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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Thu, 23 Aug 2018 11:42:39 +0900
Message-ID: <CAK7LNAQxpmGK=PMt-qMDYvaYcO=SZ9HWudGYqC11aJ-kGXaVoA@mail.gmail.com>
Subject: Re: [PATCH] include/linux/compiler*.h: make compiler-*.h mutually exclusive
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Joe Perches <joe@perches.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Arnd Bergmann <arnd@arndb.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        asmadeus@codewreck.org, Daniel Borkmann <daniel@iogearbox.net>,
        "H. Peter Anvin" <hpa@zytor.com>
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Hi Nick

2018-08-23 8:37 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>:
> Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
> recently exposed a brittle part of the build for supporting non-gcc
> compilers.
>
> Both Clang and ICC define __GNUC__, __GNUC_MINOR__, and
> __GNUC_PATCHLEVEL__ for quick compatibility with code bases that haven't
> added compiler specific checks for __clang__ or __INTEL_COMPILER.
>
> This is brittle, as they happened to get compatibility by posing as a
> certain version of GCC.  This broke when upgrading the minimal version
> of GCC required to build the kernel, to a version above what ICC and
> Clang claim to be.
>
> Rather than always including compiler-gcc.h then undefining or
> redefining macros in compiler-intel.h or compiler-clang.h, let's
> separate out the compiler specific macro definitions into mutually
> exclusive headers, do more proper compiler detection, and keep shared
> definitions in compiler_types.h.
>
> Reported-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Suggested-by: Eli Friedman <efriedma@codeaurora.org>
> Suggested-by: Joe Perches <joe@perches.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  arch/arm/kernel/asm-offsets.c     |  13 +-
>  drivers/gpu/drm/i915/i915_utils.h |   2 +-
>  drivers/watchdog/kempld_wdt.c     |   5 -
>  include/linux/compiler-clang.h    |  20 ++-
>  include/linux/compiler-gcc.h      |  88 -----------
>  include/linux/compiler-intel.h    |  13 +-
>  include/linux/compiler_types.h    | 238 ++++++++++++++----------------
>  mm/ksm.c                          |   4 +-
>  mm/migrate.c                      |   3 +-
>  9 files changed, 133 insertions(+), 253 deletions(-)


If I build ARM linux with Clang,
I see the following error.


arch/arm/firmware/trusted_foundations.c:34:13: error: variable has
incomplete type 'void'
static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2)
            ^
arch/arm/firmware/trusted_foundations.c:34:20: error: expected ';'
after top level declarator
static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2)
                   ^
                   ;
arch/arm/firmware/trusted_foundations.c:77:25: error: use of
undeclared identifier 'trusted_foundations_ops'
        register_firmware_ops(&trusted_foundations_ops);
                               ^
3 errors generated.
scripts/Makefile.build:307: recipe for target
'arch/arm/firmware/trusted_foundations.o' failed
make[2]: *** [arch/arm/firmware/trusted_foundations.o] Error 1
Makefile:1057: recipe for target 'arch/arm/firmware' failed
make[1]: *** [arch/arm/firmware] Error 2
make[1]: *** Waiting for unfinished jobs....


__naked is defined in <linux/compiler-gcc.h>


It was previous included by all compilers,
but now it is only by _true_ GCC.


Even if I move the __naked definition
to <linux/compiler_types.h>,
I see a different error.


arch/arm/firmware/trusted_foundations.c:47:10: error: parameter
references not allowed in naked functions
                : "r" (type), "r" (arg1), "r" (arg2)
                       ^
arch/arm/firmware/trusted_foundations.c:34:13: note: attribute is here
static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2)
            ^
./include/linux/compiler_types.h:277:33: note: expanded from macro '__naked'
#define __naked         __attribute__((naked))
                                       ^


I do not know what a correct fix is.


-- 
Best Regards
Masahiro Yamada