scripts/Makefile.build

   1 # SPDX-License-Identifier: GPL-2.0
   2 # ==========================================================================
   3 # Building
   4 # ==========================================================================
   5
   6 src := $(obj)
   7
   8 PHONY := __build
   9 __build:
  10
  11 # Init all relevant variables used in kbuild files so
  12 # 1) they have correct type
  13 # 2) they do not inherit any value from the environment
  14 obj-y :=
  15 obj-m :=
  16 lib-y :=
  17 lib-m :=
  18 always :=
  19 targets :=
  20 subdir-y :=
  21 subdir-m :=
  22 EXTRA_AFLAGS   :=
  23 EXTRA_CFLAGS   :=
  24 EXTRA_CPPFLAGS :=
  25 EXTRA_LDFLAGS  :=
  26 asflags-y  :=
  27 ccflags-y  :=
  28 cppflags-y :=
  29 ldflags-y  :=
  30
  31 subdir-asflags-y :=
  32 subdir-ccflags-y :=
  33
  34 # Read auto.conf if it exists, otherwise ignore
  35 -include include/config/auto.conf
  36
  37 include scripts/Kbuild.include
  38
  39 # For backward compatibility check that these variables do not change
  40 save-cflags := $(CFLAGS)
  41
  42 # The filename Kbuild has precedence over Makefile
  43 kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
  44 kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
  45 include $(kbuild-file)
  46
  47 # If the save-* variables changed error out
  48 ifeq ($(KBUILD_NOPEDANTIC),)
  49         ifneq ("$(save-cflags)","$(CFLAGS)")
  50                 $(error CFLAGS was changed in "$(kbuild-file)". Fix it to use ccflags-y)
  51         endif
  52 endif
  53
  54 include scripts/Makefile.lib
  55
  56 # Do not include host rules unless needed
  57 ifneq ($(hostprogs-y)$(hostprogs-m)$(hostlibs-y)$(hostlibs-m)$(hostcxxlibs-y)$(hostcxxlibs-m),)
  58 include scripts/Makefile.host
  59 endif
  60
  61 ifndef obj
  62 $(warning kbuild: Makefile.build is included improperly)
  63 endif
  64
  65 # ===========================================================================
  66
  67 ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
  68 lib-target := $(obj)/lib.a
  69 real-obj-y += $(obj)/lib-ksyms.o
  70 endif
  71
  72 ifneq ($(strip $(real-obj-y) $(need-builtin)),)
  73 builtin-target := $(obj)/built-in.a
  74 endif
  75
  76 modorder-target := $(obj)/modules.order
  77
  78 # We keep a list of all modules in $(MODVERDIR)
  79
  80 __build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
  81          $(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
  82          $(subdir-ym) $(always)
  83         @:
  84
  85 # Linus' kernel sanity checking tool
  86 ifneq ($(KBUILD_CHECKSRC),0)
  87   ifeq ($(KBUILD_CHECKSRC),2)
  88     quiet_cmd_force_checksrc = CHECK   $<
  89           cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
  90   else
  91       quiet_cmd_checksrc     = CHECK   $<
  92             cmd_checksrc     = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
  93   endif
  94 endif
  95
  96 ifneq ($(KBUILD_ENABLE_EXTRA_GCC_CHECKS),)
  97   cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $< ;
  98 endif
  99
 100 # Do section mismatch analysis for each module/built-in.a
 101 ifdef CONFIG_DEBUG_SECTION_MISMATCH
 102   cmd_secanalysis = ; scripts/mod/modpost $@
 103 endif
 104
 105 # Compile C sources (.c)
 106 # ---------------------------------------------------------------------------
 107
 108 # Default is built-in, unless we know otherwise
 109 modkern_cflags =                                          \
 110         $(if $(part-of-module),                           \
 111                 $(KBUILD_CFLAGS_MODULE) $(CFLAGS_MODULE), \
 112                 $(KBUILD_CFLAGS_KERNEL) $(CFLAGS_KERNEL))
 113 quiet_modtag := $(empty)   $(empty)
 114
 115 $(real-obj-m)        : part-of-module := y
 116 $(real-obj-m:.o=.i)  : part-of-module := y
 117 $(real-obj-m:.o=.s)  : part-of-module := y
 118 $(real-obj-m:.o=.lst): part-of-module := y
 119
 120 $(real-obj-m)        : quiet_modtag := [M]
 121 $(real-obj-m:.o=.i)  : quiet_modtag := [M]
 122 $(real-obj-m:.o=.s)  : quiet_modtag := [M]
 123 $(real-obj-m:.o=.lst): quiet_modtag := [M]
 124
 125 $(obj-m)             : quiet_modtag := [M]
 126
 127 quiet_cmd_cc_s_c = CC $(quiet_modtag)  $@
 128 cmd_cc_s_c       = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
 129
 130 $(obj)/%.s: $(src)/%.c FORCE
 131         $(call if_changed_dep,cc_s_c)
 132
 133 quiet_cmd_cpp_i_c = CPP $(quiet_modtag) $@
 134 cmd_cpp_i_c       = $(CPP) $(c_flags) -o $@ $<
 135
 136 $(obj)/%.i: $(src)/%.c FORCE
 137         $(call if_changed_dep,cpp_i_c)
 138
 139 # These mirror gensymtypes_S and co below, keep them in synch.
