Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <4cdd4ab9ddd16f1fb168266643264595782fd890.camel@perches.com>
References: <20180814170904.GA12768@roeck-us.net> <4cdd4ab9ddd16f1fb168266643264595782fd890.camel@perches.com>
From:   Kees Cook <keescook@chromium.org>
Date:   Sun, 19 Aug 2018 14:23:49 -0700
Message-ID: <CAGXu5jLHtT2WfYNDmnkxcZWp6yb7GmDjVscK-9umhPU+0ARRRw@mail.gmail.com>
Subject: Re: Build failures with gcc 4.5 and older
To:     Joe Perches <joe@perches.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Mike Galbraith <efault@gmx.de>,
        Dave Hansen <dave.hansen@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Aug 14, 2018 at 10:48 AM, Joe Perches <joe@perches.com> wrote:
> On Tue, 2018-08-14 at 10:09 -0700, Guenter Roeck wrote:
>> Hi,
>>
>> Since commit c1a2f7f0c0645 ("mm: Allocate the mm_cpumask
>> (mm->cpu_bitmap[]) dynamically based on nr_cpu_ids"), building
>> the Linux kernel with gcc version 4.5 and older fails as follows.
>>
>> 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.
>>
>> Does that mean that gcc 4.5 and older are now officially no longer
>> supported for compiling the kernel ?
>>
>> If so, would it make sense to update include/linux/compiler-gcc.h
>> accordingly ?
>
> And Documentation/process/changes.rst which shows a
> minimum version required of gcc as 3.2, etc...
>
> With cleaning up now unnecessary version tests in
> compiler-gcc.h, something like:

I rejoice at raising the minimum gcc to version 4.6! :)

> ---
>  Documentation/process/changes.rst |  2 +-
>  include/linux/compiler-gcc.h      | 86 ++++++++-------------------------------
>  2 files changed, 19 insertions(+), 69 deletions(-)

These look good, thanks:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> 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 573f5a7d42d4..020e4b9eee5c 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
> @@ -148,47 +158,13 @@
>  #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
> @@ -207,24 +183,19 @@
>
>  #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()
> @@ -262,10 +233,6 @@
>  #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
> @@ -274,8 +241,7 @@
>   */
>  #define __visible      __attribute__((externally_visible))
>
> -#endif /* GCC_VERSION >= 40600 */
> -
> +/* gcc version specific checks */
>
>  #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
>  /*
> @@ -309,10 +275,8 @@
>   * 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
> @@ -341,10 +305,9 @@
>   * 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
> @@ -353,16 +316,6 @@
>  #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.
> @@ -375,12 +328,9 @@
>  #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)
>
>
>


-- 
Kees Cook
Pixel Security