# 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