Text file
src/runtime/runtime-gdb.py
Documentation: runtime
1# Copyright 2010 The Go Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style
3# license that can be found in the LICENSE file.
4
5"""GDB Pretty printers and convenience functions for Go's runtime structures.
6
7This script is loaded by GDB when it finds a .debug_gdb_scripts
8section in the compiled binary. The [68]l linkers emit this with a
9path to this file based on the path to the runtime package.
10"""
11
12# Known issues:
13# - pretty printing only works for the 'native' strings. E.g. 'type
14# foo string' will make foo a plain struct in the eyes of gdb,
15# circumventing the pretty print triggering.
16
17
18from __future__ import print_function
19import re
20import sys
21import gdb
22
23print("Loading Go Runtime support.", file=sys.stderr)
24#http://python3porting.com/differences.html
25if sys.version > '3':
26 xrange = range
27# allow to manually reload while developing
28goobjfile = gdb.current_objfile() or gdb.objfiles()[0]
29goobjfile.pretty_printers = []
30
31# G state (runtime2.go)
32
33def read_runtime_const(varname, default):
34 try:
35 return int(gdb.parse_and_eval(varname))
36 except Exception:
37 return int(default)
38
39
40G_IDLE = read_runtime_const("'runtime._Gidle'", 0)
41G_RUNNABLE = read_runtime_const("'runtime._Grunnable'", 1)
42G_RUNNING = read_runtime_const("'runtime._Grunning'", 2)
43G_SYSCALL = read_runtime_const("'runtime._Gsyscall'", 3)
44G_WAITING = read_runtime_const("'runtime._Gwaiting'", 4)
45G_MORIBUND_UNUSED = read_runtime_const("'runtime._Gmoribund_unused'", 5)
46G_DEAD = read_runtime_const("'runtime._Gdead'", 6)
47G_ENQUEUE_UNUSED = read_runtime_const("'runtime._Genqueue_unused'", 7)
48G_COPYSTACK = read_runtime_const("'runtime._Gcopystack'", 8)
49G_SCAN = read_runtime_const("'runtime._Gscan'", 0x1000)
50G_SCANRUNNABLE = G_SCAN+G_RUNNABLE
51G_SCANRUNNING = G_SCAN+G_RUNNING
52G_SCANSYSCALL = G_SCAN+G_SYSCALL
53G_SCANWAITING = G_SCAN+G_WAITING
54
55sts = {
56 G_IDLE: 'idle',
57 G_RUNNABLE: 'runnable',
58 G_RUNNING: 'running',
59 G_SYSCALL: 'syscall',
60 G_WAITING: 'waiting',
61 G_MORIBUND_UNUSED: 'moribund',
62 G_DEAD: 'dead',
63 G_ENQUEUE_UNUSED: 'enqueue',
64 G_COPYSTACK: 'copystack',
65 G_SCAN: 'scan',
66 G_SCANRUNNABLE: 'runnable+s',
67 G_SCANRUNNING: 'running+s',
68 G_SCANSYSCALL: 'syscall+s',
69 G_SCANWAITING: 'waiting+s',
70}
71
72
73#
74# Value wrappers
75#
76
77class SliceValue:
78 "Wrapper for slice values."
79
80 def __init__(self, val):
81 self.val = val
82
83 @property
84 def len(self):
85 return int(self.val['len'])
86
87 @property
88 def cap(self):
89 return int(self.val['cap'])
90
91 def __getitem__(self, i):
92 if i < 0 or i >= self.len:
93 raise IndexError(i)
94 ptr = self.val["array"]
95 return (ptr + i).dereference()
96
97
98#
99# Pretty Printers
100#
101
102# The patterns for matching types are permissive because gdb 8.2 switched to matching on (we think) typedef names instead of C syntax names.
103class StringTypePrinter:
104 "Pretty print Go strings."
105
106 pattern = re.compile(r'^(struct string( \*)?|string)$')
107
108 def __init__(self, val):
109 self.val = val
110
111 def display_hint(self):
112 return 'string'
113
114 def to_string(self):
115 l = int(self.val['len'])
116 return self.val['str'].string("utf-8", "ignore", l)
117
118
119class SliceTypePrinter:
120 "Pretty print slices."
