linux-kernel - Re: [PATCH 5/7] Compiler Attributes: naked was fixed in gcc 4.6

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Message-ID: <CANiq72nOOcumNJeZ7w=UXW5p9w82+FZGXGuwJ_SA-gPuFfctow@mail.gmail.com>
Date:   Fri, 31 Aug 2018 22:26:02 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Eli Friedman <efriedma@...eaurora.org>,
        Christopher Li <sparse@...isli.org>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joe Perches <joe@...ches.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 5/7] Compiler Attributes: naked was fixed in gcc 4.6

Hi Arnd,

On Fri, Aug 31, 2018 at 9:48 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Aug 31, 2018 at 7:05 PM Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com> wrote:
>>
>> Commit 9c695203a7dd ("compiler-gcc.h: gcc-4.5 needs noclone
>> and noinline on __naked functions") added noinline and noclone
>> as a workaround for a gcc 4.5 bug, which was resolved in 4.6.0.
>>
>> Since now the minimum gcc supported version is 4.6,
>> we can clean it up.
>>
>> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44290
>> and https://godbolt.org/z/h6NMIL
>>
>
>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
>> index 66e1eb8822d9..fdf2fbe6d544 100644
>> --- a/include/linux/compiler-gcc.h
>> +++ b/include/linux/compiler-gcc.h
>> @@ -77,14 +77,8 @@
>>   * to trace naked functions because then mcount is called without
>>   * stack and frame pointer being set up and there is no chance to
>>   * restore the lr register to the value before mcount was called.
>> - *
>> - * The asm() bodies of naked functions often depend on standard calling
>> - * conventions, therefore they must be noinline and noclone.
>> - *
>> - * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
>> - * See GCC PR44290.
>>   */
>> -#define __naked                __attribute__((naked)) noinline __noclone notrace
>> +#define __naked                __attribute__((naked)) notrace
>>
>
> Good catch. Can this be moved into linux/compiler.h now so we
> don't need separate definitions for clang and gcc?

Yes, it can! :-) Actually I was writing that to Nick in the other
thread about clang, but you beat me to it. Good catch too!

Cheers,
Miguel