Commit f98fe47c authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

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



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: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
parent f5f33681

scripts/Makefile.build

+7 −14
Original line number Diff line number Diff line
@@ -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

scripts/Makefile.lib

+3 −4
Original line number Diff line number Diff line
@@ -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))

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