linux-kernel - Re: [PATCH] arm64: fix unreachable code issue with cmpxchg

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Date:   Mon, 9 Sep 2019 14:06:36 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Murray <andrew.murray@....com>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] arm64: fix unreachable code issue with cmpxchg

On Mon, Sep 9, 2019 at 1:21 PM Arnd Bergmann <arnd@...db.de> 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@...gle.com>

>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/arm64/include/asm/cmpxchg.h | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
> index a1398f2f9994..fd64dc8a235f 100644
> --- a/arch/arm64/include/asm/cmpxchg.h
> +++ b/arch/arm64/include/asm/cmpxchg.h
> @@ -19,7 +19,7 @@
>   * acquire+release for the latter.
>   */
>  #define __XCHG_CASE(w, sfx, name, sz, mb, nop_lse, acq, acq_lse, rel, cl)      \
> -static inline u##sz __xchg_case_##name##sz(u##sz x, volatile void *ptr)                \
> +static __always_inline u##sz __xchg_case_##name##sz(u##sz x, volatile void *ptr)\
>  {                                                                              \
>         u##sz ret;                                                              \
>         unsigned long tmp;                                                      \
> @@ -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)                       \
>  {                                                                      \
> @@ -103,8 +103,9 @@ __XCHG_GEN(_mb)
>  #define arch_xchg_release(...) __xchg_wrapper(_rel, __VA_ARGS__)
>  #define arch_xchg(...)         __xchg_wrapper( _mb, __VA_ARGS__)
>
> -#define __CMPXCHG_CASE(name, sz)                       \
> -static inline u##sz __cmpxchg_case_##name##sz(volatile void *ptr,      \
> +#define __CMPXCHG_CASE(name, sz)                                       \
> +static __always_inline u##sz                                           \
> +__cmpxchg_case_##name##sz(volatile void *ptr,                          \
>                                               u##sz old,                \
>                                               u##sz new)                \
>  {                                                                      \
> @@ -148,7 +149,7 @@ __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)                    \
> @@ -230,7 +231,7 @@ __CMPXCHG_GEN(_mb)
>  })
>
>  #define __CMPWAIT_CASE(w, sfx, sz)                                     \
> -static inline void __cmpwait_case_##sz(volatile void *ptr,             \
> +static __always_inline void __cmpwait_case_##sz(volatile void *ptr,    \
>                                        unsigned long val)               \
>  {                                                                      \
>         unsigned long tmp;                                              \
> @@ -255,7 +256,7 @@ __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
>
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-- 
Thanks,
~Nick Desaulniers