linux-kernel - Re: [PATCH] ARM: select HAVE_FUTEX

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Date:   Mon, 30 Aug 2021 16:31:46 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Mike Rapoport <rppt@...nel.org>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] ARM: select HAVE_FUTEX_CMPXCHG

On Mon, Aug 30, 2021 at 02:38:43PM -0700, Nick Desaulniers wrote:
> tglx notes:
>   This function [futex_detect_cmpxchg] is only needed when an
>   architecture has to runtime discover whether the CPU supports it or
>   not.  ARM has unconditional support for this, so the obvious thing to
>   do is the below.
> 
> Fixes linkage failure from Clang randconfigs:
> kernel/futex.o:(.text.fixup+0x5c): relocation truncated to fit: R_ARM_JUMP24 against `.init.text'
> and boot failures for CONFIG_THUMB2_KERNEL.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/325
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Tested-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  arch/arm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index fc196421b2ce..b760dd45b734 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -92,6 +92,7 @@ config ARM
>  	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_FUTEX_CMPXCHG if FUTEX
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
>  	select HAVE_IRQ_TIME_ACCOUNTING
> -- 
> 2.33.0.259.gc128427fd7-goog