--- a/make/CreateJmods.gmk	Tue Dec 05 23:11:27 2017 +0100
+++ b/make/CreateJmods.gmk	Tue Dec 05 23:14:35 2017 +0100
@@ -1,5 +1,4 @@
-
-# Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 #
 # This code is free software; you can redistribute it and/or modify it
@@ -33,6 +32,8 @@
   $(error MODULE must be set when calling CreateJmods.gmk)
 endif
 
+$(eval $(call IncludeCustomExtension, CreateJmods.gmk))
+
 ################################################################################
 
 JMODS_DIR := $(IMAGES_OUTPUTDIR)/jmods

--- a/make/autoconf/spec.gmk.in	Tue Dec 05 23:11:27 2017 +0100
+++ b/make/autoconf/spec.gmk.in	Tue Dec 05 23:14:35 2017 +0100
@@ -565,6 +565,7 @@
 
 BUILD_JAVA_FLAGS := @BOOTCYCLE_JVM_ARGS_BIG@
 BUILD_JAVA=@FIXPATH@ $(BUILD_JDK)/bin/java $(BUILD_JAVA_FLAGS)
+BUILD_JAR=@FIXPATH@ $(BUILD_JDK)/bin/jar
 
 # Interim langtools and rmic modules and arguments
 INTERIM_LANGTOOLS_BASE_MODULES := java.compiler jdk.compiler jdk.javadoc

--- a/make/common/JarArchive.gmk	Tue Dec 05 23:11:27 2017 +0100
+++ b/make/common/JarArchive.gmk	Tue Dec 05 23:14:35 2017 +0100
@@ -56,6 +56,7 @@
 #       added to the archive.
 #   EXTRA_MANIFEST_ATTR:=Extra attribute to add to manifest.
 #   CHECK_COMPRESS_JAR Check the COMPRESS_JAR variable
+#   JAR_CMD:=Optionally override the jar command to use when creating the archive.
 SetupJarArchive = $(NamedParamsMacroTemplate)
 define SetupJarArchiveBody
 
@@ -65,6 +66,7 @@
   $1_DELETESS_FILE:=$$(dir $$($1_JAR))_the.$$($1_JARNAME)_deletess
   $1_DELETES_FILE:=$$(dir $$($1_JAR))_the.$$($1_JARNAME)_deletes
   $1_BIN:=$$(dir $$($1_JAR))
+  $$(call SetIfEmpty, $1_JAR_CMD, $$(JAR))
 
   ifeq (,$$($1_SUFFIXES))
     # No suffix was set, default to classes.
@@ -109,7 +111,7 @@
 
   # Check if this jar needs to have its index generated.
   ifneq (,$$($1_JARINDEX))
-    $1_JARINDEX = (cd $$(dir $$@) && $(JAR) -i $$(notdir $$@))
+    $1_JARINDEX = (cd $$(dir $$@) && $$($1_JAR_CMD) -i $$(notdir $$@))
   else
     $1_JARINDEX = true
   endif
@@ -189,7 +191,7 @@
   $1_UPDATE_CONTENTS=\
       if [ "`$(WC) -l $$($1_BIN)/_the.$$($1_JARNAME)_contents | $(AWK) '{ print $$$$1 }'`" -gt "0" ]; then \
         $(ECHO) "  updating" `$(WC) -l $$($1_BIN)/_the.$$($1_JARNAME)_contents | $(AWK) '{ print $$$$1 }'` files && \
-        $(JAR) $$($1_JAR_UPDATE_OPTIONS) $$@ @$$($1_BIN)/_the.$$($1_JARNAME)_contents; \
+        $$($1_JAR_CMD) $$($1_JAR_UPDATE_OPTIONS) $$@ @$$($1_BIN)/_the.$$($1_JARNAME)_contents; \
       fi $$(NEWLINE)
   # The s-variants of the above macros are used when the jar is created from scratch.
   # NOTICE: please leave the parentheses space separated otherwise the AIX build will break!
@@ -208,7 +210,7 @@
             | $(SED) 's|$$(src)/|-C $$(src) |g' >> \
         $$($1_BIN)/_the.$$($1_JARNAME)_contents) $$(NEWLINE) )
   endif
-  $1_SUPDATE_CONTENTS=$(JAR) $$($1_JAR_UPDATE_OPTIONS) $$@ @$$($1_BIN)/_the.$$($1_JARNAME)_contents $$(NEWLINE)
+  $1_SUPDATE_CONTENTS=$$($1_JAR_CMD) $$($1_JAR_UPDATE_OPTIONS) $$@ @$$($1_BIN)/_the.$$($1_JARNAME)_contents $$(NEWLINE)
 
   # Use a slightly shorter name for logging, but with enough path to identify this jar.
   $1_NAME:=$$(subst $$(OUTPUTDIR)/,,$$($1_JAR))
@@ -226,7 +228,7 @@
   endif
 
   # Include all variables of significance in the vardeps file
-  $1_VARDEPS := $(JAR) $$($1_JAR_CREATE_OPTIONS) $$($1_MANIFEST) \
+  $1_VARDEPS := $$($1_JAR_CMD) $$($1_JAR_CREATE_OPTIONS) $$($1_MANIFEST) \
       $$($1_JARMAIN) $$($1_EXTRA_MANIFEST_ATTR) $$($1_ORIG_DEPS) $$($1_SRCS) \
       $$($1_INCLUDES) $$($1_EXCLUDES) $$($1_EXCLUDE_FILES) $$($1_EXTRA_FILES)
   $1_VARDEPS_FILE := $$(call DependOnVariable, $1_VARDEPS, $$(dir $$($1_JAR))_the.$$($1_JARNAME).vardeps)
@@ -250,7 +252,7 @@
 	  $$(if $$($1_EXTRA_MANIFEST_ATTR), \
 	    $(PRINTF) "$$($1_EXTRA_MANIFEST_ATTR)\n" >> $$($1_MANIFEST_FILE) $$(NEWLINE)) \
 	  $(ECHO) Creating $$($1_NAME) $$(NEWLINE) \
-	  $(JAR) $$($1_JAR_CREATE_OPTIONS) $$@ $$($1_MANIFEST_FILE) $$(NEWLINE) \
+	  $$($1_JAR_CMD) $$($1_JAR_CREATE_OPTIONS) $$@ $$($1_MANIFEST_FILE) $$(NEWLINE) \
 	  $$($1_SCAPTURE_CONTENTS) \
 	  $$($1_SCAPTURE_METAINF) \
 	  $$($1_SUPDATE_CONTENTS) \