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

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Date:   Fri, 31 Aug 2018 21:48:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        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>, asmadeus@...ewreck.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 5/7] Compiler Attributes: naked was fixed in gcc 4.6

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?

        Arnd