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    SubjectRe: [PATCH 4/7] Compiler Attributes: homogenize __must_be_array
    On Fri, Aug 31, 2018 at 10:05 AM Miguel Ojeda
    <miguel.ojeda.sandonis@gmail.com> wrote:
    >
    > Different definitions of __must_be_array:
    >
    > * gcc: disabled for __CHECKER__
    >
    > * clang: same definition as gcc's, but without __CHECKER__
    >
    > * intel: the comment claims __builtin_types_compatible_p()
    > is unsupported; but icc seems to support it since 13.0.1
    > (released in 2012). See https://godbolt.org/z/S0l6QQ

    Indeed. It seems that if we can't find a contact for ICC, then 13.0.1
    (the oldest version supported by godbolt) is a best effort, IMO. If
    we end up adding patches for minimal compiler versions, maybe v13.0.1
    is a good minimal for ICC. But I would really defer to someone who
    has an install of ICC (not me).

    >
    > Therefore, we can remove all of them and have a single definition
    > in compiler.h
    >
    > Cc: Eli Friedman <efriedma@codeaurora.org>
    > Cc: Christopher Li <sparse@chrisli.org>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Ingo Molnar <mingo@kernel.org>
    > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    > Cc: Arnd Bergmann <arnd@arndb.de>
    > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
    > Cc: Joe Perches <joe@perches.com>
    > Cc: Dominique Martinet <asmadeus@codewreck.org>
    > Cc: Nick Desaulniers <ndesaulniers@google.com>
    > Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
    > ---
    > include/linux/compiler-clang.h | 1 -
    > include/linux/compiler-gcc.h | 7 -------
    > include/linux/compiler-intel.h | 3 ---
    > include/linux/compiler.h | 7 +++++++
    > 4 files changed, 7 insertions(+), 11 deletions(-)
    >
    > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
    > index efda74f4eeba..0aee694d3ab8 100644
    > --- a/include/linux/compiler-clang.h
    > +++ b/include/linux/compiler-clang.h
    > @@ -41,6 +41,5 @@
    > * compilers, like ICC.
    > */
    > #define barrier() __asm__ __volatile__("" : : : "memory")
    > -#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
    > #define __assume_aligned(a, ...) \
    > __attribute__((assume_aligned(a, ## __VA_ARGS__)))
    > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
    > index dbfbecf703f8..66e1eb8822d9 100644
    > --- a/include/linux/compiler-gcc.h
    > +++ b/include/linux/compiler-gcc.h
    > @@ -68,13 +68,6 @@
    > */
    > #define uninitialized_var(x) x = x
    >
    > -#ifdef __CHECKER__
    > -#define __must_be_array(a) 0
    > -#else
    > -/* &a[0] degrades to a pointer: a different type from an array */
    > -#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
    > -#endif
    > -
    > #ifdef RETPOLINE
    > #define __noretpoline __attribute__((indirect_branch("keep")))
    > #endif
    > diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
    > index 4c7f9befa9f6..18bd4362deaa 100644
    > --- a/include/linux/compiler-intel.h
    > +++ b/include/linux/compiler-intel.h
    > @@ -29,9 +29,6 @@
    > */
    > #define OPTIMIZER_HIDE_VAR(var) barrier()
    >
    > -/* Intel ECC compiler doesn't support __builtin_types_compatible_p() */
    > -#define __must_be_array(a) 0
    > -
    > #endif
    >
    > /* icc has this, but it's called _bswap16 */
    > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
    > index e0e55eb3f242..e4a702f99e50 100644
    > --- a/include/linux/compiler.h
    > +++ b/include/linux/compiler.h
    > @@ -357,4 +357,11 @@ static inline void *offset_to_ptr(const int *off)
    > compiletime_assert(__native_word(t), \
    > "Need native word sized stores/loads for atomicity.")
    >
    > +#ifdef __CHECKER__
    > +#define __must_be_array(a) 0
    > +#else
    > +/* &a[0] degrades to a pointer: a different type from an array */
    > +#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
    > +#endif
    > +
    > #endif /* __LINUX_COMPILER_H */
    > --
    > 2.17.1
    >

    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

    --
    Thanks,
    ~Nick Desaulniers

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