mongo/buildscripts/gdb/mongo.py

"""GDB commands for MongoDB."""

import glob
import json
import os
import re
import subprocess
import sys
import warnings
from pathlib import Path

import gdb

sys.path.insert(0, str(Path(os.path.abspath(__file__)).parent.parent.parent))
from buildscripts.gdb.mongo_utils import (
    RegisterMongoCommand,
    absl_get_nodes,
    get_boost_optional,
    get_current_thread_name,
    get_decorable_info,
    get_object_decoration,
    get_thread_id,
    get_unique_ptr,
    lookup_type,
)


def detect_toolchain(progspace):
    readelf_bin = os.environ.get("MONGO_GDB_READELF", "/opt/mongodbtoolchain/v5/bin/llvm-readelf")
    if not os.path.exists(readelf_bin):
        readelf_bin = "readelf"

    gcc_version_regex = re.compile(r".*\]\s*GCC: \(GNU\) (\d+\.\d+\.\d+)\s*$")
    clang_version_regex = re.compile(r".*\]\s*MongoDB clang version (\d+\.\d+\.\d+).*")

    readelf_cmd = [readelf_bin, "-p", ".comment", progspace.filename]
    # take an educated guess as to where we could find the c++ printers, better than hardcoding
    result = subprocess.run(readelf_cmd, capture_output=True, text=True)

    gcc_version = None
    for line in result.stdout.split("\n"):
        if match := re.search(gcc_version_regex, line):
            gcc_version = match.group(1)
            break
    clang_version = None
    for line in result.stdout.split("\n"):
        if match := re.search(clang_version_regex, line):
            clang_version = match.group(1)
            break

    if clang_version:
        print(f"Detected binary built with Clang: {clang_version}")
    elif gcc_version:
        print(f"Detected binary built with GCC: {gcc_version}")
    else:
        print("Could not detect compiler.")

    # default is v4 if we can't find a version
    toolchain_ver = None
    if gcc_version:
        toolchain_ver = {
            "8": "v3",
            "11": "v4",
            "14": "v5",
        }.get(gcc_version.split(".")[0])
    elif clang_version:
        toolchain_ver = {
            "19": "v5",
        }.get(clang_version.split(".")[0])
        if int(clang_version.split(".")[0]) == 19:
            toolchain_ver = "v5"

    if not toolchain_ver:
        toolchain_ver = "v4"
        print(f"""
WARNING: could not detect a MongoDB toolchain to load matching stdcxx printers:
-----------------
command:
{' '.join(readelf_cmd)}
STDOUT:
{result.stdout.strip()}
STDERR:
{result.stderr.strip()}
-----------------
Assuming {toolchain_ver} as a default, this could cause issues with the printers.""")

    base_toolchain_dir = os.environ.get(
        "MONGO_GDB_PP_DIR", f"/opt/mongodbtoolchain/{toolchain_ver}/share"
    )
    pp = glob.glob(f"{base_toolchain_dir}/gcc-*/python/libstdcxx/v6/printers.py")
    printers = pp[0]
    return os.path.dirname(os.path.dirname(os.path.dirname(printers)))


stdcxx_printer_toolchain_paths = dict()


def load_libstdcxx_printers(progspace):
    if progspace not in stdcxx_printer_toolchain_paths:
        stdcxx_printer_toolchain_paths[progspace] = detect_toolchain(progspace)
        try:
            sys.path.insert(0, stdcxx_printer_toolchain_paths[progspace])
            global stdlib_printers
            from libstdcxx.v6 import printers as stdlib_printers
            from libstdcxx.v6 import register_libstdcxx_printers

            register_libstdcxx_printers(progspace)
            print(
                f"Loaded libstdc++ pretty printers from '{stdcxx_printer_toolchain_paths[progspace]}'"
            )
        except Exception as exc:
            print(
                f"Failed to load the libstdc++ pretty printers from {stdcxx_printer_toolchain_paths[progspace]}: {exc}"
            )


def on_new_object_file(objfile) -> None:
    """Import the libstdc++ GDB pretty printers when either the `attach <pid>` or `core-file <pathname>` commands are run in GDB."""
    progspace = objfile.new_objfile.progspace
    if progspace.filename is None:
        # The `attach` command would have filled in the filename so we only need to check if
        # a core dump has been loaded with the executable file also being loaded.
        target_info = gdb.execute("info target", to_string=True)
        if re.match(r"^Local core dump file:", target_info):
            warnings.warn(
                "Unable to locate the libstdc++ GDB pretty printers without an executable"
                " file. Try running the `file` command with the path to the executable file"
                " and reloading the core dump with the `core-file` command"
            )
        return

