path: root/js/src/gdb/mozilla/unwind.py

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this file,
# You can obtain one at http://mozilla.org/MPL/2.0/.

# mozilla/unwind.py --- unwinder and frame filter for SpiderMonkey

import gdb
import gdb.types
from gdb.FrameDecorator import FrameDecorator
import platform

# For ease of use in Python 2, we use "long" instead of "int"
# everywhere.
try:
    long
except NameError:
    long = int

# The Python 3 |map| built-in works lazily, but in Python 2 we need
# itertools.imap to get this.
try:
    from itertools import imap
except ImportError:
    imap = map

_have_unwinder = True
try:
    from gdb.unwinder import Unwinder
except ImportError:
    _have_unwinder = False
    # We need something here; it doesn't matter what as no unwinder
    # will ever be instantiated.
    Unwinder = object


def debug(something):
    # print("@@ " + something)
    pass


# Maps frametype enum base names to corresponding class.
SizeOfFramePrefix = {
    "FrameType::IonJS": "ExitFrameLayout",
    "FrameType::BaselineJS": "JitFrameLayout",
    "FrameType::BaselineStub": "BaselineStubFrameLayout",
    "FrameType::IonStub": "JitStubFrameLayout",
    "FrameType::CppToJSJit": "JitFrameLayout",
    "FrameType::WasmToJSJit": "JitFrameLayout",
    "FrameType::JSJitToWasm": "JitFrameLayout",
    "FrameType::Rectifier": "RectifierFrameLayout",
    "FrameType::IonAccessorIC": "IonAccessorICFrameLayout",
    "FrameType::IonICCall": "IonICCallFrameLayout",
    "FrameType::Exit": "ExitFrameLayout",
    "FrameType::Bailout": "JitFrameLayout",
}


# We cannot have semi-colon as identifier names, so use a colon instead,
# and forward the name resolution to the type cache class.
class UnwinderTypeCacheFrameType(object):
    def __init__(self, tc):
        self.tc = tc

    def __getattr__(self, name):
        return self.tc.__getattr__("FrameType::" + name)


class UnwinderTypeCache(object):
    # All types and symbols that we need are attached to an object that we
    # can dispose of as needed.

    def __init__(self):
        self.d = None
        self.frame_enum_names = {}
        self.frame_class_types = {}

    # We take this bizarre approach to defer trying to look up any
    # symbols until absolutely needed.  Without this, the loading
    # approach taken by the gdb-tests would cause spurious exceptions.
    def __getattr__(self, name):
        if self.d is None:
            self.initialize()
        if name == "frame_type":
            return UnwinderTypeCacheFrameType(self)
        return self.d[name]

    def value(self, name):
        return long(gdb.lookup_symbol(name)[0].value())

    def jit_value(self, name):
        return self.value("js::jit::" + name)

    def initialize(self):
        self.d = {}
        self.d["FRAMETYPE_MASK"] = (1 << self.jit_value("FRAMETYPE_BITS")) - 1
        self.d["FRAMESIZE_SHIFT"] = self.jit_value("FRAMESIZE_SHIFT")
        self.d["FRAME_HEADER_SIZE_SHIFT"] = self.jit_value("FRAME_HEADER_SIZE_SHIFT")
        self.d["FRAME_HEADER_SIZE_MASK"] = self.jit_value("FRAME_HEADER_SIZE_MASK")

        self.compute_frame_info()
        commonFrameLayout = gdb.lookup_type("js::jit::CommonFrameLayout")
        self.d["typeCommonFrameLayout"] = commonFrameLayout
        self.d["typeCommonFrameLayoutPointer"] = commonFrameLayout.pointer()
        self.d["per_tls_context"] = gdb.lookup_global_symbol("js::TlsContext")

        self.d["void_starstar"] = gdb.lookup_type("void").pointer().pointer()

        jitframe = gdb.lookup_type("js::jit::JitFrameLayout")
        self.d["jitFrameLayoutPointer"] = jitframe.pointer()

        self.d["CalleeToken_Function"] = self.jit_value("CalleeToken_Function")
        self.d["CalleeToken_FunctionConstructing"] = self.jit_value(
            "CalleeToken_FunctionConstructing"
        )
        self.d["CalleeToken_Script"] = self.jit_value("CalleeToken_Script")
        self.d["JSFunction"] = gdb.lookup_type("JSFunction").pointer()
        self.d["JSScript"] = gdb.lookup_type("JSScript").pointer()
        self.d["Value"] = gdb.lookup_type("JS::Value")

        self.d["SOURCE_SLOT"] = self.value("js::ScriptSourceObject::SOURCE_SLOT")
        self.d["NativeObject"] = gdb.lookup_type("js::NativeObject").pointer()
        self.d["HeapSlot"] = gdb.lookup_type("js::HeapSlot").pointer()
        self.d["ScriptSource"] = gdb.lookup_type("js::ScriptSource").pointer()