 140 cmd_gensymtypes_c =                                                         \
 141     $(CPP) -D__GENKSYMS__ $(c_flags) $< |                                   \
 142     $(GENKSYMS) $(if $(1), -T $(2))                                         \
 143      $(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS))                             \
 144      $(if $(KBUILD_PRESERVE),-p)                                            \
 145      -r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))
 146
 147 quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
 148 cmd_cc_symtypes_c =                                                         \
 149     set -e;                                                                 \
 150     $(call cmd_gensymtypes_c,true,$@) >/dev/null;                           \
 151     test -s $@ || rm -f $@
 152
 153 $(obj)/%.symtypes : $(src)/%.c FORCE
 154         $(call cmd,cc_symtypes_c)
 155
 156 # LLVM assembly
 157 # Generate .ll files from .c
 158 quiet_cmd_cc_ll_c = CC $(quiet_modtag)  $@
 159       cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -o $@ $<
 160
 161 $(obj)/%.ll: $(src)/%.c FORCE
 162         $(call if_changed_dep,cc_ll_c)
 163
 164 # C (.c) files
 165 # The C file is compiled and updated dependency information is generated.
 166 # (See cmd_cc_o_c + relevant part of rule_cc_o_c)
 167
 168 quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
 169
 170 ifndef CONFIG_MODVERSIONS
 171 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
 172
 173 else
 174 # When module versioning is enabled the following steps are executed:
 175 # o compile a .tmp_<file>.o from <file>.c
 176 # o if .tmp_<file>.o doesn't contain a __ksymtab version, i.e. does
 177 #   not export symbols, we just rename .tmp_<file>.o to <file>.o and
 178 #   are done.
 179 # o otherwise, we calculate symbol versions using the good old
 180 #   genksyms on the preprocessed source and postprocess them in a way
 181 #   that they are usable as a linker script
 182 # o generate <file>.o from .tmp_<file>.o using the linker to
 183 #   replace the unresolved symbols __crc_exported_symbol with
 184 #   the actual value of the checksum generated by genksyms
 185
 186 cmd_cc_o_c = $(CC) $(c_flags) -c -o $(@D)/.tmp_$(@F) $<
 187
 188 cmd_modversions_c =                                                             \
 189         if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then             \
 190                 $(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))  \
 191                     > $(@D)/.tmp_$(@F:.o=.ver);                                 \
 192                                                                                 \
 193                 $(LD) $(KBUILD_LDFLAGS) -r -o $@ $(@D)/.tmp_$(@F)               \
 194                         -T $(@D)/.tmp_$(@F:.o=.ver);                            \
 195                 rm -f $(@D)/.tmp_$(@F) $(@D)/.tmp_$(@F:.o=.ver);                \
 196         else                                                                    \
 197                 mv -f $(@D)/.tmp_$(@F) $@;                                      \
 198         fi;
 199 endif
 200
 201 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 202 ifndef CC_USING_RECORD_MCOUNT
 203 # compiler will not generate __mcount_loc use recordmcount or recordmcount.pl
 204 ifdef BUILD_C_RECORDMCOUNT
 205 ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
 206   RECORDMCOUNT_FLAGS = -w
 207 endif
 208 # Due to recursion, we must skip empty.o.
