AArch64: Implement unsafe helper functions

[knn-k]

This commit implements the unsafe helper functions for aarch64.

Signed-off-by: knn-k konno@jp.ibm.com

[knn-k]

The Travis CI build failed with:

DeadTreesElimination.cpp:742:39: error: ‘class TR::ILOpCode’ has no member named ‘isPackedExponentiation’
                if (child->getOpCode().isPackedExponentiation())

This is not caused by this commit.

[hangshao0]

I guess you also need to add vpath to module.xml for AArch64:
https://github.com/eclipse/openj9/blob/master/runtime/vm/module.xml#L148toL150

[hangshao0]

There are also changes required in https://github.com/eclipse/openj9/blob/master/runtime/vm/gphandle.c#L238 that handles SIGBUS from the unsafe helpers.

The idea is that when SIGBUS is triggered from accessing the invalid address in the unsafe helpers, we know the UNSAFE_TARGET_REGISTER (x0 here) has the invalid address, then we update this register to an writable/readable but garbage address on stack, so that we can bypass the offending instruction and turn SIGBUS into an exception.

If you are not making the above change in this PR, please put some comments in unsafeHelper.s and gphandle.c saying that this needs to be done on AArch64.

[knn-k]

@hangshao0 Thanks for your comments.

I will add vpath to module.xml. What should the spec name be for AArch64? I would say linux_aarch64. I guess I also have to put a new file in openj9/buildspecs with the same name (I am not going to do that in this PR) -- Correct?

[knn-k]

Updated files reflecting the comments.

[hangshao0]

What should the spec name be for AArch64? I would say linux_aarch64

I am fine with this name.

I guess I also have to put a new file in openj9/buildspecs with the same name (I am not going to do that in this PR) -- Correct?

Yes.

[hangshao0]

LGTM

[DanHeidinga]

lgtm assuming the linux_aarch64 spec is being added in a separate PR

[DanHeidinga]

Jenkins compile xlinux jdk8

[DanHeidinga]

@knn-k can you rebase to resolve the conflict? I think it should be fairly straightforward

[knn-k]

Resolved merge conflict.

[DanHeidinga]

Sorry @knn-k hopefully the last minor change - the end date in the copyrights of changed files must be 2019

20:12:24 runtime/vm/module.xml
20:12:24 	IBM Copyright date appears to be incorrect
[Pipeline] echo
20:12:24 runtime/vm/xr64/unsafeHelper.s
20:12:24 	IBM Copyright date appears to be incorrect

[knn-k]

Corrected copyright years.

[DanHeidinga]

Jenkins compile xlinux jdk8

[knn-k]

I would like this to be merged if the code is OK.