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

[Rabin Vincent]

On Tue, Sep 27, 2016 at 02:49:56PM -0400, Dave Anderson wrote:
> In any case, it seems counter-productive to fix this issue by essentially
> going backwards and using ANON_MEMBER_OFFSET(), which was a kludge to 
> begin with.
> 
> Would it be possible to fix this in different manner while continuing to 
> use the new-and-improved MEMBER_OFFSET()?

Just replacing ANON_MEMBER_OFFSET() with MEMBER_OFFSET() in the patch
works.  Here's an updated patch:

8<--------------------
>From 4e1b5c07911e9ef815b36970f4ffea71a52a059d Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabinv at axis.com>
Date: Tue, 27 Sep 2016 19:40:39 +0200
Subject: [PATCHv2] extensions/trace.so: fix MEMBER_OFFSET usage

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..b226ac0 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(MEMBER_OFFSET("ftrace_event_call", "tp"),
+		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