Re: [paulmck-rcu:dev.2024.05.18a 44/51] update.c:undefined reference to `cmpxchg_emu_u8'

[Paul E. McKenney]

On Wed, May 29, 2024 at 03:54:26PM +0800, Yujie Liu wrote:
> On Tue, May 28, 2024 at 12:26:43PM -0700, Paul E. McKenney wrote:
> > On Mon, May 27, 2024 at 01:25:58PM +0800, kernel test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2024.05.18a
> > > head:   0e3eb8082184e066eb389f5e6f9c7b8c2d452d66
> > > commit: c48887df74a95090e633a29ffbcef00b71cdab66 [44/51] rcu-tasks: Remove open-coded one-byte cmpxchg() emulation
> > > config: um-allyesconfig (https://download.01.org/0day-ci/archive/20240527/202405271352.XYjxKyUi-lkp@xxxxxxxxx/config)
> > > compiler: gcc-13 (Ubuntu 13.2.0-4ubuntu3) 13.2.0
> > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240527/202405271352.XYjxKyUi-lkp@xxxxxxxxx/reproduce)
> > > 
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202405271352.XYjxKyUi-lkp@xxxxxxxxx/
> > > 
> > > All errors (new ones prefixed by >>):
> > > 
> > >    /usr/bin/ld: kernel/rcu/update.o: in function `rcu_trc_cmpxchg_need_qs':
> > > >> update.c:(.text+0x27d5): undefined reference to `cmpxchg_emu_u8'
> > >    /usr/bin/ld: kernel/rcu/update.o: in function `trc_read_check_handler':
> > >    update.c:(.text+0x2839): undefined reference to `cmpxchg_emu_u8'
> > > >> /usr/bin/ld: update.c:(.text+0x2882): undefined reference to `cmpxchg_emu_u8'
> > >    /usr/bin/ld: kernel/rcu/update.o: in function `trc_inspect_reader':
> > >    update.c:(.text+0x52ce): undefined reference to `cmpxchg_emu_u8'
> > >    /usr/bin/ld: update.c:(.text+0x5330): undefined reference to `cmpxchg_emu_u8'
> > >    /usr/bin/ld: kernel/rcu/update.o:update.c:(.text+0x5933): more undefined references to `cmpxchg_emu_u8' follow
> > > >> collect2: error: ld returned 1 exit status
> > 
> > Good catch!!!
> > 
> > Does the patch below clear this up?
> 
> The patch below will select ARCH_NEED_CMPXCHG_1_EMU by default on um
> arch, so that cmpxchg-emu.o can be built, and it fixes the link error
> for me.
> 
> Tested-by: Yujie Liu <yujie.liu@xxxxxxxxx>

Thank you!  I will apply your Tested-by on my next rebase.

							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 47450c70303a11da1bd650403844ad9e688f05a4
> > Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Date:   Tue May 28 12:15:06 2024 -0700
> > 
> >     um: Emulate one-byte cmpxchg
> >     
> >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on um.
> >     
> >     Reported-by: kernel test robot <lkp@xxxxxxxxx>
> >     Closes: https://lore.kernel.org/all/202405271352.XYjxKyUi-lkp@xxxxxxxxx/
> >     Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> >     Cc: Richard Weinberger <richard@xxxxxx>
> >     Cc: Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx>
> >     Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> >     Cc: <linux-um@xxxxxxxxxxxxxxxxxxx>
> > 
> > diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> > index 93a5a8999b07e..5fc55e1d71122 100644
> > --- a/arch/um/Kconfig
> > +++ b/arch/um/Kconfig
> > @@ -11,6 +11,7 @@ config UML
> >  	select ARCH_HAS_KCOV
> >  	select ARCH_HAS_STRNCPY_FROM_USER
> >  	select ARCH_HAS_STRNLEN_USER
> > +	select ARCH_NEED_CMPXCHG_1_EMU
> >  	select ARCH_NO_PREEMPT
> >  	select HAVE_ARCH_AUDITSYSCALL
> >  	select HAVE_ARCH_KASAN if X86_64
> >