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kbuild: create object directories simpler and faster

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For the out-of-tree build, scripts/Makefile.build 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 <yamada.masahiro@socionext.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
This commit is contained in:
Masahiro Yamada
2017-11-13 19:29:37 +09:00
parent 591f668997
commit 8a78756eb5
4 changed files with 6 additions and 30 deletions
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12
scripts/Makefile.host
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@@ -48,15 +48,6 @@ host-cxxobjs := $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
host-cshobjs := $(sort $(foreach m,$(host-cshlib),$($(m:.so=-objs))))
host-cxxshobjs := $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-objs))))
# 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