Does CDS archive generation work for crossbuilds?

[Magnus Ihse Bursie]

On 2021-10-29 21:35, Anton Kozlov wrote:
> 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].
But that time excludes booting up the virtual machine, I presume.

Nevertheless, if someone is interested in going down this road to get 
CDS generation for cross-compilation, I would not object to putting it 
in the build system.

/Magnus
>
> 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
>>>>>
>>>
>>