[PATCH bpf] traceevent: ignore __attribute__ in fields format

[Ivan Prisyazhnyy <john.koepi@xxxxxxxxx>]

To support kernel (e.g. Arch linux) tracing that
have events fields with C attributes (__attribute__((xxx))),
traceevent must ignore __attribute__ parts when
parsing fields types.

An example from Arch linux kernel 4.2:

  $ cat /sys/kernel/.../sys_enter_io_submit/format
  ...
  field:struct iocb __attribute__((user)) * ...
                    ^^^

This fix adds support for fields types C attributes
parsing to event_read_fields function. When it sees
__attribute__ ((attribute-list)) expression it skips
it.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=205857
Base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/
Signed-off-by: Ivan Prisyazhnyy <john.koepi@xxxxxxxxx>
---
 tools/lib/traceevent/event-parse.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index beaa8b8c08ff..fbc1ea536742 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -1486,6 +1486,28 @@ static int event_read_fields(struct tep_event *event, struct tep_format_field **
 			    (event->flags & TEP_EVENT_FL_ISFTRACE &&
 			     type == TEP_EVENT_OP && strcmp(token, ".") == 0)) {
 
+				/* ignore C attributes: __attribute__((expr)) */
+				if (strcmp(token, "__attribute__") == 0) {
+					free(token);
+					for (int i = 0; i < 2; i++) {
+						if (read_expected_item(TEP_EVENT_DELIM, "(") < 0) {
+							goto fail_expect;
+						}
+					}
+					for (int brackets = 2; brackets > 0;) {
+						if (read_token(&token) == TEP_EVENT_NONE) {
+							do_warning_event(event, "%s: __attribute__ not full", __func__);
+							goto fail_expect;
+						}
+						if (strcmp(token, "(") == 0)
+							brackets++;
+						else if (strcmp(token, ")") == 0)
+							brackets--;
+						free(token);
+					}
+					continue;
+				}
+
 				if (strcmp(token, "*") == 0)
 					field->flags |= TEP_FIELD_IS_POINTER;
 
-- 
2.24.1