Initial support for arbitrary externs on bmv2

[engjefersonsantiago]

Dear all,

I have implemented the initial support to extern instances in the bmv2 backend compiler. I have tested with P4-16 and P4-14. It is functional with P4-16, but I've seen an issue with P4-14, where the instantiation parameters are not being taken.

Regards,
Jeferson

[hanw]

Thanks, I have an upcoming patch that already implemented this feature as part of a larger refactoring. Would you mind holding on to this till I merged the refactor in? Then you can modify the refactored backend instead.

[engjefersonsantiago]

Not problem. I'll wait then.

Regards,
Jeferson

[mihaibudiu]

We should define an annotation (@userextern), which indicates that an extern is provided by the user.
Then the warning becomes an error if the annotation is missing.

[hanw]

@engjefersonsantiago It is going to be difficult for you rebase this pull request, given the most recent refactor. I suggest you re-apply your changes to the refactor bmv2 backend code. Sorry for the trouble.

[engjefersonsantiago]

@hanw, maybe it will be a bit easier for you to check if your implementation fully contains my patch. Your changes have more than 6k LOC, mine is just 50 LOC.

[hanw]

Sure I will do that. Thanks.

[hanw]

Please submit a separate pull request for issue #604, I will close this one for now.