Kdump testing framework

setup.py

@@ -187,9 +187,20 @@ def _run_vm(self, kernel_dir):
 
         import vmtest.vm
 
-        command = fr"""cd {shlex.quote(os.getcwd())} &&
-	DRGN_RUN_LINUX_HELPER_TESTS=1 {shlex.quote(sys.executable)} -Bm \
-		unittest discover -t . -s tests/helpers/linux {"-v" if self.verbose else ""}"""
+        command = fr"""
+set -e
+
+cd {shlex.quote(os.getcwd())}
+if "$BUSYBOX" [ -e /proc/vmcore ]; then
+    "$PYTHON" -Bm unittest discover -t . -s tests/linux_kernel/vmcore {"-v" if self.verbose else ""}
+else
+    DRGN_RUN_LINUX_HELPER_TESTS=1 "$PYTHON" -Bm \
+        unittest discover -t . -s tests/helpers/linux {"-v" if self.verbose else ""}
+    "$PYTHON" vmtest/enter_kdump.py
+    # We should crash and not reach this.
+    exit 1
+fi
+"""
         try:
             returncode = vmtest.vm.run_in_vm(
                 command, Path(kernel_dir), Path(self.vmtest_dir)

tests/linux_kernel/vmcore/test_vmcore.py

@@ -0,0 +1,15 @@
+from pathlib import Path
+import unittest
+
+from drgn import Program, ProgramFlags
+
+VMCORE_PATH = Path("/proc/vmcore")
+
+
+@unittest.skipUnless(VMCORE_PATH.exists(), "not running in kdump")
+class TestAttachToVMCore(unittest.TestCase):
+    def test_attach_to_vmcore(self):
+        prog = Program()
+        prog.set_core_dump("/proc/vmcore")
+        self.assertFalse(prog.flags & ProgramFlags.IS_LIVE)
+        self.assertTrue(prog.flags & ProgramFlags.IS_LINUX_KERNEL)

vmtest/enter_kdump.py

@@ -0,0 +1,40 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# This isn't great: it's specific to x86-64, both by virtue of the syscall
+# number and because kexec_file_load isn't implemented on many architectures,
+# especially on older kernels.
+
+import ctypes
+import os
+import re
+
+SYS_kexec_file_load = 320  # On x86-64.
+KEXEC_FILE_ON_CRASH = 2
+KEXEC_FILE_NO_INITRAMFS = 4
+
+syscall = ctypes.CDLL(None, use_errno=True).syscall
+syscall.restype = ctypes.c_long
+
+with open("/proc/cmdline", "rb") as f:
+    cmdline = f.read().rstrip(b"\n")
+    cmdline = re.sub(rb"(^|\s)crashkernel=\S+", b"", cmdline)
+    # `nosmp` is required to avoid QEMU sporadically failing an internal assertion
+    # `nokaslr` is required to avoid sporadically failing to reserve space for the
+    # capture kernel
+    cmdline += b" nosmp nokaslr"
+
+with open(f"/lib/modules/{os.uname().release}/vmlinuz", "rb") as kernel:
+    if syscall(
+        ctypes.c_long(SYS_kexec_file_load),
+        ctypes.c_int(kernel.fileno()),
+        ctypes.c_int(-1),
+        ctypes.c_ulong(len(cmdline) + 1),
+        ctypes.c_char_p(cmdline + b"\0"),
+        ctypes.c_ulong(KEXEC_FILE_ON_CRASH | KEXEC_FILE_NO_INITRAMFS),
+    ):
+        errno = ctypes.get_errno()
+        raise OSError(errno, os.strerror(errno))
+
+with open("/proc/sysrq-trigger", "w") as f:
+    f.write("c")

vmtest/vm.py

@@ -24,6 +24,7 @@
 set -eu
 
 export BUSYBOX={busybox}
+export PYTHON={python}
 
 trap '"$BUSYBOX" poweroff -f' EXIT
 
@@ -214,6 +215,7 @@ def run_in_vm(command: str, kernel_dir: Path, build_dir: Path) -> int:
                 _INIT_TEMPLATE.format(
                     _9PFS_MSIZE=_9PFS_MSIZE,
                     busybox=shlex.quote(busybox),
+                    python=shlex.quote(sys.executable),
                     command=shlex.quote(command),
                 )
             )
@@ -246,7 +248,7 @@ def run_in_vm(command: str, kernel_dir: Path, build_dir: Path) -> int:
 
                 "-kernel", str(kernel_dir / "vmlinuz"),
                 "-append",
-                f"rootfstype=9p rootflags=trans=virtio,cache=loose,msize={_9PFS_MSIZE} ro console=0,115200 panic=-1 init={init}",
+                f"rootfstype=9p rootflags=trans=virtio,cache=loose,msize={_9PFS_MSIZE} ro console=0,115200 panic=-1 crashkernel=256M init={init}",
                 # fmt: on
             ],
             env=env,