[for-linus][PATCH 1/3] tracing/histograms: Fix parsing of "sym-offset" modifier

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

With the addition of simple mathematical operations (plus and minus), the
parsing of the "sym-offset" modifier broke, as it took the '-' part of the
"sym-offset" as a minus, and tried to break it up into a mathematical
operation of "field.sym - offset", in which case it failed to parse
(unless the event had a field called "offset").

Both .sym and .sym-offset modifiers should not be entered into
mathematical calculations anyway. If ".sym-offset" is found in the
modifier, then simply make it not an operation that can be calculated on.

Link: https://lkml.kernel.org/r/20210707110821.188ae255@xxxxxxxxxxxxxxxx

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 100719dcef447 ("tracing: Add simple expression support to hist triggers")
Reviewed-by: Tom Zanussi <zanussi@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index ba03b7d84fc2..0207aeed31e6 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1555,6 +1555,13 @@ static int contains_operator(char *str)
 
 	switch (*op) {
 	case '-':
+		/*
+		 * Unfortunately, the modifier ".sym-offset"
+		 * can confuse things.
+		 */
+		if (op - str >= 4 && !strncmp(op - 4, ".sym-offset", 11))
+			return FIELD_OP_NONE;
+
 		if (*str == '-')
 			field_op = FIELD_OP_UNARY_MINUS;
 		else
-- 
2.30.2