tests: linux_kernel: test built-in ORC unwinding

Unwinding through a kernel module with no DWARF info would have been
impossible without support of built-in ORC. Further, the tests here
would not pass without 329bd5d ("Make StackFrame.name fall back to
symbol/PC and add StackFrame.function_name").

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>

tests/linux_kernel/test_stack_trace.py

@@ -1,11 +1,14 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
+import logging
 import os
+import re
 import unittest
 
 from _drgn_util.platform import NORMALIZED_MACHINE_NAME
-from drgn import Object, Program, reinterpret
+from drgn import MissingDebugInfoError, Object, Program, reinterpret
+from drgn.helpers.linux import load_module_kallsyms
 from tests import assertReprPrettyEqualsStr, modifyenv
 from tests.linux_kernel import (
     LinuxKernelTestCase,
@@ -59,6 +62,54 @@ def test_by_pid_dwarf(self):
     def test_by_pid_orc(self):
         self._test_by_pid(True)
 
+    @unittest.skipUnless(
+        NORMALIZED_MACHINE_NAME == "x86_64",
+        f"{NORMALIZED_MACHINE_NAME} does not use ORC",
+    )
+    @skip_unless_have_test_kmod
+    def test_by_pid_builtin_orc(self):
+        # ORC was introduced in kernel 4.14. Detect the presence of ORC or skip
+        # the test.
+        try:
+            self.prog.symbol("__start_orc_unwind")
+        except LookupError:
+            ver = self.prog["UTS_RELEASE"].string_().decode()
+            self.skipTest(f"ORC is not available for {ver}")
+
+        # Create a program with the core kernel debuginfo loaded,
+        # but without module debuginfo. Load a symbol finder using
+        # kallsyms so that the module's stack traces can still have
+        # usable frame names.
+        prog = Program()
+        prog.set_kernel()
+        try:
+            prog.load_default_debug_info()
+        except MissingDebugInfoError:
+            pass
+        kallsyms = load_module_kallsyms(prog)
+        prog.register_symbol_finder("module_kallsyms", kallsyms, enable_index=1)
+        for thread in prog.threads():
+            if b"drgn_test_kthread".startswith(thread.object.comm.string_()):
+                pid = thread.tid
+                break
+        else:
+            self.fail("couldn't find drgn_test_kthread")
+        with self.assertLogs("drgn", logging.DEBUG) as log:
+            self._test_drgn_test_kthread_trace(prog.stack_trace(pid))
+
+        # To be sure that we actually used ORC to unwind through the drgn_test
+        # stack frames, search for the log output. We don't know which ORC
+        # version is used, so just ensure that we have a log line that mentions
+        # loading ORC.
+        expr = re.compile(
+            r"DEBUG:drgn:Loaded built-in ORC \(v\d+\) for module drgn_test"
+        )
+        for line in log.output:
+            if expr.fullmatch(line):
+                break
+        else:
+            self.fail("Did not load built-in ORC for drgn_test")
+
     @skip_unless_have_test_kmod
     def test_by_pt_regs(self):
         pt_regs = self.prog["drgn_test_kthread_pt_regs"]