linux-kernel - Re: [kbuild-all] Re: [ebiederm-user-namespace:signal-for-v5.17 4/12] arch/x86/kernel/dumpstack.o: warning: objtool: oops_end() falls through to next function show

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Date:   Tue, 14 Dec 2021 22:48:32 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Rong Chen <rong.a.chen@...el.com>
Cc:     kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: Re: [kbuild-all] Re: [ebiederm-user-namespace:signal-for-v5.17 4/12] arch/x86/kernel/dumpstack.o: warning: objtool: oops_end() falls through to next function show_opcodes()

Rong Chen <rong.a.chen@...el.com> writes:

> On 12/15/21 01:29, Eric W. Biederman wrote:
>> kernel test robot <lkp@...el.com> writes:
>>
>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git signal-for-v5.17
>>> head:   6b1248798eb6f6d5285db214299996ecc5dc1e6b
>>> commit: 0e25498f8cd43c1b5aa327f373dd094e9a006da7 [4/12] exit: Add and use make_task_dead.
>>> config: x86_64-randconfig-a011-20211213 (https://download.01.org/0day-ci/archive/20211214/202112140949.Uq5sFKR1-lkp@intel.com/config)
>>> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
>>> reproduce (this is a W=1 build):
>>>          # https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git/commit/?id=0e25498f8cd43c1b5aa327f373dd094e9a006da7
>>>          git remote add ebiederm-user-namespace https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git
>>>          git fetch --no-tags ebiederm-user-namespace signal-for-v5.17
>>>          git checkout 0e25498f8cd43c1b5aa327f373dd094e9a006da7
>>>          # save the config file to linux build tree
>>>          mkdir build_dir
>>>          make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kernel/ kernel/ lib/kunit/
>>>
>>> If you fix the issue, kindly add following tag as appropriate
>>> Reported-by: kernel test robot <lkp@...el.com>
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>>>> lib/kunit/kunit-example-test.o: warning: objtool: .text.unlikely: unexpected end of section
>>> --
>>>>> arch/x86/kernel/dumpstack.o: warning: objtool: oops_end() falls through to next function show_opcodes()
>> I am confused.  This change patches objtool to rename
>> rewind_stack_and_do_exit to rewind_stack_and_make_dead in the list
>> global_noreturns in tools/objtool/check.c
>>
>> There is no other change to oops_end other than that renaming.
>>
>> Did the robot somehow mange to run an old version of objtool while
>> building and this get this error?
>>
>> I tried and I am not currently able to reproduce this error.  Do you
>> have any additional pointers on how I might reproduce this?
>
> Hi Eric,
>
> The reproduce step in report based on a full build, I can reproduce
> the warnings with the below command:
>
>   make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

Any chance you could do "make arch/x86/kernel/dumpstack.s" and send it
to me?

I want to see what code is in your oops_end.

It really does not make sense that simply renaming a function would
trigger this error.

I did a full build (on debian 10 with gcc-8.3.0) and I did not manage to
reproduce this.  In a bit I will try with a newer debian and see if I
can get the issue to reproduce.  Still it does not make sense to me
that a simple rename would trigger this error.

Eric