121
122 pattern = re.compile(r'^(struct \[\]|\[\])')
123
124 def __init__(self, val):
125 self.val = val
126
127 def display_hint(self):
128 return 'array'
129
130 def to_string(self):
131 t = str(self.val.type)
132 if (t.startswith("struct ")):
133 return t[len("struct "):]
134 return t
135
136 def children(self):
137 sval = SliceValue(self.val)
138 if sval.len > sval.cap:
139 return
140 for idx, item in enumerate(sval):
141 yield ('[{0}]'.format(idx), item)
142
143
144class MapTypePrinter:
145 """Pretty print map[K]V types.
146
147 Map-typed go variables are really pointers. dereference them in gdb
148 to inspect their contents with this pretty printer.
149 """
150
151 pattern = re.compile(r'^map\[.*\].*$')
152
153 def __init__(self, val):
154 self.val = val
155
156 def display_hint(self):
157 return 'map'
158
159 def to_string(self):
160 return str(self.val.type)
161
162 def children(self):
163 MapBucketCount = 8 # see internal/abi.go:MapBucketCount
164 B = self.val['B']
165 buckets = self.val['buckets']
166 oldbuckets = self.val['oldbuckets']
167 flags = self.val['flags']
168 inttype = self.val['hash0'].type
169 cnt = 0
170 for bucket in xrange(2 ** int(B)):
171 bp = buckets + bucket
172 if oldbuckets:
173 oldbucket = bucket & (2 ** (B - 1) - 1)
174 oldbp = oldbuckets + oldbucket
175 oldb = oldbp.dereference()
176 if (oldb['overflow'].cast(inttype) & 1) == 0: # old bucket not evacuated yet
177 if bucket >= 2 ** (B - 1):
178 continue # already did old bucket
179 bp = oldbp
180 while bp:
181 b = bp.dereference()
182 for i in xrange(MapBucketCount):
183 if b['tophash'][i] != 0:
184 k = b['keys'][i]
185 v = b['values'][i]
186 if flags & 1:
187 k = k.dereference()
188 if flags & 2:
189 v = v.dereference()
190 yield str(cnt), k
191 yield str(cnt + 1), v
192 cnt += 2
193 bp = b['overflow']
194
195
196class ChanTypePrinter:
197 """Pretty print chan[T] types.
198
199 Chan-typed go variables are really pointers. dereference them in gdb
200 to inspect their contents with this pretty printer.
201 """
202
203 pattern = re.compile(r'^chan ')
204
205 def __init__(self, val):
206 self.val = val
207
208 def display_hint(self):
209 return 'array'
210
211 def to_string(self):
212 return str(self.val.type)
213
214 def children(self):
215 # see chan.c chanbuf(). et is the type stolen from hchan<T>::recvq->first->elem
216 et = [x.type for x in self.val['recvq']['first'].type.target().fields() if x.name == 'elem'][0]
217 ptr = (self.val.address["buf"]).cast(et)
218 for i in range(self.val["qcount"]):
219 j = (self.val["recvx"] + i) % self.val["dataqsiz"]
220 yield ('[{0}]'.format(i), (ptr + j).dereference())
221
222
223def paramtypematch(t, pattern):
224 return t.code == gdb.TYPE_CODE_TYPEDEF and str(t).startswith(".param") and pattern.match(str(t.target()))
225
226#
227# Register all the *Printer classes above.
228#
229
230def makematcher(klass):
231 def matcher(val):
232 try:
233 if klass.pattern.match(str(val.type)):
234 return klass(val)
235 elif paramtypematch(val.type, klass.pattern):
236 return klass(val.cast(val.type.target()))
237 except Exception:
238 pass
239 return matcher
240
241goobjfile.pretty_printers.extend([makematcher(var) for var in vars().values() if hasattr(var, 'pattern')])
242#
243# Utilities
244#
245
246def pc_to_int(pc):
247 # python2 will not cast pc (type void*) to an int cleanly
248 # instead python2 and python3 work with the hex string representation
249 # of the void pointer which we can parse back into an int.
