Host endian independence

[Florian Weimer]

* Damien Zammit:

> On 31/8/19 2:22 am, Joseph Myers wrote:
>> The scalar_storage_order attribute could certainly be added to an 
>> appropriately declared structure to move the endianness information 
>> entirely into how the structure is defined and out of the code using the 
>> structure.
>
> I was not aware of this attribute until now, but looks like the best
> approach to me.  I might put together a new proof of concept and send
> in a new set of patches for review.

You need to be careful where you use this features.  Some shared code
cannot use features which are GNU C only (not even the C++ frontend
supports it).  And it's always a bit risky to be an early adopter of
such compiler extensions.

> Florian Weimer wrote:
>> The problem with the existing interfaces is that that they make it hard
>> to take alignment issues into account.  See bug 20243.  When used for
>> parsing packet buffers, they also tend to introduce aliasing violations.
>
> I had a quick look at bug 20243, would it also be fixed by using the
> "packed" attribute and Joseph's idea of putting the endianness info in
> the definition of the structs with the "scalar_storage_order"
> attribute?

Note that either case will need a new struct definition.

Thanks,
Florian