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

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Message-ID: <d4483638-cba6-eedc-df85-ffe8b0895c89@arm.com>
Date:   Thu, 26 Sep 2019 11:59:44 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....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 9/26/19 9:30 AM, Catalin Marinas wrote:
> 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.
> 

Good catch I thought that it was sufficient to put it in the correct makefile,
but I missed that COMPATCC != CC. This selects the wrong binutils.

Need to add something in Kbuild for that.

-- 
Regards,
Vincenzo