Re: [linux-next:master 13398/13940] drivers/net/ethernet/sfc/ef100_nic.c:610: undefined reference to `__umoddi3'

[Edward Cree <ecree@solarflare.com>]

On 06/08/2020 00:48, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   d15fe4ec043588beee823781602ddb51d0bc84c8
> commit: adcfc3482ffff813fa2c34e5902005853f79c2aa [13398/13940] sfc_ef100: read Design Parameters at probe time
> config: microblaze-randconfig-r032-20200805 (attached as .config)
> compiler: microblaze-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout adcfc3482ffff813fa2c34e5902005853f79c2aa
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=microblaze 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>    microblaze-linux-ld: drivers/net/ethernet/sfc/ef100_nic.o: in function `ef100_process_design_param':
>>> drivers/net/ethernet/sfc/ef100_nic.c:610: undefined reference to `__umoddi3'
>    605			/* Our TXQ and RXQ sizes are always power-of-two and thus divisible by
>    606			 * EFX_MIN_DMAQ_SIZE, so we just need to check that
>    607			 * EFX_MIN_DMAQ_SIZE is divisible by GRANULARITY.
>    608			 * This is very unlikely to fail.
>    609			 */
>  > 610			if (EFX_MIN_DMAQ_SIZE % reader->value) {
So, this is (unsigned long) % (u64), whichI guess doesn't go quite
 as smoothly 32-bit microcontrollers (though the thought of plugging
 a 100-gig smartNIC into a microblaze boggles the mind a little ;).
And none of the math64.h functions seem to have the shape we want —
 div_u64_rem() wants to write the remainder through a pointer, and
 do_div() wants to modify the dividend (which is a constant in this
 case).  So whatever I do, it's gonna be ugly :(

Maybe I should add a

static inline u32 mod_u64(u64 dividend, u32 divisor)
{
        return do_div(dividend, divisor);
}

to include/linux/math64.h?  At least that way the ugly is centralised
 in the header file.