tracing: Introduce tracepoint extended structure

Shrink the struct tracepoint size from 80 bytes to 72 bytes on x86-64 by
moving the (typically NULL) regfunc/unregfunc pointers to an extended
structure.

Tested-by: Jordan Rife <jrife@google.com>
Cc: Michael Jeanson <mjeanson@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Jordan Rife <jrife@google.com>
Cc: linux-trace-kernel@vger.kernel.org
Link: https://lore.kernel.org/20241031152056.744137-2-mathieu.desnoyers@efficios.com


Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/tracepoint-defs.h

@@ -29,6 +29,11 @@ struct tracepoint_func {
 	int prio;
 };
 
+struct tracepoint_ext {
+	int (*regfunc)(void);
+	void (*unregfunc)(void);
+};
+
 struct tracepoint {
 	const char *name;		/* Tracepoint name */
 	struct static_key_false key;
@@ -36,9 +41,8 @@ struct tracepoint {
 	void *static_call_tramp;
 	void *iterator;
 	void *probestub;
-	int (*regfunc)(void);
-	void (*unregfunc)(void);
 	struct tracepoint_func __rcu *funcs;
+	struct tracepoint_ext *ext;
 };
 
 #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS

include/linux/tracepoint.h

@@ -302,7 +302,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
  * structures, so we create an array of pointers that will be used for iteration
  * on the tracepoints.
  */
-#define DEFINE_TRACE_FN(_name, _reg, _unreg, proto, args)		\
+#define __DEFINE_TRACE_EXT(_name, _ext, proto, args)			\
 	static const char __tpstrtab_##_name[]				\
 	__section("__tracepoints_strings") = #_name;			\
 	extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name);	\
@@ -316,9 +316,9 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 		.static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \
 		.iterator = &__traceiter_##_name,			\
 		.probestub = &__probestub_##_name,			\
-		.regfunc = _reg,					\
-		.unregfunc = _unreg,					\
-		.funcs = NULL };					\
+		.funcs = NULL,						\
+		.ext = _ext,						\
+	};								\
 	__TRACEPOINT_ENTRY(_name);					\
 	int __traceiter_##_name(void *__data, proto)			\
 	{								\
@@ -341,8 +341,15 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	}								\
 	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
 
-#define DEFINE_TRACE(name, proto, args)		\
-	DEFINE_TRACE_FN(name, NULL, NULL, PARAMS(proto), PARAMS(args));
+#define DEFINE_TRACE_FN(_name, _reg, _unreg, _proto, _args)		\
+	static struct tracepoint_ext __tracepoint_ext_##_name = {	\
+		.regfunc = _reg,					\
+		.unregfunc = _unreg,					\
+	};								\
+	__DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
+
+#define DEFINE_TRACE(_name, _proto, _args)				\
+	__DEFINE_TRACE_EXT(_name, NULL, PARAMS(_proto), PARAMS(_args));
 
 #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)				\
 	EXPORT_SYMBOL_GPL(__tracepoint_##name);				\

kernel/tracepoint.c

@@ -278,8 +278,8 @@ static int tracepoint_add_func(struct tracepoint *tp,
 	struct tracepoint_func *old, *tp_funcs;
 	int ret;
 
-	if (tp->regfunc && !static_key_enabled(&tp->key)) {
-		ret = tp->regfunc();
+	if (tp->ext && tp->ext->regfunc && !static_key_enabled(&tp->key)) {
+		ret = tp->ext->regfunc();
 		if (ret < 0)
 			return ret;
 	}
@@ -362,9 +362,8 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 	switch (nr_func_state(tp_funcs)) {
 	case TP_FUNC_0:		/* 1->0 */
 		/* Removed last function */
-		if (tp->unregfunc && static_key_enabled(&tp->key))
-			tp->unregfunc();
-
+		if (tp->ext && tp->ext->unregfunc && static_key_enabled(&tp->key))
+			tp->ext->unregfunc();
 		static_branch_disable(&tp->key);
 		/* Set iterator static call */
 		tracepoint_update_call(tp, tp_funcs);