-
Notifications
You must be signed in to change notification settings - Fork 1.3k
/
peek.go
378 lines (354 loc) · 12 KB
/
peek.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
// Copyright 2018 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Functions for reading values of various types from a program's memory.
// +build linux
package server
import (
"errors"
"fmt"
"cloud.google.com/go/cmd/go-cloud-debug-agent/internal/debug"
"cloud.google.com/go/cmd/go-cloud-debug-agent/internal/debug/dwarf"
)
// peekBytes reads len(buf) bytes at addr.
func (s *Server) peekBytes(addr uint64, buf []byte) error {
return s.ptracePeek(s.stoppedPid, uintptr(addr), buf)
}
// peekPtr reads a pointer at addr.
func (s *Server) peekPtr(addr uint64) (uint64, error) {
buf := make([]byte, s.arch.PointerSize)
if err := s.peekBytes(addr, buf); err != nil {
return 0, err
}
return s.arch.Uintptr(buf), nil
}
// peekUint8 reads a single byte at addr.
func (s *Server) peekUint8(addr uint64) (byte, error) {
buf := make([]byte, 1)
if err := s.peekBytes(addr, buf); err != nil {
return 0, err
}
return uint8(s.arch.UintN(buf)), nil
}
// peekInt reads an int of size n bytes at addr.
func (s *Server) peekInt(addr uint64, n int64) (int64, error) {
buf := make([]byte, n)
if err := s.peekBytes(addr, buf); err != nil {
return 0, err
}
return s.arch.IntN(buf), nil
}
// peekUint reads a uint of size n bytes at addr.
func (s *Server) peekUint(addr uint64, n int64) (uint64, error) {
buf := make([]byte, n)
if err := s.peekBytes(addr, buf); err != nil {
return 0, err
}
return s.arch.UintN(buf), nil
}
// peekSlice reads the header of a slice with the given type and address.
func (s *Server) peekSlice(t *dwarf.SliceType, addr uint64) (debug.Slice, error) {
ptr, err := s.peekPtrStructField(&t.StructType, addr, "array")
if err != nil {
return debug.Slice{}, fmt.Errorf("reading slice location: %s", err)
}
length, err := s.peekUintOrIntStructField(&t.StructType, addr, "len")
if err != nil {
return debug.Slice{}, fmt.Errorf("reading slice length: %s", err)
}
capacity, err := s.peekUintOrIntStructField(&t.StructType, addr, "cap")
if err != nil {
return debug.Slice{}, fmt.Errorf("reading slice capacity: %s", err)
}
if capacity < length {
return debug.Slice{}, fmt.Errorf("slice's capacity %d is less than its length %d", capacity, length)
}
return debug.Slice{
debug.Array{
ElementTypeID: uint64(t.ElemType.Common().Offset),
Address: uint64(ptr),
Length: length,
StrideBits: uint64(t.ElemType.Common().ByteSize) * 8,
},
capacity,
}, nil
}
// peekString reads a string of the given type at the given address.
// At most byteLimit bytes will be read. If the string is longer, "..." is appended.
func (s *Server) peekString(typ *dwarf.StringType, a uint64, byteLimit uint64) (string, error) {
ptr, err := s.peekPtrStructField(&typ.StructType, a, "str")
if err != nil {
return "", err
}
length, err := s.peekUintOrIntStructField(&typ.StructType, a, "len")
if err != nil {
return "", err
}
if length > byteLimit {
buf := make([]byte, byteLimit, byteLimit+3)
if err := s.peekBytes(ptr, buf); err != nil {
return "", err
} else {
buf = append(buf, '.', '.', '.')
return string(buf), nil
}
} else {
buf := make([]byte, length)
if err := s.peekBytes(ptr, buf); err != nil {
return "", err
} else {
return string(buf), nil
}
}
}
// peekCString reads a NUL-terminated string at the given address.
// At most byteLimit bytes will be read. If the string is longer, "..." is appended.
