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

On Thu, Aug 06, 2020 at 07:17:43PM +0100, Edward Cree wrote:

On 06/08/2020 00:48, kernel test robot wrote:

quoted

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 <redacted>

All errors (new ones prefixed by >>):

   microblaze-linux-ld: drivers/net/ethernet/sfc/ef100_nic.o: in function `ef100_process_design_param':

quoted

quoted

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);
}

Your proposed function is an exact replicate of do_div() and thus doesn't
make much sense. Also, in your case, divisor is a 64-bit value, which is
causing the problem to start with. You could try something like

	if (reader->value > EFX_MIN_DMAQ_SIZE || EFX_MIN_DMAQ_SIZE % (u32)reader->value)

If EFX_MIN_DMAQ_SIZE is indeed known to be a power of 2, you could also use
the knowledge that a 2^n value can only be divided by a smaller 2^n value,
meaning that reader->value must have exactly one bit set. This would also
avoid divide-by-0 issues if reader->value can be 0.

	if (reader->value > EFX_MIN_DMAQ_SIZE || hweight64(reader->value) != 1)

Guenter