    load_libstdcxx_printers(objfile.new_objfile.progspace)


if gdb.selected_inferior().progspace.filename:
    load_libstdcxx_printers(gdb.selected_inferior().progspace)
else:
    gdb.events.new_objfile.connect(on_new_object_file)

try:
    import bson
except ImportError:
    print("Warning: Could not load bson library for Python '" + str(sys.version) + "'.")
    print("Check with the pip command if pymongo 3.x is installed.")
    bson = None

if sys.version_info[0] < 3:
    raise gdb.GdbError(
        "MongoDB gdb extensions only support Python 3. Your GDB was compiled against Python 2"
    )


def get_process_name():
    """Return the main binary we are attached to."""
    # The return from gdb.objfiles() could include the file extension of the debug symbols.
    main_binary_name = gdb.objfiles()[0].filename
    return os.path.splitext(os.path.basename(main_binary_name))[0]


def get_global_service_context():
    """Return the global ServiceContext object."""
    return gdb.parse_and_eval("'mongo::(anonymous namespace)::globalServiceContext'").dereference()


def get_session_catalog():
    """Return the global SessionCatalog object.

    Returns None if no SessionCatalog could be found.
    """
    # The SessionCatalog is a decoration on the ServiceContext.
    session_catalog_dec = get_decoration(get_global_service_context(), "mongo::SessionCatalog")
    if session_catalog_dec is None:
        return None
    return session_catalog_dec[1]


def get_session_kv_pairs():
    """Return the SessionRuntimeInfoMap stored in the global SessionCatalog object.

    Returns a list of (LogicalSessionId, std::unique_ptr<SessionRuntimeInfo>) key-value pairs. For
    key-value pair 'session_kv', access the key with 'session_kv["first"]' and access the value with
    'session_kv["second"]'.
    """
    session_catalog = get_session_catalog()
    if session_catalog is None:
        return list()
    return list(absl_get_nodes(session_catalog["_sessions"]))


def get_wt_session(recovery_unit, recovery_unit_impl_type):
    """Return the WT_SESSION pointer stored in the WiredTigerRecoveryUnit.

    Returns None if the recovery unit is not for the WiredTiger storage engine, or if no WT_SESSION
    has been opened.
    """

    if recovery_unit_impl_type != "mongo::WiredTigerRecoveryUnit":
        return None
    if not recovery_unit:
        return None
    wt_session_handle = get_unique_ptr(recovery_unit["_session"])
    if not wt_session_handle.dereference().address:
        return None
    wt_session = wt_session_handle.dereference().cast(lookup_type("mongo::WiredTigerSession"))[
        "_session"
    ]
    return wt_session


def cast_to_decorable(obj):
    """Cast a given object to a mongo::Decorable<T> type.

    Returns the casted object.
    """
    type_name = obj.type.name
    decorable_type = lookup_type("mongo::Decorable<{}>".format(type_name))
    return obj.cast(decorable_type)


def get_decorations(obj):
    """Return an iterator to all decorations on a given object.

    Each object returned by the iterator is a tuple whose first element is the type name of the
    decoration and whose second element is the decoration object itself.
    """
    decorable = cast_to_decorable(obj)
    start, count = get_decorable_info(decorable)
    for i in range(count):
        deco_type_name, obj, _ = get_object_decoration(decorable, start, i)
        try:
            yield (deco_type_name, obj)
        except Exception as err:
            print("Failed to look up decoration type: " + deco_type_name + ": " + str(err))


def get_decoration(obj, type_name):
    """Find a decoration on 'obj' where the string 'type_name' is in the decoration's type name.