// peekCString never returns errors; if an error occurs, the string will be truncated in some way.
func (s *Server) peekCString(a uint64, byteLimit uint64) string {
buf := make([]byte, byteLimit, byteLimit+3)
s.peekBytes(a, buf)
for i, c := range buf {
if c == 0 {
return string(buf[0:i])
}
}
buf = append(buf, '.', '.', '.')
return string(buf)
}
// peekPtrStructField reads a pointer in the field fieldName of the struct
// of type t at addr.
func (s *Server) peekPtrStructField(t *dwarf.StructType, addr uint64, fieldName string) (uint64, error) {
f, err := getField(t, fieldName)
if err != nil {
return 0, fmt.Errorf("reading field %s: %s", fieldName, err)
}
if _, ok := f.Type.(*dwarf.PtrType); !ok {
return 0, fmt.Errorf("field %s is not a pointer", fieldName)
}
return s.peekPtr(addr + uint64(f.ByteOffset))
}
// peekUintOrIntStructField reads a signed or unsigned integer in the field fieldName
// of the struct of type t at addr. If the value is negative, it returns an error.
// This function is used when the value should be non-negative, but the DWARF
// type of the field may be signed or unsigned.
func (s *Server) peekUintOrIntStructField(t *dwarf.StructType, addr uint64, fieldName string) (uint64, error) {
f, err := getField(t, fieldName)
if err != nil {
return 0, fmt.Errorf("reading field %s: %s", fieldName, err)
}
ut, ok := f.Type.(*dwarf.UintType)
if ok {
return s.peekUint(addr+uint64(f.ByteOffset), ut.ByteSize)
}
it, ok := f.Type.(*dwarf.IntType)
if !ok {
return 0, fmt.Errorf("field %s is not an integer", fieldName)
}
i, err := s.peekInt(addr+uint64(f.ByteOffset), it.ByteSize)
if err != nil {
return 0, err
}
if i < 0 {
return 0, fmt.Errorf("field %s is negative", fieldName)
}
return uint64(i), nil
}
// peekUintStructField reads a uint in the field fieldName of the struct
// of type t at addr. The size of the uint is determined by the field.
func (s *Server) peekUintStructField(t *dwarf.StructType, addr uint64, fieldName string) (uint64, error) {
f, err := getField(t, fieldName)
if err != nil {
return 0, fmt.Errorf("reading field %s: %s", fieldName, err)
}
ut, ok := f.Type.(*dwarf.UintType)
if !ok {
return 0, fmt.Errorf("field %s is not an unsigned integer", fieldName)
}
return s.peekUint(addr+uint64(f.ByteOffset), ut.ByteSize)
}
// peekIntStructField reads an int in the field fieldName of the struct
// of type t at addr. The size of the int is determined by the field.
func (s *Server) peekIntStructField(t *dwarf.StructType, addr uint64, fieldName string) (int64, error) {
f, err := getField(t, fieldName)
if err != nil {
return 0, fmt.Errorf("reading field %s: %s", fieldName, err)
}
it, ok := f.Type.(*dwarf.IntType)
if !ok {
return 0, fmt.Errorf("field %s is not a signed integer", fieldName)
}
return s.peekInt(addr+uint64(f.ByteOffset), it.ByteSize)
}
// peekStringStructField reads a string field from the struct of the given type
// at the given address.
// At most byteLimit bytes will be read. If the string is longer, "..." is appended.
func (s *Server) peekStringStructField(t *dwarf.StructType, addr uint64, fieldName string, byteLimit uint64) (string, error) {
f, err := getField(t, fieldName)
if err != nil {
return "", fmt.Errorf("reading field %s: %s", fieldName, err)
}
st, ok := followTypedefs(f.Type).(*dwarf.StringType)
if !ok {
return "", fmt.Errorf("field %s is not a string", fieldName)
}
return s.peekString(st, addr+uint64(f.ByteOffset), byteLimit)
}
// peekMapLocationAndType returns the address and DWARF type of the underlying
// struct of a map variable.
func (s *Server) peekMapLocationAndType(t *dwarf.MapType, a uint64) (uint64, *dwarf.StructType, error) {
// Maps are pointers to structs.
pt, ok := t.Type.(*dwarf.PtrType)
if !ok {
return 0, nil, errors.New("bad map type: not a pointer")
}
st, ok := pt.Type.(*dwarf.StructType)
if !ok {
return 0, nil, errors.New("bad map type: not a pointer to a struct")
}
// a is the address of a pointer to a struct. Get the pointer's value.
a, err := s.peekPtr(a)
if err != nil {
return 0, nil, fmt.Errorf("reading map pointer: %s", err)
}
return a, st, nil
}
// peekMapValues reads a map at the given address and calls fn with the addresses for each (key, value) pair.
