tools lib traceevent: Fix missing equality check for strcmp [Linux 3.16.72]

This Linux kernel change "tools lib traceevent: Fix missing equality check for strcmp" is included in the Linux 3.16.72 release. This change is authored by Rikard Falkeborn <rikard.falkeborn [at] gmail.com> on Tue Apr 9 11:15:29 2019 +0200. The commit for this change in Linux stable tree is fa3c9f4 (patch) which is from upstream commit f32c287. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream f32c287.

tools lib traceevent: Fix missing equality check for strcmp

commit f32c2877bcb068a718bb70094cd59ccc29d4d082 upstream.

There was a missing comparison with 0 when checking if type is "s64" or
"u64". Therefore, the body of the if-statement was entered if "type" was
"u64" or not "s64", which made the first strcmp() redundant since if
type is "u64", it's not "s64".

If type is "s64", the body of the if-statement is not entered but since
the remainder of the function consists of if-statements which will not
be entered if type is "s64", we will just return "val", which is
correct, albeit at the cost of a few more calls to strcmp(), i.e., it
will behave just as if the if-statement was entered.

If type is neither "s64" or "u64", the body of the if-statement will be
entered incorrectly and "val" returned. This means that any type that is
checked after "s64" and "u64" is handled the same way as "s64" and
"u64", i.e., the limiting of "val" to fit in for example "s8" is never
reached.

This was introduced in the kernel tree when the sources were copied from
trace-cmd in commit f7d82350e597 ("tools/events: Add files to create
libtraceevent.a"), and in the trace-cmd repo in 1cdbae6035cei
("Implement typecasting in parser") when the function was introduced,
i.e., it has always behaved the wrong way.

Detected by cppcheck.

Signed-off-by: Rikard Falkeborn <[email protected]>
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
Cc: Tzvetomir Stoyanov <[email protected]>
Fixes: f7d82350e597 ("tools/events: Add files to create libtraceevent.a")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Ben Hutchings <[email protected]>

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 tools/lib/traceevent/event-parse.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 95b2df2..383aaae 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -2065,7 +2065,7 @@ static int set_op_prio(struct print_arg *arg)
        return val & 0xffffffff;

    if (strcmp(type, "u64") == 0 ||
-       strcmp(type, "s64"))
+       strcmp(type, "s64") == 0)
        return val;

    if (strcmp(type, "s8") == 0)

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