Explain why libgraal requires -H:+ClassForNameRespectsClassLoader

Author: olpaw

substratevm/mx.substratevm/mx_substratevm.py

@@ -1671,13 +1671,23 @@ def prevent_build_path_in_libgraal():
 ] if mx.is_interactive() else []) + svm_experimental_options([
     "-H:LibGraalClassLoader=jdk.graal.compiler.libgraal.loader.HostedLibGraalClassLoader",
     "-Dlibgraal.module.path=${.}/../../../graalvm/libgraal.jar",
-    '-H:+ClassForNameRespectsClassLoader',
     '-H:-UseServiceLoaderFeature',
     '-H:+AllowFoldMethods',
     '-Dtruffle.TruffleRuntime=',
     '-H:+JNIEnhancedErrorCodes',
     '-H:InitialCollectionPolicy=LibGraal',
 
+    # A libgraal image contains classes with the same FQN loaded by different classloaders.
+    # I.e. the SVM runtime depends on
+    # - jdk.vm.ci.* classes loaded by the bootstrap classloader
+    # - jdk.graal.compiler.options.* classes loaded by the platform classloader
+    # - org.graalvm.collections.* classes loaded by the app classloader
+    # But potentially different versions of those classes are also loaded by the
+    # LibGraalClassLoader as part of the classes that libgraal consist of.
+    # Thus, we cannot use the naive default ClassForName implementation that only
+    # works if there are no two different classes in the image with the same FQN.
+    '-H:+ClassForNameRespectsClassLoader',
+
     # Needed for initializing jdk.vm.ci.services.Services.IS_BUILDING_NATIVE_IMAGE.
     # Remove after JDK-8346781.
     '-Djdk.vm.ci.services.aot=true',