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@leepa leepa/runtime-gdb.py
Created Mar 30, 2015

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Supports pointers to strings as well as normal strings in Go
# Copyright 2010 The Go Authors. All rights reserved.
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file.
"""GDB Pretty printers and convenience functions for Go's runtime structures.
This script is loaded by GDB when it finds a .debug_gdb_scripts
section in the compiled binary. The [68]l linkers emit this with a
path to this file based on the path to the runtime package.
"""
# Known issues:
# - pretty printing only works for the 'native' strings. E.g. 'type
# foo string' will make foo a plain struct in the eyes of gdb,
# circumventing the pretty print triggering.
from __future__ import print_function
import re
import sys
print("Loading Go Runtime support.", file=sys.stderr)
#http://python3porting.com/differences.html
if sys.version > '3':
xrange = range
# allow to manually reload while developing
goobjfile = gdb.current_objfile() or gdb.objfiles()[0]
goobjfile.pretty_printers = []
#
# Value wrappers
#
class SliceValue:
"Wrapper for slice values."
def __init__(self, val):
self.val = val
@property
def len(self):
return int(self.val['len'])
@property
def cap(self):
return int(self.val['cap'])
def __getitem__(self, i):
if i < 0 or i >= self.len:
raise IndexError(i)
ptr = self.val["array"]
return (ptr + i).dereference()
#
# Pretty Printers
#
class StringTypePrinter:
"Pretty print Go strings."
pattern = re.compile(r'^struct string( \*)?$')
def __init__(self, val):
self.val = val
def display_hint(self):
return 'string'
def to_string(self):
l = int(self.val['len'])
return self.val['str'].string("utf-8", "ignore", l)
class SliceTypePrinter:
"Pretty print slices."
pattern = re.compile(r'^struct \[\]')
def __init__(self, val):
self.val = val
def display_hint(self):
return 'array'
def to_string(self):
return str(self.val.type)[6:] # skip 'struct '
def children(self):
sval = SliceValue(self.val)
if sval.len > sval.cap:
return
for idx, item in enumerate(sval):
yield ('[{0}]'.format(idx), item)
class MapTypePrinter:
"""Pretty print map[K]V types.
Map-typed go variables are really pointers. dereference them in gdb
to inspect their contents with this pretty printer.
"""
pattern = re.compile(r'^map\[.*\].*$')
def __init__(self, val):
self.val = val
def display_hint(self):
return 'map'
def to_string(self):
return str(self.val.type)
def children(self):
B = self.val['B']
buckets = self.val['buckets']
oldbuckets = self.val['oldbuckets']
flags = self.val['flags']
inttype = self.val['hash0'].type
cnt = 0
for bucket in xrange(2 ** int(B)):
bp = buckets + bucket
if oldbuckets:
oldbucket = bucket & (2 ** (B - 1) - 1)
oldbp = oldbuckets + oldbucket
oldb = oldbp.dereference()
if (oldb['overflow'].cast(inttype) & 1) == 0: # old bucket not evacuated yet
if bucket >= 2 ** (B - 1):
continue # already did old bucket
bp = oldbp
while bp:
b = bp.dereference()
for i in xrange(8):
if b['tophash'][i] != 0:
k = b['keys'][i]
v = b['values'][i]
if flags & 1:
k = k.dereference()
if flags & 2:
v = v.dereference()
yield str(cnt), k
yield str(cnt + 1), v
cnt += 2
bp = b['overflow']
class ChanTypePrinter:
"""Pretty print chan[T] types.
Chan-typed go variables are really pointers. dereference them in gdb
to inspect their contents with this pretty printer.
"""
pattern = re.compile(r'^struct hchan<.*>$')
def __init__(self, val):
self.val = val
def display_hint(self):
return 'array'
def to_string(self):
return str(self.val.type)
def children(self):
# see chan.c chanbuf(). et is the type stolen from hchan<T>::recvq->first->elem
et = [x.type for x in self.val['recvq']['first'].type.target().fields() if x.name == 'elem'][0]
ptr = (self.val.address + 1).cast(et.pointer())
for i in range(self.val["qcount"]):
j = (self.val["recvx"] + i) % self.val["dataqsiz"]
yield ('[{0}]'.format(i), (ptr + j).dereference())
