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Date:   Tue, 12 Jan 2021 13:32:26 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     syzbot <syzbot+76880518931d755473cf@syzkaller.appspotmail.com>
Cc:     linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        clang-built-linux@googlegroups.com,
        Dmitry Vyukov <dvyukov@google.com>,
        Marco Elver <elver@google.com>
Subject: Re: upstream build error (12)
Message-ID: <20210112203226.GA1055929@ubuntu-m3-large-x86>
References: <0000000000004a33a005b8b8eaab@google.com>
 <20210112194058.GA200254@ubuntu-m3-large-x86>
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On Tue, Jan 12, 2021 at 12:40:58PM -0700, Nathan Chancellor wrote:
> On Tue, Jan 12, 2021 at 11:20:27AM -0800, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    e609571b Merge tag 'nfs-for-5.11-2' of git://git.linux-nfs..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15965a00d00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=6157970d0a91b812
> > dashboard link: https://syzkaller.appspot.com/bug?extid=76880518931d755473cf
> > compiler:       clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+76880518931d755473cf@syzkaller.appspotmail.com
> > 
> > clang-11: error: unable to execute command: Aborted (core dumped)
> > clang-11: error: clang frontend command failed due to signal (use -v to see invocation)
> > 
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> Would it be possible for clang-built-linux@googlegroups.com to be CC'd
> when there is a build error and the compiler is clang? Especially if
> clang is hitting an assertion.

I cannot reproduce this with clang 11.0.1. I did a reverse bisect on
LLVM and found commit 4b0aa5724fea ("Change the INLINEASM_BR MachineInstr
to be a non-terminating instruction.") as the fix (which makes sense,
that commit has direct kernel implications). It is probably worth
upgrading syzkaller's clang to 11.0.1, where I have not seen any
assertions across all of the configurations that I test.

Ccing Dmitry and Marco directly.

Cheers,
Nathan