The following error happens after JDK-8265602 (-XX:DumpLoadedClassList should support custom loaders), because the classlist now contains unique IDs for each class.

In some cases, the failures are minor:

$ diff classlist.1 classlist.2
207,208c207,208
< jdk/internal/misc/VM id: 201
< jdk/internal/util/SystemProps id: 202
---
> jdk/internal/util/SystemProps id: 201
> jdk/internal/misc/VM id: 202

=============
Finished building target 'default (images test-image docs)' in configuration 'linux-x64-cmp-baseline'
Comparing between comparison rebuild (this/new) and baseline (other/old)
workspace/build/compare-build/linux-x64-cmp-baseline
Comparing to:
workspace/build/linux-x64-cmp-baseline

Selecting normal images for JDK compare
  workspace/build/compare-build/linux-x64-cmp-baseline/images/jdk
  workspace/build/linux-x64-cmp-baseline/images/jdk
Also comparing docs
Also comparing test image
JDK Directory structure...Identical!
JDK File names...Identical!
Docs Directory structure...Identical!
Docs File names...Identical!
Test Directory structure...Identical!
Test File names...Identical!
JDK Libraries...
 Binary : Size : Symbols : Deps : Fulldump : Disass :
Test Libraries...
 Binary : Size : Symbols : Deps : Fulldump : Disass :
JDK Executables...
 Binary : Size : Symbols : Deps : Fulldump : Disass :
Test Executables...
 Binary : Size : Symbols : Deps : Fulldump : Disass :
JDK Other files with binary differences...
./lib/classlist
Docs Other files with binary differences...
Test Other files with binary differences...
JDK Zip/tar.gz files...
Test Zip/tar.gz files...
sec-bin.zip...
JDK Jar files...
Test Jar files...
Jmod files...
JDK Permissions...Identical!
JDK File types...Identical!
Test File types...Identical!

REGRESSIONS FOUND!

workspace/open/make/Init.gmk:366: recipe for target 'post-compare-build' failed
make[1]: *** [post-compare-build] Error 1