When generating the CDS default classlist at build time, we currently run a trial application with no CDS enabled. This means we take slightly different paths through the initial bootstraps than we will when later running -Xshare:dump on a full image.

Similarly, when generating the default archive using -Xshare:dump, any pre-existing CDS archive is ignored. This again mean we take different paths through the bootstrap when dumping vs typical runtime.

By doing multiple invocations of the HelloClasslist application, with a CDS dump in between, the lib/classlist file is trimmed down:

diff -r 474a1f484ff0 make/GenerateLinkOptData.gmk
--- a/make/GenerateLinkOptData.gmk Thu Dec 19 14:47:32 2019 +0100
+++ b/make/GenerateLinkOptData.gmk Thu Dec 19 16:29:22 2019 +0100
@@ -66,6 +66,13 @@
  $(call LogInfo, Generating $(patsubst $(OUTPUTDIR)/%, %, $@))
  $(call LogInfo, Generating $(patsubst $(OUTPUTDIR)/%, %, $(JLI_TRACE_FILE)))
  $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -XX:DumpLoadedClassList=$@.raw \
+ -Duser.language=en -Duser.country=US \
+ -cp $(SUPPORT_OUTPUTDIR)/classlist.jar \
+ build.tools.classlist.HelloClasslist $(LOG_DEBUG)
+ $(GREP) -v HelloClasslist $@.raw > $(INTERIM_IMAGE_DIR)/lib/classlist
+ $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -Xshare:dump \
+ -Xmx128M -Xms128M $(LOG_INFO)
+ $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -XX:DumpLoadedClassList=$@.raw \
  -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true \
  -Duser.language=en -Duser.country=US \
  -cp $(SUPPORT_OUTPUTDIR)/classlist.jar \

This has partial effect (jdk.internal.module.SystemModules$all is excluded from base CDS).

To get full effect we need to ensure -Xshare:dump doesn't include such classes we'll not load during real startup, e.g. by having -Xshare:dump changed to not dump anything except the classes explicitly listed in the classlist file. This would reduce variance of CDS archives generated on different systems with different settings.