    Returns a tuple whose first element is the type name of the decoration and whose
    second is the decoration itself. If there are multiple such decorations, returns the first one
    that matches. Returns None if no matching decorations were found.
    """
    decorable = cast_to_decorable(obj)
    start, count = get_decorable_info(decorable)
    for i in range(count):
        entry = start[i]
        if type_name in str(entry["typeInfo"]):
            dec_type_name, dec, _ = get_object_decoration(decorable, start, i)
            return (dec_type_name, dec)
    return None


def get_field_names(value):
    """Return a list of all field names on a given GDB value."""
    return [typ.name for typ in value.type.fields()]


###################################################################################################
#
# Commands
#
###################################################################################################


class DumpGlobalServiceContext(gdb.Command):
    """Dump the Global Service Context."""

    def __init__(self):
        """Initialize DumpGlobalServiceContext."""
        RegisterMongoCommand.register(self, "mongodb-service-context", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke GDB command to print the Global Service Context."""
        gdb.execute("print *('mongo::(anonymous namespace)::globalServiceContext')")


# Register command
DumpGlobalServiceContext()


class GetMongoDecoration(gdb.Command):
    """
    Search for a decoration on an object by typename and print it.

    Example: if opCtx is a pointer to mongo::OperationContext,

    (gdb) mongodb-decoration *opCtx ReadConcernArgs

    would print out a decoration on opCtx whose type name contains the string "ReadConcernArgs".
    """

    def __init__(self):
        """Initialize GetMongoDecoration."""
        RegisterMongoCommand.register(self, "mongodb-decoration", gdb.COMMAND_DATA)

    def invoke(self, args, _from_tty):
        """Invoke GetMongoDecoration."""
        argarr = args.split(" ")
        if len(argarr) < 2:
            raise ValueError("Must provide both an object and type_name argument.")

        # The object that is decorated.
        expr = argarr[0]
        # The substring of the decoration type that is to be printed.
        type_name_substr = argarr[1]
        dec = get_decoration(gdb.parse_and_eval(expr), type_name_substr)
        if dec:
            (type_name, obj) = dec
            print(type_name, obj)
        else:
            print("No decoration found whose type name contains '" + type_name_substr + "'.")


# Register command
GetMongoDecoration()


class DumpMongoDSessionCatalog(gdb.Command):
    """Print out the mongod SessionCatalog, which maintains a table of all Sessions.

    Prints out interesting information from TransactionParticipants too, which are decorations on
    the Session. If no arguments are provided, dumps out all sessions. Can optionally provide a
    session id argument. In that case, will only print the session for the specified id, if it is
    found. e.g.

    (gdb) dump-sessions "32cb9e84-98ad-4322-acf0-e055cad3ef73"

    """

    def __init__(self):
        """Initialize DumpMongoDSessionCatalog."""
        RegisterMongoCommand.register(self, "mongod-dump-sessions", gdb.COMMAND_DATA)

    def invoke(self, args, _from_tty):
        """Invoke DumpMongoDSessionCatalog."""
        # See if a particular session id was specified.
        argarr = args.split(" ")
        lsid_to_find = None
        if argarr:
            lsid_to_find = argarr[0]

        # Get the SessionCatalog and the table of sessions.
        session_catalog = get_session_catalog()
        if session_catalog is None:
            print(
                "No SessionCatalog object was found on the ServiceContext. Not dumping any sessions."
            )
            return
        session_kv_pairs = get_session_kv_pairs()
        print("Dumping %d Session objects from the SessionCatalog" % len(session_kv_pairs))

        # Optionally search for a specified session, based on its id.
        if lsid_to_find:
            print("Only printing information for session " + lsid_to_find + ", if found.")
            lsids_to_print = [lsid_to_find]
        else:
            lsids_to_print = [str(s["first"]["_id"]) for s in session_kv_pairs]

        for session_kv in session_kv_pairs:
            # The Session objects are stored inside the SessionRuntimeInfo object.
            session_runtime_info = get_unique_ptr(session_kv["second"]).dereference()
            parent_session = session_runtime_info["parentSession"]
            child_sessions = absl_get_nodes(session_runtime_info["childSessions"])
            lsid = str(parent_session["_sessionId"]["_id"])

            # If we are only interested in a specific session, then we print out the entire Session
            # objects, to aid more detailed debugging.
            if lsid == lsid_to_find:
                self.dump_session_runtime_info(session_runtime_info)
                print(parent_session)
                for child_session_kv in child_sessions:
                    child_session = child_session_kv["second"]
                    print(child_session)
                # Terminate if this is the only session we care about.
                break

