[PATCH v2] event-parse: Zero should not be considered "not found" in eval_flag()

[Steven Rostedt <rostedt@goodmis.org>]

Guilherme Cox found that:
 There is, however, a potential bug if there is an item with code zero
 that is not the first one in the symbol list, since eval_flag(..)
 returns 0 when it doesn't find anything.

That is, if you have the following enums:

enum {
  FOO_START = 0,
  FOO_GO    = 1,
  FOO_END   = 2
}

and then have:

  __print_symbolic(foo, FOO_GO, "go", FOO_START, "start",
		        FOO_END, "end")

If none of the enums are known to pevent, then eval_flag() will return
zero, and it will match it to the first item in the list, which would
be FOO_GO, which is not zero.

Luckily, in most cases, the first element would be zero, and the parsing
would match out of sheer luck.

Reported-by: Guilherme Cox <cox@computer.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
v2 - fixed "From:" and give a bit more info in the change log. I also
created an event that I could test this issue with.

 event-parse.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/event-parse.c b/event-parse.c
index aff743710001..f2fb50141703 100644
--- a/event-parse.c
+++ b/event-parse.c
@@ -3576,7 +3576,7 @@ static const struct flag flags[] = {
 	{ "HRTIMER_RESTART", 1 },
 };
 
-static unsigned long long eval_flag(const char *flag)
+static long long eval_flag(const char *flag)
 {
 	int i;
 
@@ -3592,7 +3592,7 @@ static unsigned long long eval_flag(const char *flag)
 		if (strcmp(flags[i].name, flag) == 0)
 			return flags[i].value;
 
-	return 0;
+	return -1LL;
 }
 
 static void print_str_to_seq(struct trace_seq *s, const char *format,
@@ -3666,7 +3666,7 @@ static void print_str_arg(struct trace_seq *s, void *data, int size,
 	struct print_flag_sym *flag;
 	struct format_field *field;
 	struct printk_map *printk;
-	unsigned long long val, fval;
+	long long val, fval;
 	unsigned long addr;
 	char *str;
 	unsigned char *hex;
@@ -3725,11 +3725,11 @@ static void print_str_arg(struct trace_seq *s, void *data, int size,
 		print = 0;
 		for (flag = arg->flags.flags; flag; flag = flag->next) {
 			fval = eval_flag(flag->value);
-			if (!val && !fval) {
+			if (!val && fval < 0) {
 				print_str_to_seq(s, format, len_arg, flag->str);
 				break;
 			}
-			if (fval && (val & fval) == fval) {
+			if (fval > 0 && (val & fval) == fval) {
 				if (print && arg->flags.delim)
 					trace_seq_puts(s, arg->flags.delim);
 				print_str_to_seq(s, format, len_arg, flag->str);
-- 
1.8.3.1