        # ProcessExecutableMemory, used to identify if a pc is in the section
        # pre-allocated by the JIT.
        self.d["MaxCodeBytesPerProcess"] = self.jit_value("MaxCodeBytesPerProcess")
        self.d["execMemory"] = gdb.lookup_symbol("::execMemory")[0].value()

    # Compute maps related to jit frames.
    def compute_frame_info(self):
        t = gdb.lookup_type("enum js::jit::FrameType")
        for field in t.fields():
            # Strip off "js::jit::", remains: "FrameType::*".
            name = field.name[9:]
            enumval = long(field.enumval)
            self.d[name] = enumval
            self.frame_enum_names[enumval] = name
            class_type = gdb.lookup_type("js::jit::" + SizeOfFramePrefix[name])
            self.frame_class_types[enumval] = class_type.pointer()


class FrameSymbol(object):
    "A symbol/value pair as expected from gdb frame decorators."

    def __init__(self, sym, val):
        self.sym = sym
        self.val = val

    def symbol(self):
        return self.sym

    def value(self):
        return self.val


class JitFrameDecorator(FrameDecorator):
    """This represents a single JIT frame for the purposes of display.
    That is, the frame filter creates instances of this when it sees a
    JIT frame in the stack."""

    def __init__(self, base, info, cache):
        super(JitFrameDecorator, self).__init__(base)
        self.info = info
        self.cache = cache

    def _decode_jitframe(self, this_frame):
        calleetoken = long(this_frame["calleeToken_"])
        tag = calleetoken & 3
        calleetoken = calleetoken ^ tag
        function = None
        script = None
        if (
            tag == self.cache.CalleeToken_Function
            or tag == self.cache.CalleeToken_FunctionConstructing
        ):
            fptr = gdb.Value(calleetoken).cast(self.cache.JSFunction)
            try:
                atom = fptr["atom_"]
                if atom:
                    function = str(atom)
            except gdb.MemoryError:
                function = "(could not read function name)"
            script = fptr["u"]["scripted"]["s"]["script_"]
        elif tag == self.cache.CalleeToken_Script:
            script = gdb.Value(calleetoken).cast(self.cache.JSScript)
        return {"function": function, "script": script}

    def function(self):
        if self.info["name"] is None:
            return FrameDecorator.function(self)
        name = self.info["name"]
        result = "<<" + name
        # If we have a frame, we can extract the callee information
        # from it for display here.
        this_frame = self.info["this_frame"]
        if this_frame is not None:
            if gdb.types.has_field(this_frame.type.target(), "calleeToken_"):
                function = self._decode_jitframe(this_frame)["function"]
                if function is not None:
                    result = result + " " + function
        return result + ">>"

    def filename(self):
        this_frame = self.info["this_frame"]
        if this_frame is not None:
            if gdb.types.has_field(this_frame.type.target(), "calleeToken_"):
                script = self._decode_jitframe(this_frame)["script"]
                if script is not None:
                    obj = script["sourceObject_"]["value"]
                    # Verify that this is a ScriptSource object.
                    # FIXME should also deal with wrappers here.
                    nativeobj = obj.cast(self.cache.NativeObject)
                    # See bug 987069 and despair.  At least this
                    # approach won't give exceptions.
                    class_name = nativeobj["group_"]["value"]["clasp_"]["name"].string(
                        "ISO-8859-1"
                    )
                    if class_name != "ScriptSource":
                        return FrameDecorator.filename(self)
                    scriptsourceobj = (nativeobj + 1).cast(self.cache.HeapSlot)[
                        self.cache.SOURCE_SLOT
                    ]
                    scriptsource = scriptsourceobj["value"]["asBits_"] << 1
                    scriptsource = scriptsource.cast(self.cache.ScriptSource)
                    return scriptsource["filename_"]["mTuple"]["mFirstA"].string()
        return FrameDecorator.filename(self)

    def frame_args(self):
        this_frame = self.info["this_frame"]
        if this_frame is None:
            return FrameDecorator.frame_args(self)
        if not gdb.types.has_field(this_frame.type.target(), "numActualArgs_"):
            return FrameDecorator.frame_args(self)
        # See if this is a function call.
        if self._decode_jitframe(this_frame)["function"] is None:
            return FrameDecorator.frame_args(self)
        # Construct and return an iterable of all the arguments.
        result = []
        num_args = long(this_frame["numActualArgs_"])
        # Sometimes we see very large values here, so truncate it to
        # bypass the damage.
        if num_args > 10:
            num_args = 10
        args_ptr = (this_frame + 1).cast(self.cache.Value.pointer())
        for i in range(num_args + 1):
            # Synthesize names, since there doesn't seem to be
            # anything better to do.
            if i == 0:
                name = "this"
            else:
                name = "arg%d" % i
            result.append(FrameSymbol(name, args_ptr[i]))
        return result


class SpiderMonkeyFrameFilter(object):
    "A frame filter for SpiderMonkey."

