commit 6b12de69ad82ceed317bdbae9ede1a256f84bf4e
author Masahiro Yamada <yamada.masahiro@socionext.com> Fri Feb 22 16:40:09 2019 +0900
committer Masahiro Yamada <yamada.masahiro@socionext.com> Wed Feb 27 21:43:31 2019 +0900
tree e4c4d7bd1268398b17966407d3675ebfd46dc13a
parent b999923c29d69d795229e5bf1b49e1266491ff35

kbuild: simplify single target rules

The dependency will be checked anyway after Kbuild descends into a
sub-directory. Skip object/source dependency checks in top Makefile.

VPATH can be simpler since the top Makefile no longer checks the
presence of the source file, which is located in in the external
module directory.

One good thing is, it can compile an object from a generated source
file.

  $ make crypto/rsapubkey.asn1.o
    ...
  ASN.1   crypto/rsapubkey.asn1.c
  CC      crypto/rsapubkey.asn1.o

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

diff --git a/Makefile b/Makefile
index 418d205..14dae592 100644
--- a/Makefile
+++ b/Makefile
@@ -219,7 +219,7 @@
 src		:= $(srctree)
 obj		:= $(objtree)
 
-VPATH		:= $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
+VPATH		:= $(srctree)
 
 export srctree objtree VPATH
 
@@ -1699,31 +1699,23 @@
 #  target-dir => where to store outputfile
 #  build-dir  => directory in kernel source tree to use
 
-ifeq ($(KBUILD_EXTMOD),)
-        build-dir  = $(patsubst %/,%,$(dir $@))
-        target-dir = $(dir $@)
-else
-        zap-slash=$(filter-out .,$(patsubst %/,%,$(dir $@)))
-        build-dir  = $(KBUILD_EXTMOD)$(if $(zap-slash),/$(zap-slash))
-        target-dir = $(if $(KBUILD_EXTMOD),$(dir $<),$(dir $@))
-endif
+build-target = $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD)/)$@
+build-dir = $(patsubst %/,%,$(dir $(build-target)))
 
-%.s: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.i: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.o: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.lst: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.s: %.S prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.o: %.S prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.symtypes: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
-%.ll: %.c prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
+%.i: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.ll: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.lst: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.o: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.s: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.symtypes: prepare FORCE
+	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
+%.ko: %.o
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
 
 # Modules
 PHONY += /
@@ -1733,9 +1725,6 @@
 Documentation/ samples/: headers_install
 %/: prepare FORCE
 	$(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir)
-%.ko: prepare FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(@:.ko=.o)
-	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
 
 # FIXME Should go into a make.lib or something
 # ===========================================================================