[2/3] trace-cmd library: Add check before applying tsc2nsec offset

Commit Message

Tzvetomir Stoyanov (VMware) April 15, 2021, 8:15 a.m. UTC

When converting TSC timestamps to nanoseconds, an offset is used. That
offset is subtracted from each TSC timestamp, before the conversion.
However, if the timestamp is lower that the offset this causes an
overflow, as both timestamp and offset are unsigned long integers. A
check is added to verify the subtraction will not cause an overflow. In
case of an overflow, the timestamp is set to 0 and a warning message is
printed.

Signed-off-by: Tzvetomir Stoyanov (VMware) <[e-mail]>
---
 lib/trace-cmd/trace-input.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Patch

diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index 974879e8..991abd5f 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -1230,8 +1230,14 @@  static unsigned long long timestamp_calc(unsigned long long ts, int cpu,
 		ts *= handle->ts2secs;
 	} else if (handle->tsc_calc.mult) {
 		/* auto calculated TSC clock frequency */
-		ts -= handle->tsc_calc.offset;
-		ts = mul_u64_u32_shr(ts, handle->tsc_calc.mult, handle->tsc_calc.shift);
+		if (ts > handle->tsc_calc.offset) {
+			ts -= handle->tsc_calc.offset;
+			ts = mul_u64_u32_shr(ts, handle->tsc_calc.mult, handle->tsc_calc.shift);
+		} else {
+			tracecmd_warning("Timestamp $llu is before the initial offset %llu, set it to 0",
+					 ts, handle->tsc_calc.offset);
+			ts = 0;
+		}
 	}
 
 	/* User specified time offset with --ts-offset or --date options */