[XEN PATCH v8 06/47] build: avoid re-executing the main Makefile by introducing build.mk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

Currently, the xen/Makefile is re-parsed several times: once to start
the build process, and several more time with Rules.mk including it.
This makes it difficult to work with a Makefile used for several
purpose, and it actually slow down the build process.

So this patch introduce "build.mk" which Rules.mk will use when
present instead of the "Makefile" of a directory. (Linux's Kbuild
named that file "Kbuild".)

We have a few targets to move to "build.mk" identified by them been
build via "make -f Rules.mk" without changing directory.

As for the main targets like "build", we can have them depends on
there underscore-prefix targets like "_build" without having to use
"Rules.mk" while still retaining the check for unsupported
architecture. (Those main rules are changed to be single-colon as
there should only be a single recipe for them.)

With nearly everything needed to move to "build.mk" moved, there is a
single dependency left from "Rules.mk": the variable $(TARGET), so its
assignement is moved to the main Makefile.

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

Notes:
    v8:
    - for $(main-targets) rules, use ; on a single line instead of adding a
      recipe with only @:
    - To include build.mk instead of Makefile, use a simpler expresion with
      $(firstword) and remove the use of $(mk-dir) var
    - removed an extra blank line, and one when updating $(targets)
    - reword patch description
    
    v7:
    - new patch

 xen/Makefile | 69 +++++-----------------------------------------------
 xen/Rules.mk |  6 ++---
 xen/build.mk | 60 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 67 deletions(-)
 create mode 100644 xen/build.mk

diff --git a/xen/Makefile b/xen/Makefile
index 2ad7da7ad67b..ed61f38dd335 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -47,6 +47,8 @@ export KCONFIG_CONFIG ?= .config
 
 export CC CXX LD
 
+export TARGET := $(BASEDIR)/xen
+
 .PHONY: default
 default: build
 
@@ -293,11 +295,12 @@ export CFLAGS_UBSAN
 
 endif # need-config
 
-.PHONY: build install uninstall clean distclean MAP
-build install uninstall debug clean distclean MAP::
+main-targets := build install uninstall clean distclean MAP
+.PHONY: $(main-targets)
 ifneq ($(XEN_TARGET_ARCH),x86_32)
-       $(MAKE) -f Rules.mk _$@
+$(main-targets): %: _% ;
 else
+$(main-targets):
        echo "*** Xen x86/32 target no longer supported!"
 endif
 
@@ -406,66 +409,6 @@ $(TARGET): FORCE
        $(MAKE) -f $(BASEDIR)/Rules.mk 
arch/$(TARGET_ARCH)/include/asm/asm-offsets.h
        $(MAKE) -f $(BASEDIR)/Rules.mk -C arch/$(TARGET_ARCH) $@
 
-quiet_cmd_banner = BANNER  $@
-define cmd_banner
-    if which figlet >/dev/null 2>&1 ; then \
-       echo " Xen $(XEN_FULLVERSION)" | figlet -f $< > $@.tmp; \
-    else \
-       echo " Xen $(XEN_FULLVERSION)" > $@.tmp; \
-    fi; \
-    mv -f $@.tmp $@
-endef
-
-.banner: tools/xen.flf FORCE
-       $(call if_changed,banner)
-targets += .banner
-
-# Don't refresh this files during e.g., 'sudo make install'
-quiet_cmd_compile.h = UPD     $@
-define cmd_compile.h
-    if [ ! -r $@ -o -O $@ ]; then \
-       sed -e 's/@@date@@/$(XEN_BUILD_DATE)/g' \
-           -e 's/@@time@@/$(XEN_BUILD_TIME)/g' \
-           -e 's/@@whoami@@/$(XEN_WHOAMI)/g' \
-           -e 's/@@domain@@/$(XEN_DOMAIN)/g' \
-           -e 's/@@hostname@@/$(XEN_BUILD_HOST)/g' \
-           -e 's!@@compiler@@!$(shell $(CC) $(CFLAGS) --version 2>&1 | head 
-1)!g' \
-           -e 's/@@version@@/$(XEN_VERSION)/g' \
-           -e 's/@@subversion@@/$(XEN_SUBVERSION)/g' \
-           -e 's/@@extraversion@@/$(XEN_EXTRAVERSION)/g' \
-           -e 's!@@changeset@@!$(shell tools/scmversion $(XEN_ROOT) || echo 
"unavailable")!g' \
-           < $< > $(dot-target).tmp; \
-       sed -rf tools/process-banner.sed < .banner >> $(dot-target).tmp; \
-       mv -f $(dot-target).tmp $@; \
-    fi
-endef
-
-include/xen/compile.h: include/xen/compile.h.in .banner FORCE
-       @cat .banner
-       $(call if_changed,compile.h)
-
-targets += include/xen/compile.h
-
-asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c
-       $(CC) $(call cpp_flags,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
-       $(call move-if-changed,$@.new,$@)
-
-arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s
-       @(set -e; \
-         echo "/*"; \
-         echo " * DO NOT MODIFY."; \
-         echo " *"; \
-         echo " * This file was auto-generated from $<"; \
-         echo " *"; \
-         echo " */"; \
-         echo ""; \
-         echo "#ifndef __ASM_OFFSETS_H__"; \
-         echo "#define __ASM_OFFSETS_H__"; \
-         echo ""; \
-         sed -rne "/^[^#].*==>/{s:.*==>(.*)<==.*:\1:; s: [\$$#]: :; p;}"; \
-         echo ""; \
-         echo "#endif") <$< >$@
-
 SUBDIRS = xsm arch/$(TARGET_ARCH) common drivers lib test
 define all_sources
     ( find arch/$(TARGET_ARCH)/include -name '*.h' -print; \
diff --git a/xen/Rules.mk b/xen/Rules.mk
index d21930a7bf71..7b8b9047cfd5 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -8,9 +8,6 @@
 include $(XEN_ROOT)/Config.mk
 include $(BASEDIR)/scripts/Kbuild.include
 
