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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 28 Sep 2021 10:20:42 -0700
Message-ID: <CAKwvOdmhZiOQ1h6_qfOxTKkzoA+Go8BCp-GEUZ6LNQpd0cimzA@mail.gmail.com>
Subject: Re: [PATCH 14/14] [RFC] ARM: forbid ftrace with clang and thumb2_kernel
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Nathan Chancellor <nathan@kernel.org>, llvm@lists.linux.dev,
        Peter Smith <Peter.Smith@arm.com>,
        Kristof Beyls <Kristof.Beyls@arm.com>
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On Tue, Sep 28, 2021 at 8:42 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> clang fails to build kernels with THUMB2 and FUNCTION_TRACER
> enabled when there is any inline asm statement containing
> the frame pointer register r7:
>
> arch/arm/mach-versatile/dcscb.c:95:2: error: inline asm clobber list contains reserved registers: R7 [-Werror,-Winline-asm]

^ This file no longer exists in tree?

> arch/arm/mach-exynos/mcpm-exynos.c:154:2: error: inline asm clobber list contains reserved registers: R7 [-Werror,-Winline-asm]
> arch/arm/probes/kprobes/actions-thumb.c:449:3: error: inline asm clobber list contains reserved registers: R7 [-Werror,-Winline-asm]
>
> Apparently gcc should also have warned about this, and the
> configuration is actually invalid, though there is some
> disagreement on the bug trackers about this.
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=45826
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94986
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 0d4f3e2d50ad..7ea95bb40004 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -91,7 +91,7 @@ config ARM
>         select HAVE_FAST_GUP if ARM_LPAE
>         select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>         select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
> -       select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> +       select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
>         select HAVE_GCC_PLUGINS
>         select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
>         select HAVE_IRQ_TIME_ACCOUNTING
> --
> 2.29.2
>
>


-- 
Thanks,
~Nick Desaulniers