Re: mips64-linux-ld: div64.c:undefined reference to `__multi3'

Maciej W. Rozycki
2026-01-14T06:19:09Z

On Tue, 13 Jan 2026, David Laight wrote:

> > All errors (new ones prefixed by >>):
> >
> > mips64-linux-ld: lib/math/div64.o: in function `mul_u64_add_u64_div_u64':
> > div64.c:(.text+0x84): undefined reference to `__multi3'
> > >> mips64-linux-ld: div64.c:(.text+0x11c): undefined reference to `__multi3'
> >
>
> This looks like a bug in the mips 'port'.
> arch/mips/lib/multi3.c has the comment:
>
> /*
> * GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for
> * that specific case only we implement that intrinsic here.
> *
> * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
> */
> #if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8)
>
> So this code is excluded for gcc 8.5 but the compiler is generating the call.
>
> Looking at the git log for that file there is a comment that includes:
> "we wouldn't expect any calls to __multi3 to be generated from
> kernel code".
> Not true....
> Not sure why the link didn't fail before though, something subtle must
> have changed.
>
> I think the fix is just to remove the gcc version check.

Or rather fix the version check. The GCC fix went in with GCC 10:

$ git log -1 --pretty=oneline 48b2123f6336
48b2123f6336ba6c06846d7c8b60bd14eaeae7ec re PR target/82981 (unnecessary __multi3 call for mips64r6 linux kernel)
$ git show 48b2123f6336:gcc/BASE-VER
10.0.0
$

I don't know why the PR got it all wrong; I've fixed it now.

Maciej