            # Only print info for the necessary sessions.
            if lsid not in lsids_to_print:
                continue

            # If we are printing multiple sessions, we only print the most interesting fields for
            # each Session object for the sake of efficiency.
            self.dump_session_runtime_info(session_runtime_info)
            self.dump_session(parent_session)
            for child_session_kv in child_sessions:
                child_session = child_session_kv["second"]
                self.dump_session(child_session)

    @staticmethod
    def dump_session_runtime_info(session_runtime_info):
        """Dump the session runtime info."""

        parent_session = session_runtime_info["parentSession"]
        # TODO: Add a custom pretty printer for LogicalSessionId.
        lsid = str(parent_session["_sessionId"]["_id"])[1:-1]
        print("SessionId =", lsid)
        fields_to_print = ["checkoutOpCtx", "killsRequested"]
        for field in fields_to_print:
            # Skip fields that aren't found on the object.
            if field in get_field_names(session_runtime_info):
                print(field, "=", session_runtime_info[field])
            else:
                print("Could not find field '%s' on the SessionRuntimeInfo object." % field)
        print("")

    @staticmethod
    def dump_session(session):
        """Dump the session."""

        print("Session (" + str(session.address) + "):")
        fields_to_print = ["_sessionId", "_numWaitingToCheckOut"]
        for field in fields_to_print:
            # Skip fields that aren't found on the object.
            if field in get_field_names(session):
                print(field, "=", session[field])
            else:
                print("Could not find field '%s' on the SessionRuntimeInfo object." % field)

        # Print the information from a TransactionParticipant if a session has one.
        txn_part_dec = get_decoration(session, "TransactionParticipant")
        if txn_part_dec:
            # Only print the most interesting fields for debugging transactions issues. The
            # TransactionParticipant class encapsulates internal state in two distinct
            # structures: a 'PrivateState' type (stored in private field '_p') and an
            # 'ObservableState' type (stored in private field '_o'). The information we care
            # about here is all contained inside the 'ObservableState', so we extract fields
            # from that object. If, in the future, we want to print fields from the
            # 'PrivateState' object, we can inspect the TransactionParticipant's '_p' field.
            txn_part = txn_part_dec[1]
            txn_part_observable_state = txn_part["_o"]
            fields_to_print = ["txnState", "activeTxnNumberAndRetryCounter"]
            print("TransactionParticipant (" + str(txn_part.address) + "):")
            for field in fields_to_print:
                # Skip fields that aren't found on the object.
                if field in get_field_names(txn_part_observable_state):
                    print(field, "=", txn_part_observable_state[field])
                else:
                    print("Could not find field '%s' on the TransactionParticipant" % field)

            # The 'txnResourceStash' field is a boost::optional so we unpack it manually if it
            # is non-empty. We are only interested in its Locker object for now. TODO: Load the
            # boost pretty printers so the object will be printed clearly by default, without
            # the need for special unpacking.
            val = get_boost_optional(txn_part_observable_state["txnResourceStash"])
            if val:
                locker_addr = get_unique_ptr(val["_locker"])
                locker_obj = locker_addr.dereference().cast(lookup_type("mongo::Locker"))
                print("txnResourceStash._locker", "@", locker_addr)
                print("txnResourceStash._locker._id", "=", locker_obj["_id"])
            else:
                print("txnResourceStash", "=", None)
        print("")


# Register command
DumpMongoDSessionCatalog()


class MongoDBDumpLocks(gdb.Command):
    """Dump locks in mongod process."""

    def __init__(self):
        """Initialize MongoDBDumpLocks."""
        RegisterMongoCommand.register(self, "mongodb-dump-locks", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke MongoDBDumpLocks."""
        print("Running Hang Analyzer Supplement - MongoDBDumpLocks")

        main_binary_name = get_process_name()
        if main_binary_name == "mongod" or main_binary_name == "mongod_with_debug":
            self.dump_mongod_locks()
        else:
            print("Not invoking mongod lock dump for: %s" % (main_binary_name))

    @staticmethod
    def dump_mongod_locks():
        """GDB in-process python supplement."""

        try:
            # Call into mongod, and dump the state of lock manager
            # Note that output will go to mongod's standard output, not the debugger output window
            gdb.execute("call mongo::dumpLockManager()", from_tty=False, to_string=False)
        except gdb.error as gdberr:
            print("Ignoring error '%s' in dump_mongod_locks" % str(gdberr))


