linux-kernel - Re: ld.lld: error: undefined symbol: _

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Message-ID: <CAC2txAZpGooRGSxh4x9T7Y9b4OvfePx5=YuJoyaSwk1M_EvwtQ@mail.gmail.com>
Date:   Thu, 1 Dec 2022 21:39:22 +0300
From:   Mikhail Zhilkin <csharper2005@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Nathan Chancellor <nathan@...nel.org>
Cc:     kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        NOGUCHI Hiroshi <drvlabo@...il.com>
Subject: Re: ld.lld: error: undefined symbol: __udivdi3

Hi Miquèl, Nathan,

On 12/1/2022 7:13 PM, Miquel Raynal wrote:
> Hi Nathan,
>
> nathan@...nel.org wrote on Thu, 1 Dec 2022 09:00:57 -0700:
>
>> On Thu, Dec 01, 2022 at 09:16:10AM +0100, Miquel Raynal wrote:
>>> Hi Mikhail, Hiroshi,
>>>
>>> lkp@...el.com wrote on Thu, 1 Dec 2022 01:46:36 +0800:
>>>
>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>>>> head:   01f856ae6d0ca5ad0505b79bf2d22d7ca439b2a1
>>>> commit: 9b78ef0c7997052e9eaa0f7a4513d546fa17358c mtd: parsers: add support for Sercomm partitions
>>>> date:   6 months ago
>>>> config: mips-randconfig-r033-20221128
>>>> compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 6e4cea55f0d1104408b26ac574566a0e4de48036)
>>>> 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
>>>>         # install mips cross compiling tool for clang build
>>>>         # apt-get install binutils-mipsel-linux-gnu
>>>>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9b78ef0c7997052e9eaa0f7a4513d546fa17358c
>>>>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>>>         git fetch --no-tags linus master
>>>>         git checkout 9b78ef0c7997052e9eaa0f7a4513d546fa17358c
>>>>         # save the config file
>>>>         mkdir build_dir && cp config build_dir/.config
>>>>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash
>>>>
>>>> If you fix the issue, kindly add following tag where applicable
>>>> | Reported-by: kernel test robot <lkp@...el.com>
>>>>
>>>> All errors (new ones prefixed by >>):
>>>>
>>>>>> ld.lld: error: undefined symbol: __udivdi3
>>>>    >>> referenced by scpart.c
>>>>    >>>               mtd/parsers/scpart.o:(scpart_parse) in archive drivers/built-in.a
>>>>
>>> Can you please try to reproduce this with a mips toolchain as advised
>>> and send a fix?
>> For what it's worth, this is likely our bug:
>>
>> https://github.com/ClangBuiltLinux/linux/issues/1635
>>
>> It sounds like there are some merged LLVM patches that should help but I
>> guess not based on this report...
> Ah, yeah, thanks a lot for the share.
>
> Cheers, Miquèl

I could reproduce the issue and found that reference to __udivdi3
appears in this function:

static uint32_t scpart_desc_is_valid(struct sc_part_desc *pdesc)
{
        return ((pdesc->part_id != 0xffffffffUL) &&
                (pdesc->part_offs != 0xffffffffUL) &&
                (pdesc->part_bytes != 0xffffffffUL));
}

There is no LLVM compiler error if:

static uint32_t scpart_desc_is_valid(struct sc_part_desc *pdesc)
{
        return (0);
}

Currently I have no ideas where does __udivdi3 come from, because
there's no division here. Should I try to rewrite somehow the function
to avoid the error?
I would greatly appreciate any ideas.

--
Best regards,
Mikhail