[PATCH v4 03/12] KVM: arm64: guest debug, define API headers

[Peter Maydell]

On 15 May 2015 at 16:14, Alex Bennée <alex.bennee at linaro.org> wrote:
>
> Mark Rutland <mark.rutland at arm.com> writes:
>
>> On Fri, May 15, 2015 at 03:27:06PM +0100, Alex Bennée wrote:
>>> +/*
>>> + * See v8 ARM ARM D7.3: Debug Registers
>>> + *
>>> + * The control registers are architecturally defined as 32 bits but are
>>> + * stored as 64 bit values alongside the value registers. This is done
>>
>> Stale comment? They're stored as __u32 below.
>
> Gah yes it is.
>
>> It's possible that the registers could grow in future as happened in the
>> case of CLIDR_EL1, so it might be worth treating system registers
>> generally as u64 values.
>
> Really? I mean the existing debug *control* registers have reserved bits
> 24-31 so there is space for expansion.

Other places in the userspace ABI which deal with sysregs (notably
ONE_REG) consistently define them all as 64-bit (which makes sense
anyway since the ISA only provides 64-bit accessors to them).
"Architecturally 32 bits" only means "top 32 bits reserved".

-- PMM