scripts/Makefile.build

# SPDX-License-Identifier: GPL-2.0
# ==========================================================================
# Building
# ==========================================================================

src := $(obj)

PHONY := __build
__build:

# Init all relevant variables used in kbuild files so
# 1) they have correct type
# 2) they do not inherit any value from the environment
obj-y :=
obj-m :=
lib-y :=
lib-m :=
always-y :=
always-m :=
targets :=
subdir-y :=
subdir-m :=
EXTRA_AFLAGS   :=
EXTRA_CFLAGS   :=
EXTRA_CPPFLAGS :=
EXTRA_LDFLAGS  :=
asflags-y  :=
ccflags-y  :=
cppflags-y :=
ldflags-y  :=

subdir-asflags-y :=
subdir-ccflags-y :=

# Read auto.conf if it exists, otherwise ignore
-include include/config/auto.conf

include $(srctree)/scripts/Kbuild.include
include $(srctree)/scripts/Makefile.compiler

# The filename Kbuild has precedence over Makefile
kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
include $(kbuild-file)

include $(srctree)/scripts/Makefile.lib

# Do not include hostprogs rules unless needed.
# $(sort ...) is used here to remove duplicated words and excessive spaces.
hostprogs := $(sort $(hostprogs))
ifneq ($(hostprogs),)
include $(srctree)/scripts/Makefile.host
endif

# Do not include userprogs rules unless needed.
# $(sort ...) is used here to remove duplicated words and excessive spaces.
userprogs := $(sort $(userprogs))
ifneq ($(userprogs),)
include $(srctree)/scripts/Makefile.userprogs
endif

ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif

ifeq ($(need-modorder),)
ifneq ($(obj-m),)
$(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
$(warning You cannot use subdir-y/m to visit a module Makefile. Use obj-y/m instead.)
endif
endif

# ===========================================================================

# subdir-builtin and subdir-modorder may contain duplications. Use $(sort ...)
subdir-builtin := $(sort $(filter %/built-in.a, $(real-obj-y)))
subdir-modorder := $(sort $(filter %/modules.order, $(obj-m)))

targets-for-builtin := $(extra-y)

ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
targets-for-builtin += $(obj)/lib.a
endif

ifdef need-builtin
targets-for-builtin += $(obj)/built-in.a
endif

targets-for-modules := $(foreach x, o mod $(if $(CONFIG_TRIM_UNUSED_KSYMS), usyms), \
				$(patsubst %.o, %.$x, $(filter %.o, $(obj-m))))

ifdef CONFIG_LTO_CLANG
targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m)))
endif

ifdef need-modorder
targets-for-modules += $(obj)/modules.order
endif

targets += $(targets-for-builtin) $(targets-for-modules)

# Linus' kernel sanity checking tool
ifeq ($(KBUILD_CHECKSRC),1)
  quiet_cmd_checksrc       = CHECK   $<
        cmd_checksrc       = $(CHECK) $(CHECKFLAGS) $(c_flags) $<
else ifeq ($(KBUILD_CHECKSRC),2)
  quiet_cmd_force_checksrc = CHECK   $<
        cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $<
endif

ifneq ($(KBUILD_EXTRA_WARN),)
  cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $<
endif

# Compile C sources (.c)
# ---------------------------------------------------------------------------

quiet_cmd_cc_s_c = CC $(quiet_modtag)  $@
      cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS) $(CC_FLAGS_LTO), $(c_flags)) -fverbose-asm -S -o $@ $<

$(obj)/%.s: $(src)/%.c FORCE
	$(call if_changed_dep,cc_s_c)

quiet_cmd_cpp_i_c = CPP $(quiet_modtag) $@
cmd_cpp_i_c       = $(CPP) $(c_flags) -o $@ $<

$(obj)/%.i: $(src)/%.c FORCE
	$(call if_changed_dep,cpp_i_c)

# These mirror gensymtypes_S and co below, keep them in synch.
cmd_gensymtypes_c =                                                         \
    $(CPP) -D__GENKSYMS__ $(c_flags) $< |                                   \
    scripts/genksyms/genksyms $(if $(1), -T $(2))                           \
     $(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS))                             \
     $(if $(KBUILD_PRESERVE),-p)                                            \
     -r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))

quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
cmd_cc_symtypes_c =                                                         \
    $(call cmd_gensymtypes_c,true,$@) >/dev/null;                           \
    test -s $@ || rm -f $@

