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>
Subject: Re: div64.c:(.text.mul_u64_add_u64_div_u64+0x40): undefined reference to `__multi3'
Date: Sat, 21 Mar 2026 09:24:14 +0000 [thread overview]
Message-ID: <20260321092414.542ad642@pumpkin> (raw)
In-Reply-To: <202603211216.YTKRdi1b-lkp@intel.com>
On Sat, 21 Mar 2026 12:48:23 +0800
kernel test robot <lkp@intel.com> wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 42bddab0563fe67882b2722620a66dd98c8dbf33
> commit: 6480241f31f543333ed0c7a209962412461f6e41 lib: add mul_u64_add_u64_div_u64() and mul_u64_u64_div_u64_roundup()
> date: 4 months ago
> config: mips-randconfig-r122-20260321 (https://download.01.org/0day-ci/archive/20260321/202603211216.YTKRdi1b-lkp@intel.com/config)
> compiler: mips64-linux-gcc (GCC) 8.5.0
> sparse: v0.6.5-rc1
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260321/202603211216.YTKRdi1b-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/202603211216.YTKRdi1b-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.mul_u64_add_u64_div_u64+0x40): undefined reference to `__multi3'
>
I thought someone was going to change the #if so that __multi3 was defined
for compilers after (IIRC) 7.1 until at (also IIRC) 10.5.
But for __mips why worry that much - the function is quite small.
Just enable it unconditionally.
While this code only wants the 128bit product of two 64bit integers
(which is a single instruction) the full 128x128 product looks
faster than the fallback code that uses 32bit multiples.
More interesting is sparc64 - where __multi3 can also get called.
That function looks horrid - I presume it is carefully optimised!
Without any comment it is hard to see what it is doing.
(Not helped by me only knowing sparc32 from 1988.)
David
prev parent reply other threads:[~2026-03-21 9:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-21 4:48 div64.c:(.text.mul_u64_add_u64_div_u64+0x40): undefined reference to `__multi3' kernel test robot
2026-03-21 9:24 ` David Laight [this message]
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