linux-kernel - [PATCH v2 1/4] kbuild: add generic header check facility

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Message-Id: <20250402124656.629226-2-jani.nikula@intel.com>
Date: Wed,  2 Apr 2025 15:46:53 +0300
From: Jani Nikula <jani.nikula@...el.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Cc: jani.nikula@...el.com,
	Jason Gunthorpe <jgg@...dia.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona.vetter@...ll.ch>,
	linux-kbuild@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	intel-xe@...ts.freedesktop.org,
	intel-gfx@...ts.freedesktop.org
Subject: [PATCH v2 1/4] kbuild: add generic header check facility

Resurrect a generic header check facility. Check that the headers are
self-contained, have header guards, and (if enabled separately) pass
kernel-doc. Run header checks on .h files listed in header-check-y or
header-check-m, relative to $(src).

Hide header check artifacts under a .header-check subdirectory at the
top level of the build output directory.

Add the facility behind CONFIG_HEADER_CHECK_DISABLE, reversed to keep
the feature disabled for allmodconfig and allyesconfig builds. Also add
a proxy CONFIG_HEADER_CHECK option to simplify dependencies on the
facility. The kernel-doc check requires CONFIG_HEADER_CHECK_KERNEL_DOC.

Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: David Airlie <airlied@...il.com>
Cc: Simona Vetter <simona.vetter@...ll.ch>
Signed-off-by: Jani Nikula <jani.nikula@...el.com>

---

Cc: linux-kbuild@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org
Cc: intel-xe@...ts.freedesktop.org
Cc: intel-gfx@...ts.freedesktop.org
---
 init/Kconfig           | 25 +++++++++++++++++++++++++
 scripts/Makefile.build | 13 +++++++++++++
 scripts/Makefile.lib   |  7 +++++++
 3 files changed, 45 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 681f38ee68db..2678a5ba7b93 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -217,6 +217,31 @@ config UAPI_HEADER_TEST
 	  If you are a developer or tester and want to ensure the exported
 	  headers are self-contained, say Y here. Otherwise, choose N.
 
+# Reversed option to disable on allyesconfig/allmodconfig builds
+config HEADER_CHECK_DISABLE
+	bool "Disable extra build-time header checks"
+	default y
+	help
+	  Disable extra build-time header checks. The checks may be
+	  overzealous. They may slow down or fail the build altogether. They may
+	  create excessive dependency files in the tree. They should not be
+	  enabled for regular builds, and thus they are disabled by default.
+
+# Proxy config to allow simple "depends on HEADER_CHECK"
+config HEADER_CHECK
+	bool
+	depends on EXPERT && HEADER_CHECK_DISABLE=n
+	default !HEADER_CHECK_DISABLE
+
+config HEADER_CHECK_KERNEL_DOC
+	bool "Run kernel-doc as part of header checks"
+	depends on HEADER_CHECK
+	default n
+	help
+	  Run kernel-doc as part of header checks. In addition to compiling,
+	  also check kernel-doc comments. With CONFIG_WERROR=y, kernel-doc
+	  warnings are treated as errors.
+
 config LOCALVERSION
 	string "Local version - append to kernel release"
 	help
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 56be83024851..f963b2356b0e 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -223,6 +223,19 @@ quiet_cmd_cc_lst_c = MKLST   $@
 $(obj)/%.lst: $(obj)/%.c FORCE
 	$(call if_changed_dep,cc_lst_c)
 
+# Compile C headers (.h) for header check
+# ---------------------------------------------------------------------------
+
+# Include the header twice to detect missing include guard.
+quiet_cmd_header_check = HDRCHK  $(patsubst $(srctree)/%,%,$<)
+      cmd_header_check = \
+		$(CC) $(c_flags) -fsyntax-only -x c /dev/null -include $< -include $<; \
+		$(if $(CONFIG_HEADER_CHECK_KERNEL_DOC),$(srctree)/scripts/kernel-doc -none $(if $(CONFIG_WERROR),-Werror) $<,true); \
+		touch $@
+
+.header-check/$(obj)/%.header-check: $(src)/%.h FORCE
+	$(call if_changed_dep,header_check)
+
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
 
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 57620b439a1f..272a1b42292e 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -89,6 +89,13 @@ multi-obj-m	:= $(addprefix $(obj)/, $(multi-obj-m))
 subdir-ym	:= $(addprefix $(obj)/,$(subdir-ym))
 endif
 
+# Header checks
+# header-check-y/m contain .h files to be checked, relative to $(src)
+
+header-check-y	:= $(addprefix .header-check/$(obj)/,$(patsubst %.h,%.header-check,$(header-check-y) $(header-check-m)))
+
+always-$(CONFIG_HEADER_CHECK) += $(header-check-y)
+
 # Finds the multi-part object the current object will be linked into.
 # If the object belongs to two or more multi-part objects, list them all.
 modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
-- 
2.39.5