[Crash-utility] [PATCH] Fix the extension trace.so for RHEL7.6

[Xu Huan]

Fix the extension trace.so for RHEL7.6 ,which moved
ftrace_event_call.data into an anonymous union,and the
previous offset has changed, so the trace.so extension
module fails to load ,indicating "no commands registered:
shared object unloaded".
---
 extensions/trace.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/extensions/trace.c b/extensions/trace.c
index 7d76699..ad71951 100644
--- a/extensions/trace.c
+++ b/extensions/trace.c
@@ -853,8 +853,18 @@ static int syscall_get_enter_fields(ulong call, ulong *fields)
 	inited = 1;
 	data_offset = MAX(MEMBER_OFFSET("ftrace_event_call", "data"), 
 		MEMBER_OFFSET("trace_event_call", "data"));
-	if (data_offset < 0)
-		return -1;
+	if (data_offset < 0) {
+		/*
+		 *  rhel-7.6 moved the .data member into an anonymous union.
+		 */
+		if (MEMBER_EXISTS("ftrace_event_call", "rh_data") &&
+		    MEMBER_EXISTS("ftrace_event_data", "data")) {
+			data_offset = MEMBER_OFFSET("ftrace_event_call", "rh_data") +
+				MEMBER_OFFSET("ftrace_event_data", "data");
+			inited = 2;
+		} else
+			return -1;
+	}
 
 	enter_fields_offset = MEMBER_OFFSET("syscall_metadata", "enter_fields");
 	if (enter_fields_offset < 0)
@@ -868,6 +878,12 @@ work:
 			"read ftrace_event_call data", RETURN_ON_ERROR))
 		return -1;
 
+	if (inited == 2) {
+		if (!readmem(metadata, KVADDR, &metadata, sizeof(metadata),
+		    "read ftrace_event_call data (indirect rh_data)", RETURN_ON_ERROR))
+			return -1;
+	}
+
 	*fields = metadata + enter_fields_offset;
 	return 0;
 }
-- 
2.17.1