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SubjectRe: [PATCH v3 15/18] arm/arm64: smccc: Make function identifiers an unsigned quantity
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On 01/02/18 11:46, Marc Zyngier wrote:
> Function identifiers are a 32bit, unsigned quantity. But we never
> tell so to the compiler, resulting in the following:
>
> 4ac: b26187e0 mov x0, #0xffffffff80000001
>
> We thus rely on the firmware narrowing it for us, which is not
> always a reasonable expectation.

I think technically it might be OK, since SMCCC states "A Function
Identifier is passed in register W0.", which implies that a conforming
implementation should also read w0, not x0, but it's certainly far
easier to be completely right than to justify being possibly wrong.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Cc: stable@vger.kernel.org
> Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> include/linux/arm-smccc.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index e1ef944ef1da..dd44d8458c04 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -14,14 +14,16 @@
> #ifndef __LINUX_ARM_SMCCC_H
> #define __LINUX_ARM_SMCCC_H
>
> +#include <uapi/linux/const.h>
> +
> /*
> * This file provides common defines for ARM SMC Calling Convention as
> * specified in
> * http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
> */
>
> -#define ARM_SMCCC_STD_CALL 0
> -#define ARM_SMCCC_FAST_CALL 1
> +#define ARM_SMCCC_STD_CALL _AC(0,U)
> +#define ARM_SMCCC_FAST_CALL _AC(1,U)
> #define ARM_SMCCC_TYPE_SHIFT 31
>
> #define ARM_SMCCC_SMC_32 0
>

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