linux-kernel - Re: [PATCH v4 1/6] arm64: vdso32: Fix syncconfig errors.

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Message-ID: <20191003160041.GI21629@arrakis.emea.arm.com>
Date:   Thu, 3 Oct 2019 17:00:41 +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, luto@...nel.org
Subject: Re: [PATCH v4 1/6] arm64: vdso32: Fix syncconfig errors.

On Wed, Oct 02, 2019 at 03:41:51PM +0100, Vincenzo Frascino wrote:
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Reported-by: Will Deacon <will@...nel.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Tested-by: Catalin Marinas <catalin.marinas@....com>

If you changed the patch, please drop my reviewed/tested-by.

> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 84a3d502c5a5..dfa6a5cb99e4 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -53,20 +53,12 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
>    endif
>  endif
>  
> +COMPATCC ?= $(CROSS_COMPILE_COMPAT)gcc
> +export COMPATCC
> +
>  ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y)
> -  CROSS_COMPILE_COMPAT ?= $(CONFIG_CROSS_COMPILE_COMPAT_VDSO:"%"=%)
> -
> -  ifeq ($(CONFIG_CC_IS_CLANG), y)
> -    $(warning CROSS_COMPILE_COMPAT is clang, the compat vDSO will not be built)
> -  else ifeq ($(strip $(CROSS_COMPILE_COMPAT)),)
> -    $(warning CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built)
> -  else ifeq ($(shell which $(CROSS_COMPILE_COMPAT)gcc 2> /dev/null),)
> -    $(error $(CROSS_COMPILE_COMPAT)gcc not found, check CROSS_COMPILE_COMPAT)
> -  else
> -    export CROSS_COMPILE_COMPAT
> -    export CONFIG_COMPAT_VDSO := y
> -    compat_vdso := -DCONFIG_COMPAT_VDSO=1
> -  endif
> +  export CONFIG_COMPAT_VDSO := y
> +  compat_vdso := -DCONFIG_COMPAT_VDSO=1
>  endif

With this change, if I don't have any CROSS_COMPILE_COMPAT in my
environment, the kernel fails to build because COMPATCC becomes gcc
which cannot build the vdso32. What I really want is not to warn me, nor
fail to build the kernel when I don't care about the compat vDSO (e.g. I
have a 64-bit only machine).

What saved us before was the COMPATCC_IS_ARM_GCC check and a selection
of the GENERIC_COMPAT_VDSO dependent on this check. This was now dropped
from the previous version of the patch. We could add something like
COMPATCC_CAN_LINK.

-- 
Catalin