[foreign-abi] RFR: 8253255: Investigate replacing ABI layout attributes with custom subtypes of ValueLayout

[Maurizio Cimadamore]

On Mon, 28 Sep 2020 16:01:30 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Hi,
> 
> This patch removes ABI attributes, and replaces them with a custom ValueLayout subtype, called CValueLayout.
> 
> This, for one, allows us to override the describeConstable method to return a dynamic constant descriptor that will
> load the public constant field in CLinker. This avoids getting illegal access errors when trying to resolve the
> internal ABI attributes. The illegal access error was forcing clients, like jextract, to basically re-implement the
> describeConstable methods for FunctionDescriptor, GroupLayout, SequenceLayout and ValueLayout in order the
> 'cannonicalize' these constant descriptors to reference the fields.  Most of the needed changes were in the TypeClass
> classes, which now need to map the CValueLayout.Kind into the appropriate ABI classes (though doing this was pretty
> straight forward).  I've also added a test to make sure it is possible to resolve constant descriptors with these
> CValueLayouts inside with a public Lookup object.  Thanks, Jorn

Looks very neat - what about the equals/hashcode behavior of the new class? Will CValueLayout be considered equals with
another value layout with same attributes and charateristics?

I think so - code looks like (in ValueLayout):

@Override
 91     public boolean equals(Object other) {
 92         if (this == other) {
 93             return true;
 94         }
 95         if (!super.equals(other)) {
 96             return false;
 97         }
 98         if (!(other instanceof ValueLayout)) {
 99             return false;
100         }
101         ValueLayout v = (ValueLayout)other;
102         return order.equals(v.order) &&
103             bitSize() == v.bitSize() &&
104             alignment == v.alignment;
105     }
Let's maybe add a test on this.

-------------

PR: https://git.openjdk.java.net/panama-foreign/pull/358