test(gdb): add integ test to verify gdb works on x86

The integ test opens gdb on a subprocess which connects to Firecracker,
sets a breakpoint and continues until boot is complete. If the VM boots
correctly and the breakpoint gets hit, then the test will succeed.

This test currently only works on x86 as GDB requires a vmlinux image
(we use a uImage on ARM).

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

tests/framework/microvm.py

@@ -287,6 +287,8 @@ def __init__(
 
         self.help = MicrovmHelpers(self)
 
+        self.gdb_socket = None
+
     def __repr__(self):
         return f"<Microvm id={self.id}>"
 
@@ -1198,6 +1200,11 @@ def wait_for_ssh_up(self):
         # run commands. The actual connection retry loop happens in SSHConnection._init_connection
         _ = self.ssh_iface(0)
 
+    def enable_gdb(self):
+        """Enables GDB debugging"""
+        self.gdb_socket = "gdb.socket"
+        self.api.machine_config.patch(gdb_socket_path=self.gdb_socket)
+
 
 class MicroVMFactory:
     """MicroVM factory"""

tests/integration_tests/build/test_gdb.py

@@ -2,15 +2,86 @@
 # SPDX-License-Identifier: Apache-2.0
 """A test that ensures that firecracker builds with GDB feature enabled at integration time."""
 
+import os
 import platform
+import pytest
+import signal
+import subprocess
+import tempfile
+from pathlib import Path
 
 import host_tools.cargo_build as host
+from framework.defs import LOCAL_BUILD_PATH
+from framework.microvm import MicroVMFactory
 
 MACHINE = platform.machine()
 TARGET = "{}-unknown-linux-musl".format(MACHINE)
+BUILD_PATH = LOCAL_BUILD_PATH / "gdb"
+
+
+def build_gdb():
+    """Builds Firecracker with GDB feature enabled"""
+
+    host.cargo(
+        "build",
+        f"--features gdb --target {TARGET} --all",
+        env={"CARGO_TARGET_DIR": BUILD_PATH},
+    )
 
 
 def test_gdb_compiles():
     """Checks that Firecracker compiles with GDB enabled"""
 
-    host.cargo("build", f"--features gdb --target {TARGET}")
+    build_gdb()
+
+@pytest.mark.skipif(
+    platform.machine() != "x86_64", reason="GDB requires a vmlinux but we ship a uImage for ARM in our CI"
+)
+def test_gdb_connects(guest_kernel_linux_6_1, rootfs):
+    """Checks that GDB works in a FC VM"""
+
+    build_gdb()
+
+    vmfcty = MicroVMFactory(BUILD_PATH / TARGET / "debug")
+    kernel_dbg = guest_kernel_linux_6_1.parent / "debug" / guest_kernel_linux_6_1.name
+    uvm = vmfcty.build(kernel_dbg, rootfs)
+    uvm.spawn(validate_api=False)
+    uvm.add_net_iface()
+    uvm.basic_config()
+    uvm.enable_gdb()
+
+    chroot_gdb_socket = Path(uvm.jailer.chroot_path(), uvm.gdb_socket)
+
+    gdb_commands = f"""
+    target remote {chroot_gdb_socket}
+    hbreak start_kernel
+    # continue to start_kernel
+    continue
+    # continue boot until interrupted
+    continue
+    """
+
+    with tempfile.NamedTemporaryFile(
+        mode="w", suffix=".gdb", delete=False, prefix="fc_gdb_"
+    ) as f:
+        f.write(gdb_commands)
+        gdb_script = f.name
+
+    gdb_proc = subprocess.Popen(f"""
+        until [ -S {chroot_gdb_socket} ]; do
+            echo 'waiting for {chroot_gdb_socket}';
+            sleep 1;
+        done;
+        gdb {kernel_dbg} -batch -x {gdb_script}
+        """,
+        shell=True,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True
+    )
+    uvm.start()
+    os.kill(uvm.firecracker_pid, signal.SIGKILL)
+    gdb_proc.terminate()
+    uvm.mark_killed()
+    stdout, stderr = gdb_proc.communicate(timeout=10)
+    assert "hit Breakpoint 1, start_kernel" in stdout, f"Breakpoint wasn't hit:\nstdout:\n{stdout}\n\nstderr:\n{stderr}"