[PATCH v8 42/43] dyndbg: add DEBUG-biased fallback stubs for _dynamic_func_call_cls

From: Jim Cromie <jim.cromie@gmail.com>

When the dynamic debug core is enabled (CONFIG_DYNAMIC_DEBUG_CORE=y) but
the global CONFIG_DYNAMIC_DEBUG is disabled, subsystems can opt-in to
dynamic debug by defining DYNAMIC_DEBUG_MODULE.

However, for built-in code (like DRM core) where DYNAMIC_DEBUG_MODULE
is not defined, the macros fall back to the disabled #else block in
include/linux/dynamic_debug.h.

In this block, the family of _dynamic_func_call_cls macros were
completely undefined. This caused build failures (implicit declarations)
in subsystems (like DRM) that attempt to use these macros to wrap their
own debug functions even when dynamic debug is disabled.

Add stub definitions that mirror the enabled behavior and respect the
DEBUG macro, similar to pr_debug. If DEBUG is defined, they inject NULL
as the first argument (to satisfy the expected descriptor pointer) and
pass the arguments through, allowing the wrapped function's own slow-path
fallback logic to execute. If DEBUG is not defined, they use an if (0)
statement-expression to compile out the call while returning 0, achieving
zero overhead while maintaining compile-time argument checking.

Reported-by: kernel test robot <redacted>
Closes: https://lore.kernel.org/oe-kbuild-all/202605201408.x1sHT6fx-lkp@intel.com/ (local)
Assisted-by: Gemini-CLI:gemini-2.5-pro
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/linux/dynamic_debug.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 0e3af8948a56..ce142ad366dc 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h

@@ -538,6 +538,23 @@ void ddebug_increment_call_count(void);
 #define DYNAMIC_DEBUG_BRANCH(descriptor) false
 #define DECLARE_DYNDBG_CLASSMAP(...)
 
+#if defined(DEBUG)
+#define _dynamic_func_call_cls(cls, fmt, func, ...)		\
+	do { func(NULL, ##__VA_ARGS__); } while (0)
+#define _dynamic_func_call_cls_no_desc(cls, fmt, func, ...)	\
+	do { func(__VA_ARGS__); } while (0)
+#else
+#define _dynamic_func_call_cls(cls, fmt, func, ...)		\
+	do { if (0) func(NULL, ##__VA_ARGS__); } while (0)
+#define _dynamic_func_call_cls_no_desc(cls, fmt, func, ...)	\
+	do { if (0) func(__VA_ARGS__); } while (0)
+#endif
+
+#define _dynamic_func_call(fmt, func, ...)			\
+	_dynamic_func_call_cls(_DPRINTK_CLASS_DFLT, fmt, func, ##__VA_ARGS__)
+#define _dynamic_func_call_no_desc(fmt, func, ...)		\
+	_dynamic_func_call_cls_no_desc(_DPRINTK_CLASS_DFLT, fmt, func, ##__VA_ARGS__)
+
 #define dynamic_pr_debug(fmt, ...)					\
 	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #define dynamic_dev_dbg(dev, fmt, ...)					\

-- 
2.55.0