 209 # The empty.o file is created in the make process in order to determine
 210 # the target endianness and word size. It is made before all other C
 211 # files, including recordmcount.
 212 sub_cmd_record_mcount =                                 \
 213         if [ $(@) != "scripts/mod/empty.o" ]; then      \
 214                 $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)";   \
 215         fi;
 216 recordmcount_source := $(srctree)/scripts/recordmcount.c \
 217                     $(srctree)/scripts/recordmcount.h
 218 else
 219 sub_cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
 220         "$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
 221         "$(if $(CONFIG_64BIT),64,32)" \
 222         "$(OBJDUMP)" "$(OBJCOPY)" "$(CC) $(KBUILD_CFLAGS)" \
 223         "$(LD) $(KBUILD_LDFLAGS)" "$(NM)" "$(RM)" "$(MV)" \
 224         "$(if $(part-of-module),1,0)" "$(@)";
 225 recordmcount_source := $(srctree)/scripts/recordmcount.pl
 226 endif # BUILD_C_RECORDMCOUNT
 227 cmd_record_mcount =                                             \
 228         if [ "$(findstring $(CC_FLAGS_FTRACE),$(_c_flags))" =   \
 229              "$(CC_FLAGS_FTRACE)" ]; then                       \
 230                 $(sub_cmd_record_mcount)                        \
 231         fi;
 232 endif # CC_USING_RECORD_MCOUNT
 233 endif # CONFIG_FTRACE_MCOUNT_RECORD
 234
 235 ifdef CONFIG_STACK_VALIDATION
 236 ifneq ($(SKIP_STACK_VALIDATION),1)
 237
 238 __objtool_obj := $(objtree)/tools/objtool/objtool
 239
 240 objtool_args = $(if $(CONFIG_UNWINDER_ORC),orc generate,check)
 241
 242 objtool_args += $(if $(part-of-module), --module,)
 243
 244 ifndef CONFIG_FRAME_POINTER
 245 objtool_args += --no-fp
 246 endif
 247 ifdef CONFIG_GCOV_KERNEL
 248 objtool_args += --no-unreachable
 249 endif
 250 ifdef CONFIG_RETPOLINE
 251 ifneq ($(RETPOLINE_CFLAGS),)
 252   objtool_args += --retpoline
 253 endif
 254 endif
 255
 256
 257 ifdef CONFIG_MODVERSIONS
 258 objtool_o = $(@D)/.tmp_$(@F)
 259 else
 260 objtool_o = $(@)
 261 endif
 262
 263 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
 264 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
 265 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
 266 cmd_objtool = $(if $(patsubst y%,, \
 267         $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 268         $(__objtool_obj) $(objtool_args) "$(objtool_o)";)
 269 objtool_obj = $(if $(patsubst y%,, \
 270         $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 271         $(__objtool_obj))
 272
 273 endif # SKIP_STACK_VALIDATION
 274 endif # CONFIG_STACK_VALIDATION
 275
 276 # Rebuild all objects when objtool changes, or is enabled/disabled.