#
# Register all the *Printer classes above.
#
def makematcher(klass):
def matcher(val):
try:
if klass.pattern.match(str(val.type)):
return klass(val)
except Exception:
pass
return matcher
goobjfile.pretty_printers.extend([makematcher(var) for var in vars().values() if hasattr(var, 'pattern')])
#
# For reference, this is what we're trying to do:
# eface: p *(*(struct 'runtime.rtype'*)'main.e'->type_->data)->string
# iface: p *(*(struct 'runtime.rtype'*)'main.s'->tab->Type->data)->string
#
# interface types can't be recognized by their name, instead we check
# if they have the expected fields. Unfortunately the mapping of
# fields to python attributes in gdb.py isn't complete: you can't test
# for presence other than by trapping.
def is_iface(val):
try:
return str(val['tab'].type) == "struct runtime.itab *" and str(val['data'].type) == "void *"
except gdb.error:
pass
def is_eface(val):
try:
return str(val['_type'].type) == "struct runtime._type *" and str(val['data'].type) == "void *"
except gdb.error:
pass
def lookup_type(name):
try:
return gdb.lookup_type(name)
except gdb.error:
pass
try:
return gdb.lookup_type('struct ' + name)
except gdb.error:
pass
try:
return gdb.lookup_type('struct ' + name[1:]).pointer()
except gdb.error:
pass
def iface_commontype(obj):
if is_iface(obj):
go_type_ptr = obj['tab']['_type']
elif is_eface(obj):
go_type_ptr = obj['_type']
else:
return
return go_type_ptr.cast(gdb.lookup_type("struct reflect.rtype").pointer()).dereference()
def iface_dtype(obj):
"Decode type of the data field of an eface or iface struct."
# known issue: dtype_name decoded from runtime.rtype is "nested.Foo"
# but the dwarf table lists it as "full/path/to/nested.Foo"
dynamic_go_type = iface_commontype(obj)
if dynamic_go_type is None:
return
dtype_name = dynamic_go_type['string'].dereference()['str'].string()
dynamic_gdb_type = lookup_type(dtype_name)
if dynamic_gdb_type is None:
return
type_size = int(dynamic_go_type['size'])
uintptr_size = int(dynamic_go_type['size'].type.sizeof) # size is itself an uintptr
if type_size > uintptr_size:
dynamic_gdb_type = dynamic_gdb_type.pointer()
return dynamic_gdb_type
def iface_dtype_name(obj):
"Decode type name of the data field of an eface or iface struct."
dynamic_go_type = iface_commontype(obj)
if dynamic_go_type is None:
return
return dynamic_go_type['string'].dereference()['str'].string()
class IfacePrinter:
"""Pretty print interface values
Casts the data field to the appropriate dynamic type."""
def __init__(self, val):
self.val = val
def display_hint(self):
return 'string'
def to_string(self):
if self.val['data'] == 0:
return 0x0
try:
dtype = iface_dtype(self.val)
except Exception:
return "<bad dynamic type>"
if dtype is None: # trouble looking up, print something reasonable
return "({0}){0}".format(iface_dtype_name(self.val), self.val['data'])
try:
return self.val['data'].cast(dtype).dereference()
except Exception:
pass
return self.val['data'].cast(dtype)
def ifacematcher(val):
if is_iface(val) or is_eface(val):
return IfacePrinter(val)
goobjfile.pretty_printers.append(ifacematcher)
#
# Convenience Functions
#
class GoLenFunc(gdb.Function):
"Length of strings, slices, maps or channels"
how = ((StringTypePrinter, 'len'), (SliceTypePrinter, 'len'), (MapTypePrinter, 'count'), (ChanTypePrinter, 'qcount'))
def __init__(self):
gdb.Function.__init__(self, "len")
def invoke(self, obj):
typename = str(obj.type)
for klass, fld in self.how:
if klass.pattern.match(typename):
return obj[fld]
class GoCapFunc(gdb.Function):
"Capacity of slices or channels"
how = ((SliceTypePrinter, 'cap'), (ChanTypePrinter, 'dataqsiz'))
def __init__(self):
gdb.Function.__init__(self, "cap")
def invoke(self, obj):
typename = str(obj.type)
for klass, fld in self.how:
if klass.pattern.match(typename):
return obj[fld]
class DTypeFunc(gdb.Function):
"""Cast Interface values to their dynamic type.
For non-interface types this behaves as the identity operation.