    # |state_holder| is either None, or an instance of
    # SpiderMonkeyUnwinder.  If the latter, then this class will
    # reference the |unwinder_state| attribute to find the current
    # unwinder state.
    def __init__(self, cache, state_holder):
        self.name = "SpiderMonkey"
        self.enabled = True
        self.priority = 100
        self.state_holder = state_holder
        self.cache = cache

    def maybe_wrap_frame(self, frame):
        if self.state_holder is None or self.state_holder.unwinder_state is None:
            return frame
        base = frame.inferior_frame()
        info = self.state_holder.unwinder_state.get_frame(base)
        if info is None:
            return frame
        return JitFrameDecorator(frame, info, self.cache)

    def filter(self, frame_iter):
        return imap(self.maybe_wrap_frame, frame_iter)


class SpiderMonkeyFrameId(object):
    "A frame id class, as specified by the gdb unwinder API."

    def __init__(self, sp, pc):
        self.sp = sp
        self.pc = pc


class UnwinderState(object):
    """This holds all the state needed during a given unwind.  Each time a
    new unwind is done, a new instance of this class is created.  It
    keeps track of all the state needed to unwind JIT frames.  Note that
    this class is not directly instantiated.

    This is a base class, and must be specialized for each target
    architecture, both because we need to use arch-specific register
    names, and because entry frame unwinding is arch-specific.
    See https://sourceware.org/bugzilla/show_bug.cgi?id=19286 for info
    about the register name issue.

    Each subclass must define SP_REGISTER, PC_REGISTER, and
    SENTINEL_REGISTER (see x64UnwinderState for info); and implement
    unwind_entry_frame_registers."""

    def __init__(self, typecache):
        self.next_sp = None
        self.next_type = None
        self.activation = None
        # An unwinder instance is specific to a thread.  Record the
        # selected thread for later verification.
        self.thread = gdb.selected_thread()
        self.frame_map = {}
        self.typecache = typecache

    # If the given gdb.Frame was created by this unwinder, return the
    # corresponding informational dictionary for the frame.
    # Otherwise, return None.  This is used by the frame filter to
    # display extra information about the frame.
    def get_frame(self, frame):
        sp = long(frame.read_register(self.SP_REGISTER))
        if sp in self.frame_map:
            return self.frame_map[sp]
        return None

    # Add information about a frame to the frame map.  This map is
    # queried by |self.get_frame|.  |sp| is the frame's stack pointer,
    # and |name| the frame's type as a string, e.g. "FrameType::Exit".
    def add_frame(self, sp, name=None, this_frame=None):
        self.frame_map[long(sp)] = {"name": name, "this_frame": this_frame}

    # See whether |pc| is claimed by the Jit.
    def is_jit_address(self, pc):
        execMem = self.typecache.execMemory
        base = long(execMem["base_"])
        length = self.typecache.MaxCodeBytesPerProcess

        # If the base pointer is null, then no memory got allocated yet.
        if long(base) == 0:
            return False

        # If allocated, then we allocated MaxCodeBytesPerProcess.
        return base <= pc and pc < base + length

    # Check whether |self| is valid for the selected thread.
    def check(self):
        return gdb.selected_thread() is self.thread

    # Essentially js::TlsContext.get().
    def get_tls_context(self):
        return self.typecache.per_tls_context.value()["mValue"]

    # |common| is a pointer to a CommonFrameLayout object.  Return a
    # tuple (local_size, header_size, frame_type), where |size| is the
    # integer size of the previous frame's locals; |header_size| is
    # the size of this frame's header; and |frame_type| is an integer
    # representing the previous frame's type.
    def unpack_descriptor(self, common):
        value = long(common["descriptor_"])
        local_size = value >> self.typecache.FRAMESIZE_SHIFT
        header_size = (
            value >> self.typecache.FRAME_HEADER_SIZE_SHIFT
        ) & self.typecache.FRAME_HEADER_SIZE_MASK
        header_size = header_size * self.typecache.void_starstar.sizeof
        frame_type = long(value & self.typecache.FRAMETYPE_MASK)
        if frame_type == self.typecache.frame_type.CppToJSJit:
            # Trampoline-x64.cpp pushes a JitFrameLayout object, but
            # the stack pointer is actually adjusted as if a
            # CommonFrameLayout object was pushed.
            header_size = self.typecache.typeCommonFrameLayout.sizeof
        return (local_size, header_size, frame_type)