 277 objtool_dep = $(objtool_obj)                                    \
 278               $(wildcard include/config/orc/unwinder.h          \
 279                          include/config/stack/validation.h)
 280
 281 define rule_cc_o_c
 282         $(call echo-cmd,checksrc) $(cmd_checksrc)                         \
 283         $(call cmd_and_fixdep,cc_o_c)                                     \
 284         $(cmd_checkdoc)                                                   \
 285         $(call echo-cmd,objtool) $(cmd_objtool)                           \
 286         $(cmd_modversions_c)                                              \
 287         $(call echo-cmd,record_mcount) $(cmd_record_mcount)
 288 endef
 289
 290 define rule_as_o_S
 291         $(call cmd_and_fixdep,as_o_S)                                     \
 292         $(call echo-cmd,objtool) $(cmd_objtool)                           \
 293         $(cmd_modversions_S)
 294 endef
 295
 296 # List module undefined symbols (or empty line if not enabled)
 297 ifdef CONFIG_TRIM_UNUSED_KSYMS
 298 cmd_undef_syms = $(NM) $@ | sed -n 's/^  *U //p' | xargs echo
 299 else
 300 cmd_undef_syms = echo
 301 endif
 302
 303 # Built-in and composite module parts
 304 $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
 305         $(call cmd,force_checksrc)
 306         $(call if_changed_rule,cc_o_c)
 307
 308 # Single-part modules are special since we need to mark them in $(MODVERDIR)
 309
 310 $(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
 311         $(call cmd,force_checksrc)
 312         $(call if_changed_rule,cc_o_c)
 313         @{ echo $(@:.o=.ko); echo $@; \
 314            $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
 315
 316 quiet_cmd_cc_lst_c = MKLST   $@
 317       cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
 318                      $(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
 319                                      System.map $(OBJDUMP) > $@
 320
 321 $(obj)/%.lst: $(src)/%.c FORCE
 322         $(call if_changed_dep,cc_lst_c)
 323
 324 # Compile assembler sources (.S)
 325 # ---------------------------------------------------------------------------
 326
 327 modkern_aflags := $(KBUILD_AFLAGS_KERNEL) $(AFLAGS_KERNEL)
 328
 329 $(real-obj-m)      : modkern_aflags := $(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE)
 330 $(real-obj-m:.o=.s): modkern_aflags := $(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE)
 331
 332 # .S file exports must have their C prototypes defined in asm/asm-prototypes.h
 333 # or a file that it includes, in order to get versioned symbols. We build a
 334 # dummy C file that includes asm-prototypes and the EXPORT_SYMBOL lines from
 335 # the .S file (with trailing ';'), and run genksyms on that, to extract vers.
 336 #
 337 # This is convoluted. The .S file must first be preprocessed to run guards and
 338 # expand names, then the resulting exports must be constructed into plain
 339 # EXPORT_SYMBOL(symbol); to build our dummy C file, and that gets preprocessed
 340 # to make the genksyms input.
 341 #
 342 # These mirror gensymtypes_c and co above, keep them in synch.
 343 cmd_gensymtypes_S =                                                         \
 344     (echo "\#include <linux/kernel.h>" ;                                    \
 345      echo "\#include <asm/asm-prototypes.h>" ;                              \
 346     $(CPP) $(a_flags) $< |                                                  \
 347      grep "\<___EXPORT_SYMBOL\>" |                                          \
 348      sed 's/.*___EXPORT_SYMBOL[[:space:]]*\([a-zA-Z0-9_]*\)[[:space:]]*,.*/EXPORT_SYMBOL(\1);/' ) | \
 349     $(CPP) -D__GENKSYMS__ $(c_flags) -xc - |                                \
 350     $(GENKSYMS) $(if $(1), -T $(2))                                         \
 351      $(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS))                             \
 352      $(if $(KBUILD_PRESERVE),-p)                                            \
 353      -r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))
 354
 355 quiet_cmd_cc_symtypes_S = SYM $(quiet_modtag) $@
 356 cmd_cc_symtypes_S =                                                         \
 357     set -e;                                                                 \
 358     $(call cmd_gensymtypes_S,true,$@) >/dev/null;                           \
 359     test -s $@ || rm -f $@
 360
 361 $(obj)/%.symtypes : $(src)/%.S FORCE
 362         $(call cmd,cc_symtypes_S)
 363
 364
 365 quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@
 366 cmd_cpp_s_S       = $(CPP) $(a_flags) -o $@ $<
 367
 368 $(obj)/%.s: $(src)/%.S FORCE
 369         $(call if_changed_dep,cpp_s_S)
 370
 371 quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
 372
 373 ifndef CONFIG_MODVERSIONS
 374 cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
 375
 376 else
 377
 378 ASM_PROTOTYPES := $(wildcard $(srctree)/arch/$(SRCARCH)/include/asm/asm-prototypes.h)
 379
 380 ifeq ($(ASM_PROTOTYPES),)
 381 cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
 382
 383 else
 384
 385 # versioning matches the C process described above, with difference that
 386 # we parse asm-prototypes.h C header to get function definitions.
