Re: [Qemu-devel] [PATCH 4/5] target-arm: get_phys_addr_lpae: more xn control

[Peter Maydell <peter.maydell@linaro.org>]

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On 10 March 2015 at 17:28, Andrew Jones <drjones@redhat.com> wrote:
> On Tue, Mar 10, 2015 at 05:14:21PM +0000, Peter Maydell wrote:[?]
>> No, because patch 2 doesn't do anything in the callers to
>> make them pass only bits [2:1]. So after patch 2 get_rw_prot
>> still requires bits [2:0]. Except it's broken, because the
>> function itself assumes it gets bits [2:1].
>
> You've lost me. Patch 2 adds support for 2-bit ap, but
> doesn't remove support for 3-bit. There are not callers
> expecting it to support the simple model as 2 or 3 bits
> at that time, except v6, but that was broken already, and
> we fix it in patch 5 (and we add the ap shift there too).
> IOW, how can preparing a function for new callers, while
> still supporting the old callers, be 'broken'?

(This is all somewhat academic at this point given we're
splitting the two functions up, but:)

Because it's not being consistent with itself -- if
it wants to accept AP[2:1] only then the v6 callsite
needs to change, otherwise it needs to handle AP[2:0] and
look only at bits 2:1 in that. You eventually fixed
this in patch 5 with an extra shift, but if you wanted
to do it that way then that part should have been in
patch 2...

-- PMM

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