Re: [RFC][PATCH] A generic boolean

H. Peter Anvin
2006-08-04T19:05:31Z

Jes Sorensen wrote:
>>
>> And what will break if you make that switch?
>
> If we are lucky, some binary only modules? :-)
>
> But you're right, it may just have to be documented as one of those
> nasty issues to watch out for.
>

What is really poisonous is structures which get padded when all the
members are naturally aligned. Unfortunately gcc produces really crap
code with __attribute__((packed)) on some architectures, so just using
that isn't a good solution. On the other hand, non-AEABI ARM sometimes
needs it!

For the lack of a __attribute__((nopad)) that would throw a warning or
error on excessive padding, I fear that our best option is an __abi
annotation which would enforce certain rules using sparse, and
presumably provide __attribute__((packed)) on ARM:

- All padding must be explicit.
- All members must be naturally aligned.
- No unportable constructs, like non-int-sized bitfields.

-hpa