linux-kernel - Re: [PATCH] arm64: write_sysreg asm illegal for aarch32

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Message-ID: <35cf2062-f27e-16e6-19b1-cae5200d7081@arm.com>
Date:   Wed, 1 Nov 2017 17:14:33 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Mark Salyzyn <salyzyn@...roid.com>, linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Christoffer Dall <cdall@...aro.org>,
        Stefan Traby <stefan@...lo-penguin.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: write_sysreg asm illegal for aarch32

On 01/11/17 16:58, Mark Salyzyn wrote:
> Cross compiling to aarch32 (for vdso32) using clang correctly
> identifies that (the unused) write_sysreg inline asm directive is
> illegal in that architectural context:
> 
> arch/arm64/include/asm/arch_timer.h: error: invalid input constraint 'rZ' in asm
>         write_sysreg(cntkctl, cntkctl_el1);
>         ^
> arch/arm64/include/asm/sysreg.h: note: expanded from macro 'write_sysreg'
>                      : : "rZ" (__val));
>                          ^
> 
> GCC normally checks for correctness everywhere. But uniquely for
> unused asm, will optimize out and suppress the error report.

It sounds more like some paths are wrong in the compat vDSO build if
it's pulling in this header in the first place - nothing in this file is
relevant to AArch32.

Robin.

> Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Christoffer Dall <cdall@...aro.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Stefan Traby <stefan@...lo-penguin.com>
> Cc: Dave Martin <Dave.Martin@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  arch/arm64/include/asm/sysreg.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index f707fed5886f..a7b61c9327db 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -492,11 +492,15 @@ asm(
>   * The "Z" constraint normally means a zero immediate, but when combined with
>   * the "%x0" template means XZR.
>   */
> +#if defined(__aarch64__)
>  #define write_sysreg(v, r) do {					\
>  	u64 __val = (u64)(v);					\
>  	asm volatile("msr " __stringify(r) ", %x0"		\
>  		     : : "rZ" (__val));				\
>  } while (0)
> +#else
> +#define write_sysreg(v, r) BUG()
> +#endif
>  
>  /*
>   * For registers without architectural names, or simply unsupported by
>