$(obj)/%.symtypes : $(src)/%.c FORCE
	$(call cmd,cc_symtypes_c)

# LLVM assembly
# Generate .ll files from .c
quiet_cmd_cc_ll_c = CC $(quiet_modtag)  $@
      cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -o $@ $<

$(obj)/%.ll: $(src)/%.c FORCE
	$(call if_changed_dep,cc_ll_c)

# C (.c) files
# The C file is compiled and updated dependency information is generated.
# (See cmd_cc_o_c + relevant part of rule_cc_o_c)

quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
      cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<

ifdef CONFIG_MODVERSIONS
# When module versioning is enabled the following steps are executed:
# o compile a <file>.o from <file>.c
# o if <file>.o doesn't contain a __ksymtab version, i.e. does
#   not export symbols, it's done.
# o otherwise, we calculate symbol versions using the good old
#   genksyms on the preprocessed source and postprocess them in a way
#   that they are usable as a linker script
# o generate .tmp_<file>.o from <file>.o using the linker to
#   replace the unresolved symbols __crc_exported_symbol with
#   the actual value of the checksum generated by genksyms
# o remove .tmp_<file>.o to <file>.o

ifdef CONFIG_LTO_CLANG
# Generate .o.symversions files for each .o with exported symbols, and link these
# to the kernel and/or modules at the end.
cmd_modversions_c =								\
	if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then			\
		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
		    > $@.symversions;						\
	else									\
		rm -f $@.symversions;						\
	fi;
else
cmd_modversions_c =								\
	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
		    > $(@D)/.tmp_$(@F:.o=.ver);					\
										\
		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
			-T $(@D)/.tmp_$(@F:.o=.ver);				\
		mv -f $(@D)/.tmp_$(@F) $@;					\
		rm -f $(@D)/.tmp_$(@F:.o=.ver);					\
	fi
endif
endif

ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
# compiler will not generate __mcount_loc use recordmcount or recordmcount.pl
ifdef BUILD_C_RECORDMCOUNT
ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
  RECORDMCOUNT_FLAGS = -w
endif
# Due to recursion, we must skip empty.o.
# The empty.o file is created in the make process in order to determine
# the target endianness and word size. It is made before all other C
# files, including recordmcount.
sub_cmd_record_mcount =					\
	if [ $(@) != "scripts/mod/empty.o" ]; then	\
		$(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)";	\
	fi;
recordmcount_source := $(srctree)/scripts/recordmcount.c \
		    $(srctree)/scripts/recordmcount.h
else
sub_cmd_record_mcount = perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
	"$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
	"$(if $(CONFIG_64BIT),64,32)" \
	"$(OBJDUMP)" "$(OBJCOPY)" "$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)" \
	"$(LD) $(KBUILD_LDFLAGS)" "$(NM)" "$(RM)" "$(MV)" \
	"$(if $(part-of-module),1,0)" "$(@)";
recordmcount_source := $(srctree)/scripts/recordmcount.pl
endif # BUILD_C_RECORDMCOUNT
cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)),	\
	$(sub_cmd_record_mcount))
endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT

ifdef CONFIG_STACK_VALIDATION

objtool_args =								\
	$(if $(CONFIG_UNWINDER_ORC),orc generate,check)			\
	$(if $(part-of-module), --module)				\
	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\
	$(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
	$(if $(CONFIG_RETPOLINE), --retpoline)				\
	$(if $(CONFIG_RETHUNK), --rethunk)				\
	$(if $(CONFIG_X86_SMAP), --uaccess)				\
	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
	$(if $(CONFIG_SLS), --sls)

ifndef CONFIG_LTO_CLANG

__objtool_obj := $(objtree)/tools/objtool/objtool

# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
cmd_objtool = $(if $(patsubst y%,, \
	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
	$(__objtool_obj) $(objtool_args) $@)
objtool_obj = $(if $(patsubst y%,, \
	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
	$(__objtool_obj))