    # Create a new frame for gdb.  This makes a new unwind info object
    # and fills it in, then returns it.  It also registers any
    # pertinent information with the frame filter for later display.
    #
    # |pc| is the PC from the pending frame
    # |sp| is the stack pointer to use
    # |frame| points to the CommonFrameLayout object
    # |frame_type| is a integer, one of the |enum FrameType| values,
    # describing the current frame.
    # |pending_frame| is the pending frame (see the gdb unwinder
    # documentation).
    def create_frame(self, pc, sp, frame, frame_type, pending_frame):
        # Make a frame_id that claims that |frame| is sort of like a
        # frame pointer for this frame.
        frame_id = SpiderMonkeyFrameId(frame, pc)

        # Read the frame layout object to find the next such object.
        # This lets us unwind the necessary registers for the next
        # frame, and also update our internal state to match.
        common = frame.cast(self.typecache.typeCommonFrameLayoutPointer)
        next_pc = common["returnAddress_"]
        (local_size, header_size, next_type) = self.unpack_descriptor(common)
        next_sp = frame + header_size + local_size

        # Compute the type of the next oldest frame's descriptor.
        this_class_type = self.typecache.frame_class_types[frame_type]
        this_frame = frame.cast(this_class_type)

        # Register this frame so the frame filter can find it.  This
        # is registered using SP because we don't have any other good
        # approach -- you can't get the frame id from a gdb.Frame.
        # https://sourceware.org/bugzilla/show_bug.cgi?id=19800
        frame_name = self.typecache.frame_enum_names[frame_type]
        self.add_frame(sp, name=frame_name, this_frame=this_frame)

        # Update internal state for the next unwind.
        self.next_sp = next_sp
        self.next_type = next_type

        unwind_info = pending_frame.create_unwind_info(frame_id)
        unwind_info.add_saved_register(self.PC_REGISTER, next_pc)
        unwind_info.add_saved_register(self.SP_REGISTER, next_sp)
        # FIXME it would be great to unwind any other registers here.
        return unwind_info

    # Unwind an "ordinary" JIT frame.  This is used for JIT frames
    # other than enter and exit frames.  Returns the newly-created
    # unwind info for gdb.
    def unwind_ordinary(self, pc, pending_frame):
        return self.create_frame(
            pc, self.next_sp, self.next_sp, self.next_type, pending_frame
        )

    # Unwind an exit frame.  Returns None if this cannot be done;
    # otherwise returns the newly-created unwind info for gdb.
    def unwind_exit_frame(self, pc, pending_frame):
        if self.activation == 0:
            # Reached the end of the list.
            return None
        elif self.activation is None:
            cx = self.get_tls_context()
            self.activation = cx["jitActivation"]["value"]
        else:
            self.activation = self.activation["prevJitActivation_"]

        packedExitFP = self.activation["packedExitFP_"]
        if packedExitFP == 0:
            return None

        exit_sp = pending_frame.read_register(self.SP_REGISTER)
        frame_type = self.typecache.frame_type.Exit
        return self.create_frame(pc, exit_sp, packedExitFP, frame_type, pending_frame)

    # A wrapper for unwind_entry_frame_registers that handles
    # architecture-independent boilerplate.
    def unwind_entry_frame(self, pc, pending_frame):
        sp = self.next_sp
        # Notify the frame filter.
        self.add_frame(sp, name="FrameType::CppToJSJit")
        # Make an unwind_info for the per-architecture code to fill in.
        frame_id = SpiderMonkeyFrameId(sp, pc)
        unwind_info = pending_frame.create_unwind_info(frame_id)
        self.unwind_entry_frame_registers(sp, unwind_info)
        self.next_sp = None
        self.next_type = None
        return unwind_info

    # The main entry point that is called to try to unwind a JIT frame
    # of any type.  Returns None if this cannot be done; otherwise
    # returns the newly-created unwind info for gdb.
    def unwind(self, pending_frame):
        pc = pending_frame.read_register(self.PC_REGISTER)

        # If the jit does not claim this address, bail.  GDB defers to our
        # unwinder by default, but we don't really want that kind of power.
        if not self.is_jit_address(long(pc)):
            return None

        if self.next_sp is not None:
            if self.next_type == self.typecache.frame_type.CppToJSJit:
                return self.unwind_entry_frame(pc, pending_frame)
            return self.unwind_ordinary(pc, pending_frame)
        # Maybe we've found an exit frame.  FIXME I currently don't
        # know how to identify these precisely, so we'll just hope for
        # the time being.
        return self.unwind_exit_frame(pc, pending_frame)


class x64UnwinderState(UnwinderState):
    "The UnwinderState subclass for x86-64."

