[Crash-utility] [PATCH] Fix trace extension for v3.15+

[Rabin Vincent]

Since Linux v3.15 (specifically, the following commit), the event name is
optionally moved to another structure.

commit de7b2973903c6cc50b31ee5682a69b2219b9919d
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Tue Apr 8 17:26:21 2014 -0400

    tracepoint: Use struct pointer instead of name hash for reg/unreg tracepoints

-       char                    *name;
+       union {
+               char                    *name;
+               /* Set TRACE_EVENT_FL_TRACEPOINT flag when using "tp" */
+               struct tracepoint       *tp;
+       };

This patch handles this in the trace extension so that both kernels with and
without that commit work.
---
 extensions/trace.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 4 deletions(-)

diff --git a/extensions/trace.c b/extensions/trace.c
index a09f6a1..8639fb2 100644
--- a/extensions/trace.c
+++ b/extensions/trace.c
@@ -988,19 +988,42 @@ static void ftrace_destroy_event_types(void)
 	free(ftrace_common_fields);
 }
 
+#define TRACE_EVENT_FL_TRACEPOINT 0x40
+
 static
 int ftrace_get_event_type_name(ulong call, char *name, int len)
 {
 	static int inited;
 	static int name_offset;
+	static int flags_offset;
+	static int tp_name_offset;
+	uint flags;
 
 	ulong name_addr;
 
-	if (!inited) {
-		inited = 1;
-		name_offset = MEMBER_OFFSET("ftrace_event_call", "name");
-	}
+	if (inited)
+		goto work;
+
+	inited = 1;
+	name_offset = MEMBER_OFFSET("ftrace_event_call", "name");
+	if (name_offset >= 0)
+		goto work;
 
+	name_offset = ANON_MEMBER_OFFSET("ftrace_event_call", "name");
+	if (name_offset < 0)
+		return -1;
+
+	flags_offset = MEMBER_OFFSET("ftrace_event_call", "flags");
+	if (flags_offset < 0)
+		return -1;
+
+	tp_name_offset = MEMBER_OFFSET("tracepoint", "name");
+	if (tp_name_offset < 0)
+		return -1;
+
+	inited = 2;
+
+work:
 	if (name_offset < 0)
 		return -1;
 
@@ -1008,6 +1031,21 @@ int ftrace_get_event_type_name(ulong call, char *name, int len)
 			"read ftrace_event_call name_addr", RETURN_ON_ERROR))
 		return -1;
 
+	if (inited == 2) {
+		if (!readmem(call + flags_offset, KVADDR, &flags,
+			     sizeof(flags), "read ftrace_event_call flags",
+			     RETURN_ON_ERROR))
+			return -1;
+
+		if (flags & TRACE_EVENT_FL_TRACEPOINT) {
+			if (!readmem(name_addr + tp_name_offset, KVADDR,
+				     &name_addr, sizeof(name_addr),
+				     "read tracepoint name", RETURN_ON_ERROR))
+				return -1;
+		}
+
+	}
+
 	if (!read_string(name_addr, name, len))
 		return -1;
 
-- 
2.1.4