Re: ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko] undefined!

[Geert Uytterhoeven]

On Mon, May 31, 2021 at 2:05 AM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> On 5/29/21 4:25 PM, kernel test robot wrote:
> > First bad commit (maybe != root cause):
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   df8c66c4cfb91f2372d138b9b714f6df6f506966
> > commit: a9770eac511ad82390b9f4a3c1728e078c387ac7 net: mdio: Move MDIO drivers into a new subdirectory
> > date:   9 months ago
> > config: sh-allmodconfig (attached as .config)
> > compiler: sh4-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
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a9770eac511ad82390b9f4a3c1728e078c387ac7
> >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >         git fetch --no-tags linus master
> >         git checkout a9770eac511ad82390b9f4a3c1728e078c387ac7
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=sh
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> >
> > All errors (new ones prefixed by >>, old ones prefixed by <<):
> >
> >>> ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko] undefined!
>
> Just a comment here.  kernel test robot has reported this issue
> 5 times in 2021 that I know of -- and I could have missed some.
>
> I see that Geert recently (June 2020) reverted the
> EXPORT_SYMBOL(__delay) in arch/sh/lib/delay.c, with this comment:
>
>     __delay() is an internal implementation detail on several architectures.
>     Drivers should not call __delay() directly, as it has non-standardized
>     semantics, or may not even exist.
>     Hence there is no need to export __delay() to modules.
>
>     See also include/asm-generic/delay.h:
>
>         /* Undefined functions to get compile-time errors */
>         ...
>         extern void __delay(unsigned long loops);
>
> However, s/several architectures/all but one architecture: SH/.
> All architectures except for SH provide either an exported function,
> an inline function, or a macro for __delay(). Yeah, they probably
> don't all do the same delay.

Hence it must not be used by drivers, as it might give the false assumption
of working everywhere.  While drivers/net/mdio/mdio-cavium is
platform-specific, code might be copied in a new driver, less restricted
to a specific platform.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds