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SubjectRe: [PATCH] [v2] arm64: fix unreachable code issue with cmpxchg
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@google.com>
> Reported-by: Nathan Chancellor <natechancellor@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/648
> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
> Tested-by: Nathan Chancellor <natechancellor@gmail.com>
> Reviewed-by: Andrew Murray <andrew.murray@arm.com>
> Tested-by: Andrew Murray <andrew.murray@arm.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> 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

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