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

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Date:   Tue, 1 Oct 2019 15:20:35 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     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 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.

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?

-- 
Regards,
Vincenzo