The future of 32-bit?

[Thomas Stüfe]

Hi,

Continuing our discussion at the last FOSDEM workshop, I would like to know
what we think about the future of 32-bit support.

Supporting 32-bit became a lot more cumbersome after the x86 port was
removed. Before, one could easily build 32-bit on the ubiquitous x64
platforms with --target-bits=32; that is not an option anymore.

We have two remaining 32-bit platforms, at least in theory:

- arm32
- zero 32-bit

Zero 32-bit has been broken for a long while now; see
https://bugs.openjdk.org/browse/JDK-8353699. I try this occasionally and
don't remember the last time it built successfully.

Arm32 is the last bastion of serious 32-bit support, and the last option
for testing 32-bit coding. So, one needs to build arm32 (best done via
crossbuild), then spin up an arm32 system to test the changes. I do this
with a slow-as-molasses Raspberry. It is not fun.

Unfortunately, maintaining 32-bit is not as easy as "make sure it builds
and fix smaller things". It requires real development, especially in the
context of ongoing object header work.

32-bit also means we need to keep some form of uncompressed class pointers
around, which makes the eventual removal of uncompressed class pointers
(see [2]) more difficult. The current plan is to implement some sort of
fake-compressed-class-pointer mode [3], which sounds easy in theory but is
still tricky work I'd rather avoid.

Keeping up 32-bit development in the face of dwindling options to build and
test is a struggle. It has been a struggle for some time now. Even the
comparatively well-maintained arm32 platform had periodic weeks of
brokenness after heavy upstream changes. And this is not intended to
diminish the effort put in by the arm32-maintainers. They are few, and they
do good work.

But I expect this periodic brokenness to worsen now after the removal of
x86. This is not a good situation.

Thank you, Thomas

[1] https://bugs.openjdk.org/browse/JDK-8353699
[2] https://bugs.openjdk.org/browse/JDK-8350754
[3]
https://bugs.openjdk.org/browse/JDK-8350754?focusedId=14757275&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14757275
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