250 # int(pc) will not work.
251 try:
252 # python3 / newer versions of gdb
253 pc = int(pc)
254 except gdb.error:
255 # str(pc) can return things like
256 # "0x429d6c <runtime.gopark+284>", so
257 # chop at first space.
258 pc = int(str(pc).split(None, 1)[0], 16)
259 return pc
260
261
262#
263# For reference, this is what we're trying to do:
264# eface: p *(*(struct 'runtime.rtype'*)'main.e'->type_->data)->string
265# iface: p *(*(struct 'runtime.rtype'*)'main.s'->tab->Type->data)->string
266#
267# interface types can't be recognized by their name, instead we check
268# if they have the expected fields. Unfortunately the mapping of
269# fields to python attributes in gdb.py isn't complete: you can't test
270# for presence other than by trapping.
271
272
273def is_iface(val):
274 try:
275 return str(val['tab'].type) == "struct runtime.itab *" and str(val['data'].type) == "void *"
276 except gdb.error:
277 pass
278
279
280def is_eface(val):
281 try:
282 return str(val['_type'].type) == "struct runtime._type *" and str(val['data'].type) == "void *"
283 except gdb.error:
284 pass
285
286
287def lookup_type(name):
288 try:
289 return gdb.lookup_type(name)
290 except gdb.error:
291 pass
292 try:
293 return gdb.lookup_type('struct ' + name)
294 except gdb.error:
295 pass
296 try:
297 return gdb.lookup_type('struct ' + name[1:]).pointer()
298 except gdb.error:
299 pass
300
301
302def iface_commontype(obj):
303 if is_iface(obj):
304 go_type_ptr = obj['tab']['_type']
305 elif is_eface(obj):
306 go_type_ptr = obj['_type']
307 else:
308 return
309
310 return go_type_ptr.cast(gdb.lookup_type("struct reflect.rtype").pointer()).dereference()
311
312
313def iface_dtype(obj):
314 "Decode type of the data field of an eface or iface struct."
315 # known issue: dtype_name decoded from runtime.rtype is "nested.Foo"
316 # but the dwarf table lists it as "full/path/to/nested.Foo"
317
318 dynamic_go_type = iface_commontype(obj)
319 if dynamic_go_type is None:
320 return
321 dtype_name = dynamic_go_type['string'].dereference()['str'].string()
322
323 dynamic_gdb_type = lookup_type(dtype_name)
324 if dynamic_gdb_type is None:
325 return
326
327 type_size = int(dynamic_go_type['size'])
328 uintptr_size = int(dynamic_go_type['size'].type.sizeof) # size is itself a uintptr
329 if type_size > uintptr_size:
330 dynamic_gdb_type = dynamic_gdb_type.pointer()
331
332 return dynamic_gdb_type
333
334
335def iface_dtype_name(obj):
336 "Decode type name of the data field of an eface or iface struct."
337
338 dynamic_go_type = iface_commontype(obj)
339 if dynamic_go_type is None:
340 return
341 return dynamic_go_type['string'].dereference()['str'].string()
342
343
344class IfacePrinter:
