linux-kernel - Re: [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f

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Message-ID: <cab93459-5c44-4049-ae7e-096e37d43737@infradead.org>
Date:   Wed, 7 Feb 2018 10:38:41 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [linus:master] BUILD REGRESSION
 a2e5790d841658485d642196dbb0927303d6c22f

On 02/07/2018 10:13 AM, Linus Torvalds wrote:
> Adding more people for this funky warning from the kbuild robot.
> 
> Something is confused. UD0 is 0f ff, the bytes after that shouldn't
> matter. But I guess they can be interpreted as modrm bytes, and
> somebody started doing that.
> 
> That said, intel only _documents_ UD2 (0f 0b).

Intel Order Number: 325383-064US, October 2017, documents UD0, UD1, and UD2.
Section A.2.5, Table A-1, says:

Use the 0F0B opcode (UD2 instruction), the 0FB9H opcode (UD1 instruction), or the 0FFFH opcode (UD0 instruction) when deliberately trying to generate an invalid opcode exception (#UD).

Could this regression be a result of:

commit f5b5fab1780c98b74526dbac527574bd02dc16f8
Author: Randy Dunlap <rdunlap@...radead.org>
Date:   Mon Dec 11 10:38:36 2017 -0800

    x86/decoder: Fix and update the opcodes map
    
    Update x86-opcode-map.txt based on the October 2017 Intel SDM publication.
    Fix INVPID to INVVPID.
    Add UD0 and UD1 instruction opcodes.


> Maybe we should avoid using UD0/UD1 entirely.
> 
>               Linus
> 
> On Wed, Feb 7, 2018 at 3:44 AM, kbuild test robot
> <fengguang.wu@...el.com> wrote:
>> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master
>> branch HEAD: a2e5790d841658485d642196dbb0927303d6c22f  Merge branch 'akpm' (patches from Andrew)
>>
>> Regressions in current branch:
>>
>> arch/x86/tools/insn_decoder_test: warning: ffffffff810010d7:    0f ff eb                ud0    %ebx,%ebp
>> arch/x86/tools/insn_decoder_test: warning: ffffffff81001152:    0f ff bf 09 00 00 00    ud0    0x9(%rdi),%edi
>> arch/x86/tools/insn_decoder_test: warning: ffffffff81001275:    0f ff eb                ud0    %ebx,%ebp
>> arch/x86/tools/insn_decoder_test: warning: ffffffff810013fd:    0f ff bf 09 00 00 00    ud0    0x9(%rdi),%edi
>> arch/x86/tools/insn_decoder_test: warning: ffffffff81001499:    0f ff bf 09 00 00 00    ud0    0x9(%rdi),%edi
>> arch/x86/tools/insn_decoder_test: warning: ffffffff812296eb:    0f ff e8                ud0    %eax,%ebp


-- 
~Randy