endif # CONFIG_LTO_CLANG
endif # CONFIG_STACK_VALIDATION

# Rebuild all objects when objtool changes, or is enabled/disabled.
objtool_dep = $(objtool_obj)					\
	      $(wildcard include/config/ORC_UNWINDER		\
			 include/config/STACK_VALIDATION)

ifdef CONFIG_TRIM_UNUSED_KSYMS
cmd_gen_ksymdeps = \
	$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
endif

define rule_cc_o_c
	$(call cmd_and_fixdep,cc_o_c)
	$(call cmd,gen_ksymdeps)
	$(call cmd,checksrc)
	$(call cmd,checkdoc)
	$(call cmd,objtool)
	$(call cmd,modversions_c)
	$(call cmd,record_mcount)
endef

define rule_as_o_S
	$(call cmd_and_fixdep,as_o_S)
	$(call cmd,gen_ksymdeps)
	$(call cmd,objtool)
	$(call cmd,modversions_S)
endef

# Built-in and composite module parts
.SECONDEXPANSION:
$(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
	$(call if_changed_rule,cc_o_c)
	$(call cmd,force_checksrc)

ifdef CONFIG_LTO_CLANG
# Module .o files may contain LLVM bitcode, compile them into native code
# before ELF processing
quiet_cmd_cc_lto_link_modules = LTO [M] $@
cmd_cc_lto_link_modules =						\
	$(LD) $(ld_flags) -r -o $@					\
		$(shell [ -s $(@:.lto.o=.o.symversions) ] &&		\
			echo -T $(@:.lto.o=.o.symversions))		\
		--whole-archive $(filter-out FORCE,$^)

ifdef CONFIG_STACK_VALIDATION
# objtool was skipped for LLVM bitcode, run it now that we have compiled
# modules into native code
cmd_cc_lto_link_modules += ;						\
	$(objtree)/tools/objtool/objtool $(objtool_args) --module $@
endif

$(obj)/%.lto.o: $(obj)/%.o FORCE
	$(call if_changed,cc_lto_link_modules)
endif

cmd_mod = printf '%s\n' $(call real-search, $*.o, .o, -objs -y -m) | \
	$(AWK) '!x[$$0]++ { print("$(obj)/"$$0) }' > $@

$(obj)/%.mod: FORCE
	$(call if_changed,mod)

# List module undefined symbols
cmd_undefined_syms = $(NM) $< | sed -n 's/^  *U //p' > $@

$(obj)/%.usyms: $(obj)/%$(mod-prelink-ext).o FORCE
	$(call if_changed,undefined_syms)

quiet_cmd_cc_lst_c = MKLST   $@
      cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
		     $(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
				     System.map $(OBJDUMP) > $@

$(obj)/%.lst: $(src)/%.c FORCE
	$(call if_changed_dep,cc_lst_c)

# Compile assembler sources (.S)
# ---------------------------------------------------------------------------

# .S file exports must have their C prototypes defined in asm/asm-prototypes.h
# or a file that it includes, in order to get versioned symbols. We build a
# dummy C file that includes asm-prototypes and the EXPORT_SYMBOL lines from
# the .S file (with trailing ';'), and run genksyms on that, to extract vers.
#
# This is convoluted. The .S file must first be preprocessed to run guards and
# expand names, then the resulting exports must be constructed into plain
# EXPORT_SYMBOL(symbol); to build our dummy C file, and that gets preprocessed
# to make the genksyms input.
#
# These mirror gensymtypes_c and co above, keep them in synch.
cmd_gensymtypes_S =                                                         \
   { echo "\#include <linux/kernel.h>" ;                                    \
     echo "\#include <asm/asm-prototypes.h>" ;                              \
    $(CPP) $(a_flags) $< |                                                  \
     grep "\<___EXPORT_SYMBOL\>" |                                          \
     sed 's/.*___EXPORT_SYMBOL[[:space:]]*\([a-zA-Z0-9_]*\)[[:space:]]*,.*/EXPORT_SYMBOL(\1);/' ; } | \
    $(CPP) -D__GENKSYMS__ $(c_flags) -xc - |                                \
    scripts/genksyms/genksyms $(if $(1), -T $(2))                           \
     $(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS))                             \
     $(if $(KBUILD_PRESERVE),-p)                                            \
     -r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))

quiet_cmd_cc_symtypes_S = SYM $(quiet_modtag) $@
cmd_cc_symtypes_S =                                                         \
    $(call cmd_gensymtypes_S,true,$@) >/dev/null;                           \
    test -s $@ || rm -f $@