345 """Pretty print interface values
346
347 Casts the data field to the appropriate dynamic type."""
348
349 def __init__(self, val):
350 self.val = val
351
352 def display_hint(self):
353 return 'string'
354
355 def to_string(self):
356 if self.val['data'] == 0:
357 return 0x0
358 try:
359 dtype = iface_dtype(self.val)
360 except Exception:
361 return "<bad dynamic type>"
362
363 if dtype is None: # trouble looking up, print something reasonable
364 return "({typename}){data}".format(
365 typename=iface_dtype_name(self.val), data=self.val['data'])
366
367 try:
368 return self.val['data'].cast(dtype).dereference()
369 except Exception:
370 pass
371 return self.val['data'].cast(dtype)
372
373
374def ifacematcher(val):
375 if is_iface(val) or is_eface(val):
376 return IfacePrinter(val)
377
378goobjfile.pretty_printers.append(ifacematcher)
379
380#
381# Convenience Functions
382#
383
384
385class GoLenFunc(gdb.Function):
386 "Length of strings, slices, maps or channels"
387
388 how = ((StringTypePrinter, 'len'), (SliceTypePrinter, 'len'), (MapTypePrinter, 'count'), (ChanTypePrinter, 'qcount'))
389
390 def __init__(self):
391 gdb.Function.__init__(self, "len")
392
393 def invoke(self, obj):
394 typename = str(obj.type)
395 for klass, fld in self.how:
396 if klass.pattern.match(typename) or paramtypematch(obj.type, klass.pattern):
397 return obj[fld]
398
399
400class GoCapFunc(gdb.Function):
401 "Capacity of slices or channels"
402
403 how = ((SliceTypePrinter, 'cap'), (ChanTypePrinter, 'dataqsiz'))
404
405 def __init__(self):
406 gdb.Function.__init__(self, "cap")
407
408 def invoke(self, obj):
409 typename = str(obj.type)
410 for klass, fld in self.how:
411 if klass.pattern.match(typename) or paramtypematch(obj.type, klass.pattern):
412 return obj[fld]
413
414
415class DTypeFunc(gdb.Function):
416 """Cast Interface values to their dynamic type.
417
418 For non-interface types this behaves as the identity operation.
419 """
420
421 def __init__(self):
422 gdb.Function.__init__(self, "dtype")
423
424 def invoke(self, obj):
425 try:
426 return obj['data'].cast(iface_dtype(obj))
427 except gdb.error:
428 pass
429 return obj
430
431#
432# Commands
433#
434
435def linked_list(ptr, linkfield):
436 while ptr:
437 yield ptr
438 ptr = ptr[linkfield]
439
440
441class GoroutinesCmd(gdb.Command):
442 "List all goroutines."
443
444 def __init__(self):
445 gdb.Command.__init__(self, "info goroutines", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
446
447 def invoke(self, _arg, _from_tty):
448 # args = gdb.string_to_argv(arg)
449 vp = gdb.lookup_type('void').pointer()
450 for ptr in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
451 if ptr['atomicstatus']['value'] == G_DEAD:
452 continue
453 s = ' '
454 if ptr['m']:
455 s = '*'
456 pc = ptr['sched']['pc'].cast(vp)
457 pc = pc_to_int(pc)
458 blk = gdb.block_for_pc(pc)
459 status = int(ptr['atomicstatus']['value'])
460 st = sts.get(status, "unknown(%d)" % status)
461 print(s, ptr['goid'], "{0:8s}".format(st), blk.function)
462
463
464def find_goroutine(goid):
465 """
466 find_goroutine attempts to find the goroutine identified by goid.
467 It returns a tuple of gdb.Value's representing the stack pointer
468 and program counter pointer for the goroutine.
469
470 @param int goid
471
472 @return tuple (gdb.Value, gdb.Value)
473 """
474 vp = gdb.lookup_type('void').pointer()
475 for ptr in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
476 if ptr['atomicstatus']['value'] == G_DEAD:
477 continue
478 if ptr['goid'] == goid:
479 break
480 else:
481 return None, None
482 # Get the goroutine's saved state.
483 pc, sp = ptr['sched']['pc'], ptr['sched']['sp']
484 status = ptr['atomicstatus']['value']&~G_SCAN
485 # Goroutine is not running nor in syscall, so use the info in goroutine
486 if status != G_RUNNING and status != G_SYSCALL:
487 return pc.cast(vp), sp.cast(vp)
488
489 # If the goroutine is in a syscall, use syscallpc/sp.
490 pc, sp = ptr['syscallpc'], ptr['syscallsp']
491 if sp != 0:
492 return pc.cast(vp), sp.cast(vp)
493 # Otherwise, the goroutine is running, so it doesn't have
494 # saved scheduler state. Find G's OS thread.
