[PATCH 1/3] kbuild: do not create built-in.a that is never linked to vmlinux

[PATCH 1/3] kbuild: do not create built-in.a that is never linked to vmlinux

[Masahiro Yamada]

Both 'obj-y += foo/' and 'obj-m += foo/' requrest Kbuild to visit the
sub-directory foo/, but the difference is that only the former combines
foo/built-in.a into the built-in.a of the current directory because
everything in sub-directories visited by obj-m is supposed to be modular.

So, it makes sense to create built-in.a only if that sub-directory is
reachable by the chain of obj-y. Otherwise, built-in.a will not be
linked into vmlinux anyway. If an orphan built-in.a is created, it is
very likely a Makefile bug.

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

 scripts/Makefile.build | 2 +-
 scripts/Makefile.lib   | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 9fa09361aa5d..54fc68168686 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -66,7 +66,7 @@ lib-target := $(obj)/lib.a
 real-obj-y += $(obj)/lib-ksyms.o
 endif
 
-ifneq ($(strip $(real-obj-y) $(need-builtin)),)
+ifdef need-builtin
 builtin-target := $(obj)/built-in.a
 endif
 
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 264611972c4a..07095d3789a1 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -35,7 +35,11 @@ __subdir-y	:= $(patsubst %/,%,$(filter %/, $(obj-y)))
 subdir-y	+= $(__subdir-y)
 __subdir-m	:= $(patsubst %/,%,$(filter %/, $(obj-m)))
 subdir-m	+= $(__subdir-m)
+ifdef need-builtin
 obj-y		:= $(patsubst %/, %/built-in.a, $(obj-y))
+else
+obj-y		:= $(filter-out %/, $(obj-y))
+endif
 obj-m		:= $(filter-out %/, $(obj-m))
 
 # Subdirectories we need to descend into
-- 
2.17.1

[PATCH 2/3] kbuild: warn orphan obj-y objects

[Masahiro Yamada]

obj-y specifies objects linked into vmlinux, but they are actually
linked if and only if that sub-directory is visited by the chain of
obj-y. If you have an orphan obj-y object, it is a bug, but may not
easy to notice. This commit provides build-time warning.

I tested allmodconfig based on v5.3-rc4, and I saw one warning:

scripts/Makefile.build:57: 'sound/soc/sprd/sprd-mcdt.o' will not be linked to vmlinux even though obj-y is specified.

This is a proper warning. sound/soc/sprd/sprd-mcdt.o is compiled as
built-in since CONFIG_SND_SOC_SPRD_MCDT is boolean. However, CONFIG_SND
and CONFIG_SND_SOC are tristate, and set to m by allmodconfig.
So, Kbuild descends into sound/soc/, then sound/soc/sprd/ by obj-m.
sound/soc/sprd/sprd-mcdt.o is not linked to vmlinux.

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

 scripts/Makefile.build  | 6 ++++++
 scripts/link-vmlinux.sh | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 54fc68168686..d30b04707fec 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -52,6 +52,12 @@ ifndef obj
 $(warning kbuild: Makefile.build is included improperly)
 endif
 
+ifeq ($(need-builtin),)
+ifneq ($(real-obj-y),)
+$(warning '$(real-obj-y)' will not be linked to vmlinux even though obj-y is specified.)
+endif
+endif
+
 ifeq ($(need-modorder),)
 ifneq ($(obj-m),)
 $(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 2438a9faf3f1..8961d999b86b 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -216,7 +216,7 @@ else
 fi;
 
 # final build of init/
-${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init
+${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1
 
 #link vmlinux.o
 info LD vmlinux.o
-- 
2.17.1

[PATCH 3/3] kbuild: change need-modorder implementation slightly

[Masahiro Yamada]

Align with the need-builtin implementation.

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

 scripts/Makefile.build | 2 +-
 scripts/Makefile.lib   | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index d30b04707fec..91617b9d7a34 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -528,7 +528,7 @@ $(subdir-ym):
 	$(Q)$(MAKE) $(build)=$@ \
 	$(if $(filter $@/, $(KBUILD_SINGLE_TARGETS)),single-build=) \
 	need-builtin=$(if $(filter $@/built-in.a, $(subdir-obj-y)),1) \
-	need-modorder=$(if $(need-modorder),$(if $(filter $@/modules.order, $(modorder)),1))
+	need-modorder=$(if $(filter $@/modules.order, $(modorder)),1)
 
 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 07095d3789a1..034e92ea72c6 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -23,7 +23,9 @@ lib-y := $(filter-out $(obj-y), $(sort $(lib-y) $(lib-m)))
 # Determine modorder.
 # Unfortunately, we don't have information about ordering between -y
 # and -m subdirs.  Just put -y's first.
+ifdef need-modorder
 modorder	:= $(patsubst %/,%/modules.order, $(filter %/, $(obj-y)) $(obj-m:.o=.ko))
+endif
 
 # Handle objects in subdirs
 # ---------------------------------------------------------------------------
-- 
2.17.1