[PATCH] trace-cmd: Don't SIGSEGV when event field format cannot be parsed (v2).

[David Daney <ddaney@caviumnetworks.com>]

>From the MIPS kernel we get things like:

print fmt: "page=%p pfn=%lu order=%d migratetype=%d", REC->page, ({ struct page *__pg = (REC->page); int __sec = page_to_section(__pg); (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec))); }), REC->order, REC->migratetype

This cannot be parsed, leading to a NULL struct event_format* being
passed to pevent_get_common_field_val, which produces a SIGSEGV.  It
would be good to get a parsable format from the kernel, but to
remediate the problem for legacy kernels, we can just return an error
indicator in this case.  This allows some output from trace-cmd
report, although perhaps with some missing data.  But this is better
than crashing.

(v2): Do the check in all pevent_get_*

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
---
 parse-events.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/parse-events.c b/parse-events.c
index 1e854e2..595ba90 100644
--- a/parse-events.c
+++ b/parse-events.c
@@ -4464,6 +4464,9 @@ int pevent_get_field_val(struct trace_seq *s, struct event_format *event,
 {
 	struct format_field *field;
 
+	if (!event)
+		return -1;
+
 	field = pevent_find_field(event, name);
 
 	return get_field_val(s, field, name, record, val, err);
@@ -4486,6 +4489,9 @@ int pevent_get_common_field_val(struct trace_seq *s, struct event_format *event,
 {
 	struct format_field *field;
 
+	if (!event)
+		return -1;
+
 	field = pevent_find_common_field(event, name);
 
 	return get_field_val(s, field, name, record, val, err);
@@ -4508,6 +4514,9 @@ int pevent_get_any_field_val(struct trace_seq *s, struct event_format *event,
 {
 	struct format_field *field;
 
+	if (!event)
+		return -1;
+
 	field = pevent_find_any_field(event, name);
 
 	return get_field_val(s, field, name, record, val, err);
-- 
1.7.1.1