495 m = ptr['m']
496 if m == 0:
497 return None, None
498 for thr in gdb.selected_inferior().threads():
499 if thr.ptid[1] == m['procid']:
500 break
501 else:
502 return None, None
503 # Get scheduler state from the G's OS thread state.
504 curthr = gdb.selected_thread()
505 try:
506 thr.switch()
507 pc = gdb.parse_and_eval('$pc')
508 sp = gdb.parse_and_eval('$sp')
509 finally:
510 curthr.switch()
511 return pc.cast(vp), sp.cast(vp)
512
513
514class GoroutineCmd(gdb.Command):
515 """Execute gdb command in the context of goroutine <goid>.
516
517 Switch PC and SP to the ones in the goroutine's G structure,
518 execute an arbitrary gdb command, and restore PC and SP.
519
520 Usage: (gdb) goroutine <goid> <gdbcmd>
521
522 You could pass "all" as <goid> to apply <gdbcmd> to all goroutines.
523
524 For example: (gdb) goroutine all <gdbcmd>
525
526 Note that it is ill-defined to modify state in the context of a goroutine.
527 Restrict yourself to inspecting values.
528 """
529
530 def __init__(self):
531 gdb.Command.__init__(self, "goroutine", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
532
533 def invoke(self, arg, _from_tty):
534 goid_str, cmd = arg.split(None, 1)
535 goids = []
536
537 if goid_str == 'all':
538 for ptr in SliceValue(gdb.parse_and_eval("'runtime.allgs'")):
539 goids.append(int(ptr['goid']))
540 else:
541 goids = [int(gdb.parse_and_eval(goid_str))]
542
543 for goid in goids:
544 self.invoke_per_goid(goid, cmd)
545
546 def invoke_per_goid(self, goid, cmd):
547 pc, sp = find_goroutine(goid)
548 if not pc:
549 print("No such goroutine: ", goid)
550 return
551 pc = pc_to_int(pc)
552 save_frame = gdb.selected_frame()
553 gdb.parse_and_eval('$save_sp = $sp')
554 gdb.parse_and_eval('$save_pc = $pc')
555 # In GDB, assignments to sp must be done from the
556 # top-most frame, so select frame 0 first.
557 gdb.execute('select-frame 0')
558 gdb.parse_and_eval('$sp = {0}'.format(str(sp)))
559 gdb.parse_and_eval('$pc = {0}'.format(str(pc)))
560 try:
561 gdb.execute(cmd)
562 finally:
563 # In GDB, assignments to sp must be done from the
564 # top-most frame, so select frame 0 first.
565 gdb.execute('select-frame 0')
566 gdb.parse_and_eval('$pc = $save_pc')
567 gdb.parse_and_eval('$sp = $save_sp')
568 save_frame.select()
569
570
571class GoIfaceCmd(gdb.Command):
572 "Print Static and dynamic interface types"
573
574 def __init__(self):
575 gdb.Command.__init__(self, "iface", gdb.COMMAND_DATA, gdb.COMPLETE_SYMBOL)
576
577 def invoke(self, arg, _from_tty):
578 for obj in gdb.string_to_argv(arg):
579 try:
580 #TODO fix quoting for qualified variable names
581 obj = gdb.parse_and_eval(str(obj))
582 except Exception as e:
583 print("Can't parse ", obj, ": ", e)
584 continue
585
586 if obj['data'] == 0:
587 dtype = "nil"
588 else:
589 dtype = iface_dtype(obj)
590
591 if dtype is None:
592 print("Not an interface: ", obj.type)
593 continue
594
595 print("{0}: {1}".format(obj.type, dtype))
596
597# TODO: print interface's methods and dynamic type's func pointers thereof.
598#rsc: "to find the number of entries in the itab's Fn field look at
599# itab.inter->numMethods
600# i am sure i have the names wrong but look at the interface type
601# and its method count"
602# so Itype will start with a commontype which has kind = interface
603
604#
605# Register all convenience functions and CLI commands
606#
607GoLenFunc()
608GoCapFunc()
609DTypeFunc()
610GoroutinesCmd()
611GoroutineCmd()
612GoIfaceCmd()
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