Re: [PATCH] [v2] arm64: fix unreachable code issue with cmpxchg

[Nathan Chancellor]

On Tue, Sep 10, 2019 at 01:56:22PM +0200, Arnd Bergmann wrote:
> On arm64 build with clang, sometimes the __cmpxchg_mb is not inlined
> when CONFIG_OPTIMIZE_INLINING is set.
> Clang then fails a compile-time assertion, because it cannot tell at
> compile time what the size of the argument is:
> 
> mm/memcontrol.o: In function `__cmpxchg_mb':
> memcontrol.c:(.text+0x1a4c): undefined reference to `__compiletime_assert_175'
> memcontrol.c:(.text+0x1a4c): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `__compiletime_assert_175'
> 
> Mark all of the cmpxchg() style functions as __always_inline to
> ensure that the compiler can see the result.
> 
> Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> Link: https://github.com/ClangBuiltLinux/linux/issues/648
> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> Reviewed-by: Andrew Murray <andrew.murray@xxxxxxx>
> Tested-by: Andrew Murray <andrew.murray@xxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> v2: skip unneeded changes, as suggested by Andrew Murray
> ---
>  arch/arm64/include/asm/cmpxchg.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
> index a1398f2f9994..f9bef42c1411 100644
> --- a/arch/arm64/include/asm/cmpxchg.h
> +++ b/arch/arm64/include/asm/cmpxchg.h
> @@ -62,7 +62,7 @@ __XCHG_CASE( ,  ,  mb_, 64, dmb ish, nop,  , a, l, "memory")
>  #undef __XCHG_CASE
>  
>  #define __XCHG_GEN(sfx)							\
> -static inline unsigned long __xchg##sfx(unsigned long x,		\
> +static __always_inline  unsigned long __xchg##sfx(unsigned long x,	\
>  					volatile void *ptr,		\
>  					int size)			\
>  {									\
> @@ -148,7 +148,7 @@ __CMPXCHG_DBL(_mb)
>  #undef __CMPXCHG_DBL
>  
>  #define __CMPXCHG_GEN(sfx)						\
> -static inline unsigned long __cmpxchg##sfx(volatile void *ptr,		\
> +static __always_inline unsigned long __cmpxchg##sfx(volatile void *ptr,	\
>  					   unsigned long old,		\
>  					   unsigned long new,		\
>  					   int size)			\
> @@ -255,7 +255,7 @@ __CMPWAIT_CASE( ,  , 64);
>  #undef __CMPWAIT_CASE
>  
>  #define __CMPWAIT_GEN(sfx)						\
> -static inline void __cmpwait##sfx(volatile void *ptr,			\
> +static __always_inline void __cmpwait##sfx(volatile void *ptr,		\
>  				  unsigned long val,			\
>  				  int size)				\
>  {									\
> -- 
> 2.20.0
> 

Looks like the arm64 pull request happened without this patch so clang
all{mod,yes}config builds are broken. Did the maintainers have any
further comments on it or could this make it in with the next one?

Cheers,
Nathan