Re: [Xen-devel] [PATCH v1 3/8] xen/arm: Support sign-extension for every read access

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 25/09/15 17:44, Ian Campbell wrote:
> On Fri, 2015-09-25 at 15:51 +0100, Julien Grall wrote:
> I think you meant s/bit sign/sign bit/ but more correct would be "Sign
> extend if required".
> 
>> +     * Note that we expect the read handler to have zeroed the bit
>> +     * unused in the register.
> 
> "... to have zeroed the unused bits in the register".
> 
> But I think "unused" is a bit misleading, you mean the ones outside the
> requested access size, those bits are still "used" IYSWIM. I can't think of
> a terse term for "outside the requested access size I'm afraid.

I will switch to "Note that we expect the read handler to have zeroed
the bits outside the requested access size."

> 
> Did you confirm that all existing handlers meet this requirement?

Yes, we always do *r in the existing handlers.

> Perhaps an ASSERT would be handy?

What about:

ASSERT((*r & ((~0UL) >> (BITS_PER_LONG - size))) == 0)

Regards,

-- 
Julien Grall

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