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# 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
# mozilla/ --- unwinder and frame filter for SpiderMonkey
import platform
import gdb
import gdb.types
from gdb.FrameDecorator import FrameDecorator
from mozilla.JSObject import get_function_name, get_function_script
from mozilla.prettyprinters import TypeCache
# For ease of use in Python 2, we use "long" instead of "int"
# everywhere.
except NameError:
long = int
# The Python 3 |map| built-in works lazily, but in Python 2 we need
# itertools.imap to get this.
from itertools import imap
except ImportError:
imap = map
_have_unwinder = True
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)
# Maps frametype enum base names to corresponding class.
SizeOfFramePrefix = {
"FrameType::IonJS": "ExitFrameLayout",
"FrameType::BaselineJS": "JitFrameLayout",
"FrameType::BaselineStub": "BaselineStubFrameLayout",
"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): = tc
def __getattr__(self, name):
return"FrameType::" + name)
class UnwinderTypeCache(TypeCache):
# 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 = {}
super(UnwinderTypeCache, self).__init__(None)
# 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:
if name == "frame_type":
return UnwinderTypeCacheFrameType(self)
if name not in self.d:
return None
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")
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(
self.d["CalleeToken_Script"] = self.jit_value("CalleeToken_Script")
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 =[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) = 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
value = gdb.Value(calleetoken)
function = get_function_name(value, self.cache)
script = get_function_script(value, self.cache)
elif tag == self.cache.CalleeToken_Script:
script = gdb.Value(calleetoken).cast(self.cache.JSScript)
return {"function": function, "script": script}
def function(self):
if["name"] is None:
return FrameDecorator.function(self)
name =["name"]
result = "<<" + name
# If we have a frame, we can extract the callee information
# from it for display here.
this_frame =["this_frame"]
if this_frame is not None:
if gdb.types.has_field(, "calleeToken_"):
function = self._decode_jitframe(this_frame)["function"]
if function is not None:
result = result + " " + function
return result + ">>"
def filename(self):
this_frame =["this_frame"]
if this_frame is not None:
if gdb.types.has_field(, "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(
if class_name != "ScriptSource":
return FrameDecorator.filename(self)
scriptsourceobj = (nativeobj + 1).cast(self.cache.HeapSlot)[
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 =["this_frame"]
if this_frame is None:
return FrameDecorator.frame_args(self)
if not gdb.types.has_field(, "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"
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): = "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.
about the register name issue.
Each subclass must define SP_REGISTER, PC_REGISTER, and
SENTINEL_REGISTER (see x64UnwinderState for info); and implement
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.
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"]
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."
# 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.
# 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
"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(, "breakpoint_created"):
# We need to invalidate the unwinder state whenever the
# inferior starts executing. This avoids having a stale
# cache.
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.
# So, we look at each known architecture and see if the
# corresponding "unique register" is known.
for unwinder in self.UNWINDERS:
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.
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