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Commit 3812b8c5 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: make -r/-R effective in top Makefile for old Make versions 



Adding -rR to MAKEFLAGS is important because we do not want to
be bothered by built-in implicit rules or variables.

One problem that used to exist in older GNU Make versions is

  MAKEFLAGS += -rR

... does not become effective in the current Makefile. When you are
building with O= option, it becomes effective in the top Makefile
since it recurses via 'sub-make' target. Otherwise, the top Makefile
tries implicit rules. That is why we explicitly add empty rules for
Makefiles, but we often miss to do that.

In fact, adding -d option to older GNU Make versions shows it is
trying a bunch of implicit pattern rules.

 Considering target file `scripts/Makefile.kcov'.
  Looking for an implicit rule for `scripts/Makefile.kcov'.
  Trying pattern rule with stem `Makefile.kcov'.
  Trying implicit prerequisite `scripts/Makefile.kcov.o'.
  Trying pattern rule with stem `Makefile.kcov'.
  Trying implicit prerequisite `scripts/Makefile.kcov.c'.
  Trying pattern rule with stem `Makefile.kcov'.
  Trying implicit prerequisite `scripts/Makefile.kcov.cc'.
  Trying pattern rule with stem `Makefile.kcov'.
  Trying implicit prerequisite `scripts/Makefile.kcov.C'.
  ...

This issue was fixed by GNU Make commit 58dae243526b ("[Savannah #20501]
Handle adding -r/-R to MAKEFLAGS in the makefile"). So, it is no longer
a problem if you use GNU Make 4.0 or later. However, older versions are
still widely used.

So, I decided to patch the kernel Makefile to invoke sub-make regardless
of O= option. This will allow further cleanups.

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
parent f47a23ce

Makefile

+26 −22
Original line number Diff line number Diff line
@@ -15,19 +15,6 @@ NAME = Shy Crocodile 
PHONY := _all

_all:



# Do not use make's built-in rules and variables

# (this increases performance and avoids hard-to-debug behaviour)

MAKEFLAGS += -rR



# Avoid funny character set dependencies

unexport LC_ALL

LC_COLLATE=C

LC_NUMERIC=C

export LC_COLLATE LC_NUMERIC



# Avoid interference with shell env settings

unexport GREP_OPTIONS



# We are using a recursive build, so we need to do a little thinking

# to get the ordering right.

#
@@ -44,6 +31,21 @@ unexport GREP_OPTIONS 
# descending is started. They are now explicitly listed as the

# prepare rule.



ifneq ($(sub-make-done),1)



# Do not use make's built-in rules and variables

# (this increases performance and avoids hard-to-debug behaviour)

MAKEFLAGS += -rR



# Avoid funny character set dependencies

unexport LC_ALL

LC_COLLATE=C

LC_NUMERIC=C

export LC_COLLATE LC_NUMERIC



# Avoid interference with shell env settings

unexport GREP_OPTIONS



# Beautify output

# ---------------------------------------------------------------------------

#
@@ -111,7 +113,6 @@ export quiet Q KBUILD_VERBOSE 


# KBUILD_SRC is not intended to be used by the regular user (for now),

# it is set on invocation of make with KBUILD_OUTPUT or O= specified.

ifeq ($(KBUILD_SRC),)



# OK, Make called in directory where kernel src resides

# Do we want to locate output files in a separate directory?
@@ -141,6 +142,13 @@ $(if $(KBUILD_OUTPUT),, \ 
# 'sub-make' below.

MAKEFLAGS += --include-dir=$(CURDIR)



else



# Do not print "Entering directory ..." at all for in-tree build.

MAKEFLAGS += --no-print-directory



endif # ifneq ($(KBUILD_OUTPUT),)



PHONY += $(MAKECMDGOALS) sub-make



$(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
@@ -148,16 +156,12 @@ $(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make 


# Invoke a second make in the output directory, passing relevant variables

sub-make:

	$(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \

	$(Q)$(MAKE) sub-make-done=1 \

	$(if $(KBUILD_OUTPUT),-C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR)) \

	-f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))



# Leave processing to above invocation of make

skip-makefile := 1

endif # ifneq ($(KBUILD_OUTPUT),)

endif # ifeq ($(KBUILD_SRC),)



else # sub-make-done

# We process the rest of the Makefile if this is the final invocation of make

ifeq ($(skip-makefile),)



# Do not print "Entering directory ...",

# but we want to display it when entering to the output directory
@@ -1762,7 +1766,7 @@ $(cmd_files): ; # Do not try to update included dependency files 


endif   # ifeq ($(config-targets),1)

endif   # ifeq ($(mixed-targets),1)

endif	# skip-makefile

endif   # sub-make-done



PHONY += FORCE

FORCE: