diff --git a/core/Makefile b/core/Makefile
index 40293ef..59432be 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1430,7 +1430,7 @@
 # the dependency will be set up later in build/core/main.mk.
 $(EMMA_META_ZIP) :
 	@echo "Collecting Emma coverage meta files."
-	$(hide) find $(TARGET_COMMON_OUT_ROOT) -name "coverage.em" | \
+	$(hide) find $(TARGET_COMMON_OUT_ROOT) $(HOST_COMMON_OUT_ROOT) -name "coverage.em" | \
 		zip -@ -q $@
 
 endif # EMMA_INSTRUMENT=true
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index 3287b57..2a8f18f 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -20,22 +20,64 @@
 
 #######################################
 include $(BUILD_SYSTEM)/host_java_library_common.mk
+#######################################
+
+# Enable emma instrumentation only if the module asks so.
+ifeq (true,$(LOCAL_EMMA_INSTRUMENT))
+ifneq (true,$(EMMA_INSTRUMENT))
+LOCAL_EMMA_INSTRUMENT :=
+endif
+endif
+
+full_classes_compiled_jar := $(intermediates.COMMON)/classes-full-debug.jar
+emma_intermediates_dir := $(intermediates.COMMON)/emma_out
+# emma is hardcoded to use the leaf name of its input for the output file --
+# only the output directory can be changed
+full_classes_emma_jar := $(emma_intermediates_dir)/lib/$(notdir $(full_classes_compiled_jar))
+
+LOCAL_INTERMEDIATE_TARGETS += \
+    $(full_classes_compiled_jar) \
+    $(full_classes_emma_jar)
+
+#######################################
 include $(BUILD_SYSTEM)/base_rules.mk
 #######################################
 
-$(full_classes_compiled_jar): PRIVATE_JAVAC_DEBUG_FLAGS := -g
+ifeq (true,$(LOCAL_EMMA_INSTRUMENT))
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILE := $(intermediates.COMMON)/coverage.em
+$(full_classes_emma_jar): PRIVATE_EMMA_INTERMEDIATES_DIR := $(emma_intermediates_dir)
+ifdef LOCAL_EMMA_COVERAGE_FILTER
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := $(LOCAL_EMMA_COVERAGE_FILTER)
+else
+# by default, avoid applying emma instrumentation onto emma classes itself,
+# otherwise there will be exceptions thrown
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := *,-emma,-emmarun,-com.vladium.*
+endif
+# this rule will generate both $(PRIVATE_EMMA_COVERAGE_FILE) and
+# $(full_classes_emma_jar)
+$(full_classes_emma_jar) : $(full_classes_compiled_jar) | $(EMMA_JAR)
+	$(transform-classes.jar-to-emma)
 
-java_alternative_checked_module :=
+$(LOCAL_BUILT_MODULE) : $(full_classes_emma_jar)
+	@echo Copying: $@
+	$(hide) $(ACP) -fp $< $@
+
+else # LOCAL_EMMA_INSTRUMENT
+# Directly build into LOCAL_BUILT_MODULE.
+full_classes_compiled_jar := $(LOCAL_BUILT_MODULE)
+endif # LOCAL_EMMA_INSTRUMENT
+
+$(full_classes_compiled_jar): PRIVATE_JAVAC_DEBUG_FLAGS := -g
 
 # The layers file allows you to enforce a layering between java packages.
 # Run build/tools/java-layers.py for more details.
 layers_file := $(addprefix $(LOCAL_PATH)/, $(LOCAL_JAVA_LAYERS_FILE))
 
-$(LOCAL_BUILT_MODULE): PRIVATE_JAVA_LAYERS_FILE := $(layers_file)
-$(LOCAL_BUILT_MODULE): PRIVATE_JAVACFLAGS := $(LOCAL_JAVACFLAGS)
-$(LOCAL_BUILT_MODULE): PRIVATE_JAR_EXCLUDE_FILES :=
-$(LOCAL_BUILT_MODULE): PRIVATE_JAR_PACKAGES :=
-$(LOCAL_BUILT_MODULE): PRIVATE_RMTYPEDEFS :=
-$(LOCAL_BUILT_MODULE): $(java_sources) $(java_resource_sources) $(full_java_lib_deps) \
+$(full_classes_compiled_jar): PRIVATE_JAVA_LAYERS_FILE := $(layers_file)
+$(full_classes_compiled_jar): PRIVATE_JAVACFLAGS := $(LOCAL_JAVACFLAGS)
+$(full_classes_compiled_jar): PRIVATE_JAR_EXCLUDE_FILES :=
+$(full_classes_compiled_jar): PRIVATE_JAR_PACKAGES :=
+$(full_classes_compiled_jar): PRIVATE_RMTYPEDEFS :=
+$(full_classes_compiled_jar): $(java_sources) $(java_resource_sources) $(full_java_lib_deps) \
 		$(jar_manifest_file) $(proto_java_sources_file_stamp) $(LOCAL_ADDITIONAL_DEPENDENCIES)
 	$(transform-host-java-to-package)