[PATCH v2] libtraceevent: Handle parsing of "(REC)->" case

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a trace event wraps the special __entry variable to dereference it with
parenthesis, it shows up in the trace event format file wrapping the
"(REC)" as well. For example, the "func_repeats" event passed the __entry
into a helper macro in the TP_printk() portion, and the macro correctly
wrapped its parameter in parenthesis. This caused the output to show:

 "(((u64)(REC)->top_delta_ts << 32) | (REC)->bottom_delta_ts)"

The parser then failed to parse the "(REC)->" portion, as it expected the
"->" to appear directly after the "REC". This is not a requirement, and
the parser should be able to handle such cases.

When this occurred, trace-cmd would error with the following message:

trace-cmd: No such file or directory
  Error: expected type 4 but read 5

Fixes: 6582b0a ("tools/events: Add files to create libtraceevent.a")
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---

Changes since v1:
    Update the change log to show the error message, in case
    it happens again, it can be something to reference.

 src/event-parse.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/event-parse.c b/src/event-parse.c
index 97c1a97..1217491 100644
--- a/src/event-parse.c
+++ b/src/event-parse.c
@@ -2311,8 +2311,19 @@ process_entry(struct tep_event *event __maybe_unused, struct tep_print_arg *arg,
 	char *field;
 	char *token;
 
-	if (read_expected(TEP_EVENT_OP, "->") < 0)
-		goto out_err;
+	type = read_token_item(&token);
+	/*
+	 * Check if REC happens to be surrounded by parenthesis, and
+	 * return if that's the case, as "(REC)->" is valid.
+	 * but return TEP_EVENT_ITEM.
+	 */
+	if (type == TEP_EVENT_DELIM && strcmp(token, ")") == 0) {
+		*tok = token;
+		return TEP_EVENT_ITEM;
+	}
+
+	if (test_type_token(type, token,  TEP_EVENT_OP, "->"))
+		goto out_free;
 
 	if (read_expect_type(TEP_EVENT_ITEM, &token) < 0)
 		goto out_free;
@@ -2338,7 +2349,6 @@ process_entry(struct tep_event *event __maybe_unused, struct tep_print_arg *arg,
 
  out_free:
 	free_token(token);
- out_err:
 	*tok = NULL;
 	return TEP_EVENT_ERROR;
 }
@@ -3033,6 +3043,17 @@ process_paren(struct tep_event *event, struct tep_print_arg *arg, char **tok)
 	if (type == TEP_EVENT_ERROR)
 		goto out_free;
 
+	/*
+	 * If REC is surrounded by parenthesis, the process_arg()
+	 * will return TEP_EVENT_ITEM with token == ")". In
+	 * this case, we need to continue processing the item
+	 * and return.
+	 */
+	if (type == TEP_EVENT_ITEM && strcmp(token, ")") == 0) {
+		free_token(token);
+		return process_entry(event, arg, tok);
+	}
+
 	if (test_type_token(type, token, TEP_EVENT_DELIM, ")"))
 		goto out_free;
 
-- 
2.29.2