JEP 388: Windows/AArch64 Port

Authors	Monica Beckwith, Ludovic Henry, Bernhard Urban-Forster
Owner	Vladimir Kozlov
Type	Feature
Scope	Implementation
Status	Closed / Delivered
Release	16
Component	hotspot / runtime
Discussion	aarch64 dash port dash dev at openjdk dot java dot net
Effort	M
Duration	S
Blocks	JEP 391: macOS/AArch64 Port
Reviewed by	Vladimir Kozlov
Endorsed by	Mark Reinhold, Vladimir Kozlov
Created	2020/06/29 19:13
Updated	2024/07/26 14:26
Issue	8248496

Summary

Port the JDK to Windows/AArch64.

Motivation

With the release of new consumer and server-class AArch64 (ARM64) hardware, Windows/AArch64 has become an important platform due to end-user demand.

Description

We have ported the JDK to Windows/AArch64, by extending the work previously done for the Linux/AArch64 port (JEP 237). This port includes the template interpreter, the C1 and C2 JIT compilers, and garbage collectors (serial, parallel, G1, Z and Shenandoah). It supports both the Windows 10 and Windows Server 2016 operating systems.

The focus of this JEP is not the porting effort itself, which is mostly complete, but rather the integration of the port into the JDK main-line repository.

Currently, we have a little over a dozen changesets. We have kept the changes to the shared code to a minimum. Our changes extend the support of the AArch64 memory model to Windows, address some MSVC issues, add LLP64 support to the AArch64 port, and perform CPU feature detection on Windows. We have also modified the build scripts to better support cross-compilation and the Windows toolchain.

The new platform code by itself is confined to 15 (+4) files and 1222 lines (+322).

Early-access binaries are available here.

Testing

We have done thorough functional, performance, and regression testing on AArch64 test systems including Ampere eMAG1s, Marvell ThunderX2s (with SMT both on and off), and Surface Pro Xs. Our test suites include JTReg, JCStress, jmh-jdk-microbenchmarks, JFC applications and applets (demo/jfc), SPECJBB2005, SPECJBB2015, SPEC SERT, SPECJVM2008, DaCapo, and a few smaller benchmarks. Two of the test matrices are documented in detail: JTReg and SPECJBB2015.

Apart from the AArch64 systems, we have also tested our patches on x64 systems (Intel Skylakes). Our test coverage includes Linux/AArch64, Windows/AArch64, Windows/x64, and, only for functional testing, Linux/x64.

We have a robust CI for functional tests and will continue running our patches through the CI as we make further changes.

Risks and Assumptions

We have made changes to shared code in the Linux/AArch64 backend to extend LP64 (64-bit long ints and pointers) to accommodate the long-long ints and pointers (LLP64) needed by the 64-bit Windows platform.
We have also modified shared code on Windows, as mentioned above.
We need to rework the usage of register x18, which on Windows/AArch64 is used for the Windows Thread Environment Block (TEB). We are working together with the Lead of the AArch64 Port project to find a graceful solution.