kconfig: add kconfig-sym-check static checker

Add 'make kconfig-sym-check', a static checker that finds Kconfig
symbols referenced in expressions (select, depends on, default, etc.)
but never defined via config/menuconfig anywhere in the tree. New
dangling symbols are reported as errors (exit 1) unless they are
listed in an exclusion file, e.g.

 KCONFIG_SYM_CHECK_EXCLUDES=sym-check-excludes make kconfig-sym-check

The exclusion file lists one symbol per line; blank lines and lines
starting with '#' are ignored.

The checker also warns about uppercase N/Y/M used as tristate literal
values following the same logic as checkpatch.

This new static checker is the script used for [1] with a few
improvements to avoid some false positives.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216748 [1]
Assisted-by: Claude:claude-sonnet-4-6
Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Julian Braha <julianbraha@gmail.com>
Tested-by: Nicolas Schier <nsc@kernel.org>
Acked-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/20260527142703.107110-1-andrew.jones@linux.dev
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

1 files changed, 14 insertions, 9 deletions

diff --git a/Makefile b/Makefile
index 857f08dcc952..37fdb454b637 100644
--- a/Makefile
+++ b/Makefile
@@ -293,6 +293,7 @@ version_h := include/generated/uapi/linux/version.h
 clean-targets := %clean mrproper cleandocs
 no-dot-config-targets := $(clean-targets) \
 			 cscope gtags TAGS tags help% %docs check% coccicheck \
+			 kconfig-sym-check \
 			 $(version_h) headers headers_% archheaders archscripts \
 			 %asm-generic kernelversion %src-pkg dt_binding_check \
 			 outputmakefile rustavailable rustfmt rustfmtcheck \
@@ -1800,14 +1801,15 @@ help:
 	 echo  '                    (default: $(INSTALL_HDR_PATH))'; \
 	 echo  ''
 	@echo  'Static analysers:'
-	@echo  '  checkstack      - Generate a list of stack hogs and consider all functions'
-	@echo  '                    with a stack size larger than MINSTACKSIZE (default: 100)'
-	@echo  '  versioncheck    - Sanity check on version.h usage'
-	@echo  '  includecheck    - Check for duplicate included header files'
-	@echo  '  headerdep       - Detect inclusion cycles in headers'
-	@echo  '  coccicheck      - Check with Coccinelle'
-	@echo  '  clang-analyzer  - Check with clang static analyzer'
-	@echo  '  clang-tidy      - Check with clang-tidy'
+	@echo  '  checkstack        - Generate a list of stack hogs and consider all functions'
+	@echo  '                      with a stack size larger than MINSTACKSIZE (default: 100)'
+	@echo  '  versioncheck      - Sanity check on version.h usage'
+	@echo  '  includecheck      - Check for duplicate included header files'
+	@echo  '  headerdep         - Detect inclusion cycles in headers'
+	@echo  '  coccicheck        - Check with Coccinelle'
+	@echo  '  kconfig-sym-check - Check for dangling Kconfig symbol references'
+	@echo  '  clang-analyzer    - Check with clang static analyzer'
+	@echo  '  clang-tidy        - Check with clang-tidy'
 	@echo  ''
 	@echo  'Tools:'
 	@echo  '  nsdeps          - Generate missing symbol namespace dependencies'
@@ -2227,7 +2229,7 @@ endif
 # Scripts to check various things for consistency
 # ---------------------------------------------------------------------------
 
-PHONY += includecheck versioncheck coccicheck
+PHONY += includecheck versioncheck coccicheck kconfig-sym-check
 
 includecheck:
 	find $(srctree)/* $(RCS_FIND_IGNORE) \
@@ -2242,6 +2244,9 @@ versioncheck:
 coccicheck:
 	$(Q)$(BASH) $(srctree)/scripts/$@
 
+kconfig-sym-check:
+	$(Q)$(PERL) $(srctree)/scripts/kconfig/kconfig-sym-check.pl $(srctree) $(KCONFIG_SYM_CHECK_EXCLUDES)
+
 PHONY += checkstack kernelrelease kernelversion image_name
 
 # UML needs a little special treatment here.  It wants to use the host