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    Subject[PATCH] Raise the minimum required gcc version to 4.6
    Date
    Various architectures fail to build properly with older versions
    of the gcc compiler.

    An example from Guenter Roeck via this thread:
    https://lore.kernel.org/lkml/20180814170904.GA12768@roeck-us.net/

    ----------------------
    In file included from ./include/linux/mm.h:17:0,
    from ./include/linux/pid_namespace.h:7,
    from ./include/linux/ptrace.h:10,
    from arch/openrisc/kernel/asm-offsets.c:32:
    ./include/linux/mm_types.h:497:16: error: flexible array member in otherwise empty struct

    This is just an example with gcc 4.5.1 for or32. I have seen the problem
    with gcc 4.4 (for unicore32) as well.
    ----------------------

    So update the minimum required version of gcc to 4.6.

    Miscellanea:

    o Update Documentation/process/changes.rst
    o Remove and consolidate version test blocks in compiler-gcc.h
    for versions lower than 4.6

    Signed-off-by: Joe Perches <joe@perches.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    ---
    Documentation/process/changes.rst | 2 +-
    include/linux/compiler-gcc.h | 86 ++++++++-------------------------------
    2 files changed, 19 insertions(+), 69 deletions(-)

    diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
    index 7a92a06f90de..61f918b10a0c 100644
    --- a/Documentation/process/changes.rst
    +++ b/Documentation/process/changes.rst
    @@ -29,7 +29,7 @@ you probably needn't concern yourself with isdn4k-utils.
    ====================== =============== ========================================
    Program Minimal version Command to check the version
    ====================== =============== ========================================
    -GNU C 3.2 gcc --version
    +GNU C 4.6 gcc --version
    GNU make 3.81 make --version
    binutils 2.20 ld -v
    flex 2.5.35 flex --version
    diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
    index 3e70b7d4e9ed..250b9b7cfd60 100644
    --- a/include/linux/compiler-gcc.h
    +++ b/include/linux/compiler-gcc.h
    @@ -10,6 +10,10 @@
    + __GNUC_MINOR__ * 100 \
    + __GNUC_PATCHLEVEL__)

    +#if GCC_VERSION < 40600
    +# error Sorry, your compiler is too old - please upgrade it.
    +#endif
    +
    /* Optimization barrier */

    /* The "volatile" is due to gcc bugs */
    @@ -58,6 +62,12 @@
    #define OPTIMIZER_HIDE_VAR(var) \
    __asm__ ("" : "=r" (var) : "0" (var))

    +/*
    + * A trick to suppress uninitialized variable warning without generating any
    + * code
    + */
    +#define uninitialized_var(x) x = x
    +
    #ifdef __CHECKER__
    #define __must_be_array(a) 0
    #else
    @@ -91,7 +101,7 @@
    * A lot of inline functions can cause havoc with function tracing.
    */
    #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
    - !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
    + !defined(CONFIG_OPTIMIZE_INLINING)
    #define inline \
    inline __attribute__((always_inline, unused)) notrace __gnu_inline
    #else
    @@ -147,47 +157,13 @@
    #define __always_unused __attribute__((unused))
    #define __mode(x) __attribute__((mode(x)))

    -/* gcc version specific checks */
    -
    -#if GCC_VERSION < 30200
    -# error Sorry, your compiler is too old - please upgrade it.
    -#endif
    -
    -#if GCC_VERSION < 30300
    -# define __used __attribute__((__unused__))
    -#else
    -# define __used __attribute__((__used__))
    -#endif
    -
    -#ifdef CONFIG_GCOV_KERNEL
    -# if GCC_VERSION < 30400
    -# error "GCOV profiling support for gcc versions below 3.4 not included"
    -# endif /* __GNUC_MINOR__ */
    -#endif /* CONFIG_GCOV_KERNEL */
    -
    -#if GCC_VERSION >= 30400
    #define __must_check __attribute__((warn_unused_result))
    #define __malloc __attribute__((__malloc__))
    -#endif
    -
    -#if GCC_VERSION >= 40000
    -
    -/* GCC 4.1.[01] miscompiles __weak */
    -#ifdef __KERNEL__
    -# if GCC_VERSION >= 40100 && GCC_VERSION <= 40101
    -# error Your version of gcc miscompiles the __weak directive
    -# endif
    -#endif