# Register command
MongoDBDumpLocks()


class MongoDBDumpRecoveryUnits(gdb.Command):
    """Dump recovery unit info for each client and session in a mongod process."""

    def __init__(self):
        """Initialize MongoDBDumpRecoveryUnits."""
        RegisterMongoCommand.register(self, "mongodb-dump-recovery-units", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke MongoDBDumpRecoveryUnits."""
        print("Dumping recovery unit info for all clients and sessions")

        if not arg:
            arg = "mongo::WiredTigerRecoveryUnit"  # default to "mongo::WiredTigerRecoveryUnit"

        main_binary_name = get_process_name()
        if main_binary_name == "mongod":
            self.dump_recovery_units(arg)
        else:
            print("Not invoking mongod recovery unit dump for: %s" % (main_binary_name))

    @staticmethod
    def dump_recovery_units(recovery_unit_impl_type):
        """GDB in-process python supplement."""

        # Temporarily disable printing static members to make the output more readable
        out = gdb.execute("show print static-members", from_tty=False, to_string=True)
        enabled_at_start = False
        if out.startswith("Printing of C++ static members is on"):
            enabled_at_start = True
            gdb.execute("set print static-members off")

        # Dump active recovery unit info for each client in a mongod process
        service_context = get_global_service_context()
        client_set = absl_get_nodes(service_context["_clients"])

        for client_handle in client_set:
            client = client_handle.dereference().dereference()

            # Prepare structured output doc
            client_name = str(client["_desc"])[1:-1]
            operation_context_handle = client["_opCtx"]
            output_doc = {"client": client_name, "opCtx": hex(operation_context_handle)}

            recovery_unit_handle = None
            recovery_unit = None
            if operation_context_handle:
                operation_context = operation_context_handle.dereference()
                recovery_unit_handle = get_unique_ptr(operation_context["_recoveryUnit"])
                # By default, cast the recovery unit as "mongo::WiredTigerRecoveryUnit"
                recovery_unit = recovery_unit_handle.dereference().cast(
                    lookup_type(recovery_unit_impl_type)
                )

            output_doc["recoveryUnit"] = hex(recovery_unit_handle) if recovery_unit else "0x0"
            wt_session = get_wt_session(recovery_unit, recovery_unit_impl_type)
            if wt_session:
                output_doc["WT_SESSION"] = hex(wt_session)
            print(json.dumps(output_doc))
            if recovery_unit:
                print(recovery_unit)

        # Dump stashed recovery unit info for each session in a mongod process
        for session_kv in get_session_kv_pairs():
            # The Session objects are stored inside the SessionRuntimeInfo object.
            session_runtime_info = get_unique_ptr(session_kv["second"]).dereference()
            parent_session = session_runtime_info["parentSession"]
            child_sessions = absl_get_nodes(session_runtime_info["childSessions"])

            MongoDBDumpRecoveryUnits.dump_session(parent_session, recovery_unit_impl_type)
            for child_session_kv in child_sessions:
                child_session = child_session_kv["second"]
                MongoDBDumpRecoveryUnits.dump_session(child_session, recovery_unit_impl_type)

        if enabled_at_start:
            gdb.execute("set print static-members on")

    @staticmethod
    def dump_session(session, recovery_unit_impl_type):
        """Dump the session."""

        # Prepare structured output doc
        lsid = session["_sessionId"]
        output_doc = {"session": str(lsid["_id"])[1:-1], "txnResourceStash": "0x0"}
        txn_participant_dec = get_decoration(session, "TransactionParticipant")
        recovery_unit_handle = None
        recovery_unit = None

        if txn_participant_dec:
            txn_participant_observable_state = txn_participant_dec[1]["_o"]
            txn_resource_stash = get_boost_optional(
                txn_participant_observable_state["txnResourceStash"]
            )
            if txn_resource_stash:
                output_doc["txnResourceStash"] = str(txn_resource_stash.address)
                recovery_unit_handle = get_unique_ptr(txn_resource_stash["_recoveryUnit"])
                # By default, cast the recovery unit as "mongo::WiredTigerRecoveryUnit"
                recovery_unit = recovery_unit_handle.dereference().cast(
                    lookup_type(recovery_unit_impl_type)
                )

        output_doc["recoveryUnit"] = hex(recovery_unit_handle) if recovery_unit else "0x0"
        wt_session = get_wt_session(recovery_unit, recovery_unit_impl_type)
        if wt_session:
            output_doc["WT_SESSION"] = hex(wt_session)

        print(json.dumps(output_doc))
        print(lsid)
        if recovery_unit:
            print(recovery_unit)


