test/py: support running sandbox under gdbserver

Implement command--line option --gdbserver COMM, which does two things:

a) Run the sandbox process under gdbserver, using COMM as gdbserver's
   communication channel.

b) Disables all timeouts, so that if U-Boot is halted under the debugger,
   tests don't fail. If the user gives up in the middle of a debugging
   session, they can simply CTRL-C the test script to abort it.

This allows easy debugging of test failures without having to manually
re-create the failure conditions. Usage is:

Window 1:
./test/py/test.py --bd sandbox --gdbserver localhost:1234

Window 2:
gdb ./build-sandbox/u-boot -ex 'target remote localhost:1234'

When using this option, it likely makes sense to use pytest's -k option
to limit the set of tests that are executed.

Simply running U-Boot directly under gdb (rather than gdbserver) was
also considered. However, this was rejected because:

a) gdb's output would then be processed by the test script, and likely
   confuse it causing false failures.

b) pytest by default hides stdout from tests, which would prevent the
   user from interacting with gdb.

   While gdb can be told to redirect the debugee's stdio to a separate
   PTY, this would appear to leave gdb's stdio directed at the test
   scripts and the debugee's stdio directed elsewhere, which is the
   opposite of the desired effect. Perhaps some complicated PTY muxing
   and process hierarchy could invert this. However, the current scheme
   is simple to implement and use, so it doesn't seem worth complicating
   matters.

c) Using gdbserver allows arbitrary debuggers to be used, even those with
   a GUI. If the test scripts invoked the debugger themselves, they'd have
   to know how to execute arbitary applications. While the user could hide
   this all in a wrapper script, this feels like extra complication.

An interesting future idea might be a --gdb-screen option, which could
spawn both U-Boot and gdb separately, and spawn the screen into a newly
created window under screen. Similar options could be envisaged for
creating a new xterm/... too.

--gdbserver  currently only supports sandbox, and not real hardware.
That's primarily because the test hooks are responsible for all aspects of
hardware control, so there's nothing for the test scripts themselves can
do to enable gdbserver on real hardware. We might consider introducing a
separate --disable-timeouts option to support use of debuggers on real
hardware, and having --gdbserver imply that option.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

test/py/conftest.py

@@ -71,6 +71,9 @@ def pytest_addoption(parser):
         help='U-Boot board identity/instance')
     parser.addoption('--build', default=False, action='store_true',
         help='Compile U-Boot before running tests')
+    parser.addoption('--gdbserver', default=None,
+        help='Run sandbox under gdbserver. The argument is the channel '+
+        'over which gdbserver should communicate, e.g. localhost:1234')
 
 def pytest_configure(config):
     """pytest hook: Perform custom initialization at startup time.
@@ -110,6 +113,10 @@ def pytest_configure(config):
         persistent_data_dir = build_dir + '/persistent-data'
     mkdir_p(persistent_data_dir)
 
+    gdbserver = config.getoption('gdbserver')
+    if gdbserver and board_type != 'sandbox':
+        raise Exception('--gdbserver only supported with sandbox')
+
     import multiplexed_log
     log = multiplexed_log.Logfile(result_dir + '/test-log.html')
 
@@ -169,6 +176,7 @@ def pytest_configure(config):
     ubconfig.persistent_data_dir = persistent_data_dir
     ubconfig.board_type = board_type
     ubconfig.board_identity = board_identity
+    ubconfig.gdbserver = gdbserver
 
     env_vars = (
         'board_type',

test/py/tests/test_sleep.py

@@ -15,6 +15,7 @@ def test_sleep(u_boot_console):
     u_boot_console.run_command('sleep %d' % sleep_time)
     tend = time.time()
     elapsed = tend - tstart
-    delta_to_expected = abs(elapsed - sleep_time)
-    # 0.25s margin is hopefully enough to account for any system overhead.
-    assert delta_to_expected < 0.25
+    assert elapsed >= sleep_time
+    if not u_boot_console.config.gdbserver:
+        # 0.25s margin is hopefully enough to account for any system overhead.
+        assert elapsed < (sleep_time + 0.25)

test/py/u_boot_console_base.py

@@ -300,7 +300,8 @@ class ConsoleBase(object):
             # text if LCD is enabled. This value may need tweaking in the
             # future, possibly per-test to be optimal. This works for 'help'
             # on board 'seaboard'.
-            self.p.timeout = 30000
+            if not self.config.gdbserver:
+                self.p.timeout = 30000
             self.p.logfile_read = self.logstream
             if self.config.buildconfig.get('CONFIG_SPL', False) == 'y':
                 m = self.p.expect([pattern_u_boot_spl_signon] + self.bad_patterns)

test/py/u_boot_console_sandbox.py

@@ -39,7 +39,10 @@ class ConsoleSandbox(ConsoleBase):
             A u_boot_spawn.Spawn object that is attached to U-Boot.
         """
 
-        cmd = [
+        cmd = []
+        if self.config.gdbserver:
+            cmd += ['gdbserver', self.config.gdbserver]
+        cmd += [
             self.config.build_dir + '/u-boot',
             '-d',
             self.config.build_dir + '/arch/sandbox/dts/test.dtb'

test/py/u_boot_spawn.py

@@ -148,10 +148,14 @@ class Spawn(object):
                     self.buf = self.buf[posafter:]
                     return earliest_pi
                 tnow_s = time.time()
-                tdelta_ms = (tnow_s - tstart_s) * 1000
-                if tdelta_ms > self.timeout:
-                    raise Timeout()
-                events = self.poll.poll(self.timeout - tdelta_ms)
+                if self.timeout:
+                    tdelta_ms = (tnow_s - tstart_s) * 1000
+                    poll_maxwait = self.timeout - tdelta_ms
+                    if tdelta_ms > self.timeout:
+                        raise Timeout()
+                else:
+                    poll_maxwait = None
+                events = self.poll.poll(poll_maxwait)
                 if not events:
                     raise Timeout()
                 c = os.read(self.fd, 1024)