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kbuild: link $(real-obj-y) instead of $(obj-y) into built-in.a

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In Kbuild, Makefiles can add the same object to obj-y multiple
times.  So,

   obj-y += foo.o
   obj-y += foo.o

is fine.

However, this is not true when the same object is added multiple
times via composite objects.  For example,

   obj-y    += foo.o bar.o
   foo-objs := foo-bar-common.o foo-only.o
   bar-objs := foo-bar-common.o bar-only.o

causes build error because two instances of foo-bar-common.o are
linked into the vmlinux.

Makefiles tend to invent ugly work-around, for example
  - lib/zstd/Makefile
  - drivers/net/ethernet/cavium/liquidio/Makefile

The technique used in Kbuild to avoid the multiple definition error
is to use $(filter $(obj-y), $^).  Here, $^ lists the names of all
the prerequisites with duplicated names removed.

By replacing it with $(filter $(real-obj-y), $^) we can do likewise
for composite objects.  For built-in objects, we do not need to keep
the composite object structure.  We can simply expand them, and link
$(real-obj-y) to built-in.a.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
This commit is contained in:
Masahiro Yamada 2018-03-19 20:26:08 +09:00
parent f5f336812c
commit f98fe47ce5
2 changed files with 10 additions and 18 deletions
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21
scripts/Makefile.build
View file

@ -73,10 +73,10 @@ endif
ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
lib-target := $(obj)/lib.a
obj-y += $(obj)/lib-ksyms.o
real-obj-y += $(obj)/lib-ksyms.o
endif
ifneq ($(strip $(obj-y) $(need-builtin)),)
ifneq ($(strip $(real-obj-y) $(need-builtin)),)
builtin-target := $(obj)/built-in.a
endif
@ -412,7 +412,7 @@ endif
$(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
$(call if_changed_rule,as_o_S)
targets += $(real-obj-y) $(real-obj-m) $(lib-y)
targets += $(filter-out $(subdir-obj-y), $(real-obj-y)) $(real-obj-m) $(lib-y)
targets += $(extra-y) $(MAKECMDGOALS) $(always)
# Linker scripts preprocessor (.lds.S -> .lds)
@ -455,12 +455,12 @@ cmd_make_empty_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
quiet_cmd_link_o_target = AR $@
# If the list of objects to link is empty, just create an empty built-in.a
cmd_link_o_target = $(if $(strip $(obj-y)),\
$(cmd_make_builtin) $@ $(filter $(obj-y), $^) \
cmd_link_o_target = $(if $(strip $(real-obj-y)),\
$(cmd_make_builtin) $@ $(filter $(real-obj-y), $^) \
$(cmd_secanalysis),\
$(cmd_make_empty_builtin) $@)
$(builtin-target): $(obj-y) FORCE
$(builtin-target): $(real-obj-y) FORCE
$(call if_changed,link_o_target)
targets += $(builtin-target)
@ -534,23 +534,16 @@ $($(subst $(obj)/,,$(@:.o=-m)))), $^)
cmd_link_multi-link = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)
quiet_cmd_link_multi-y = AR $@
cmd_link_multi-y = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(link_multi_deps)
quiet_cmd_link_multi-m = LD [M] $@
cmd_link_multi-m = $(cmd_link_multi-link)
$(multi-used-y): FORCE
$(call if_changed,link_multi-y)
$(call multi_depend, $(multi-used-y), .o, -objs -y)
$(multi-used-m): FORCE
$(call if_changed,link_multi-m)
@{ echo $(@:.o=.ko); echo $(link_multi_deps); \
$(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
$(call multi_depend, $(multi-used-m), .o, -objs -y -m)
targets += $(multi-used-y) $(multi-used-m)
targets += $(multi-used-m)
targets := $(filter-out $(PHONY), $(targets))
# Descending

7
scripts/Makefile.lib
View file

@ -51,8 +51,9 @@ single-used-m := $(sort $(filter-out $(multi-used-m),$(obj-m)))
# tell kbuild to descend
subdir-obj-y := $(filter %/built-in.a, $(obj-y))
# Replace multi-part objects by their individual parts, look at local dir only
real-obj-y := $(foreach m, $(filter-out $(subdir-obj-y), $(obj-y)), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))
# Replace multi-part objects by their individual parts,
# including built-in.a from subdirectories
real-obj-y := $(foreach m, $(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))
real-obj-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m))),$($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m)),$(m)))
# DTB
@ -66,14 +67,12 @@ extra-y := $(addprefix $(obj)/,$(extra-y))
always := $(addprefix $(obj)/,$(always))
targets := $(addprefix $(obj)/,$(targets))
modorder := $(addprefix $(obj)/,$(modorder))
obj-y := $(addprefix $(obj)/,$(obj-y))
obj-m := $(addprefix $(obj)/,$(obj-m))
lib-y := $(addprefix $(obj)/,$(lib-y))
subdir-obj-y := $(addprefix $(obj)/,$(subdir-obj-y))
real-obj-y := $(addprefix $(obj)/,$(real-obj-y))
real-obj-m := $(addprefix $(obj)/,$(real-obj-m))
single-used-m := $(addprefix $(obj)/,$(single-used-m))
multi-used-y := $(addprefix $(obj)/,$(multi-used-y))
multi-used-m := $(addprefix $(obj)/,$(multi-used-m))
subdir-ym := $(addprefix $(obj)/,$(subdir-ym))