[PATCH] arm64: write_sysreg asm illegal for aarch32

[Robin Murphy]

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 at android.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Christoffer Dall <cdall at linaro.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Marc Zyngier <marc.zyngier at arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
> Cc: Stefan Traby <stefan at hello-penguin.com>
> Cc: Dave Martin <Dave.Martin at arm.com>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-kernel at vger.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
>