Make time exit status behavior saner

Match `timeout(1)` in error code where possible (the main benefit is
that unusual errors result in high error codes).

Signed-off-by: Tej Chajed <[email protected]>

benchmarking/src/time_bench.rs

@@ -126,7 +126,6 @@ struct RawRunMeasurement {
     self_usage: Usage,
     timed_out: bool,
     status: Option<i32>,
-    signal: Option<Signal>,
 }
 
 fn time_val_to_duration(time: TimeVal) -> Duration {
@@ -174,10 +173,6 @@ impl Time {
             WaitStatus::Exited(_, status) => Some(status),
             _ => None,
         };
-        let signal = match wstatus {
-            WaitStatus::Signaled(_, signal, _) => Some(signal),
-            _ => None,
-        };
         let real_time = start.elapsed();
         let timed_out = *timeout.lock().unwrap();
         let usage = getrusage(UsageWho::RUSAGE_CHILDREN)?;
@@ -188,7 +183,6 @@ impl Time {
             self_usage,
             timed_out,
             status,
-            signal,
         };
         Ok(measurement)
     }
@@ -214,9 +208,6 @@ impl Time {
                     // to match behavior of `timeout(1)`
                     return Ok(ExitCode::from(124u8));
                 }
-                if measurements.signal.is_some() {
-                    return Ok(ExitCode::FAILURE);
-                }
                 if let Some(code) = measurements.status {
                     return Ok(ExitCode::from(code as u8));
                 }
@@ -230,11 +221,14 @@ impl Time {
                 dup2(null, io::stdout().as_raw_fd()).expect("could not replace stdout with null");
                 let err = exec::Command::new(&self.prog).args(&self.args).exec();
                 eprintln!("exec failed: {err}");
-                Ok(ExitCode::FAILURE)
+                // mimic `timeout(1)` (although it distinguishes the command
+                // being found vs not found)
+                Ok(ExitCode::from(126))
             }
             Err(err) => {
                 eprintln!("fork failed: {err}");
-                Ok(ExitCode::FAILURE)
+                // mimic `timeout(1)`
+                Ok(ExitCode::from(125))
             }
         }
     }