Panama foreign on AArch64?

[Maurizio Cimadamore]

Hi Nick,
overall, the ABI interface is relatively stable:

http://hg.openjdk.java.net/panama/dev/file/6b1f1666f5f6/src/java.base/share/classes/jdk/internal/foreign/abi/SystemABI.java

This is the interface used by the Panama binder for all system-specific 
stuff - it is conceptually easy, in that it takes a description of a 
function (e.g. native layouts, Java carriers) and return a MethodHandle 
that the client can use to make the call. A similar strategy is used for 
creating callbacks.

Panama supports two ABI implementation for now:

* SysVABI (Linux):
http://hg.openjdk.java.net/panama/dev/file/6b1f1666f5f6/src/java.base/share/classes/jdk/internal/foreign/abi/x64/sysv/SysVx64ABI.java

* Windows ABI:
http://hg.openjdk.java.net/panama/dev/file/6b1f1666f5f6/src/java.base/share/classes/jdk/internal/foreign/abi/x64/windows/Windowsx64ABI.java

Within each ABI implementation, there is a certain degree of freedom on 
how the method handles are generated - for instance, Linux supports two 
MH strategies: universal and direct invoker; Windows has only the 
universal invoker one.

We are also working on an alternate backend, called linkToNative - which 
will eventually obsolete the Linux direct invoker - and make these 
optimizations more portable across the board.

So, if you are looking to add ARM support, I'd suggest looking at what's 
been done for Windows: that is port the universal invoker/upcall 
implementation to ARM - that should be enough to be able to run the 
binder on ARM. When, in the future, linkToNative will land on the main 
'foreign' branch, some tweaks will probably be needed in order to adjust 
the linkToNative logic to ARM - but looking at the work done for Windows 
by Jorn [1, 2], these adjustments seem to be rather small.

Let me know if you need extra pointers. I think this would be a very 
valuable experiment, as it might point out areas where we made 
incorrect, platform-dependent assumptions.

Cheers
Maurizio


[1] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004271.html
[2] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004199.html


On 19/02/2019 07:54, Nick Gasson (Arm Technology China) wrote:
> Hi,
>
> The panama foreign branch currently only has an implementation for x86.
> Is anyone working on or planning to work on an AArch64 port? If not, is
> this something we (Arm) could usefully contribute to now, or would it be
> better to wait until the architecture-specific interfaces are more
> finalised?
>
> Thanks,
> Nick