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

[Nick Desaulniers]

On Mon, Sep 9, 2019 at 2:06 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:
>
> On Mon, Sep 9, 2019 at 1:21 PM Arnd Bergmann <arnd@xxxxxxxx> 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>

Also, I think a Link tag may be appropriate as I believe it fixes this report:

Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/648

>
> >
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> >  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



-- 
Thanks,
~Nick Desaulniers