kbuild: rename KBUILD_ENABLE_EXTRA_GCC_CHECKS to KBUILD_EXTRA_WARN

KBUILD_ENABLE_EXTRA_GCC_CHECKS started as a switch to add extra warning
options for GCC, but now it is a historical misnomer since we use it
also for Clang, DTC, and even kernel-doc.

Rename it to more sensible, shorter KBUILD_EXTRA_WARN.

For the backward compatibility, KBUILD_ENABLE_EXTRA_GCC_CHECKS is still
supported (but not advertised in the documentation).

I also fixed up 'make help', and updated the documentation.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Reviewed-by: Nick Desaulniers <[e-mail]>
Reviewed-by: Sedat Dilek <[e-mail]>

Documentation/kbuild/kbuild.rst

···
 
 Setting "O=..." takes precedence over KBUILD_OUTPUT.
 
+KBUILD_EXTRA_WARN
+-----------------
+Specify the extra build checks. The same value can be assigned by passing
+W=... from the command line.
+
+See `make help` for the list of the supported values.
+
+Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
+
 KBUILD_DEBARCH
 --------------
 For the deb-pkg target, allows overriding the normal heuristics deployed by
···
 To get all available archs you can also specify all. E.g.::
 
     $ make ALLSOURCE_ARCHS=all tags
-
-KBUILD_ENABLE_EXTRA_GCC_CHECKS
-------------------------------
-If enabled over the make command line with "W=1", it turns on additional
-gcc -W... options for more extensive build-time checking.
 
 KBUILD_BUILD_TIMESTAMP
 ----------------------

Makefile

···
 	@echo  '  make C=1   [targets] Check re-compiled c source with $$CHECK (sparse by default)'
 	@echo  '  make C=2   [targets] Force check of all c source with $$CHECK'
 	@echo  '  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections'
-	@echo  '  make W=n   [targets] Enable extra gcc checks, n=1,2,3 where'
+	@echo  '  make W=n   [targets] Enable extra build checks, n=1,2,3 where'
 	@echo  '		1: warnings which may be relevant and do not occur too often'
 	@echo  '		2: warnings which occur quite often but may still be relevant'
 	@echo  '		3: more obscure warnings, can most likely be ignored'

scripts/Makefile.build

···
         cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $<
 endif
 
-ifneq ($(KBUILD_ENABLE_EXTRA_GCC_CHECKS),)
+ifneq ($(KBUILD_EXTRA_WARN),)
   cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $<
 endif
 

scripts/Makefile.extrawarn

···
 
 KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
 
+# backward compatibility
+KBUILD_EXTRA_WARN ?= $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)
+
 ifeq ("$(origin W)", "command line")
-  export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
+  KBUILD_EXTRA_WARN := $(W)
 endif
+
+export KBUILD_EXTRA_WARN
 
 #
 # W=1 - warnings which may be relevant and do not occur too often
 #
-ifneq ($(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 
 KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
 KBUILD_CFLAGS += -Wmissing-declarations
···
 #
 # W=2 - warnings which occur quite often but may still be relevant
 #
-ifneq ($(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
 
 KBUILD_CFLAGS += -Wcast-align
 KBUILD_CFLAGS += -Wdisabled-optimization
···
 #
 # W=3 - more obscure warnings, can most likely be ignored
 #
-ifneq ($(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
 
 KBUILD_CFLAGS += -Wbad-function-cast
 KBUILD_CFLAGS += -Wcast-qual

scripts/Makefile.lib

···
 DTC ?= $(objtree)/scripts/dtc/dtc
 
 # Disable noisy checks by default
-ifeq ($(findstring 1,$(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifeq ($(findstring 1,$(KBUILD_EXTRA_WARN)),)
 DTC_FLAGS += -Wno-unit_address_vs_reg \
 	-Wno-unit_address_format \
 	-Wno-avoid_unnecessary_addr_size \
···
 	-Wno-pci_device_reg
 endif
 
-ifneq ($(findstring 2,$(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifneq ($(findstring 2,$(KBUILD_EXTRA_WARN)),)
 DTC_FLAGS += -Wnode_name_chars_strict \
 	-Wproperty_name_chars_strict
 endif

scripts/genksyms/Makefile

···
 #
 # Just in case, run "$(YACC) --version" without suppressing stderr
 # so that 'bison: not found' will be displayed if it is missing.
-ifeq ($(findstring 1,$(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+ifeq ($(findstring 1,$(KBUILD_EXTRA_WARN)),)
 
 quiet_cmd_bison_no_warn = $(quiet_cmd_bison)
       cmd_bison_no_warn = $(YACC) --version >/dev/null; \