In the old build we have the following logic to deal with some of the platform specific files being located in a source repository instead of being generated at build time (this is for cross-compilation):

./java/nio/Makefile

ifdef NIO_PLATFORM_CLASSES_ROOT_DIR
$(SCH_GEN)/SocketOptionRegistry.java: $(NIO_PLATFORM_CLASSES_ROOT_DIR)/sun/nio/ch/SocketOptionRegistry-$(PLATFORM)-$(ARCH).j
ava
        $(prep-target)
        $(CP) $< $@
else
$(SCH_GEN)/SocketOptionRegistry.java: $(GENSOR_EXE)
        $(prep-target)
        NAWK="$(NAWK)" SH="$(SH)" $(SH) -e addNotices.sh "$(SOR_COPYRIGHT_YEARS)" > $@
        $(GENSOR_EXE) >> $@
endif


In build-infra the NIO_PLATFORM_CLASSES_ROOT_DIR path variable wasn't used and instead we have hardwired a path to src/closed

ifneq ($(wildcard $(JDK_TOPDIR)/src/closed/solaris/classes/sun/nio/ch/SocketOptionRegistry-$(OPENJDK_TARGET_OS)-$(OPENJDK_TA
RGET_CPU_ARCH).java),)
  HAS_SOCKET_OPTION_REGISTRY:=true
endif

ifneq ($(HAS_SOCKET_OPTION_REGISTRY),true)
...
else
...
endif


This affects both the SocketOptionRegistry and UnixConstants