# ==========================================================================
  #
  # make W=... settings
  #
  # W=1 - warnings that may be relevant and does not occur too often
  # W=2 - warnings that occur quite often but may still be relevant
  # W=3 - the more obscure warnings, can most likely be ignored
  #
  # $(call cc-option, -W...) handles gcc -W.. options which
  # are not supported by all versions of the compiler
  # ==========================================================================
  
  ifeq ("$(origin W)", "command line")
    export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
  endif
  
  ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
  warning-  := $(empty)
  
  warning-1 := -Wextra -Wunused -Wno-unused-parameter
  warning-1 += -Wmissing-declarations
  warning-1 += -Wmissing-format-attribute
  warning-1 += $(call cc-option, -Wmissing-prototypes)
  warning-1 += -Wold-style-definition
  warning-1 += $(call cc-option, -Wmissing-include-dirs)
  warning-1 += $(call cc-option, -Wunused-but-set-variable)
  warning-1 += $(call cc-disable-warning, missing-field-initializers)

  warning-2 := -Waggregate-return
  warning-2 += -Wcast-align
  warning-2 += -Wdisabled-optimization
  warning-2 += -Wnested-externs
  warning-2 += -Wshadow
  warning-2 += $(call cc-option, -Wlogical-op)
  warning-2 += $(call cc-option, -Wmissing-field-initializers)
  
  warning-3 := -Wbad-function-cast
  warning-3 += -Wcast-qual
  warning-3 += -Wconversion
  warning-3 += -Wpacked
  warning-3 += -Wpadded
  warning-3 += -Wpointer-arith
  warning-3 += -Wredundant-decls
  warning-3 += -Wswitch-default
  warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
  warning-3 += $(call cc-option, -Wvla)
  
  warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
  warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
  warning += $(warning-$(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
  
  ifeq ("$(strip $(warning))","")
          $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
  endif
  
  KBUILD_CFLAGS += $(warning)

  else
  
  ifeq ($(COMPILER),clang)
  KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
  KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
  KBUILD_CFLAGS += $(call cc-disable-warning, format)
  KBUILD_CFLAGS += $(call cc-disable-warning, unknown-warning-option)
  KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
  KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
  KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
  endif

  endif