    SP_REGISTER = "rsp"
    PC_REGISTER = "rip"

    # A register unique to this architecture, that is also likely to
    # have been saved in any frame.  The best thing to use here is
    # some arch-specific name for PC or SP.
    SENTINEL_REGISTER = "rip"

    # Must be in sync with Trampoline-x64.cpp:generateEnterJIT.  Note
    # that rip isn't pushed there explicitly, but rather by the
    # previous function's call.
    PUSHED_REGS = ["r15", "r14", "r13", "r12", "rbx", "rbp", "rip"]

    # Fill in the unwound registers for an entry frame.
    def unwind_entry_frame_registers(self, sp, unwind_info):
        sp = sp.cast(self.typecache.void_starstar)
        # Skip the "result" push.
        sp = sp + 1
        for reg in self.PUSHED_REGS:
            data = sp.dereference()
            sp = sp + 1
            unwind_info.add_saved_register(reg, data)
            if reg == "rbp":
                unwind_info.add_saved_register(self.SP_REGISTER, sp)


class SpiderMonkeyUnwinder(Unwinder):
    """The unwinder object.  This provides the "user interface" to the JIT
    unwinder, and also handles constructing or destroying UnwinderState
    objects as needed."""

    # A list of all the possible unwinders.  See |self.make_unwinder|.
    UNWINDERS = [x64UnwinderState]

    def __init__(self, typecache):
        super(SpiderMonkeyUnwinder, self).__init__("SpiderMonkey")
        self.typecache = typecache
        self.unwinder_state = None

        # Disabled by default until we figure out issues in gdb.
        self.enabled = False
        gdb.write(
            "SpiderMonkey unwinder is disabled by default, to enable it type:\n"
            + "\tenable unwinder .* SpiderMonkey\n"
        )
        # Some versions of gdb did not flush the internal frame cache
        # when enabling or disabling an unwinder.  This was fixed in
        # the same release of gdb that added the breakpoint_created
        # event.
        if not hasattr(gdb.events, "breakpoint_created"):
            gdb.write("\tflushregs\n")

        # We need to invalidate the unwinder state whenever the
        # inferior starts executing.  This avoids having a stale
        # cache.
        gdb.events.cont.connect(self.invalidate_unwinder_state)
        assert self.test_sentinels()

    def test_sentinels(self):
        # Self-check.
        regs = {}
        for unwinder in self.UNWINDERS:
            if unwinder.SENTINEL_REGISTER in regs:
                return False
            regs[unwinder.SENTINEL_REGISTER] = 1
        return True

    def make_unwinder(self, pending_frame):
        # gdb doesn't provide a good way to find the architecture.
        # See https://sourceware.org/bugzilla/show_bug.cgi?id=19399
        # So, we look at each known architecture and see if the
        # corresponding "unique register" is known.
        for unwinder in self.UNWINDERS:
            try:
                pending_frame.read_register(unwinder.SENTINEL_REGISTER)
            except Exception:
                # Failed to read the register, so let's keep going.
                # This is more fragile than it might seem, because it
                # fails if the sentinel register wasn't saved in the
                # previous frame.
                continue
            return unwinder(self.typecache)
        return None

    def __call__(self, pending_frame):
        if self.unwinder_state is None or not self.unwinder_state.check():
            self.unwinder_state = self.make_unwinder(pending_frame)
        if not self.unwinder_state:
            return None
        return self.unwinder_state.unwind(pending_frame)

    def invalidate_unwinder_state(self, *args, **kwargs):
        self.unwinder_state = None


def register_unwinder(objfile):
    """Register the unwinder and frame filter with |objfile|.  If |objfile|
    is None, register them globally."""

    type_cache = UnwinderTypeCache()
    unwinder = None
    # This currently only works on Linux, due to parse_proc_maps.
    if _have_unwinder and platform.system() == "Linux":
        unwinder = SpiderMonkeyUnwinder(type_cache)
        gdb.unwinder.register_unwinder(objfile, unwinder, replace=True)
    # We unconditionally register the frame filter, because at some
    # point we'll add interpreter frame filtering.
    filt = SpiderMonkeyFrameFilter(type_cache, unwinder)
    if objfile is None:
        objfile = gdb
    objfile.frame_filters[filt.name] = filt