# Register command
MongoDBDumpRecoveryUnits()


class MongoDBDumpStorageEngineInfo(gdb.Command):
    """Dump storage engine info in mongod process."""

    def __init__(self):
        """Initialize MongoDBDumpStorageEngineInfo."""
        RegisterMongoCommand.register(self, "mongodb-dump-storage-engine-info", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke MongoDBDumpStorageEngineInfo."""
        print("Running Hang Analyzer Supplement - MongoDBDumpStorageEngineInfo")

        main_binary_name = get_process_name()
        if main_binary_name == "mongod":
            self.dump_mongod_storage_engine_info()
        else:
            print("Not invoking mongod storage engine info dump for: %s" % (main_binary_name))

    @staticmethod
    def dump_mongod_storage_engine_info():
        """GDB in-process python supplement."""

        try:
            # Call into mongod, and dump the state of storage engine
            # Note that output will go to mongod's standard output, not the debugger output window
            gdb.execute(
                "call mongo::getGlobalServiceContext()->_storageEngine._ptr._value._M_b._M_p->dump()",
                from_tty=False,
                to_string=False,
            )
        except gdb.error as gdberr:
            print("Ignoring error '%s' in dump_mongod_storage_engine_info" % str(gdberr))


# Register command
MongoDBDumpStorageEngineInfo()


class BtIfActive(gdb.Command):
    """Print stack trace or a short message if the current thread is idle."""

    def __init__(self):
        """Initialize BtIfActive."""
        RegisterMongoCommand.register(self, "mongodb-bt-if-active", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke GDB to print stack trace."""
        try:
            idle_location = gdb.parse_and_eval("mongo::for_debuggers::idleThreadLocation")
        except gdb.error:
            idle_location = None  # If unsure, print a stack trace.

        if idle_location:
            print("Thread is idle at " + idle_location.string())
        else:
            gdb.execute("bt")


# Register command
BtIfActive()


class MongoDBUniqueStack(gdb.Command):
    """Print unique stack traces of all threads in current process."""

    _HEADER_FORMAT = "Thread {gdb_thread_num}: {name} (Thread {pthread} (LWP {lwpid})):"

    def __init__(self):
        """Initialize MongoDBUniqueStack."""
        RegisterMongoCommand.register(self, "mongodb-uniqstack", gdb.COMMAND_DATA)

    def invoke(self, arg, _from_tty):
        """Invoke GDB to dump stacks."""
        stacks = {}
        if not arg:
            arg = "bt"  # default to 'bt'

        current_thread = gdb.selected_thread()
        try:
            for thread in gdb.selected_inferior().threads():
                if not thread.is_valid():
                    continue
                thread.switch()
                self._process_thread_stack(arg, stacks, thread)
            self._dump_unique_stacks(stacks)
        finally:
            if current_thread and current_thread.is_valid():
                current_thread.switch()

    @staticmethod
    def _process_thread_stack(arg, stacks, thread):
        """Process the thread stack."""
        thread_info = {}  # thread dict to hold per thread data
        thread_info["pthread"] = get_thread_id()
        thread_info["gdb_thread_num"] = thread.num
        thread_info["lwpid"] = thread.ptid[1]
        thread_info["name"] = get_current_thread_name()

        if sys.platform.startswith("linux"):
            header_format = "Thread {gdb_thread_num}: {name} (Thread 0x{pthread:x} (LWP {lwpid}))"
        elif sys.platform.startswith("sunos"):
            (_, _, thread_tid) = thread.ptid
            if thread_tid != 0 and thread_info["lwpid"] != 0:
                header_format = "Thread {gdb_thread_num}: {name} (Thread {pthread} (LWP {lwpid}))"
            elif thread_info["lwpid"] != 0:
                header_format = "Thread {gdb_thread_num}: {name} (LWP {lwpid})"
            else:
                header_format = "Thread {gdb_thread_num}: {name} (Thread {pthread})"
        else:
            raise ValueError("Unsupported platform: {}".format(sys.platform))
        thread_info["header"] = header_format.format(**thread_info)

        addrs = []  # list of return addresses from frames
        frame = gdb.newest_frame()
        while frame:
            addrs.append(frame.pc())
            try:
                frame = frame.older()
            except gdb.error as err:
                print("{} {}".format(thread_info["header"], err))
                break
        addrs_tuple = tuple(addrs)  # tuples are hashable, lists aren't.

