baremetal: allow arbitrary exit status with the magic string

test-baremetal: fix missing setting x0 return value

Examples were just returning on ret without setting x0, which led to
failures... those were not noticed because of how broken the testing system
was ;-)

run

@@ -15,18 +15,6 @@ class Main(common.LkmcCliFunction):
         super().__init__(
             description='''\
 Run some content on an emulator.
-'''
-        )
-        self.add_argument(
-            '--background',
-            default=False,
-            help='''\
-Send QEMU serial output to a file instead of the terminal so it does not require a
-terminal attached to run on the background. Interactive input cannot be given.
-TODO: use a port instead. If only there was a way to redirect a serial to multiple
-places, both to a port and a file? We use the file currently to be able to have
-any output at all.
-https://superuser.com/questions/1373226/how-to-redirect-qemu-serial-output-to-both-a-file-and-the-terminal-or-a-port
 '''
         )
         self.add_argument(
@@ -241,10 +229,11 @@ Setup a kernel init parameter that makes the emulator quit immediately after boo
             '--terminal',
             default=False,
             help='''\
-Output to the terminal, don't pipe to tee as the default.
-Does not save the output to a file, but allows you to use debuggers.
-Set automatically by --debug-vm, but you still need this option to debug
-gem5 Python scripts with pdb.
+Output directly to the terminal, don't pipe to tee as the default.
+With this, we don't not save the output to a file as is done by default,
+but we are able to do things that require not having a pipe suh as you to
+using debuggers. This option issSet automatically by --debug-vm, but you still need
+it to debug gem5 Python scripts with pdb.
 '''
         )
         self.add_argument(
@@ -570,7 +559,7 @@ Extra options to append at the end of the emulator command line.
                     serial_monitor = []
                 else:
                     if self.env['background']:
-                        serial_monitor = ['-serial', 'file:{}'.format(self.env['qemu_background_serial_file']), LF]
+                        serial_monitor = ['-serial', 'file:{}'.format(self.env['guest_terminal_file']), LF]
                         if self.env['quiet']:
                             show_stdout = False
                     else:
@@ -752,34 +741,36 @@ Extra options to append at the end of the emulator command line.
             show_stdout=show_stdout,
         )
         if exit_status == 0:
-            # Check if guest panicked.
-            if self.env['emulator'] == 'gem5':
-                # We have to do some parsing here because gem5 exits with status 0 even when panic happens.
-                # Grepping for '^panic: ' does not work because some errors don't show that message.
-                panic_msg = b'--- BEGIN LIBC BACKTRACE ---$'
-            else:
-                panic_msg = b'Kernel panic - not syncing'
-            panic_re = re.compile(panic_msg)
             error_string_found = False
             exit_status = 0
             if out_file is not None and not self.env['dry_run']:
-                with open(self.env['termout_file'], 'br') as logfile:
-                    line = None
-                    for line in logfile:
-                        if panic_re.search(line):
-                            exit_status = 1
-                    if line is not None:
-                        last_line = line.rstrip()
-                        match = re.search(b'Simulated exit code not 0! Exit code is (\d+)', last_line)
-                        if match:
-                            exit_status = int(match.group(1))
+                if self.env['emulator'] == 'gem5':
+                    with open(self.env['termout_file'], 'br') as logfile:
+                        # We have to do some parsing here because gem5 exits with status 0 even when panic happens.
+                        # Grepping for '^panic: ' does not work because some errors don't show that message...
+                        gem5_panic_re = re.compile(b'--- BEGIN LIBC BACKTRACE ---$')
+                        line = None
+                        for line in logfile:
+                            if gem5_panic_re.search(line):
+                                exit_status = 1
+                        if self.env['userland']:
+                            if line is not None:
+                                last_line = line.rstrip()
+                                match = re.search(b'Simulated exit code not 0! Exit code is (\d+)', last_line)
+                                if match:
+                                    exit_status = int(match.group(1))
                 if not self.env['userland']:
                     if os.path.exists(self.env['guest_terminal_file']):
                         with open(self.env['guest_terminal_file'], 'br') as logfile:
+                            linux_panic_re = re.compile(b'Kernel panic - not syncing')
+                            serial_magic_exit_status_regexp = re.compile(self.env['serial_magic_exit_status_regexp_string'])
                             for line in logfile.readlines():
-                                if line.rstrip() == self.env['magic_fail_string']:
+                                line = line.rstrip()
+                                if not self.env['baremetal'] and linux_panic_re.search(line):
                                     exit_status = 1
-                                    break
+                                match = serial_magic_exit_status_regexp.match(line)
+                                if match:
+                                    exit_status = int(match.group(1))
             if exit_status != 0 and self.env['show_stdout']:
                 self.log_error('simulation error detected by parsing logs')
         return exit_status