linux-kernel - Re: [PATCH] arm64: disable patchable function entry on big-endian clang builds

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Message-ID: <20200506173416.hmdp5cgkslunfko7@google.com>
Date:   Wed, 6 May 2020 10:34:16 -0700
From:   Fangrui Song <maskray@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Torsten Duwe <duwe@....de>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Amit Daniel Kachhap <amit.kachhap@....com>,
        Torsten Duwe <duwe@...e.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Julien Thierry <jthierry@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alexandre Ghiti <alex@...ti.fr>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Steve Capper <steve.capper@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] arm64: disable patchable function entry on big-endian
 clang builds

On 2020-05-06, Nick Desaulniers wrote:
>On Wed, May 6, 2020 at 8:46 AM 'Fangrui Song' via Clang Built Linux
><clang-built-linux@...glegroups.com> wrote:
>> Created https://reviews.llvm.org/D79495 to allow the function attribute
>> 'patchable_function_entry' on aarch64_be.
>> I think -fpatchable-function-entry= just works.
>>
>> Note, LLD does not support aarch64_be
>> (https://github.com/ClangBuiltLinux/linux/issues/380).
>
>I've approved the patch. Thanks for the quick fix.  Looks like we
>backported -fpatchable-function-entry= to the clang-10 release, so we
>should cherry pick your fix to the release-10 branch for the clang
>10.1 release.
>
>I'd rather have this fixed on the toolchain side.

+1.

Cherry picked to release/10.x
https://github.com/llvm/llvm-project/commit/98f9f73f6d2367aa8001c4d16de9d3b347febb08
I did not use any endianness-sensitive in the original implementation,
so hopefully this will not run into issues.


The scheduled rc1 of LLVM 10.0.1 will happen on May 18, 2020
(https://lists.llvm.org/pipermail/llvm-dev/2020-April/141128.html)
We should be quick if we want to test it on qemu or real hardware.