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Re: [PATCH] Arm32: MSR to SPSR needs qualification

  • To: Julien Grall <julien.grall@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 11 Jun 2021 15:02:53 +0200
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  • Cc: Julien Grall <julien.grall.oss@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • Delivery-date: Fri, 11 Jun 2021 13:03:14 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 11.06.2021 12:41, Julien Grall wrote:
> On Fri, 11 Jun 2021, 11:16 Jan Beulich, <jbeulich@xxxxxxxx> wrote:
>> On 11.06.2021 10:00, Julien Grall wrote:
>>> On Fri, 11 Jun 2021, 08:55 Jan Beulich, <jbeulich@xxxxxxxx> wrote:
>>>> The Arm ARM's description of MSR doesn't even allow for plain "SPSR"
>>>> here, and while gas accepts this, it takes it to mean SPSR_cf. Yet
>>>> surely all of SPSR wants updating on this path, not just the lowest and
>>>> highest 8 bits.
>>> Can you provide a reference to the Arm Arm? This would help to navigate
>>> through the 8000 pages.
>> Referencing the instruction page would be enough, I thought (as
>> even I, not being an Arm person, have no difficulty locating it).
>> If it isn't, how is a canonical doc ref supposed to look like on
>> Arm? On x86, we avoid recording document versions, section
>> numbers, or even page numbers in code comments or commit messages
>> (which isn't to say we have none of these, but we try to avoid
>> new ones to appear), as these tend to change with every new
>> version of the doc. Therefore, to me, the offending commit's "ARM
>> DDI 0487D.b page G8-5993" doesn't look like something I wanted to
>> clone from. But if you tell me otherwise, then well - so be it.
> The Arm website provides a link for nearly every revision on the specs. As
> the wording can change between version, it is useful to know which spec the
> understanding is based from.
>  Note that for Arm32 we should quote the Armv7 spec and not the Armv8 one
> because we only follow the former (there are a few small differences).

Thanks for having me dig out an up-to-date Armv7 spec. I find this
puzzling in particular because you didn't care to have the earlier
commit provide a v7 doc ref. Initially I did intentionally use (a
newer version of) the doc that was pointed at there (which I also
think is better structured than the v7 one).




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