Does CDS archive generation work for crossbuilds?

[Anton Kozlov]

QEMU user space emulation [1] works pretty fast. On my linux-x86 laptop native
java -Xshare:dump completes in 0.4 sec, and with qemu-aarch64 it's about 2.3
sec. GHA now provides a runnable instruction on how to create the sysroot [2].

Regarding problems, different page size for linux-aarch64 first comes to mind,
but it should be fixed by JDK-8268396: "CDS archive with 4K alignment unusable
on machines with 64k pages"

Thanks,
Anton

[1] https://www.qemu.org/docs/master/user/main.html
[2] https://github.com/openjdk/jdk/blob/master/.github/workflows/submit.yml#L514



On 10/29/21 14:35, Magnus Ihse Bursie wrote:
> On 2021-10-28 22:56, Ioi Lam wrote:
>> How reliable would it be to use qemu to run the cross-compiled binaries? Has anyone tried that recently?
> I experimented with qemu and the JDK build some years ago (so not really recently). As I remember it, the takeaway was that it probably was reliable, but it was slow as h*ll, up to the point of being practically unusable.
> 
> Add to this the fact that you need to prepare an entire OS image, complete with all tools needed to build the JDK... I set up a few such images for my own use (I think it was emulating linux-aarch64 on x64) to run testing. I had an idea of describing how I did to share the knowledge, but in the end it was just too complicated and slow to even consider recommending.
> 
> /Magnus
>>
>>
>> On 10/23/21 5:48 AM, Thomas Stüfe wrote:
>>> Hi Alan,
>>>
>>> On Sat, Oct 23, 2021 at 9:58 AM Alan Bateman <Alan.Bateman at oracle.com>
>>> wrote:
>>>
>>>>
>>>> On 23/10/2021 07:57, Thomas Stüfe wrote:
>>>>> Hi,
>>>>>
>>>>> when I crossbuild (for linux aarch64, using a devkit, building on linux
>>>>> x64), for some reason I don't
>>>>> get the classes.jsa generated inside the images directory.
>>>>>
>>>>> My configure options:
>>>>>
>>>>>
>>>> --with-devkit=/shared/projects/openjdk/devkits/x86_64-linux-gnu-to-aarch64-linux-gnu
>>>>> --openjdk-target=aarch64-linux-gnu
>>>>> --with-boot-jdk=/shared/projects/openjdk/jdks/sapmachine17
>>>>>
>>>> --with-build-jdk=/shared/projects/openjdk/jdk-jdk/output-release/images/jdk
>>>>> --with-gtest=/shared/projects/openjdk/gtest/googletest
>>>>> --with-debug-level=fastdebug
>>>>>
>>>>> The build jdk is a freshly build x64 release VM from the same source
>>>> tree.
>>>>> Am I missing something obvious? Is CDS archive generation even supported
>>>>> for crossbuilds?
>>>> It needs the generate run-time to execute "java -Xshare:dump" so I don't
>>>> expect so. hotspot-runtime-dev is probably the place to discuss the
>>>> details. BTW: this came up recently in the context of the jlink plugin
>>>> that generates the CDS archive. The plugin needed a check to ensure that
>>>> the target platform matched the current platform as it could launch the
>>>> target VM to create the dump.
>>>>
>>>>
>>> Thinking for a second, probably it cannot work since we copy binary
>>> structures verbatim to the archive; I guess the chance that they are binary
>>> compatible between platforms is very small. But it should be easily
>>> rectified by calling Xshare:dump on the target platform.
>>>
>>> Thank you!
>>>
>>> ..Thomas
>>>
>>>
>>>> -Alan
>>>>
>>
>