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]

On 12/15/21 12:48, Eric W. Biederman wrote:
> Rong Chen <rong.a.chen@xxxxxxxxx> writes:
>
> > On 12/15/21 01:29, Eric W. Biederman wrote:
> > > kernel test robot <lkp@xxxxxxxxx> 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@xxxxxxxxx/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@xxxxxxxxx>
> > > >
> > > > 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?

$ make O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kernel/dumpstack.s
make[1]: Entering directory '/mnt/memdrive/linux/build_dir'
  GEN     Makefile
  CALL    ../scripts/checksyscalls.sh
  CALL    ../scripts/atomic/check-atomics.sh
  DESCEND objtool
  CC      arch/x86/kernel/dumpstack.s
make[1]: Leaving directory '/mnt/memdrive/linux/build_dir'

$ make O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kernel/
make[1]: Entering directory '/mnt/memdrive/linux/build_dir'
  GEN     Makefile
  CALL    ../scripts/checksyscalls.sh
  CALL    ../scripts/atomic/check-atomics.sh
  DESCEND objtool
  CC      arch/x86/kernel/dumpstack.o
arch/x86/kernel/dumpstack.o: warning: objtool: oops_end() falls through 
to next function show_opcodes()
  AR      arch/x86/kernel/built-in.a
make[1]: Leaving directory '/mnt/memdrive/linux/build_dir'

Best Regards,
Rong Chen

> 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