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kbuild: create built-in.o automatically if parent directory wants it
"obj-y += foo/" syntax requires Kbuild to visit the "foo" subdirectory
and link built-in.o from that directory. This means foo/Makefile is
responsible for creating built-in.o even if there is no object to
link (in this case, built-in.o is an empty archive).
We have had several fixups like commit 4b024242e8
("kbuild: Fix
linking error built-in.o no such file or directory"), then ended up
with a complex condition as follows:
ifneq ($(strip $(obj-y) $(obj-m) $(obj-) $(subdir-m) $(lib-target)),)
builtin-target := $(obj)/built-in.o
endif
We still have more cases not covered by the above, so we need to add
obj- := dummy.o
in several places just for creating empty built-in.o.
A key point is, the parent Makefile knows whether built-in.o is needed
or not. If a subdirectory needs to create built-in.o, its parent can
tell the fact when descending.
If non-empty $(need-builtin) flag is passed from the parent, built-in.o
should be created. $(obj-y) should be still checked to support the
single target "%/". All of ugly tricks will go away.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
This commit is contained in:
parent
16f8259ca7
commit
f7adc3124d
2
Makefile
2
Makefile
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@ -1009,7 +1009,7 @@ $(sort $(vmlinux-deps)): $(vmlinux-dirs) ;
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PHONY += $(vmlinux-dirs)
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$(vmlinux-dirs): prepare scripts
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$(Q)$(MAKE) $(build)=$@
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$(Q)$(MAKE) $(build)=$@ need-builtin=1
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define filechk_kernel.release
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echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
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@ -76,7 +76,7 @@ lib-target := $(obj)/lib.a
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obj-y += $(obj)/lib-ksyms.o
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endif
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ifneq ($(strip $(obj-y) $(obj-m) $(obj-) $(subdir-m) $(lib-target)),)
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ifneq ($(strip $(obj-y) $(need-builtin)),)
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builtin-target := $(obj)/built-in.o
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endif
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@ -561,7 +561,7 @@ targets := $(filter-out $(PHONY), $(targets))
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PHONY += $(subdir-ym)
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$(subdir-ym):
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$(Q)$(MAKE) $(build)=$@
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$(Q)$(MAKE) $(build)=$@ need-builtin=$(if $(findstring $@,$(subdir-obj-y)),1)
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# Add FORCE to the prequisites of a target to force it to be always rebuilt.
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# ---------------------------------------------------------------------------
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