diff options
authorMasahiro Yamada <>2017-11-13 19:29:37 +0900
committerMasahiro Yamada <>2017-11-16 09:07:35 +0900
commit8a78756eb545a6fb8007fa154a626ca2bc208027 (patch)
parent591f66899784ae0afa13ff9a3eb5ce0a4358e48b (diff)
kbuild: create object directories simpler and faster
For the out-of-tree build, scripts/ creates output directories, but this operation is not efficient. scripts/Makefile.lib calculates obj-dirs as follows: obj-dirs := $(dir $(multi-objs) $(obj-y)) Please notice $(sort ...) is not used here. Usually the result is as many "./" as objects here. For a lot of duplicated paths, the following command is invoked. _dummy := $(foreach d,$(obj-dirs), $(shell [ -d $(d) ] || mkdir -p $(d))) Then, the costly shell command is run over and over again. I see many points for optimization: [1] Use $(sort ...) to cut down duplicated paths before passing them to system call [2] Use single $(shell ...) instead of repeating it with $(foreach ...) This will reduce forking. [3] We can calculate obj-dirs more simply. Most of objects are already accumulated in $(targets). So, $(dir $(targets)) is fine and more comprehensive. I also removed ugly code in arch/x86/entry/vdso/Makefile. This is now really unnecessary. Signed-off-by: Masahiro Yamada <> Acked-by: Ingo Molnar <> Tested-by: Douglas Anderson <>
4 files changed, 6 insertions, 30 deletions
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index d5409660f5de..f8e3d85256ad 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -129,10 +129,6 @@ $(obj)/ $(src)/ $(vobjx32s) FORCE = $( = -m32 -Wl,-m,elf_i386 -Wl,
-# This makes sure the $(obj) subdirectory exists even though vdso32/
-# is not a kbuild sub-make subdirectory.
-override obj-dirs = $(dir $(obj)) $(obj)/vdso32/
targets += vdso32/
targets += vdso32/note.o vdso32/system_call.o vdso32/sigreturn.o
targets += vdso32/vclock_gettime.o
diff --git a/scripts/ b/scripts/
index 6f603770b08e..496ecd825c71 100644
--- a/scripts/
+++ b/scripts/
@@ -64,15 +64,6 @@ ifneq ($(hostprogs-y)$(hostprogs-m)$(hostlibs-y)$(hostlibs-m)$(hostcxxlibs-y)$(h
include scripts/
-ifneq ($(KBUILD_SRC),)
-# Create output directory if not already present
-_dummy := $(shell [ -d $(obj) ] || mkdir -p $(obj))
-# Create directories for object files if directory does not exist
-# Needed when obj-y := dir/file.o syntax is used
-_dummy := $(foreach d,$(obj-dirs), $(shell [ -d $(d) ] || mkdir -p $(d)))
ifndef obj
$(warning kbuild: is included improperly)
@@ -589,6 +580,12 @@ ifneq ($(cmd_files),)
include $(cmd_files)
+ifneq ($(KBUILD_SRC),)
+# Create directories for object files if they do not exist
+obj-dirs := $(sort $(obj) $(patsubst %/,%, $(dir $(targets))))
+$(shell mkdir -p $(obj-dirs))
# Declare the contents of the .PHONY variable as phony. We keep that
# information in a variable se we can use it in if_changed and friends.
diff --git a/scripts/ b/scripts/
index 9cfd5c84d76f..a5e03838eca8 100644
--- a/scripts/
+++ b/scripts/
@@ -48,15 +48,6 @@ host-cxxobjs := $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
host-cshobjs := $(sort $(foreach m,$(host-cshlib),$($(
host-cxxshobjs := $(sort $(foreach m,$(host-cxxshlib),$($(
-# output directory for programs/.o files
-# hostprogs-y := tools/build may have been specified.
-# Retrieve also directory of .o files from prog-objs or prog-cxxobjs notation
-host-objdirs := $(dir $(__hostprogs) $(host-cobjs) $(host-cxxobjs))
-host-objdirs := $(strip $(sort $(filter-out ./,$(host-objdirs))))
-__hostprogs := $(addprefix $(obj)/,$(__hostprogs))
host-csingle := $(addprefix $(obj)/,$(host-csingle))
host-cmulti := $(addprefix $(obj)/,$(host-cmulti))
host-cobjs := $(addprefix $(obj)/,$(host-cobjs))
@@ -66,9 +57,6 @@ host-cshlib := $(addprefix $(obj)/,$(host-cshlib))
host-cxxshlib := $(addprefix $(obj)/,$(host-cxxshlib))
host-cshobjs := $(addprefix $(obj)/,$(host-cshobjs))
host-cxxshobjs := $(addprefix $(obj)/,$(host-cxxshobjs))
-host-objdirs := $(addprefix $(obj)/,$(host-objdirs))
-obj-dirs += $(host-objdirs)
# Handle options to gcc. Support building with separate output directory
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 4d88ad70fd96..5fbc46daa0f8 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -50,15 +50,11 @@ single-used-m := $(sort $(filter-out $(multi-used-m),$(obj-m)))
# objects depend on those (obviously)
multi-objs-y := $(foreach m, $(multi-used-y), $($(m:.o=-objs)) $($(m:.o=-y)))
multi-objs-m := $(foreach m, $(multi-used-m), $($(m:.o=-objs)) $($(m:.o=-y)))
-multi-objs := $(multi-objs-y) $(multi-objs-m)
# $(subdir-obj-y) is the list of objects in $(obj-y) which uses dir/ to
# tell kbuild to descend
subdir-obj-y := $(filter %/built-in.o, $(obj-y))
-# $(obj-dirs) is a list of directories that contain object files
-obj-dirs := $(dir $(multi-objs) $(obj-y))
# Replace multi-part objects by their individual parts, look at local dir only
real-objs-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))) $(extra-y)
real-objs-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)))
@@ -81,7 +77,6 @@ multi-used-m := $(addprefix $(obj)/,$(multi-used-m))
multi-objs-y := $(addprefix $(obj)/,$(multi-objs-y))
multi-objs-m := $(addprefix $(obj)/,$(multi-objs-m))
subdir-ym := $(addprefix $(obj)/,$(subdir-ym))
-obj-dirs := $(addprefix $(obj)/,$(obj-dirs))
# These flags are needed for modversions and compiling, so we define them here
# $(modname_flags) defines KBUILD_MODNAME as the name of the module it will