$(obj)/%.symtypes : $(src)/%.S FORCE
	$(call cmd,cc_symtypes_S)


quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@
cmd_cpp_s_S       = $(CPP) $(a_flags) -o $@ $<

$(obj)/%.s: $(src)/%.S FORCE
	$(call if_changed_dep,cpp_s_S)

quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
      cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<

ifdef CONFIG_ASM_MODVERSIONS

# versioning matches the C process described above, with difference that
# we parse asm-prototypes.h C header to get function definitions.

cmd_modversions_S =								\
	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
		$(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
		    > $(@D)/.tmp_$(@F:.o=.ver);					\
										\
		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
			-T $(@D)/.tmp_$(@F:.o=.ver);				\
		mv -f $(@D)/.tmp_$(@F) $@;					\
		rm -f $(@D)/.tmp_$(@F:.o=.ver);					\
	fi
endif

$(obj)/%.o: $(src)/%.S $$(objtool_dep) FORCE
	$(call if_changed_rule,as_o_S)

targets += $(filter-out $(subdir-builtin), $(real-obj-y))
targets += $(filter-out $(subdir-modorder), $(real-obj-m))
targets += $(real-dtb-y) $(lib-y) $(always-y) $(MAKECMDGOALS)

# Linker scripts preprocessor (.lds.S -> .lds)
# ---------------------------------------------------------------------------
quiet_cmd_cpp_lds_S = LDS     $@
      cmd_cpp_lds_S = $(CPP) $(cpp_flags) -P -U$(ARCH) \
	                     -D__ASSEMBLY__ -DLINKER_SCRIPT -o $@ $<

$(obj)/%.lds: $(src)/%.lds.S FORCE
	$(call if_changed_dep,cpp_lds_S)

# ASN.1 grammar
# ---------------------------------------------------------------------------
quiet_cmd_asn1_compiler = ASN.1   $(basename $@).[ch]
      cmd_asn1_compiler = $(objtree)/scripts/asn1_compiler $< \
				$(basename $@).c $(basename $@).h

$(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
	$(call cmd,asn1_compiler)

# Build the compiled-in targets
# ---------------------------------------------------------------------------

# To build objects in subdirs, we need to descend into the directories
$(subdir-builtin): $(obj)/%/built-in.a: $(obj)/% ;
$(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ;

# combine symversions for later processing
ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
      cmd_update_lto_symversions =					\
	rm -f $@.symversions						\
	$(foreach n, $(filter-out FORCE,$^),				\
		$(if $(shell test -s $(n).symversions && echo y),	\
			; cat $(n).symversions >> $@.symversions))
else
      cmd_update_lto_symversions = echo >/dev/null
endif

#
# Rule to compile a set of .o files into one .a file (without symbol table)
#

quiet_cmd_ar_builtin = AR      $@
      cmd_ar_builtin = rm -f $@; $(AR) cDPrST $@ $(real-prereqs)

quiet_cmd_ar_and_symver = AR      $@
      cmd_ar_and_symver = $(cmd_update_lto_symversions); $(cmd_ar_builtin)

$(obj)/built-in.a: $(real-obj-y) FORCE
	$(call if_changed,ar_and_symver)

#
# Rule to create modules.order file
#
# Create commands to either record .ko file or cat modules.order from
# a subdirectory
# Add $(obj-m) as the prerequisite to avoid updating the timestamp of
# modules.order unless contained modules are updated.

cmd_modules_order = { $(foreach m, $(real-prereqs), \
	$(if $(filter %/modules.order, $m), cat $m, echo $(patsubst %.o,%.ko,$m));) :; } \
	| $(AWK) '!x[$$0]++' - > $@

$(obj)/modules.order: $(obj-m) FORCE
	$(call if_changed,modules_order)

#
# Rule to compile a set of .o files into one .a file (with symbol table)
#
quiet_cmd_ar_lib = AR      $@
      cmd_ar_lib = $(cmd_update_lto_symversions); $(cmd_ar)

