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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 27 May 2020 10:28:43 -0700
Message-ID: <CAKwvOdn637hSboMnMV=S5f1wbiEnc6qtnrn=fpeCGtvr2W_Daw@mail.gmail.com>
Subject: Re: [PATCH] arm64: disable -fsanitize=shadow-call-stack for big-endian
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Fangrui Song <maskray@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Kees Cook <keescook@chromium.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, May 27, 2020 at 8:24 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Wed, May 27, 2020 at 03:39:46PM +0200, Arnd Bergmann wrote:
> > clang-11 and earlier do not support -fsanitize=shadow-call-stack
> > in combination with -mbig-endian, but the Kconfig check does not
> > pass the endianess flag, so building a big-endian kernel with
> > this fails at build time:
> >
> > clang: error: unsupported option '-fsanitize=shadow-call-stack' for target 'aarch64_be-unknown-linux'
> >
> > Change the Kconfig check to let Kconfig figure this out earlier
> > and prevent the broken configuration. I assume this is a bug
> > in clang that needs to be fixed, but we also have to work
> > around existing releases.
> >
> > Fixes: 5287569a790d ("arm64: Implement Shadow Call Stack")
> > Link: https://bugs.llvm.org/show_bug.cgi?id=46076
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> I suspect this is similar to the patchable-function-entry issue, and
> this is an oversight that we'd rather fix toolchain side.
>
> Nick, Fangrui, thoughts?

Exactly, Fangrui already has a fix: https://reviews.llvm.org/D80647.
Thanks Fangrui!
It seems it's easy in the codebase to check the specific ABI, which
isn't explicitly LE, rather than use a method that checks the ISA
regardless of endianness.

-- 
Thanks,
~Nick Desaulniers