[XEN PATCH for-4.17 v6 2/5] libs/light: Rework targets prerequisites

[Anthony PERARD <anthony.perard@citrix.com>]

No need for $(AUTOSRCS), GNU make can generate them as needed when
trying to build them as needed when trying to build the object. Also,
those two AUTOSRCS don't need to be a prerequisite of "all". As for
the "clean" target, those two files are already removed via "_*.c".

We don't need $(AUTOINCS) either:
- As for both _libxl_save_msgs*.h headers, we are adding more
  selective dependencies so the headers will still be generated as
  needed.
- "clean" rule already delete the _*.h files, so AUTOINCS aren't needed
  there.

"libxl_internal_json.h" doesn't seems to have ever existed, so the
dependency is removed.

Rework objects prerequisites, to have them dependents on either
"libxl.h" or "libxl_internal.h". "libxl.h" is not normally included
directly in the source code as "libxl_internal.h" is used instead, but
we have "libxl.h" as prerequisite of "libxl_internal.h", so generated
headers will still be generated as needed.

Make doesn't need "libxl.h" to generate "testidl.c", "libxl.h" is only
needed later when building "testidl.o". This avoid the need to
regenerate "testidl.c" when only "libxl.h" changed. Also use automatic
variables $< and $@.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    v6:
    - rebased, part of the patch commited as 4ff0811
    - reword commit message
    
    v4:
    - new patch

 tools/libs/light/Makefile | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/tools/libs/light/Makefile b/tools/libs/light/Makefile
index cd3fa855e1..b28447a2ae 100644
--- a/tools/libs/light/Makefile
+++ b/tools/libs/light/Makefile
@@ -148,9 +148,6 @@ LIBXL_TEST_OBJS += $(foreach t, $(LIBXL_TESTS_INSIDE),libxl_test_$t.opic)
 TEST_PROG_OBJS += $(foreach t, $(LIBXL_TESTS_PROGS),test_$t.o) test_common.o
 TEST_PROGS += $(foreach t, $(LIBXL_TESTS_PROGS),test_$t)
 
-AUTOINCS = _libxl_save_msgs_callout.h _libxl_save_msgs_helper.h
-AUTOSRCS = _libxl_save_msgs_callout.c _libxl_save_msgs_helper.c
-
 CLIENTS = testidl libxl-save-helper
 
 SAVE_HELPER_OBJS = libxl_save_helper.o _libxl_save_msgs_helper.o
@@ -178,13 +175,13 @@ libxl_x86_acpi.o libxl_x86_acpi.opic: CFLAGS += -I$(XEN_ROOT)/tools
 $(SAVE_HELPER_OBJS): CFLAGS += $(CFLAGS_libxenctrl) $(CFLAGS_libxenevtchn) $(CFLAGS_libxenguest)
 
 testidl.o: CFLAGS += $(CFLAGS_libxenctrl) $(CFLAGS_libxenlight)
-testidl.c: libxl_types.idl gentest.py $(XEN_INCLUDE)/libxl.h $(AUTOINCS)
-	$(PYTHON) gentest.py libxl_types.idl testidl.c.new
-	mv testidl.c.new testidl.c
+testidl.c: libxl_types.idl gentest.py
+	$(PYTHON) gentest.py $< $@.new
+	mv -f $@.new $@
 
-all: $(CLIENTS) $(TEST_PROGS) $(AUTOSRCS) $(AUTOINCS)
+all: $(CLIENTS) $(TEST_PROGS)
 
-$(OBJS-y) $(PIC_OBJS) $(SAVE_HELPER_OBJS) $(LIBXL_TEST_OBJS) $(TEST_PROG_OBJS): $(AUTOINCS) libxl.api-ok
+$(OBJS-y) $(PIC_OBJS) $(SAVE_HELPER_OBJS) $(LIBXL_TEST_OBJS) $(TEST_PROG_OBJS): libxl.api-ok
 
 $(DSDT_FILES-y): acpi
 
@@ -196,7 +193,7 @@ libxl.api-ok: check-libxl-api-rules _libxl.api-for-check
 	$(PERL) $^
 	touch $@
 
-_libxl.api-for-check: $(XEN_INCLUDE)/libxl.h $(AUTOINCS)
+_libxl.api-for-check: $(XEN_INCLUDE)/libxl.h
 	$(CC) $(CPPFLAGS) $(CFLAGS) -c -E $< $(APPEND_CFLAGS) \
 		-DLIBXL_EXTERNAL_CALLERS_ONLY=LIBXL_EXTERNAL_CALLERS_ONLY \
 		>$@.new
@@ -208,14 +205,22 @@ _libxl_save_msgs_helper.h _libxl_save_msgs_callout.h: \
 	$(PERL) -w $< $@ >$@.new
 	$(call move-if-changed,$@.new,$@)
 
+#
+# headers dependencies on generated headers
+#
 $(XEN_INCLUDE)/libxl.h: $(XEN_INCLUDE)/_libxl_types.h
 $(XEN_INCLUDE)/libxl_json.h: $(XEN_INCLUDE)/_libxl_types_json.h
 libxl_internal.h: $(XEN_INCLUDE)/libxl.h $(XEN_INCLUDE)/libxl_json.h
 libxl_internal.h: _libxl_types_internal.h _libxl_types_private.h _libxl_types_internal_private.h
-libxl_internal_json.h: _libxl_types_internal_json.h
+libxl_internal.h: _libxl_save_msgs_callout.h
 
-$(OBJS-y) $(PIC_OBJS) $(LIBXL_TEST_OBJS) $(TEST_PROG_OBJS) $(SAVE_HELPER_OBJS): $(XEN_INCLUDE)/libxl.h
+#
+# objects dependencies on headers that depends on generated headers
+#
+$(TEST_PROG_OBJS): $(XEN_INCLUDE)/libxl.h
 $(OBJS-y) $(PIC_OBJS) $(LIBXL_TEST_OBJS): libxl_internal.h
+$(SAVE_HELPER_OBJS): $(XEN_INCLUDE)/libxl.h _libxl_save_msgs_helper.h
+testidl.o: $(XEN_INCLUDE)/libxl.h
 
 # This exploits the 'multi-target pattern rule' trick.
 # gentypes.py should be executed only once to make all the targets.
@@ -262,5 +267,4 @@ clean::
 	$(RM) testidl.c.new testidl.c *.api-ok
 	$(RM) $(TEST_PROGS) libxenlight_test.so libxl_test_*.opic
 	$(RM) -r __pycache__
-	$(RM) $(AUTOSRCS) $(AUTOINCS)
 	$(MAKE) -C $(ACPI_PATH) ACPI_BUILD_DIR=$(CURDIR) clean
-- 
Anthony PERARD