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    SubjectRe: [PATCH] compiler, clang: Add always_inline attribute to inline
    On Tue, 20 Jun 2017, Mark Rutland wrote:

    > As with my reply to David, my preference would be that we:
    >
    > 1) Align compiler-clang.h with the compiler-gcc.h inlining behaviour, so
    > that things work by default.
    >
    > 2) Fix up the arm64 core code (and drivers for architected / common
    > peripherals) to use __always_inline where we always require inlining.
    >
    > 3) Have arm64 select CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING, and have
    > people test-build configurations with CONFIG_OPTIMIZE_INLINING, with
    > both GCC and clang.
    >
    > 4) Fix up drivers, etc, as appropriate.
    >
    > 5) Once that's largely stable, and if there's a benefit, have arm64
    > select CONFIG_OPTIMIZE_INLINING by default.
    >
    > That should avoid undue breakage, while enabling this ASAP.
    >

    Sounds good, but I think we should simply deal with the
    __attribute__((unused)) needed for clang as part of compiler-gcc.h by
    simply adding it to the inline override there to avoid duplicated code.

    diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
    --- a/include/linux/compiler-clang.h
    +++ b/include/linux/compiler-clang.h
    @@ -15,11 +15,3 @@
    * with any version that can compile the kernel
    */
    #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
    -
    -/*
    - * GCC does not warn about unused static inline functions for
    - * -Wunused-function. This turns out to avoid the need for complex #ifdef
    - * directives. Suppress the warning in clang as well.
    - */
    -#undef inline
    -#define inline inline __attribute__((unused)) notrace
    diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
    index 0efef9cf014f..71fe0994cf1a 100644
    --- a/include/linux/compiler-gcc.h
    +++ b/include/linux/compiler-gcc.h
    @@ -66,18 +66,22 @@

    /*
    * Force always-inline if the user requests it so via the .config,
    - * or if gcc is too old:
    + * or if gcc is too old.
    + * GCC does not warn about unused static inline functions for
    + * -Wunused-function. This turns out to avoid the need for complex #ifdef
    + * directives. Suppress the warning in clang as well by using "unused"
    + * function attribute, which is redundant but not harmful for gcc.
    */
    #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
    -#define inline inline __attribute__((always_inline)) notrace
    -#define __inline__ __inline__ __attribute__((always_inline)) notrace
    -#define __inline __inline __attribute__((always_inline)) notrace
    +#define inline inline __attribute__((always_inline,unused)) notrace
    +#define __inline__ __inline__ __attribute__((always_inline,unused)) notrace
    +#define __inline __inline __attribute__((always_inline,unused)) notrace
    #else
    /* A lot of inline functions can cause havoc with function tracing */
    -#define inline inline notrace
    -#define __inline__ __inline__ notrace
    -#define __inline __inline notrace
    +#define inline inline __attribute__((unused)) notrace
    +#define __inline__ __inline__ __attribute__((unused)) notrace
    +#define __inline __inline __attribute__((unused)) notrace
    #endif

    #define __always_inline inline __attribute__((always_inline))
    \
     
     \ /
      Last update: 2017-06-21 01:13    [W:3.642 / U:0.360 seconds]
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