RFR: 8303002: Reject packed structs from linker [v6]

[Maurizio Cimadamore]

On Thu, 20 Apr 2023 01:12:44 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch adds checks in AbstractLinker to reject packed structs and structs with excess padding (e.g. unnamed bitfields), since both of those are currently not supported, and the ABI/spec seems too vague to base support on.
>
> Jorn Vernee has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - restrictions -> characteristics
>  - polish pt. 2
>  - polish wording
>  - review comments

Looks good.

One (optional, for future?) thing that came to mind, is that if we wanted to speed up the check we could compute whether a layout is canonical or not on construction (since for structs we already have to go through all the elements and check alignment).

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Marked as reviewed by mcimadamore (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13164#pullrequestreview-1393584926