linux-kernel - [PATCH 22/30] dyndbg: check DYNAMIC_DEBUG_CLASSMAP

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Message-ID: <20250911213823.374806-23-jim.cromie@gmail.com>
Date: Thu, 11 Sep 2025 15:38:15 -0600
From: Jim Cromie <jim.cromie@...il.com>
To: jbaron@...mai.com
Cc: gregkh@...uxfoundation.org,
	ukaszb@...omium.org,
	louis.chauvet@...tlin.com,
	linux-kernel@...r.kernel.org,
	Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH 22/30] dyndbg: check DYNAMIC_DEBUG_CLASSMAP_DEFINE args at compile-time

Add __DYNAMIC_DEBUG_CLASSMAP_CHECK to implement the following
arg-checks at compile-time:

	0 <= _base < 63
	class_names is not empty
	class_names[0] is a string
	(class_names.length + _base) < 63

These compile-time checks will prevent several simple misuses, and
will issue obvious errors if violated.

4 such examples are added to test_dynamic_debug_submod.ko, and will
fail compilation if -DDD_MACRO_ARGCHECK is added to cflags.  This
wouldn't be a useful CONFIG_ item, since it breaks the build.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
v4- deconflict after pulling macro-stubs forward
v3- $macro_name =~ s/DYNDBG/DYNAMIC_DEBUG/

prev-
- split static-asserts to __DYNDBG_CLASSMAP_CHECK
- move __DYNDBG_CLASSMAP_CHECK above kdoc for DYNDBG_CLASSMAP_DEFINE
  silences kernel-doc warnings
---
 include/linux/dynamic_debug.h |  9 +++++++++
 lib/test_dynamic_debug.c      | 13 ++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 2c64f2401e51..b96f069290bd 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -180,6 +180,14 @@ struct _ddebug_class_param {
  * __pr_debug_cls(22, "no such class"); compiles but is not reachable
  */
 
+#define __DYNAMIC_DEBUG_CLASSMAP_CHECK(_clnames, _base)			\
+	static_assert(((_base) >= 0 && (_base) < _DPRINTK_CLASS_DFLT),	\
+		      "_base must be in 0..62");			\
+	static_assert(ARRAY_SIZE(_clnames) > 0,				\
+		      "classnames array size must be > 0");		\
+	static_assert((ARRAY_SIZE(_clnames) + (_base)) < _DPRINTK_CLASS_DFLT, \
+		      "_base + classnames.length exceeds range")
+
 /**
  * DYNAMIC_DEBUG_CLASSMAP_DEFINE - define debug classes used by a module.
  * @_var:   name of the classmap, exported for other modules coordinated use.
@@ -193,6 +201,7 @@ struct _ddebug_class_param {
  */
 #define DYNAMIC_DEBUG_CLASSMAP_DEFINE(_var, _mapty, _base, ...)		\
 	static const char *_var##_classnames[] = { __VA_ARGS__ };	\
+	__DYNAMIC_DEBUG_CLASSMAP_CHECK(_var##_classnames, (_base));	\
 	extern struct _ddebug_class_map _var;				\
 	struct _ddebug_class_map __aligned(8) __used			\
 		__section("__dyndbg_class_maps") _var = {		\
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index 1ba4be9a403a..b2bdfdfb6ba1 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -133,7 +133,7 @@ DYNAMIC_DEBUG_CLASSMAP_PARAM(level_num, p);
  * Enable with -Dflag on compile to test overlapping class-id range
  * detection.  This should warn on modprobes.
  */
-DYNDBG_CLASSMAP_DEFINE(classid_range_conflict, 0, D2_CORE + 1, "D3_CORE");
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(classid_range_conflict, 0, D2_CORE + 1, "D3_CORE");
 #endif
 
 #else /* TEST_DYNAMIC_DEBUG_SUBMOD */
@@ -146,8 +146,19 @@ DYNDBG_CLASSMAP_DEFINE(classid_range_conflict, 0, D2_CORE + 1, "D3_CORE");
 DYNAMIC_DEBUG_CLASSMAP_USE(map_disjoint_bits);
 DYNAMIC_DEBUG_CLASSMAP_USE(map_level_num);
 
+#if defined(DD_MACRO_ARGCHECK)
+/*
+ * Exersize compile-time arg-checks in DYNAMIC_DEBUG_CLASSMAP_DEFINE.
+ * These will break compilation.
+ */
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(fail_base_neg, 0, -1, "NEGATIVE_BASE_ARG");
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(fail_base_big, 0, 100, "TOOBIG_BASE_ARG");
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(fail_str_type, 0, 0, 1 /* not a string */);
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(fail_emptyclass, 0, 0 /* ,empty */);
 #endif
 
+#endif /* TEST_DYNAMIC_DEBUG_SUBMOD */
+
 /* stand-in for all pr_debug etc */
 #define prdbg(SYM) __pr_debug_cls(SYM, #SYM " msg\n")
 
-- 
2.51.0