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Re: Backport request (was: [PATCH v2] tools: convert bitfields to unsigned type)
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 4 Jul 2023 18:16:41 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>
- Delivery-date: Tue, 04 Jul 2023 16:16:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.07.2023 18:10, Roger Pau Monné wrote:
> On Tue, Jul 04, 2023 at 06:04:36PM +0200, Jan Beulich wrote:
>> On 04.07.2023 17:55, Roger Pau Monné wrote:
>>> On Tue, Jul 04, 2023 at 05:42:33PM +0200, Jan Beulich wrote:
>>>> Plus is the mentioned
>>>> "potential ABI change" safe to take on a stable branch? There's not going
>>>> to
>>>> be any SONAME change ...
>>>
>>> Is there any ABI change in practice? Both fields will still have a 1bit
>>> size.
>>
>> But what a consumer of the interface reads out of such a field would change
>> in case their compiler settings arrange for signed bitfields when signedness
>> isn't explicit. We don't dictate, after all, what compiler settings to use
>> with our interfaces (which generally is good, but which bites us here).
>
> Hm, I see. I would argue that sign doesn't matter here, as those are
> intended to be booleans, so anything different than 0 would map to
> `true`. But implementation might have hard coded TRUE to -1, and the
> change would then break them?
That's a possible scenario I'm wary of here, yes.
> I'm failing to see that, because those implementations would still use
> the old struct declarations they have been built with, and hence would
> still threat it as signed?
Until they rebuild against the updated header, without any change to
their code.
Anthony - do you have any thoughts here?
Jan
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