zhang]

On 2025/1/9 14:29, Arnd Bergmann wrote:
> > On 2025/1/8 22:13, Niklas Cassel wrote:
> > > > > Ok. Looking at do_div(), it seems to be the correct API to use
> > > > > for this problem. Just change bar_size type to u64 (instead of casting)
> > > > > and use do_div() ? That is how it is seems to be used in other drivers.
> > > >
> > > > I think using div_u64_rem() instead of do_div() would make this
> > > > more readable as this is always an inline function, so the type can
> > > > remain resource_size_t, and the division gets optimized well when
> > > > that is a 32-bit type.
> > >
> > > After patch 1/2, we no longer care about the remainder, so I guess
> > > div64_u64() is the correct function to use then?
>
> div_u64() is the correct interface here, div64_u64() is the
> even slower version where both arguments are 64-bit wide.
>
> >   >> drivers/misc/pci_endpoint_test.c:311:11: warning: comparison of
> > distinct pointer types ('typeof ((bar_size)) *' (aka 'unsigned int *')
> > and 'uint64_t *' (aka 'unsigned long long *'))
> > [-Wcompare-distinct-pointer-types]
> >        311 |         remain = do_div(bar_size, buf_size);
> >            |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~
>
> You don't use div_u64() or div64_u64() here, do_div() is the macro
> version that must be called with a 64-bit argument.
>
>      Arnd

Thank you so much Niklas and Arnd.

Best regards
Hans