executor: support wrapping executor with an external sandbox process

If an external sandbox process wraps executor, the out pipe will be closed
before the sandbox process exits this will make ipc package kill the sandbox.
As the result sandbox process will exit with exit status 9 instead of the executor
exit status (notably kRetryStatus). Consequently, ipc will treat it as hard
failure rather than a temporal failure. So we duplicate the exit status on the pipe.

1 files changed, 36 insertions, 21 deletions

diff --git a/ipc/ipc.go b/ipc/ipc.go
index ceff20134..29feb8b85 100644
--- a/ipc/ipc.go
+++ b/ipc/ipc.go
@@ -48,6 +48,10 @@ const (
 
 	outputSize   = 16 << 20
 	signalOffset = 15 << 20
+
+	statusFail  = 67
+	statusError = 68
+	statusRetry = 69
 )
 
 var (
@@ -493,7 +497,7 @@ func (c *command) waitServing() error {
 				sys := c.cmd.ProcessState.Sys()
 				if ws, ok := sys.(syscall.WaitStatus); ok {
 					// Magic values returned by executor.
-					if ws.ExitStatus() == 67 {
+					if ws.ExitStatus() == statusFail {
 						err = ExecutorFailure(fmt.Sprintf("executor is not serving:\n%s", output))
 					}
 				}
@@ -537,12 +541,19 @@ func (c *command) exec(cover, dedup bool) (output []byte, failed, hanged, restar
 	}()
 	readN, readErr := c.inrp.Read(flags[:])
 	close(done)
+	status := 0
 	if readErr == nil {
 		if readN != len(flags) {
 			panic(fmt.Sprintf("executor %v: read only %v bytes", c.pid, readN))
 		}
-		<-hang
-		return
+		status = int(flags[0])
+		if status == 0 {
+			<-hang
+			return
+		}
+		// Executor writes magic values into the pipe before exiting,
+		// so proceed with killing and joining it.
+		status = int(flags[0])
 	}
 	err0 = fmt.Errorf("executor did not answer")
 	c.kill()
@@ -552,26 +563,30 @@ func (c *command) exec(cover, dedup bool) (output []byte, failed, hanged, restar
 		output = append(output, []byte(err.Error())...)
 		output = append(output, '\n')
 	}
-	if c.cmd.ProcessState != nil {
-		sys := c.cmd.ProcessState.Sys()
-		if ws, ok := sys.(syscall.WaitStatus); ok {
-			// Magic values returned by executor.
-			if ws.ExitStatus() == 67 {
-				err0 = ExecutorFailure(fmt.Sprintf("executor failed: %s", output))
-			}
-			if ws.ExitStatus() == 68 {
-				failed = true
-			}
-			if ws.ExitStatus() == 69 {
-				// This is a temporal error (ENOMEM) or an unfortunate
-				// program that messes with testing setup (e.g. kills executor
-				// loop process). Pretend that nothing happened.
-				// It's better than a false crash report.
-				err0 = nil
-				hanged = false
-				restart = true
+	switch status {
+	case statusFail, statusError, statusRetry:
+	default:
+		if c.cmd.ProcessState != nil {
+			sys := c.cmd.ProcessState.Sys()
+			if ws, ok := sys.(syscall.WaitStatus); ok {
+				status = ws.ExitStatus()
 			}
 		}
 	}
+	// Handle magic values returned by executor.
+	switch status {
+	case statusFail:
+		err0 = ExecutorFailure(fmt.Sprintf("executor failed: %s", output))
+	case statusError:
+		failed = true
+	case statusRetry:
+		// This is a temporal error (ENOMEM) or an unfortunate
+		// program that messes with testing setup (e.g. kills executor
+		// loop process). Pretend that nothing happened.
+		// It's better than a false crash report.
+		err0 = nil
+		hanged = false
+		restart = true
+	}
 	return
 }