[foreign-memaccess+abi] RFR: 8315917: Passing struct by values seems under specified [v2]

[Maurizio Cimadamore]

On Mon, 11 Sep 2023 15:14:21 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> As discussed in the JBS issue, the exceptions thrown by a downcall method handle for invalid by-value struct arguments are currently not specified.
>> 
>> There are two cases in which we access a memory segment passed as an argument when unboxing it as part of a downcall handle invocation:
>> 1. In the impl of the `BufferLoad` binding, where we call `MemorySegment::get`. This is on platforms that decompose the struct into registers, such as SysV. 
>> 2. In the impl of `Copy`, where we call `MemorySegment::copy`. This is on Windows where we need to copy a struct to implement by-value semantics.
>> 
>> Since these by-value struct memory segments are given to us by the user, there can be various reasons why these segments can not be accessed, such as the scope already being closed, or the segment belonging to a different thread. The following exceptions may occur: `IllegalStateException`, `WrongThreadException`, `IndexOutOfBoundsException`, `UnsupportedOperationException`, and `IllegalArgumentException` (as specified by MS::get and MS::copy).
>> 
>> Solution: update the specification of `Linker::downcallHandle` to specify that an exception thrown by MS::get or MS::copy might be thrown when invoking the downcall handle.
>
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Clarify text
>   
>   Co-authored-by: Maurizio Cimadamore <54672762+mcimadamore at users.noreply.github.com>

Marked as reviewed by mcimadamore (Committer).

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PR Review: https://git.openjdk.org/panama-foreign/pull/881#pullrequestreview-1620262905