tests: gdbstub: qemu: Cross-validate test behavior

Add a testcase to run the same test application and GDB script
which we use for Zephyr GDB stub testing, but now with
the GDB stub enabled at QEMU itself using it as a reference
RDP backend implementation. This allows to check the Zephyr's
gdbstub implementation has similar behavior as the reference.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>

tests/subsys/debug/gdbstub/pytest/test_gdbstub.py

@@ -18,7 +18,7 @@ from twisterlib.cmakecache import CMakeCache
 logger = logging.getLogger(__name__)
 
 @pytest.fixture()
-def gdb_process(dut: DeviceAdapter, gdb_script, gdb_timeout, gdb_target_remote):
+def gdb_process(dut: DeviceAdapter, gdb_script, gdb_timeout, gdb_target_remote) -> subprocess.CompletedProcess:
     build_dir = dut.device_config.build_dir
     cmake_cache = CMakeCache.from_file(os.path.join(build_dir, 'CMakeCache.txt'))
     gdb_exec = cmake_cache.get('CMAKE_GDB', None)
@@ -59,7 +59,15 @@ def expected_gdb():
     re.compile(r'GDB:PASSED'),
     ]
 
-def test_gdbstub(dut: DeviceAdapter, gdb_process, expected_app, expected_gdb):
+@pytest.fixture(scope="module")
+def expected_gdb_detach():
+    return [
+    re.compile(r'Inferior.*will be killed'),  # Zephyr gdbstub
+    re.compile(r'Inferior.*detached')  # QEMU gdbstub
+    ]
+
+
+def test_gdbstub(dut: DeviceAdapter, gdb_process, expected_app, expected_gdb, expected_gdb_detach):
     """
     Test gdbstub feature using a GDB script. We connect to the DUT, run the
     GDB script then evaluate return code and expected patterns at the GDB
@@ -68,7 +76,7 @@ def test_gdbstub(dut: DeviceAdapter, gdb_process, expected_app, expected_gdb):
     logger.debug(f"GDB output:\n{gdb_process.stdout}\n")
     assert gdb_process.returncode == 0
     assert all([ex_re.search(gdb_process.stdout, re.MULTILINE) for ex_re in expected_gdb]), 'No expected GDB output'
-    assert 'Inferior 1 [Remote target] will be killed' in gdb_process.stdout,'Expecting explicit quit from the GDB script and kill QEMU test app.'
+    assert any([ex_re.search(gdb_process.stdout, re.MULTILINE) for ex_re in expected_gdb_detach]), 'No expected GDB quit'
     app_output = '\n'.join(dut.readlines(print_output = False))
     logger.debug(f"App output:\n{app_output}\n")
     assert all([ex_re.search(app_output, re.MULTILINE) for ex_re in expected_app]), 'No expected Application output'

tests/subsys/debug/gdbstub/testcase.yaml

@@ -5,6 +5,7 @@
 #
 
 tests:
+  # Connect to Zephyr gdbstub and run a simple GDB script
   debug.gdbstub.breakpoints:
     platform_allow: qemu_x86
     harness: pytest
@@ -17,11 +18,42 @@ tests:
         - "--gdb_script"
         - "test_breakpoints.gdbinit"
         - "--gdb_target_remote"
-        - "tcp:127.0.0.1:5678"
+        - "tcp::5678"
     tags:
       - debug
       - gdbstub
     extra_configs:
       # Make sure the gdbstub port chosen is unique for this test to avoid conflicts
       # when Twister runs tests in parallel on the same host.
-      - CONFIG_QEMU_EXTRA_FLAGS="-serial tcp:127.0.0.1:5678,server"
+      - CONFIG_QEMU_EXTRA_FLAGS="-serial tcp::5678,server"
+
+  # Connect to QEMU gdbstub backend and run the same GDB test script
+  # to check it against a reference RDP backend implementation expecting
+  # similar behavior as for Zephyr's gdbstub.
+  # Use non-default QEMU gdbstub port 1235 for this test to avoid conflicts
+  # with some other test on QEMU running in parallel.
+  debug.gdbstub_qemu.breakpoints:
+    platform_allow: qemu_x86
+    harness: pytest
+    harness_config:
+      pytest_root:
+        - "pytest/test_gdbstub.py"
+      pytest_args:
+        - "--gdb_timeout"
+        - "20"
+        - "--gdb_script"
+        - "test_breakpoints.gdbinit"
+        - "--gdb_target_remote"
+        - "tcp::1235"
+    tags:
+      - debug
+      - gdbstub
+    extra_configs:
+      # Turn off Zephyr's gdbstub for this test case.
+      - CONFIG_GDBSTUB=n
+      - CONFIG_GDBSTUB_SERIAL_BACKEND=n
+      # Make sure the gdbstub port chosen is unique for this test to avoid conflicts
+      # when Twister runs tests in parallel on the same host.
+      - CONFIG_QEMU_EXTRA_FLAGS="-S -gdb tcp::1235"
+      # Clear QEMU default 'tcp::1234'
+      - CONFIG_QEMU_GDBSERVER_LISTEN_DEV=""