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Date: Thu, 30 May 2024 16:30:53 -0700
From: Nathan Chancellor <nathan@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Russell King <linux@armlinux.org.uk>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	open list <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	lkft-triage@lists.linaro.org,
	Linux Regressions <regressions@lists.linux.dev>,
	rcu <rcu@vger.kernel.org>, Dan Carpenter <dan.carpenter@linaro.org>,
	Joel Fernandes <joel@joelfernandes.org>, neeraj.upadhyay@kernel.org,
	John Ogness <john.ogness@linutronix.de>, broonie@kernel.org
Subject: Re: arm-linux-gnueabihf-ld:
 kernel/rcu/update.o:update.c:(.text+0x1cc4): more undefined references to
 `__bad_cmpxchg' follow
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In-Reply-To: <583e2476-50c5-4f9c-85af-f4489a53083b@paulmck-laptop>

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.

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"