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SubjectRE: [kbuild-all] arch/x86/tools/insn_decoder_test: warning: ffffffff810005ac: 0f ff e9 ud0 %ecx, %ebp
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 [] On Behalf Of Masami
>Sent: Thursday, February 8, 2018 10:34 PM
>To: Wu, Fengguang <>
>Cc: Ingo Molnar <>;; linux-
>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 <> wrote:
>> tree: 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)
>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
>> ---
>> 0-DAY kernel test infrastructure Open Source Technology Center
>> Intel Corporation
>Masami Hiramatsu <>
>kbuild-all mailing list

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