[XEN PATCH 02/15] build: rework asm-offsets.* build step to use kbuild

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

Use $(if_changed_dep, ) macro to generate "asm-offsets.s" and remove
the use of $(move-if-changes,). That mean that "asm-offset.s" will be
changed even when the output doesn't change.

But "asm-offsets.s" is only used to generated "asm-offsets.h". So
instead of regenerating "asm-offsets.h" every time "asm-offsets.s"
change, we will use "$(filechk, )" to only update the ".h" when the
output change. Also, with "$(filechk, )", the file does get
regenerated when the rule change in the makefile.

This changes also result in a cleaner build log.

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

Instead of having a special $(cmd_asm-offsets.s) command, we could
probably reuse $(cmd_cc_s_c) from Rules.mk, but that would mean that
an hypothetical additional flags "-flto" in CFLAGS would not be
removed anymore, not sure if that matter here.

But then we could write this:

targets += arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s
arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s: CFLAGS-y += -g0
arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: 
arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s FORCE

instead of having to write a rule for asm-offsets.s
---
 xen/build.mk | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/xen/build.mk b/xen/build.mk
index 758590c68e..e2a78aa806 100644
--- a/xen/build.mk
+++ b/xen/build.mk
@@ -40,13 +40,15 @@ include/xen/compile.h: include/xen/compile.h.in .banner 
FORCE
 
 targets += include/xen/compile.h
 
--include $(wildcard .asm-offsets.s.d)
-asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c
-       $(CC) $(call cpp_flags,$(c_flags)) -S -g0 -o $@.new -MQ $@ $<
-       $(call move-if-changed,$@.new,$@)
+quiet_cmd_asm-offsets.s = CC      $@
+cmd_asm-offsets.s = $(CC) $(call cpp_flags,$(c_flags)) -S -g0 $< -o $@
 
-arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s
-       @(set -e; \
+asm-offsets.s: arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.c FORCE
+       $(call if_changed_dep,asm-offsets.s)
+
+targets += asm-offsets.s
+
+define filechk_asm-offsets.h
          echo "/*"; \
          echo " * DO NOT MODIFY."; \
          echo " *"; \
@@ -57,9 +59,13 @@ arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s
          echo "#ifndef __ASM_OFFSETS_H__"; \
          echo "#define __ASM_OFFSETS_H__"; \
          echo ""; \
-         sed -rne "/^[^#].*==>/{s:.*==>(.*)<==.*:\1:; s: [\$$#]: :; p;}"; \
+         sed -rne "/^[^#].*==>/{s:.*==>(.*)<==.*:\1:; s: [\$$#]: :; p;}" $<; \
          echo ""; \
-         echo "#endif") <$< >$@
+         echo "#endif"
+endef
+
+arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: asm-offsets.s FORCE
+       $(call filechk,asm-offsets.h)
 
 build-dirs := $(patsubst %/built_in.o,%,$(filter %/built_in.o,$(ALL_OBJS) 
$(ALL_LIBS)))
 
-- 
Anthony PERARD