From: David Laight <david.laight.linux@gmail.com>
To: kernel test robot <lkp@intel.com>
Cc: oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Linux Memory Management List <linux-mm@kvack.org>,
Nicolas Pitre <npitre@baylibre.com>,
linux-mips@vger.kernel.org, tsbogend@alpha.franken.de
Subject: Re: mips64-linux-ld: div64.c:undefined reference to `__multi3'
Date: Tue, 13 Jan 2026 21:58:08 +0000 [thread overview]
Message-ID: <20260113215808.135dc8b6@pumpkin> (raw)
In-Reply-To: <20260113200455.3dffe121@pumpkin>
On Tue, 13 Jan 2026 20:04:55 +0000
David Laight <david.laight.linux@gmail.com> wrote:
Resend fixing Thomas's email
> On Wed, 14 Jan 2026 01:59:24 +0800
> kernel test robot <lkp@intel.com> wrote:
>
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head: b71e635feefc852405b14620a7fc58c4c80c0f73
> > commit: d10bb374c41e4c4dced04ae7d2fe2d782a5858a0 lib: mul_u64_u64_div_u64(): optimise the divide code
> > date: 8 weeks ago
> > config: mips-randconfig-r113-20260113 (https://download.01.org/0day-ci/archive/20260114/202601140146.hMLODc6v-lkp@intel.com/config)
> > compiler: mips64-linux-gcc (GCC) 8.5.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260114/202601140146.hMLODc6v-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202601140146.hMLODc6v-lkp@intel.com/
> >
> > 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.
> The code itself just adds the results of four multiply instructions together.
>
> David
prev parent reply other threads:[~2026-01-13 21:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-13 17:59 kernel test robot
2026-01-13 20:04 ` David Laight
2026-01-13 21:58 ` David Laight [this message]
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