gem5Connection: Catch EOF errors & make more user friendly

Previously, when the gem5 simulation crashed, one would get errors
relating to pexpect reaching EOF, rather than an informative message
stating the gem5 itself had crashed. With this change, we catch some
of the common cases where this can happen, and inform the user if gem5
itself has crashed. In the event that the gem5 simulation itself has
not reported an error, we instead re-throw the original pexpect error.

devlib/utils/ssh.py

@@ -554,6 +554,19 @@ class Gem5Connection(TelnetConnection):
 
         self.connect_gem5(port, gem5_simulation, gem5_interact_dir, gem5_out_dir)
 
+    # Handle the EOF exception raised by pexpect
+    def _gem5_EOF_handler(self, gem5_simulation, gem5_out_dir, err):
+        # If we have reached the "EOF", it typically means
+        # that gem5 crashed and closed the connection. Let's
+        # check and actually tell the user what happened here,
+        # rather than spewing out pexpect errors.
+        if gem5_simulation.poll():
+            message = "The gem5 process has crashed with error code {}!\n\tPlease see {} for details."
+            raise TargetError(message.format(gem5_simulation.poll(), gem5_out_dir))
+        else:
+            # Let's re-throw the exception in this case.
+            raise err
+
     # This function connects to the gem5 simulation
     def connect_gem5(self, port, gem5_simulation, gem5_interact_dir,
                       gem5_out_dir):
@@ -591,6 +604,8 @@ class Gem5Connection(TelnetConnection):
                 break
             except pxssh.ExceptionPxssh:
                 pass
+            except EOF, err:
+                self._gem5_EOF_handler(gem5_simulation, gem5_out_dir, err)
         else:
             gem5_simulation.kill()
             raise TargetError("Failed to connect to the gem5 telnet session.")
@@ -611,6 +626,9 @@ class Gem5Connection(TelnetConnection):
                 self._login_to_device()
             except TIMEOUT:
                 pass
+            except EOF, err:
+                self._gem5_EOF_handler(gem5_simulation, gem5_out_dir, err)
+
             try:
                 # Try and force a prompt to be shown
                 self.conn.send('\n')
@@ -618,6 +636,8 @@ class Gem5Connection(TelnetConnection):
                 prompt_found = True
             except TIMEOUT:
                 pass
+            except EOF, err:
+                self._gem5_EOF_handler(gem5_simulation, gem5_out_dir, err)
 
         gem5_logger.info("Successfully logged in")
         gem5_logger.info("Setting unique prompt...")