 387
 388 cmd_as_o_S = $(CC) $(a_flags) -c -o $(@D)/.tmp_$(@F) $<
 389
 390 cmd_modversions_S =                                                             \
 391         if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then             \
 392                 $(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))  \
 393                     > $(@D)/.tmp_$(@F:.o=.ver);                                 \
 394                                                                                 \
 395                 $(LD) $(KBUILD_LDFLAGS) -r -o $@ $(@D)/.tmp_$(@F)               \
 396                         -T $(@D)/.tmp_$(@F:.o=.ver);                            \
 397                 rm -f $(@D)/.tmp_$(@F) $(@D)/.tmp_$(@F:.o=.ver);                \
 398         else                                                                    \
 399                 mv -f $(@D)/.tmp_$(@F) $@;                                      \
 400         fi;
 401 endif
 402 endif
 403
 404 $(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
 405         $(call if_changed_rule,as_o_S)
 406
 407 targets += $(filter-out $(subdir-obj-y), $(real-obj-y)) $(real-obj-m) $(lib-y)
 408 targets += $(extra-y) $(MAKECMDGOALS) $(always)
 409
 410 # Linker scripts preprocessor (.lds.S -> .lds)
 411 # ---------------------------------------------------------------------------
 412 quiet_cmd_cpp_lds_S = LDS     $@
 413       cmd_cpp_lds_S = $(CPP) $(cpp_flags) -P -U$(ARCH) \
 414                              -D__ASSEMBLY__ -DLINKER_SCRIPT -o $@ $<
 415
 416 $(obj)/%.lds: $(src)/%.lds.S FORCE
 417         $(call if_changed_dep,cpp_lds_S)
 418
 419 # ASN.1 grammar
 420 # ---------------------------------------------------------------------------
 421 quiet_cmd_asn1_compiler = ASN.1   $@
 422       cmd_asn1_compiler = $(objtree)/scripts/asn1_compiler $< \
 423                                 $(subst .h,.c,$@) $(subst .c,.h,$@)
 424
 425 $(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
 426         $(call cmd,asn1_compiler)
 427
 428 # Build the compiled-in targets
 429 # ---------------------------------------------------------------------------
 430
 431 # To build objects in subdirs, we need to descend into the directories
 432 $(sort $(subdir-obj-y)): $(subdir-ym) ;
 433
 434 #
 435 # Rule to compile a set of .o files into one .o file
 436 #
 437 ifdef builtin-target
 438
 439 # built-in.a archives are made with no symbol table or index which
 440 # makes them small and fast, but unable to be used by the linker.
 441 # scripts/link-vmlinux.sh builds an aggregate built-in.a with a symbol
 442 # table and index.
 443 quiet_cmd_ar_builtin = AR      $@
 444       cmd_ar_builtin = rm -f $@; \
 445                      $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(filter $(real-obj-y), $^)
 446
 447 $(builtin-target): $(real-obj-y) FORCE
 448         $(call if_changed,ar_builtin)
 449
 450 targets += $(builtin-target)
 451 endif # builtin-target
 452
 453 #
 454 # Rule to create modules.order file
 455 #
 456 # Create commands to either record .ko file or cat modules.order from
 457 # a subdirectory
 458 modorder-cmds =                                         \
 459         $(foreach m, $(modorder),                       \
 460                 $(if $(filter %/modules.order, $m),     \
 461                         cat $m;, echo kernel/$m;))
 462
 463 $(modorder-target): $(subdir-ym) FORCE
 464         $(Q)(cat /dev/null; $(modorder-cmds)) > $@
 465
 466 #
 467 # Rule to compile a set of .o files into one .a file
 468 #
 469 ifdef lib-target
 470 quiet_cmd_link_l_target = AR      $@
 471
 472 # lib target archives do get a symbol table and index
 473 cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(lib-y)
 474
 475 $(lib-target): $(lib-y) FORCE
 476         $(call if_changed,link_l_target)
 477
 478 targets += $(lib-target)
 479
 480 dummy-object = $(obj)/.lib_exports.o
 481 ksyms-lds = $(dot-target).lds
