netdev - Re: [net-next:master 488/665] verifier.c:undefined reference to `_

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Date:   Sun, 12 Nov 2017 09:34:18 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Alexei Starovoitov <ast@...com>
Cc:     kbuild-all@...org, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [net-next:master 488/665] verifier.c:undefined reference to
 `__multi3'

On Sun, Nov 12, 2017 at 09:23:52AM +0800, Alexei Starovoitov wrote:
>On 11/12/17 9:18 AM, Fengguang Wu wrote:
>> On Sun, Nov 12, 2017 at 09:14:14AM +0800, Alexei Starovoitov wrote:
>>> On 11/12/17 8:23 AM, kbuild test robot wrote:
>>>> tree:
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git
>>>> master
>>>> head:   7c5556decd0a629e9ee02e93653f75ba7b7da03c
>>>> commit: 638f5b90d46016372a8e3e0a434f199cc5e12b8c [488/665] bpf:
>>>> reduce verifier memory consumption
>>>> config: mips-64r6el_defconfig (attached as .config)
>>>> compiler: mips64el-linux-gnuabi64-gcc (Debian 7.2.0-11) 7.2.0
>>>> reproduce:
>>>>         git checkout 638f5b90d46016372a8e3e0a434f199cc5e12b8c
>>>>         # save the attached .config to linux build tree
>>>>         make.cross ARCH=mips
>>>>
>>>> All errors (new ones prefixed by >>):
>>>>
>>>>    kernel/bpf/verifier.o: In function `realloc_verifier_state.isra.19':
>>>>>> verifier.c:(.text+0x36fc): undefined reference to `__multi3'
>>>
>>> that's a known issue with gcc 7 on mips that is "optimizing"
>>> normal 64-bit multiply into 128-bit variant.
>>> Nothing to fix on the kernel side.
>>
>> Good to know that! Do you think it a good idea to blacklist __multi3
>> errors in mips builds?
>
>I would do so. yes.

OK.

>Though digging further this function was added to
>arch/sparc/lib/multi3.S
>since gcc doing the same "optimization" there.
>Adding asm code doesn't look right to me. I'd rather push
>gcc folks to avoid such codegen.

Sure, I just forwarded the original report to GCC list.

Thanks,
Fengguang