[PATCH v2 1/4] kbuild: do not create built-in.a that is never linked to vmlinux

[PATCH v2 1/4] 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, useless orphan built-in.a
files are generated.

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

Changes in v2: None

 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 f72aba64d611..6c3e6cb0c0af 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 4a0cdd6f5909..26ac638525cb 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 v2 2/4] kbuild: warn orphan built-in 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
be easy to notice. This commit provides build-time warning.

I tested x86 allmodconfig based on v5.3-rc4, and I saw one warning:

warning: '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.
Thus, sound/soc/sprd/sprd-mcdt.o is not linked to vmlinux.

More warnings for arm allmodconfig, all of which are valid:

warning: 'drivers/video/fbdev/mmp/hw/mmp_ctrl.o' 'drivers/video/fbdev/mmp/hw/mmp_spi.o' will not be linked to vmlinux even though obj-y is specified.
warning: 'drivers/video/fbdev/mmp/panel/tpo_tj032md01bw.o' will not be linked to vmlinux even though obj-y is specified.
warning: 'sound/soc/pxa/mmp-pcm.o' will not be linked to vmlinux even though obj-y is specified.

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

Changes in v2:
 - fix false-positive warning for arm64

 scripts/Makefile.build  | 12 ++++++++----
 scripts/link-vmlinux.sh |  2 +-
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 6c3e6cb0c0af..fb29c898604a 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -52,6 +52,10 @@ ifndef obj
 $(warning kbuild: Makefile.build is included improperly)
 endif
 
+PHONY += __warn-orphan-obj-y
+__warn-orphan-obj-y:
+	@echo "warning: $(patsubst %,'%',$(real-obj-y)) will not be linked to vmlinux even though obj-y is specified." >&2
+
 ifeq ($(need-modorder),)
 ifneq ($(obj-m),)
 $(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
@@ -68,6 +72,8 @@ endif
 
 ifdef need-builtin
 builtin-target := $(obj)/built-in.a
+else ifneq ($(real-obj-y),)
+builtin-target := __warn-orphan-obj-y
 endif
 
 ifeq ($(CONFIG_MODULES)$(need-modorder),y1)
@@ -386,16 +392,14 @@ $(sort $(subdir-obj-y)): $(subdir-ym) ;
 #
 # Rule to compile a set of .o files into one .a file (without symbol table)
 #
-ifdef builtin-target
 
 quiet_cmd_ar_builtin = AR      $@
       cmd_ar_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(real-prereqs)
 
-$(builtin-target): $(real-obj-y) FORCE
+$(obj)/built-in.a: $(real-obj-y) FORCE
 	$(call if_changed,ar_builtin)
 
-targets += $(builtin-target)
-endif # builtin-target
+targets += $(obj)/built-in.a
 
 #
 # Rule to create modules.order file
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 v2 3/4] kbuild: clear KBUILD_MODULES in top Makefile if CONFIG_MODULES=n

[Masahiro Yamada]

Do not try to build any module-related artifacts when CONFIG_MODULES
is disabled.

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

Changes in v2:
  - New patch

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

diff --git a/Makefile b/Makefile
index adc0cabe2382..0ecc62dbe234 100644
--- a/Makefile
+++ b/Makefile
@@ -1797,6 +1797,10 @@ single-build = $(if $(filter-out $@/, $(single-no-ko)),1)
 
 endif
 
+ifndef CONFIG_MODULES
+KBUILD_MODULES :=
+endif
+
 # FIXME Should go into a make.lib or something
 # ===========================================================================
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index fb29c898604a..aab9a14fa78d 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -76,7 +76,7 @@ else ifneq ($(real-obj-y),)
 builtin-target := __warn-orphan-obj-y
 endif
 
-ifeq ($(CONFIG_MODULES)$(need-modorder),y1)
+ifdef need-modorder
 modorder-target := $(obj)/modules.order
 endif
 
-- 
2.17.1

[PATCH v2 4/4] kbuild: change need-modorder implementation slightly

[Masahiro Yamada]

Align with the need-builtin implementation.

I also added need-modorder=1 to scripts/link-vmlinux.sh to make it more
future-proof; currently, we have no module in the init/ directory, but
if we had a one, scripts/Makefile.build would show a false positive
warning.

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

Changes in v2:
  - do not show orphan obj-m warning unless you are building modules

 scripts/Makefile.build  | 16 ++++++++--------
 scripts/Makefile.lib    |  2 ++
 scripts/link-vmlinux.sh |  2 +-
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index aab9a14fa78d..3b04ff23deb1 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -56,12 +56,10 @@ PHONY += __warn-orphan-obj-y
 __warn-orphan-obj-y:
 	@echo "warning: $(patsubst %,'%',$(real-obj-y)) will not be linked to vmlinux even though obj-y is specified." >&2
 
-ifeq ($(need-modorder),)
-ifneq ($(obj-m),)
-$(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
-$(warning You cannot use subdir-y/m to visit a module Makefile. Use obj-y/m instead.)
-endif
-endif
+PHONY += __warn-orphan-obj-m
+__warn-orphan-obj-m:
+	@echo "warning: $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified." >&2
+	@echo "warning: You cannot use subdir-y/m to visit a module Makefile. Use obj-y/m instead." >&2
 
 # ===========================================================================
 
@@ -78,6 +76,8 @@ endif
 
 ifdef need-modorder
 modorder-target := $(obj)/modules.order
+else ifneq ($(obj-m),)
+modorder-target := __warn-orphan-obj-m
 endif
 
 mod-targets := $(patsubst %.o, %.mod, $(obj-m))
@@ -406,7 +406,7 @@ targets += $(obj)/built-in.a
 #
 # Create commands to either record .ko file or cat modules.order from
 # a subdirectory
-$(modorder-target): $(subdir-ym) FORCE
+$(obj)/modules.order: $(subdir-ym) FORCE
 	$(Q){ $(foreach m, $(modorder), \
 	$(if $(filter %/modules.order, $m), cat $m, echo $m);) :; } \
 	| $(AWK) '!x[$$0]++' - > $@
@@ -513,7 +513,7 @@ $(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 26ac638525cb..23e524027740 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
 # ---------------------------------------------------------------------------
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 8961d999b86b..d9edfba54d84 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 need-builtin=1
+${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1 need-modorder=1
 
 #link vmlinux.o
 info LD vmlinux.o
-- 
2.17.1