[Crash-utility] [PATCH] extensions/trace.so: fix MEMBER_OFFSET usage

[Rabin Vincent]

From: Rabin Vincent <rabinv at axis.com>

In Linux v3.15 the name field of ftrace_event_fall moved into an
anonymous union (along with a new tp field).  The trace extension
attempt to handle this by first checking if the offset can be
determined by MEMBER_OFFSET, and if that's the case, assuming that the
name is not in an anonymous union and thus that the kernel is pre-v3.15.

This used to work, but since the following commit, MEMBER_OFFSET seems
to even find fields inside anonymous unions, so the code always hits the
pre-v3.15 path even on newer kernels, preventing the trace extension
from successfully loading.

Fix this by reworking the checks to check for the tp field first and
using the presence of that field to identify a post-v3.15 kernel.

 commit 5e6fbde738b827e2575aa9ec9ba4b3eb02ac65c5
 Author: Dave Anderson <anderson at redhat.com>
 Date:   Thu Aug 25 14:26:58 2016 -0400

     Enhancement to determine structure member data if the member is
     contained within an anonymous structure or union.  Without the patch,
     it is necessary to parse the output of a discrete gdb "printf"
     command to determine the offset of such a structure member.
     (Alexandr_Terekhov at epam.com)
---
 extensions/trace.c | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/extensions/trace.c b/extensions/trace.c
index f8ccd91..b5901c4 100644
--- a/extensions/trace.c
+++ b/extensions/trace.c
@@ -1030,30 +1030,27 @@ int ftrace_get_event_type_name(ulong call, char *name, int len)
 	if (inited)
 		goto work;
 
-	inited = 1;
-	name_offset = MAX(MEMBER_OFFSET("ftrace_event_call", "name"),
-		MEMBER_OFFSET("trace_event_call", "name"));
-	if (name_offset >= 0)
-		goto work;
-
-	name_offset = MAX(ANON_MEMBER_OFFSET("ftrace_event_call", "name"),
-		ANON_MEMBER_OFFSET("trace_event_call", "name"));
-	if (name_offset < 0)
-		return -1;
-
-	flags_offset = MAX(MEMBER_OFFSET("ftrace_event_call", "flags"),
-		MEMBER_OFFSET("trace_event_call", "flags"));
-	if (flags_offset < 0)
-		return -1;
+	name_offset = MAX(ANON_MEMBER_OFFSET("ftrace_event_call", "tp"),
+		ANON_MEMBER_OFFSET("trace_event_call", "tp"));
+	if (name_offset >= 0) {
+		flags_offset = MAX(MEMBER_OFFSET("ftrace_event_call", "flags"),
+			MEMBER_OFFSET("trace_event_call", "flags"));
+		if (flags_offset < 0)
+			return -1;
 
-	tp_name_offset = MEMBER_OFFSET("tracepoint", "name");
-	if (tp_name_offset < 0)
-		return -1;
+		tp_name_offset = MEMBER_OFFSET("tracepoint", "name");
+		if (tp_name_offset < 0)
+			return -1;
 
-	if (!enumerator_value("TRACE_EVENT_FL_TRACEPOINT", &tracepoint_flag))
-		return -1;
+		if (!enumerator_value("TRACE_EVENT_FL_TRACEPOINT", &tracepoint_flag))
+			return -1;
 
-	inited = 2;
+		inited = 2;
+	} else {
+		name_offset = MAX(MEMBER_OFFSET("ftrace_event_call", "name"),
+			MEMBER_OFFSET("trace_event_call", "name"));
+		inited = 1;
+	}
 
 work:
 	if (name_offset < 0)
-- 
2.1.4