# SPDX-License-Identifier: GPL-2.0

  ifneq ($(O),)

  ifeq ($(origin O), command line)

  	dummy := $(if $(shell cd $(PWD); test -d $(O) || echo $(O)),$(error O=$(O) does not exist),)
  	ABSOLUTE_O := $(shell cd $(PWD); cd $(O) ; pwd)

  	OUTPUT := $(ABSOLUTE_O)/$(if $(subdir),$(subdir)/)

  	COMMAND_O := O=$(ABSOLUTE_O)

  ifeq ($(objtree),)
  	objtree := $(O)
  endif

  endif

  endif

  # check that the output directory actually exists

  ifneq ($(OUTPUT),)

  OUTDIR := $(shell cd $(OUTPUT) && pwd)

  $(if $(OUTDIR),, $(error output directory "$(OUTPUT)" does not exist))
  endif
  
  #
  # Include saner warnings here, which can catch bugs:
  #

  EXTRA_WARNINGS := -Wbad-function-cast
  EXTRA_WARNINGS += -Wdeclaration-after-statement
  EXTRA_WARNINGS += -Wformat-security
  EXTRA_WARNINGS += -Wformat-y2k
  EXTRA_WARNINGS += -Winit-self
  EXTRA_WARNINGS += -Wmissing-declarations
  EXTRA_WARNINGS += -Wmissing-prototypes
  EXTRA_WARNINGS += -Wnested-externs
  EXTRA_WARNINGS += -Wno-system-headers
  EXTRA_WARNINGS += -Wold-style-definition
  EXTRA_WARNINGS += -Wpacked
  EXTRA_WARNINGS += -Wredundant-decls

  EXTRA_WARNINGS += -Wstrict-prototypes
  EXTRA_WARNINGS += -Wswitch-default
  EXTRA_WARNINGS += -Wswitch-enum
  EXTRA_WARNINGS += -Wundef
  EXTRA_WARNINGS += -Wwrite-strings
  EXTRA_WARNINGS += -Wformat

  CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)

  # Makefiles suck: This macro sets a default value of $(2) for the
  # variable named by $(1), unless the variable has been set by
  # environment or command line. This is necessary for CC and AR
  # because make sets default values, so the simpler ?= approach
  # won't work as expected.
  define allow-override
    $(if $(or $(findstring environment,$(origin $(1))),\
              $(findstring command line,$(origin $(1)))),,\
      $(eval $(1) = $(2)))
  endef
  
  # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
  $(call allow-override,CC,$(CROSS_COMPILE)gcc)
  $(call allow-override,AR,$(CROSS_COMPILE)ar)
  $(call allow-override,LD,$(CROSS_COMPILE)ld)
  $(call allow-override,CXX,$(CROSS_COMPILE)g++)
  $(call allow-override,STRIP,$(CROSS_COMPILE)strip)

  ifeq ($(CC_NO_CLANG), 1)

  EXTRA_WARNINGS += -Wstrict-aliasing=3
  endif

  # Hack to avoid type-punned warnings on old systems such as RHEL5:
  # We should be changing CFLAGS and checking gcc version, but this
  # will do for now and keep the above -Wstrict-aliasing=3 in place
  # in newer systems.
  # Needed for the __raw_cmpxchg in tools/arch/x86/include/asm/cmpxchg.h

  #
  # See https://lkml.org/lkml/2006/11/28/253 and https://gcc.gnu.org/gcc-4.8/changes.html,
  # that takes into account Linus's comments (search for Wshadow) for the reasoning about
  # -Wshadow not being interesting before gcc 4.8.

  ifneq ($(filter 3.%,$(MAKE_VERSION)),)  # make-3
  EXTRA_WARNINGS += -fno-strict-aliasing

  EXTRA_WARNINGS += -Wno-shadow
  else
  EXTRA_WARNINGS += -Wshadow

  endif

  ifneq ($(findstring $(MAKEFLAGS), w),w)
  PRINT_DIR = --no-print-directory
  else
  NO_SUBDIR = :
  endif

  ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)

    silent=1
  endif

  #
  # Define a callable command for descending to a new directory
  #
  # Call by doing: $(call descend,directory[,target])
  #
  descend = \

  	+mkdir -p $(OUTPUT)$(1) && \

  	$(MAKE) $(COMMAND_O) subdir=$(if $(subdir),$(subdir)/$(1),$(1)) $(PRINT_DIR) -C $(1) $(2)

  QUIET_SUBDIR0  = +$(MAKE) $(COMMAND_O) -C # space to separate -C and subdir

  QUIET_SUBDIR1  =

  ifneq ($(silent),1)

    ifneq ($(V),1)
  	QUIET_CC       = @echo '  CC       '$@;

  	QUIET_CC_FPIC  = @echo '  CC FPIC  '$@;

  	QUIET_CLANG    = @echo '  CLANG    '$@;

  	QUIET_AR       = @echo '  AR       '$@;
  	QUIET_LINK     = @echo '  LINK     '$@;
  	QUIET_MKDIR    = @echo '  MKDIR    '$@;
  	QUIET_GEN      = @echo '  GEN      '$@;

  	QUIET_SUBDIR0  = +@subdir=

  	QUIET_SUBDIR1  = ;$(NO_SUBDIR) \
  			  echo '  SUBDIR   '$$subdir; \

  			 $(MAKE) $(PRINT_DIR) -C $$subdir

  	QUIET_FLEX     = @echo '  FLEX     '$@;
  	QUIET_BISON    = @echo '  BISON    '$@;

  
  	descend = \

  		+@echo	       '  DESCEND  '$(1); \

  		mkdir -p $(OUTPUT)$(1) && \

  		$(MAKE) $(COMMAND_O) subdir=$(if $(subdir),$(subdir)/$(1),$(1)) $(PRINT_DIR) -C $(1) $(2)

  
  	QUIET_CLEAN    = @printf '  CLEAN    %s
  ' $1;
  	QUIET_INSTALL  = @printf '  INSTALL  %s
  ' $1;

  	QUIET_UNINST   = @printf '  UNINST   %s
  ' $1;

    endif

  endif

  
  pound := \#