linux-kernel - Re: [PATCH 1/4] arm64: vdso32: Introduce COMPAT_CC_IS

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Message-ID: <20190926080616.GB26802@iMac.local>
Date:   Thu, 26 Sep 2019 09:06:33 +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 1/4] arm64: vdso32: Introduce COMPAT_CC_IS_GCC

On Thu, Sep 26, 2019 at 07:03:50AM +0100, Vincenzo Frascino wrote:
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 37c610963eee..afe8c948b493 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -110,7 +110,7 @@ config ARM64
>  	select GENERIC_STRNLEN_USER
>  	select GENERIC_TIME_VSYSCALL
>  	select GENERIC_GETTIMEOFDAY
> -	select GENERIC_COMPAT_VDSO if (!CPU_BIG_ENDIAN && COMPAT)
> +	select GENERIC_COMPAT_VDSO if (!CPU_BIG_ENDIAN && COMPAT && COMPAT_CC_IS_GCC)
>  	select HANDLE_DOMAIN_IRQ
>  	select HARDIRQS_SW_RESEND
>  	select HAVE_PCI
> @@ -313,6 +313,9 @@ config KASAN_SHADOW_OFFSET
>  	default 0xeffffff900000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
>  	default 0xffffffffffffffff
>  
> +config COMPAT_CC_IS_GCC
> +	def_bool $(success,$(CROSS_COMPILE_COMPAT)gcc --version | head -n 1 | grep -q arm)

Nitpick: I prefer COMPATCC instead of COMPAT_CC for consistency with
HOSTCC.

Now, could we not generate a COMPATCC in the Makefile and use
$(COMPATCC) here instead of $(CROSS_COMPILE_COMPAT)gcc? It really
doesn't make sense to check that gcc is gcc.

A next step would be to check that COMPATCC can actually generate 32-bit
objects. But it's not essential at this stage.

> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 84a3d502c5a5..34f53eb11878 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -54,19 +54,8 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
>  endif
>  
>  ifeq ($(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

Has CONFIG_CROSS_COMPILE_COMPAT_VDSO actually been removed from
lib/vdso/Kconfig? (I haven't checked the subsequent patches).

-- 
Catalin