linux-kernel - Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to avoid useless register saving

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Date:   Thu, 4 Jun 2020 17:05:46 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        Sven Schnelle <svens@...ckframe.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        Naohiro Aota <naohiro.aota@....com>,
        Alexander Monakov <amonakov@...ras.ru>,
        Mathias Krause <minipli@...glemail.com>,
        PaX Team <pageexec@...email.hu>,
        Brad Spengler <spender@...ecurity.net>,
        Laura Abbott <labbott@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, gcc@....gnu.org,
        notify@...nel.org
Subject: Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to
 avoid useless register saving

Hi Alexander,

On Thu, Jun 4, 2020 at 3:50 PM Alexander Popov <alex.popov@...ux.com> wrote:
>
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index cdf016596659..522d57ae8532 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -41,6 +41,7 @@
>  # define __GCC4_has_attribute___nonstring__           0
>  # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
>  # define __GCC4_has_attribute___fallthrough__         0
> +# define __GCC4_has_attribute___no_caller_saved_registers__ 0
>  #endif

Nit: if you do another version, please move it before `noclone` to
keep the order (`fallthrough` was added in the wrong place).

Otherwise don't worry, I will sort it together with `fallthrough` when
I send a patch.

> +/*
> + * Optional: only supported since gcc >= 7
> + *
> + *   gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
> + */
> +#if __has_attribute(__no_caller_saved_registers__)
> +# define __no_caller_saved_registers   __attribute__((__no_caller_saved_registers__))
> +#else
> +# define __no_caller_saved_registers
> +#endif

Ditto.

Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>

Cheers,
Miguel