linux-kernel - Re: [PATCH v4 05/13] Compiler Attributes: naked was fixed in gcc 4.6

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Date:   Mon, 10 Sep 2018 10:45:33 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        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>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joe Perches <joe@...ches.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-sparse@...r.kernel.org, linux-kernel-owner@...r.kernel.org
Subject: Re: [PATCH v4 05/13] Compiler Attributes: naked was fixed in gcc 4.6

Hi,

On 08.09.2018 14:24, Miguel Ojeda 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
> 
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> Cc: Luc Van Oostenryck <luc.vanoostenryck@...il.com>
> Cc: Eli Friedman <efriedma@...eaurora.org>
> Cc: Christopher Li <sparse@...isli.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Joe Perches <joe@...ches.com>
> Cc: Dominique Martinet <asmadeus@...ewreck.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: linux-sparse@...r.kernel.org
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
> ---
>  include/linux/compiler-gcc.h | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index 76f4907ef707..4cd5e9264bce 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.

I think this is also no longer required since GCC 4.6 and newer only
have the new mcount interface:

https://lore.kernel.org/lkml/20180826214022.4889-1-stefan@agner.ch/T/#u

That said, I am not sure whether it is a good idea to enable tracing for
naked functions even with the mcount interface.

--
Stefan


> - *
> - * 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
>  
>  #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)