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@xxxxxxxxxxxxx>
---
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
