linux-kernel - Re: [PATCH v3 1/5] arm64: vdso32: Introduce COMPAT_CC_IS

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Date:   Tue, 1 Oct 2019 14:27:31 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        ard.biesheuvel@...aro.org, ndesaulniers@...gle.com,
        tglx@...utronix.de
Subject: Re: [PATCH v3 1/5] arm64: vdso32: Introduce COMPAT_CC_IS_GCC

On Tue, Oct 01, 2019 at 02:14:23PM +0100, Will Deacon wrote:
> On Thu, Sep 26, 2019 at 10:43:38PM +0100, Vincenzo Frascino wrote:
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 37c610963eee..0e5beb928af5 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 && COMPATCC_IS_ARM_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 COMPATCC_IS_ARM_GCC
> > +	def_bool $(success,$(COMPATCC) --version | head -n 1 | grep -q "arm-.*-gcc")
> 
> I've seen toolchains where the first part of the tuple is "armv7-", so they
> won't get detected here. However, do we really need to detect this? If
> somebody passes a duff compiler, then the build will fail in the same way as
> if they passed it to CROSS_COMPILE=.

Not sure what happens if we pass an aarch64 compiler. Can we end up with
a 64-bit compat vDSO?

-- 
Catalin