Re: Backport request (was: [PATCH v2] tools: convert bitfields to unsigned type)

[Jan Beulich <jbeulich@suse.com>]

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