linux-kernel - Re: [PATCH 2/4] arm64: vdso32: Detect binutils support for dmb ishld

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Date:   Thu, 26 Sep 2019 09:30:39 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        ard.biesheuvel@...aro.org, ndesaulniers@...gle.com,
        will@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH 2/4] arm64: vdso32: Detect binutils support for dmb ishld

On Thu, Sep 26, 2019 at 07:03:51AM +0100, Vincenzo Frascino wrote:
> diff --git a/arch/arm64/include/asm/vdso/compat_barrier.h b/arch/arm64/include/asm/vdso/compat_barrier.h
> index fb60a88b5ed4..3fd8fd6d8fc2 100644
> --- a/arch/arm64/include/asm/vdso/compat_barrier.h
> +++ b/arch/arm64/include/asm/vdso/compat_barrier.h
> @@ -20,7 +20,7 @@
>  
>  #define dmb(option) __asm__ __volatile__ ("dmb " #option : : : "memory")
>  
> -#if __LINUX_ARM_ARCH__ >= 8
> +#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
>  #define aarch32_smp_mb()	dmb(ish)
>  #define aarch32_smp_rmb()	dmb(ishld)
>  #define aarch32_smp_wmb()	dmb(ishst)
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index 1fba0776ed40..1a3299d901b1 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -55,6 +55,9 @@ endif
>  VDSO_CAFLAGS += -fPIC -fno-builtin -fno-stack-protector
>  VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
>  
> +# Check for binutils support for dmb ishld
> +dmbinstr := $(call as-instr,dmb ishld,-DCONFIG_AS_DMB_ISHLD=1)

Is this check for the compat gas or the native one? Looking at
scripts/Kbuild.include, as-instr uses CC but you'd need a COMPATCC here
instead.

I may have missed something but I don't think this fixes the issue
Will's issue since he reported the problem with an old compat binutils.

-- 
Catalin