        unique = stacks.setdefault(addrs_tuple, {"threads": []})
        unique["threads"].append(thread_info)
        if "output" not in unique:
            try:
                unique["output"] = gdb.execute(arg, to_string=True).rstrip()
            except gdb.error as err:
                print("{} {}".format(thread_info["header"], err))

    @staticmethod
    def _dump_unique_stacks(stacks):
        """Dump the unique stacks."""

        def first_tid(stack):
            """Return the first tid."""
            return stack["threads"][0]["gdb_thread_num"]

        for stack in sorted(list(stacks.values()), key=first_tid, reverse=True):
            for i, thread in enumerate(stack["threads"]):
                prefix = "" if i == 0 else "Duplicate "
                print(prefix + thread["header"])
            print(stack["output"])
            print()  # leave extra blank line after each thread stack


# Register command
MongoDBUniqueStack()


class MongoDBJavaScriptStack(gdb.Command):
    """Print the JavaScript stack from a MongoDB process."""

    # Looking to test your changes to this? Really easy!
    # 1. install-jstestshell to build the mongo shell binary (mongo)
    # 2. launch it: ./path/to/bin/mongo --nodb
    # 3. in the shell, run: sleep(99999999999). (do not use --eval)
    # 4. ps ax | grep nodb to find the PID
    # 5. gdb -p <PID>.
    # 6. Run this command, mongodb-javascript-stack

    def __init__(self):
        """Initialize MongoDBJavaScriptStack."""
        RegisterMongoCommand.register(self, "mongodb-javascript-stack", gdb.COMMAND_STATUS)

    def invoke(self, arg, _from_tty):
        """Invoke GDB to dump JS stacks."""
        print("Running Print JavaScript Stack Supplement")

        main_binary_name = get_process_name()
        if main_binary_name.endswith("mongod") or main_binary_name.endswith("mongo"):
            self.javascript_stack()
        else:
            print("No JavaScript stack print done for: %s" % (main_binary_name))

    @staticmethod
    def atomic_get_ptr(atomic_scope: gdb.Value):
        """Fetch the underlying pointer from std::atomic."""

        # Awkwardly, the gdb.Value type does not support a check like
        # `'_M_b' in atomic_scope`, so exceptions for flow control it is. :|
        try:
            # reach into std::atomic and grab the pointer. This is for libc++
            return atomic_scope["_M_b"]["_M_p"]
        except gdb.error:
            # Worst case scenario: try and use .load(), but it's probably
            # inlined. parse_and_eval required because you can't call methods
            # in gdb on the Python API
            return gdb.parse_and_eval(
                f"((std::atomic<mongo::mozjs::MozJSImplScope*> *)({atomic_scope.address}))->load()"
            )

        return None

    # Returns the current JS scope above the currently selected frame, or throws a GDB exception if
    # it cannot be found.
    @staticmethod
    def get_js_scope():
        # GDB needs to be switched to a frame that will allow it to actually know about the
        # mongo::mozjs namespace. We can't know ahead of time which frame will guarantee
        # finding the namespace, so we check all of them and stop at the first one that works.
        # The bottom of the stack notably never works, so we start one frame above.
        frame = gdb.selected_frame().older()
        last_error = None
        while frame:
            frame.select()
            frame = frame.older()
            try:
                return gdb.parse_and_eval("mongo::mozjs::currentJSScope")
            except gdb.error as err:
                last_error = err
        raise last_error

    @staticmethod
    def javascript_stack():
        """GDB in-process python supplement."""

