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From: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>
To: rostedt@goodmis.org
Cc: linux-trace-devel@vger.kernel.org
Subject: [PATCH v2 2/3] trace-cmd library: Add check before applying tsc2nsec offset
Date: Fri, 16 Apr 2021 13:34:08 +0300	[thread overview]
Message-ID: <20210416103409.24597-3-tz.stoyanov@gmail.com> (raw)
In-Reply-To: <20210416103409.24597-1-tz.stoyanov@gmail.com>

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) <tz.stoyanov@gmail.com>
---
 lib/trace-cmd/trace-input.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

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 */
-- 
2.30.2


  parent reply	other threads:[~2021-04-16 10:34 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 10:34 [PATCH v2 0/3] Fix overflow when applying tsc2nsec calculations Tzvetomir Stoyanov (VMware)
2021-04-16 10:34 ` [PATCH v2 1/3] trace-cmd library: Add new trace-cmd library APIs for guest ts corrections Tzvetomir Stoyanov (VMware)
2021-04-16 10:34 ` Tzvetomir Stoyanov (VMware) [this message]
2021-04-16 20:12   ` [PATCH v2 2/3] trace-cmd library: Add check before applying tsc2nsec offset Steven Rostedt
2021-04-19  8:08     ` Tzvetomir Stoyanov
2021-04-19 13:45       ` Steven Rostedt
2021-04-19 15:14         ` Steven Rostedt
2021-04-28 12:31           ` Tzvetomir Stoyanov
2021-04-16 10:34 ` [PATCH v2 3/3] trace-cmd: Get the timestamp of the first recorded event as TSC offset Tzvetomir Stoyanov (VMware)
2021-04-16 19:28   ` Steven Rostedt

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