// If fn returns false, peekMapValues stops.
func (s *Server) peekMapValues(t *dwarf.MapType, a uint64, fn func(keyAddr, valAddr uint64, keyType, valType dwarf.Type) bool) error {
a, st, err := s.peekMapLocationAndType(t, a)
if err != nil {
return err
}
if a == 0 {
// The pointer was nil, so the map is empty.
return nil
}
// Gather information about the struct type and the map bucket type.
b, err := s.peekUintStructField(st, a, "B")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
buckets, err := s.peekPtrStructField(st, a, "buckets")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
oldbuckets, err := s.peekPtrStructField(st, a, "oldbuckets")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
bf, err := getField(st, "buckets")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
bucketPtrType, ok := bf.Type.(*dwarf.PtrType)
if !ok {
return errors.New("bad map bucket type: not a pointer")
}
bt, ok := bucketPtrType.Type.(*dwarf.StructType)
if !ok {
return errors.New("bad map bucket type: not a pointer to a struct")
}
bucketSize := uint64(bucketPtrType.Type.Size())
tophashField, err := getField(bt, "tophash")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
bucketCnt := uint64(tophashField.Type.Size())
tophashFieldOffset := uint64(tophashField.ByteOffset)
keysField, err := getField(bt, "keys")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
keysType, ok := keysField.Type.(*dwarf.ArrayType)
if !ok {
return errors.New(`bad map bucket type: "keys" is not an array`)
}
keyType := keysType.Type
keysStride := uint64(keysType.StrideBitSize / 8)
keysFieldOffset := uint64(keysField.ByteOffset)
valuesField, err := getField(bt, "values")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
valuesType, ok := valuesField.Type.(*dwarf.ArrayType)
if !ok {
return errors.New(`bad map bucket type: "values" is not an array`)
}
valueType := valuesType.Type
valuesStride := uint64(valuesType.StrideBitSize / 8)
valuesFieldOffset := uint64(valuesField.ByteOffset)
overflowField, err := getField(bt, "overflow")
if err != nil {
return fmt.Errorf("reading map: %s", err)
}
overflowFieldOffset := uint64(overflowField.ByteOffset)
// Iterate through the two arrays of buckets.
bucketArrays := [2]struct {
addr uint64
size uint64
}{
{buckets, 1 << b},
{oldbuckets, 1 << (b - 1)},
}
for _, bucketArray := range bucketArrays {
if bucketArray.addr == 0 {
continue
}
for i := uint64(0); i < bucketArray.size; i++ {
bucketAddr := bucketArray.addr + i*bucketSize
// Iterate through the linked list of buckets.
// TODO: check for repeated bucket pointers.
for bucketAddr != 0 {
// Iterate through each entry in the bucket.
for j := uint64(0); j < bucketCnt; j++ {
tophash, err := s.peekUint8(bucketAddr + tophashFieldOffset + j)
if err != nil {
return errors.New("reading map: " + err.Error())
}
// From runtime/hashmap.go
const minTopHash = 4
if tophash < minTopHash {
continue
}
keyAddr := bucketAddr + keysFieldOffset + j*keysStride
valAddr := bucketAddr + valuesFieldOffset + j*valuesStride
if !fn(keyAddr, valAddr, keyType, valueType) {
return nil
}
}
var err error
bucketAddr, err = s.peekPtr(bucketAddr + overflowFieldOffset)
if err != nil {
return errors.New("reading map: " + err.Error())
}
}
}
}
return nil
}
// peekMapLength returns the number of elements in a map at the given address.
func (s *Server) peekMapLength(t *dwarf.MapType, a uint64) (uint64, error) {
a, st, err := s.peekMapLocationAndType(t, a)
if err != nil {
return 0, err
}
if a == 0 {
// The pointer was nil, so the map is empty.
return 0, nil
}
length, err := s.peekUintOrIntStructField(st, a, "count")
if err != nil {
return 0, fmt.Errorf("reading map: %s", err)
}
return uint64(length), nil
}