        for thread in gdb.selected_inferior().threads():
            try:
                if not thread.is_valid():
                    print("Ignoring invalid thread %d in javascript_stack" % thread.num)
                    continue
                thread.switch()
            except gdb.error as err:
                print("Ignoring GDB error '%s' in javascript_stack" % str(err))
                continue

            try:
                # The following block is roughly equivalent to this:
                # namespace mongo::mozjs {
                #   std::atomic<MozJSImplScope*> currentJSScope = ...;
                # }
                # if (!scope || scope->_inOp == 0) { continue; }
                # print(scope->buildStackString()->c_str());
                atomic_scope = MongoDBJavaScriptStack.get_js_scope()
                ptr = MongoDBJavaScriptStack.atomic_get_ptr(atomic_scope)
                if not ptr:
                    continue

                scope = ptr.dereference()
                if scope["_inOp"] == 0:
                    continue

                gdb.execute("thread", from_tty=False, to_string=False)
                # gdb continues to not support calling methods through Python,
                # so work around it by casting the raw ptr back to its type,
                # and calling the method through execute darkness
                gdb.execute(
                    f'printf "%s\\n", ((mongo::mozjs::MozJSImplScope*)({ptr}))->buildStackString().c_str()',
                    from_tty=False,
                    to_string=False,
                )

            except gdb.error as err:
                print("Ignoring GDB error '%s' in javascript_stack" % str(err))
                continue


# Register command
MongoDBJavaScriptStack()


class MongoDBPPrintBsonAtPointer(gdb.Command):
    """Interprets a pointer into raw memory as the start of a bson object. Pretty print the results."""

    def __init__(self):
        """Init."""
        RegisterMongoCommand.register(self, "mongodb-pprint-bson", gdb.COMMAND_STATUS)

    def invoke(self, args, _from_tty):
        """Invoke."""
        args = args.split(" ")
        if len(args) == 0 or (len(args) == 1 and len(args[0]) == 0):
            print("Usage: mongodb-pprint-bson <ptr> <optional length>")
            return

        ptr = eval(args[0])
        size = 20 * 1024
        if len(args) >= 2:
            size = int(args[1])
        print("Pretty printing bson object at %s (%d bytes)" % (ptr, size))

        memory = gdb.selected_inferior().read_memory(ptr, size).tobytes()
        bsonobj = next(bson.decode_iter(memory))

        from pprint import pprint

        pprint(bsonobj)


MongoDBPPrintBsonAtPointer()


class MongoDBOpMsg(gdb.Command):
    """Parse and display OpMsg/OpMsgRequest from a Message variable (dbMsg or dbQuery).

    Example: mongodb-opmsg msg
    """

    def __init__(self):
        """Init."""
        RegisterMongoCommand.register(self, "mongodb-opmsg", gdb.COMMAND_DATA)

    def invoke(self, args, _from_tty):
        """Invoke."""
        args = args.strip()
        if not args:
            print("Usage: mongodb-opmsg <message-variable>")
            return
        try:
            val = gdb.parse_and_eval(args)
            pp = gdb.default_visualizer(val)
            if pp and hasattr(pp, "get_op_msg_display"):
                result = pp.get_op_msg_display()
                if result:
                    print(result)
                else:
                    print("Could not parse OpMsg (not a request message or parse failed)")
            else:
                print("Not a mongo::Message or pretty printer unavailable")
        except gdb.error as e:
            print("Error: %s" % e)


MongoDBOpMsg()


class MongoDBOpMsgBson(gdb.Command):
    """Print the OpMsg body from a Message as a BSON object using the BSON pretty-printer.

    Example: mongodb-opmsg-bson msg
    """

    def __init__(self):
        """Init."""
        RegisterMongoCommand.register(self, "mongodb-opmsg-bson", gdb.COMMAND_DATA)

    def invoke(self, args, _from_tty):
        """Invoke."""
        args = args.strip()
        if not args:
            print("Usage: mongodb-opmsg-bson <message-variable>")
            return
        try:
            val = gdb.parse_and_eval(args)
            pp = gdb.default_visualizer(val)
            if pp and hasattr(pp, "print_op_msg_body_as_bson"):
                pp.print_op_msg_body_as_bson()
            else:
                print("Not a mongo::Message or pretty printer unavailable")
        except gdb.error as e:
            print("Error: %s" % e)


MongoDBOpMsgBson()


class MongoDBHelp(gdb.Command):
    """Dump list of mongodb commands."""

    def __init__(self):
        """Initialize MongoDBHelp."""
        gdb.Command.__init__(self, "mongodb-help", gdb.COMMAND_SUPPORT)

    def invoke(self, arg, _from_tty):
        """Register the mongo print commands."""
        RegisterMongoCommand.print_commands()


# Register command
MongoDBHelp()

print("MongoDB GDB commands loaded, run 'mongodb-help' for list of commands")