Re: arm-linux-gnueabihf-ld: kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to `__bad_cmpxchg' follow

["Paul E. McKenney" <paulmck@kernel.org>]

On Thu, May 30, 2024 at 04:30:53PM -0700, Nathan Chancellor wrote:
> On Thu, May 30, 2024 at 03:05:21PM -0700, Paul E. McKenney wrote:
> > On Thu, May 30, 2024 at 02:52:48PM -0700, Nathan Chancellor wrote:
> > > On Thu, May 30, 2024 at 10:24:05AM -0700, Paul E. McKenney wrote:
> > > > And for an untested first attempt at a fix.
> > > > 
> > > > What did I mess up this time?  ;-)
> > > 
> > > An include for cmpxchg-emu.h ;)
> > > 
> > >   In file included from arch/arm/include/asm/atomic.h:16,
> > >                    from include/linux/atomic.h:7,
> > >                    from include/asm-generic/bitops/lock.h:5,
> > >                    from arch/arm/include/asm/bitops.h:245,
> > >                    from include/linux/bitops.h:63,
> > >                    from include/linux/log2.h:12,
> > >                    from kernel/bounds.c:13:
> > >   arch/arm/include/asm/cmpxchg.h: In function '__cmpxchg':
> > >   arch/arm/include/asm/cmpxchg.h:167:26: error: implicit declaration of function 'cmpxchg_emu_u8' [-Werror=implicit-function-declaration]
> > >     167 |                 oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > >         |                          ^~~~~~~~~~~~~~
> > >   cc1: some warnings being treated as errors
> > 
> > Good catch, and thank you for testing this!  Does the updated version
> > shown below do better?
> 
> Yes, that matches what I tested locally before I replied initially.

Very good!  May I please add your Tested-by?

							Thanx, Paul

> Thanks for the quick fix!
> 
> Cheers,
> Nathan
> 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 74e3470afacaa9d2f37db4773a5fef887ac4ef56
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Thu May 30 10:11:31 2024 -0700
> > 
> >     ARM: Emulate one-byte cmpxchg
> >     
> >     Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> >     with ARCH < ARMv6K.
> >     
> >     [ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]
> >     
> >     Reported-by: Mark Brown <broonie@kernel.org>
> >     Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
> >     Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> >     Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
> >     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> >     Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
> >     Cc: Arnd Bergmann <arnd@arndb.de>
> >     Cc: Andrew Davis <afd@ti.com>
> >     Cc: Andrew Morton <akpm@linux-foundation.org>
> >     Cc: Linus Walleij <linus.walleij@linaro.org>
> >     Cc: Eric DeVolder <eric.devolder@oracle.com>
> >     Cc: Rob Herring <robh@kernel.org>
> >     Cc: <linux-arm-kernel@lists.infradead.org>
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index ee5115252aac4..a867a7d967aa5 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -34,6 +34,7 @@ config ARM
> >  	select ARCH_MIGHT_HAVE_PC_PARPORT
> >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> > +	select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
> >  	select ARCH_SUPPORTS_ATOMIC_RMW
> >  	select ARCH_SUPPORTS_CFI_CLANG
> >  	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
> > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> > index 44667bdb4707a..a428e06fe94ee 100644
> > --- a/arch/arm/include/asm/cmpxchg.h
> > +++ b/arch/arm/include/asm/cmpxchg.h
> > @@ -5,6 +5,7 @@
> >  #include <linux/irqflags.h>
> >  #include <linux/prefetch.h>
> >  #include <asm/barrier.h>
> > +#include <linux/cmpxchg-emu.h>
> >  
> >  #if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
> >  /*
> > @@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
> >  	prefetchw((const void *)ptr);
> >  
> >  	switch (size) {
> > -#ifndef CONFIG_CPU_V6	/* min ARCH >= ARMv6K */
> > +#ifdef CONFIG_CPU_V6	/* min ARCH < ARMv6K */
> > +	case 1:
> > +		oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
> > +		break;
> > +#else /* min ARCH >= ARMv6K */
> >  	case 1:
> >  		do {
> >  			asm volatile("@ __cmpxchg1\n"