On 11/5/21 9:38 AM, Magnus Ihse Bursie wrote:
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.
I think user space emulation doesn't spin up a new virtual machine. It
runs on the same kernel as the build host. QEMU does the translation
between the the user program and the OS (system calls, signals, etc). So
the start-up overhead is pretty minimal.
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.
I filed https://bugs.openjdk.java.net/browse/JDK-8276791 in case there
are any volunteers :-)
Thanks
- Ioi
/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.bate...@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
