tracing: Use a global field list for all syscall exit events

All syscall exit events have the same fields.

The kernel size drops 2.5K:

   text    data     bss     dec     hex filename
7018612 2034376 7251132 16304120         f8c7f8 vmlinux.o.orig
7018612 2031888 7251132 16301632         f8be40 vmlinux.o
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4BFA3746.8070100@cn.fujitsu.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>

include/linux/syscalls.h

@@ -165,7 +165,6 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 		.enter_event	= &event_enter_##sname,		\
 		.exit_event	= &event_exit_##sname,		\
 		.enter_fields	= LIST_HEAD_INIT(__syscall_meta_##sname.enter_fields), \
-		.exit_fields	= LIST_HEAD_INIT(__syscall_meta_##sname.exit_fields), \
 	};
 
 #define SYSCALL_DEFINE0(sname)					\
@@ -180,7 +179,6 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 		.enter_event	= &event_enter__##sname,	\
 		.exit_event	= &event_exit__##sname,		\
 		.enter_fields	= LIST_HEAD_INIT(__syscall_meta__##sname.enter_fields), \
-		.exit_fields	= LIST_HEAD_INIT(__syscall_meta__##sname.exit_fields), \
 	};							\
 	asmlinkage long sys_##sname(void)
 #else

include/trace/syscall.h

@@ -26,7 +26,6 @@ struct syscall_metadata {
 	const char	**types;
 	const char	**args;
 	struct list_head enter_fields;
-	struct list_head exit_fields;
 
 	struct ftrace_event_call *enter_event;
 	struct ftrace_event_call *exit_event;

kernel/trace/trace_syscalls.c

@@ -23,6 +23,9 @@ static int syscall_exit_register(struct ftrace_event_call *event,
 static int syscall_enter_define_fields(struct ftrace_event_call *call);
 static int syscall_exit_define_fields(struct ftrace_event_call *call);
 
+/* All syscall exit events have the same fields */
+static LIST_HEAD(syscall_exit_fields);
+
 static struct list_head *
 syscall_get_enter_fields(struct ftrace_event_call *call)
 {
@@ -34,9 +37,7 @@ syscall_get_enter_fields(struct ftrace_event_call *call)
 static struct list_head *
 syscall_get_exit_fields(struct ftrace_event_call *call)
 {
-	struct syscall_metadata *entry = call->data;
-
-	return &entry->exit_fields;
+	return &syscall_exit_fields;
 }
 
 struct trace_event_functions enter_syscall_print_funcs = {