    #define __used __attribute__((__used__))
    #define __compiler_offsetof(a, b) \
    __builtin_offsetof(a, b)

    -#if GCC_VERSION >= 40100
    -# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
    -#endif
    -
    -#if GCC_VERSION >= 40300
    /* Mark functions as cold. gcc will assume any path leading to a call
    * to them will be unlikely. This means a lot of manual unlikely()s
    * are unnecessary now for any paths leading to the usual suspects
    @@ -206,24 +182,19 @@

    #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)

    -#ifndef __CHECKER__
    -# define __compiletime_warning(message) __attribute__((warning(message)))
    -# define __compiletime_error(message) __attribute__((error(message)))
    -#endif /* __CHECKER__ */
    -#endif /* GCC_VERSION >= 40300 */
    -
    -#if GCC_VERSION >= 40400
    #define __optimize(level) __attribute__((__optimize__(level)))
    #define __nostackprotector __optimize("no-stack-protector")
    -#endif /* GCC_VERSION >= 40400 */

    -#if GCC_VERSION >= 40500
    +#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)

    #ifndef __CHECKER__
    +#define __compiletime_warning(message) __attribute__((warning(message)))
    +#define __compiletime_error(message) __attribute__((error(message)))
    +
    #ifdef LATENT_ENTROPY_PLUGIN
    #define __latent_entropy __attribute__((latent_entropy))
    #endif
    -#endif
    +#endif /* __CHECKER__ */

    /*
    * calling noreturn functions, __builtin_unreachable() and __builtin_trap()
    @@ -261,10 +232,6 @@
    #define randomized_struct_fields_end } __randomize_layout;
    #endif

    -#endif /* GCC_VERSION >= 40500 */
    -
    -#if GCC_VERSION >= 40600
    -
    /*
    * When used with Link Time Optimization, gcc can optimize away C functions or
    * variables which are referenced only from assembly code. __visible tells the
    @@ -273,8 +240,7 @@
    */
    #define __visible __attribute__((externally_visible))

    -#endif /* GCC_VERSION >= 40600 */
    -
    +/* gcc version specific checks */

    #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
    /*
    @@ -308,10 +274,8 @@
    * folding in __builtin_bswap*() (yet), so don't set these for it.
    */
    #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
    -#if GCC_VERSION >= 40400
    #define __HAVE_BUILTIN_BSWAP32__
    #define __HAVE_BUILTIN_BSWAP64__
    -#endif
    #if GCC_VERSION >= 40800
    #define __HAVE_BUILTIN_BSWAP16__
    #endif
    @@ -340,10 +304,9 @@
    * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
    */
    #define __designated_init __attribute__((designated_init))
    +#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
    #endif

    -#endif /* gcc version >= 40000 specific checks */
    -
    #if !defined(__noclone)
    #define __noclone /* not needed */
    #endif
    @@ -352,16 +315,6 @@
    #define __no_sanitize_address
    #endif

    -/*
    - * A trick to suppress uninitialized variable warning without generating any
    - * code
    - */
    -#define uninitialized_var(x) x = x
    -
    -#if GCC_VERSION >= 50100
    -#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
    -#endif
    -
    /*
    * Turn individual warnings and errors on and off locally, depending
    * on version.
    @@ -374,12 +327,9 @@
    #define __diag_GCC_warn warning
    #define __diag_GCC_error error

    -/* Compilers before gcc-4.6 do not understand "#pragma GCC diagnostic push" */
    -#if GCC_VERSION >= 40600
    #define __diag_str1(s) #s
    #define __diag_str(s) __diag_str1(s)
    #define __diag(s) _Pragma(__diag_str(GCC diagnostic s))
    -#endif

    #if GCC_VERSION >= 80000
    #define __diag_GCC_8(s) __diag(s)
    --
    2.15.0
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