On 05/08/2022 11:18, Craig Raw wrote:
I am having an issue concerning the reproducibility of the JVM
libraries produced by JLink. When running the same build script across
different machines with the same JDK, sometimes the binaries and libs
in the lib/runtime/bin and lib/runtime/lib folders are different. If
one of the *.so files is different, they all are. However, the
lib/runtime/lib/modules file produced by JLink is consistently
identical. The machines running the builds are all Linux running
flavours of Ubuntu.
On examining the issue more closely, I notice that sometimes the files
are identical to the ones in the JDK installation, and sometimes they
are not. They are not significantly different, for example:
JDK:
-rw-rw-r-- 1 xxx xxx 16560 Aug 4 18:08 libjsig.so
JLink:
-rw-rw-r-- 1 xxx xxx 17136 Aug 4 19:23 libjsig.so
Further, I've tried running the java binaries in each, and they differ
in that one is 'sharing' and the other not:
xxx@yyy:~$ ~/.sdkman/candidates/java/18.0.1-tem/bin/java --version
openjdk 18.0.1 2022-04-19
OpenJDK Runtime Environment Temurin-18.0.1+10 (build 18.0.1+10)
OpenJDK 64-Bit Server VM Temurin-18.0.1+10 (build 18.0.1+10, mixed
mode, sharing)
xxx@yyy:~$ ~/project/build/image/bin/java --version
openjdk 18.0.1 2022-04-19
OpenJDK Runtime Environment Temurin-18.0.1+10 (build 18.0.1+10)
OpenJDK 64-Bit Server VM Temurin-18.0.1+10 (build 18.0.1+10, mixed mode)
What would cause JLink to modify the JVM itself? Is there a way I can
achieve a consistently reproducible JVM image?
I assume the jlink command used to generate project/build/image doesn't
specify --generate-cds-archive so that will explain why you don't see
"sharing" in the java -version output. You can use
project/build/image/bin/java -Xshare:dump to do the generate it too.
For the .so file it is possible that your jlink command specifies
-strip-debug or --strip-native-debug-symbols? That might explain why the
sizes are different to the initial image. The stripping of debug symbols
from shared objects runs the objcopy command. Off-hand I don't know if
this is reproducible but maybe there are different versions on the
Ubuntu systems? If you aren't stripping debug symbols then another
possibility is that that the package modules (jmod files) used on the
different versions are identical - this is something you can quickly check.
-Alan.