 482
 483 quiet_cmd_export_list = EXPORTS $@
 484 cmd_export_list = $(OBJDUMP) -h $< | \
 485         sed -ne '/___ksymtab/s/.*+\([^ ]*\).*/EXTERN(\1)/p' >$(ksyms-lds);\
 486         rm -f $(dummy-object);\
 487         echo | $(CC) $(a_flags) -c -o $(dummy-object) -x assembler -;\
 488         $(LD) $(ld_flags) -r -o $@ -T $(ksyms-lds) $(dummy-object);\
 489         rm $(dummy-object) $(ksyms-lds)
 490
 491 $(obj)/lib-ksyms.o: $(lib-target) FORCE
 492         $(call if_changed,export_list)
 493
 494 targets += $(obj)/lib-ksyms.o
 495
 496 endif
 497
 498 #
 499 # Rule to link composite objects
 500 #
 501 #  Composite objects are specified in kbuild makefile as follows:
 502 #    <composite-object>-objs := <list of .o files>
 503 #  or
 504 #    <composite-object>-y    := <list of .o files>
 505 #  or
 506 #    <composite-object>-m    := <list of .o files>
 507 #  The -m syntax only works if <composite object> is a module
 508 link_multi_deps =                     \
 509 $(filter $(addprefix $(obj)/,         \
 510 $($(subst $(obj)/,,$(@:.o=-objs)))    \
 511 $($(subst $(obj)/,,$(@:.o=-y)))       \
 512 $($(subst $(obj)/,,$(@:.o=-m)))), $^)
 513
 514 quiet_cmd_link_multi-m = LD [M]  $@
 515 cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)
 516
 517 $(multi-used-m): FORCE
 518         $(call if_changed,link_multi-m)
 519         @{ echo $(@:.o=.ko); echo $(link_multi_deps); \
 520            $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
 521 $(call multi_depend, $(multi-used-m), .o, -objs -y -m)
 522
 523 targets += $(multi-used-m)
 524 targets := $(filter-out $(PHONY), $(targets))
 525
 526 # Add intermediate targets:
 527 # When building objects with specific suffix patterns, add intermediate
 528 # targets that the final targets are derived from.
 529 intermediate_targets = $(foreach sfx, $(2), \
 530                                 $(patsubst %$(strip $(1)),%$(sfx), \
 531                                         $(filter %$(strip $(1)), $(targets))))
 532 # %.asn1.o <- %.asn1.[ch] <- %.asn1
 533 # %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
 534 # %.lex.o <- %.lex.c <- %.l
 535 # %.tab.o <- %.tab.[ch] <- %.y
 536 targets += $(call intermediate_targets, .asn1.o, .asn1.c .asn1.h) \
 537            $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
 538            $(call intermediate_targets, .lex.o, .lex.c) \
 539            $(call intermediate_targets, .tab.o, .tab.c .tab.h)
 540
 541 # Descending
 542 # ---------------------------------------------------------------------------
 543
 544 PHONY += $(subdir-ym)
 545 $(subdir-ym):
 546         $(Q)$(MAKE) $(build)=$@ need-builtin=$(if $(findstring $@,$(subdir-obj-y)),1)
 547
 548 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 549 # ---------------------------------------------------------------------------
 550
 551 PHONY += FORCE
 552
 553 FORCE:
 554
 555 # Read all saved command lines and dependencies for the $(targets) we
 556 # may be building above, using $(if_changed{,_dep}). As an
 557 # optimization, we don't need to read them if the target does not
 558 # exist, we will rebuild anyway in that case.
 559
 560 cmd_files := $(wildcard $(foreach f,$(sort $(targets)),$(dir $(f)).$(notdir $(f)).cmd))
 561
 562 ifneq ($(cmd_files),)
 563   include $(cmd_files)
 564 endif
 565
 566 ifneq ($(KBUILD_SRC),)
 567 # Create directories for object files if they do not exist
 568 obj-dirs := $(sort $(obj) $(patsubst %/,%, $(dir $(targets))))
 569 # If cmd_files exist, their directories apparently exist.  Skip mkdir.
 570 exist-dirs := $(sort $(patsubst %/,%, $(dir $(cmd_files))))
 571 obj-dirs := $(strip $(filter-out $(exist-dirs), $(obj-dirs)))
 572 ifneq ($(obj-dirs),)
 573 $(shell mkdir -p $(obj-dirs))
 574 endif
 575 endif
 576
 577 # Some files contained in $(targets) are intermediate artifacts.
 578 # We never want them to be removed automatically.
 579 .SECONDARY: $(targets)
 580
 581 .PHONY: $(PHONY)