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SubjectRe: [PATCH v3 15/18] arm/arm64: smccc: Make function identifiers an unsigned quantity
On 1 February 2018 at 12:40, Robin Murphy <robin.murphy@arm.com> wrote:
> 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>
>

In my case, the function identifier wasn't the issue, but the
argument, which, for SMCCC_ARCH_FEATURES is also defined as uint32_t,
but did end up being interpreted incorrectly by the SMCCCv1.1
implementation that is now upstream in ARM-TF



>
>> 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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