RE: [kbuild-all] arch/x86/tools/insn_decoder_test: warning: ffffffff810005ac: 0f ff e9 ud0 %ecx, %ebp

[Hao, Shun]

Thanks Masami, so that explains why a lot of these warnings come out just after 
we upgrading to gcc-7.3 (now the objdump version is 2.30). 
Currently we've already ignore these warnings and won't send this report. 

>-----Original Message-----
>From: kbuild-all [mailto:kbuild-all-bounces@xxxxxxxxxxxx] On Behalf Of Masami
>Hiramatsu
>Sent: Thursday, February 8, 2018 10:34 PM
>To: Wu, Fengguang <fengguang.wu@xxxxxxxxx>
>Cc: Ingo Molnar <mingo@xxxxxxxxxx>; kbuild-all@xxxxxx; linux-
>kernel@xxxxxxxxxxxxxxx
>Subject: Re: [kbuild-all] arch/x86/tools/insn_decoder_test: warning: ffffffff810005ac:
>0f ff e9 ud0 %ecx, %ebp
>
>On Thu, 8 Feb 2018 06:04:45 +0800
>kbuild test robot <fengguang.wu@xxxxxxxxx> wrote:
>
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   7590e37bdaeec25ae325f4ba450be13e2aac6c8d
>> commit: 10c91577d5e631773a6394e14cf60125389b71ae x86/tools: Standardize
>output format of insn_decode_test
>> date:   8 weeks ago
>> config: x86_64-randconfig-s2-02072130 (attached as .config)
>> compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
>> reproduce:
>>         git checkout 10c91577d5e631773a6394e14cf60125389b71ae
>>         # save the attached .config to linux build tree
>>         make ARCH=x86_64
>>
>> All warnings (new ones prefixed by >>):
>>
>>    arch/x86/tools/insn_decoder_test: warning: Found an x86 instruction decoder bug,
>please report this.
>> >> arch/x86/tools/insn_decoder_test: warning: ffffffff810005ac:	0f ff e9
>	ud0    %ecx,%ebp
>
>Does UD0 really take an operand? Hmm, indeed, the latest Intel SDM (December2017)
>says
>
>NOTES:
>1. Some older processors decode the UD0 instruction without a ModR/M byte. As a
>result, those processors would deliver an invalid-
>opcode exception instead of a fault on instruction fetch when the instruction with a
>ModR/M byte (and any implied bytes) would
>cross a page or segment boundary.
>
>and older SDM (e.g. March 2017) says UD0 has no modrm byte.
>It is easy to change x86-opecode-map.txt, but this means this test may fail with older
>objdump...
>
>>
>> ---
>> 0-DAY kernel test infrastructure                Open Source Technology Center
>> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
>
>
>--
>Masami Hiramatsu <mhiramat@xxxxxxxxxx>
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