-
-TARGET := $(BASEDIR)/xen
-
 # Note that link order matters!
 ALL_OBJS-y               += $(BASEDIR)/common/built_in.o
 ALL_OBJS-y               += $(BASEDIR)/drivers/built_in.o
@@ -36,7 +33,8 @@ SPECIAL_DATA_SECTIONS := rodata $(foreach a,1 2 4 8 16, \
                                             rodata.cst$(a)) \
                          $(foreach r,rel rel.ro,data.$(r).local)
 
-include Makefile
+# The filename build.mk has precedence over Makefile
+include $(firstword $(wildcard build.mk) Makefile)
 
 # Linking
 # ---------------------------------------------------------------------------
diff --git a/xen/build.mk b/xen/build.mk
new file mode 100644
index 000000000000..622e841c1cc0
--- /dev/null
+++ b/xen/build.mk
@@ -0,0 +1,60 @@
+quiet_cmd_banner = BANNER  $@
+define cmd_banner
+    if which figlet >/dev/null 2>&1 ; then \
+       echo " Xen $(XEN_FULLVERSION)" | figlet -f $< > $@.tmp; \
+    else \
+       echo " Xen $(XEN_FULLVERSION)" > $@.tmp; \
+    fi; \
+    mv -f $@.tmp $@
+endef
+
+.banner: tools/xen.flf FORCE
+       $(call if_changed,banner)
+
+targets += .banner
+
+# Don't refresh this files during e.g., 'sudo make install'
+quiet_cmd_compile.h = UPD     $@
+define cmd_compile.h
+    if [ ! -r $@ -o -O $@ ]; then \
+       sed -e 's/@@date@@/$(XEN_BUILD_DATE)/g' \
+           -e 's/@@time@@/$(XEN_BUILD_TIME)/g' \
+           -e 's/@@whoami@@/$(XEN_WHOAMI)/g' \
+           -e 's/@@domain@@/$(XEN_DOMAIN)/g' \
+           -e 's/@@hostname@@/$(XEN_BUILD_HOST)/g' \
+           -e 's!@@compiler@@!$(shell $(CC) $(CFLAGS) --version 2>&1 | head 
-1)!g' \
+           -e 's/@@version@@/$(XEN_VERSION)/g' \
+           -e 's/@@subversion@@/$(XEN_SUBVERSION)/g' \
+           -e 's/@@extraversion@@/$(XEN_EXTRAVERSION)/g' \
+           -e 's!@@changeset@@!$(shell tools/scmversion $(XEN_ROOT) || echo 
"unavailable")!g' \
+           < $< > $(dot-target).tmp; \
+       sed -rf tools/process-banner.sed < .banner >> $(dot-target).tmp; \
+       mv -f $(dot-target).tmp $@; \
+    fi
+endef
+
+include/xen/compile.h: include/xen/compile.h.in .banner FORCE
+       @cat .banner
+       $(call if_changed,compile.h)
+
+targets += include/xen/compile.h
+
+asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c
+       $(CC) $(call cpp_flags,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
+       $(call move-if-changed,$@.new,$@)
+
+arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s
+       @(set -e; \
+         echo "/*"; \
+         echo " * DO NOT MODIFY."; \
+         echo " *"; \
+         echo " * This file was auto-generated from $<"; \
+         echo " *"; \
+         echo " */"; \
+         echo ""; \
+         echo "#ifndef __ASM_OFFSETS_H__"; \
+         echo "#define __ASM_OFFSETS_H__"; \
+         echo ""; \
+         sed -rne "/^[^#].*==>/{s:.*==>(.*)<==.*:\1:; s: [\$$#]: :; p;}"; \
+         echo ""; \
+         echo "#endif") <$< >$@
-- 
Anthony PERARD