"""
def __init__(self):
gdb.Function.__init__(self, "dtype")
def invoke(self, obj):
try:
return obj['data'].cast(iface_dtype(obj))
except gdb.error:
pass
return obj
#
# Commands
#
sts = ('idle', 'runnable', 'running', 'syscall', 'waiting', 'moribund', 'dead', 'recovery')
def linked_list(ptr, linkfield):
while ptr:
yield ptr
ptr = ptr[linkfield]
class GoroutinesCmd(gdb.Command):
"List all goroutines."
def __init__(self):
gdb.Command.__init__(self, "info goroutines", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
def invoke(self, _arg, _from_tty):
# args = gdb.string_to_argv(arg)
vp = gdb.lookup_type('void').pointer()
for ptr in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
if ptr['atomicstatus'] == 6: # 'gdead'
continue
s = ' '
if ptr['m']:
s = '*'
pc = ptr['sched']['pc'].cast(vp)
# python2 will not cast pc (type void*) to an int cleanly
# instead python2 and python3 work with the hex string representation
# of the void pointer which we can parse back into an int.
# int(pc) will not work.
try:
#python3 / newer versions of gdb
pc = int(pc)
except gdb.error:
# str(pc) can return things like
# "0x429d6c <runtime.gopark+284>", so
# chop at first space.
pc = int(str(pc).split(None, 1)[0], 16)
blk = gdb.block_for_pc(pc)
print(s, ptr['goid'], "{0:8s}".format(sts[int(ptr['atomicstatus'])]), blk.function)
def find_goroutine(goid):
"""
find_goroutine attempts to find the goroutine identified by goid.
It returns a touple of gdv.Value's representing the stack pointer
and program counter pointer for the goroutine.
@param int goid
@return tuple (gdb.Value, gdb.Value)
"""
vp = gdb.lookup_type('void').pointer()
for ptr in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
if ptr['atomicstatus'] == 6: # 'gdead'
continue
if ptr['goid'] == goid:
return (ptr['sched'][x].cast(vp) for x in ('pc', 'sp'))
return None, None
class GoroutineCmd(gdb.Command):
"""Execute gdb command in the context of goroutine <goid>.
Switch PC and SP to the ones in the goroutine's G structure,
execute an arbitrary gdb command, and restore PC and SP.
Usage: (gdb) goroutine <goid> <gdbcmd>
Note that it is ill-defined to modify state in the context of a goroutine.
Restrict yourself to inspecting values.
"""
def __init__(self):
gdb.Command.__init__(self, "goroutine", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
def invoke(self, arg, _from_tty):
goid, cmd = arg.split(None, 1)
goid = gdb.parse_and_eval(goid)
pc, sp = find_goroutine(int(goid))
if not pc:
print("No such goroutine: ", goid)
return
try:
#python3 / newer versions of gdb
pc = int(pc)
except gdb.error:
pc = int(str(pc), 16)
save_frame = gdb.selected_frame()
gdb.parse_and_eval('$save_pc = $pc')
gdb.parse_and_eval('$save_sp = $sp')
gdb.parse_and_eval('$pc = {0}'.format(str(pc)))
gdb.parse_and_eval('$sp = {0}'.format(str(sp)))
try:
gdb.execute(cmd)
finally:
gdb.parse_and_eval('$pc = $save_pc')
gdb.parse_and_eval('$sp = $save_sp')
save_frame.select()
class GoIfaceCmd(gdb.Command):
"Print Static and dynamic interface types"
def __init__(self):
gdb.Command.__init__(self, "iface", gdb.COMMAND_DATA, gdb.COMPLETE_SYMBOL)
def invoke(self, arg, _from_tty):
for obj in gdb.string_to_argv(arg):
try:
#TODO fix quoting for qualified variable names
obj = gdb.parse_and_eval(str(obj))
except Exception as e:
print("Can't parse ", obj, ": ", e)
continue
if obj['data'] == 0:
dtype = "nil"
else:
dtype = iface_dtype(obj)
if dtype is None:
print("Not an interface: ", obj.type)
continue
print("{0}: {1}".format(obj.type, dtype))
# TODO: print interface's methods and dynamic type's func pointers thereof.
#rsc: "to find the number of entries in the itab's Fn field look at
# itab.inter->numMethods
# i am sure i have the names wrong but look at the interface type
# and its method count"
# so Itype will start with a commontype which has kind = interface
#
# Register all convenience functions and CLI commands
#
GoLenFunc()
GoCapFunc()
DTypeFunc()
GoroutinesCmd()
GoroutineCmd()
GoIfaceCmd()
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