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

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Date:   Tue, 1 Oct 2019 15:20:38 +0100
From:   Will Deacon <will@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Catalin Marinas <catalin.marinas@....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 03:20:35PM +0100, Vincenzo Frascino wrote:
> On 10/1/19 2:27 PM, Catalin Marinas wrote:
> > 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?
> > 
> 
> I agree with Catalin here. The problem is not only when you pass and aarch64
> toolchain but even an x86 and so on.

I disagree. What happens if you do:

$ make ARCH=arm64 CROSS_COMPILE=x86_64-linux-gnu-

on your x86 box?

> If the problem is related to armv7- we can change the rule as "arm.*-gcc" which
> should detect them as well. Do you know what is the triple that an armv7-
> toolchain prints?

'fraid not, since I don't have one to hand. I think you'd end up matching
arm*-gcc, which is pretty broad.

Will