$(obj)/lib.a: $(lib-y) FORCE
	$(call if_changed,ar_lib)

ifdef CONFIG_LTO_CLANG
quiet_cmd_link_multi-m = AR [M]  $@
cmd_link_multi-m =						\
	$(cmd_update_lto_symversions);				\
	rm -f $@; 						\
	$(AR) cDPrsT $@ @$(patsubst %.o,%.mod,$@)
else
quiet_cmd_link_multi-m = LD [M]  $@
      cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ @$(patsubst %.o,%.mod,$@)
endif

$(multi-obj-m): %.o: %.mod FORCE
	$(call if_changed,link_multi-m)
$(call multi_depend, $(multi-obj-m), .o, -objs -y -m)

targets := $(filter-out $(PHONY), $(targets))

# Add intermediate targets:
# When building objects with specific suffix patterns, add intermediate
# targets that the final targets are derived from.
intermediate_targets = $(foreach sfx, $(2), \
				$(patsubst %$(strip $(1)),%$(sfx), \
					$(filter %$(strip $(1)), $(targets))))
# %.asn1.o <- %.asn1.[ch] <- %.asn1
# %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
# %.lex.o <- %.lex.c <- %.l
# %.tab.o <- %.tab.[ch] <- %.y
targets += $(call intermediate_targets, .asn1.o, .asn1.c .asn1.h) \
	   $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
	   $(call intermediate_targets, .lex.o, .lex.c) \
	   $(call intermediate_targets, .tab.o, .tab.c .tab.h)

# Build
# ---------------------------------------------------------------------------

ifdef single-build

KBUILD_SINGLE_TARGETS := $(filter $(obj)/%, $(KBUILD_SINGLE_TARGETS))

curdir-single := $(sort $(foreach x, $(KBUILD_SINGLE_TARGETS), \
			$(if $(filter $(x) $(basename $(x)).o, $(targets)), $(x))))

# Handle single targets without any rule: show "Nothing to be done for ..." or
# "No rule to make target ..." depending on whether the target exists.
unknown-single := $(filter-out $(addsuffix /%, $(subdir-ym)), \
			$(filter-out $(curdir-single), $(KBUILD_SINGLE_TARGETS)))

single-subdirs := $(foreach d, $(subdir-ym), \
			$(if $(filter $(d)/%, $(KBUILD_SINGLE_TARGETS)), $(d)))

__build: $(curdir-single) $(single-subdirs)
ifneq ($(unknown-single),)
	$(Q)$(MAKE) -f /dev/null $(unknown-single)
endif
	@:

ifeq ($(curdir-single),)
# Nothing to do in this directory. Do not include any .*.cmd file for speed-up
targets :=
else
targets += $(curdir-single)
endif

else

__build: $(if $(KBUILD_BUILTIN), $(targets-for-builtin)) \
	 $(if $(KBUILD_MODULES), $(targets-for-modules)) \
	 $(subdir-ym) $(always-y)
	@:

endif

# Descending
# ---------------------------------------------------------------------------

PHONY += $(subdir-ym)
$(subdir-ym):
	$(Q)$(MAKE) $(build)=$@ \
	$(if $(filter $@/, $(KBUILD_SINGLE_TARGETS)),single-build=) \
	need-builtin=$(if $(filter $@/built-in.a, $(subdir-builtin)),1) \
	need-modorder=$(if $(filter $@/modules.order, $(subdir-modorder)),1)

# Add FORCE to the prequisites of a target to force it to be always rebuilt.
# ---------------------------------------------------------------------------

PHONY += FORCE

FORCE:

# Read all saved command lines and dependencies for the $(targets) we
# may be building above, using $(if_changed{,_dep}). As an
# optimization, we don't need to read them if the target does not
# exist, we will rebuild anyway in that case.

existing-targets := $(wildcard $(sort $(targets)))

-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)

# Create directories for object files if they do not exist
obj-dirs := $(sort $(patsubst %/,%, $(dir $(targets))))
# If targets exist, their directories apparently exist. Skip mkdir.
existing-dirs := $(sort $(patsubst %/,%, $(dir $(existing-targets))))
obj-dirs := $(strip $(filter-out $(existing-dirs), $(obj-dirs)))
ifneq ($(obj-dirs),)
$(shell mkdir -p $(obj-dirs))
endif

.PHONY: $(PHONY)