UnwindMap.cpp revision 0c572d01afdf9bfee340ab5c167d744ea91316bf 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include <pthread.h>
18#include <stdint.h>
19#include <stdlib.h>
20#include <sys/types.h>
21#include <unistd.h>
22
23#include <backtrace/BacktraceMap.h>
24
25#include <libunwind.h>
26
27#include "BacktraceLog.h"
28#include "UnwindMap.h"
29
30//-------------------------------------------------------------------------
31// libunwind has a single shared address space for the current process
32// aka local. If multiple maps are created for the current pid, then
33// only update the local address space once, and keep a reference count
34// of maps using the same map cursor.
35//-------------------------------------------------------------------------
36UnwindMap::UnwindMap(pid_t pid) : BacktraceMap(pid) {
37  unw_map_cursor_clear(&map_cursor_);
38}
39
40UnwindMapRemote::UnwindMapRemote(pid_t pid) : UnwindMap(pid) {
41}
42
43UnwindMapRemote::~UnwindMapRemote() {
44  unw_map_cursor_destroy(&map_cursor_);
45  unw_map_cursor_clear(&map_cursor_);
46}
47
48bool UnwindMapRemote::GenerateMap() {
49  // Use the map_cursor information to construct the BacktraceMap data
50  // rather than reparsing /proc/self/maps.
51  unw_map_cursor_reset(&map_cursor_);
52
53  unw_map_t unw_map;
54  while (unw_map_cursor_get_next(&map_cursor_, &unw_map)) {
55    backtrace_map_t map;
56
57    map.start = unw_map.start;
58    map.end = unw_map.end;
59    map.offset = unw_map.offset;
60    map.load_base = unw_map.load_base;
61    map.flags = unw_map.flags;
62    map.name = unw_map.path;
63
64    // The maps are in descending order, but we want them in ascending order.
65    maps_.push_front(map);
66  }
67
68  return true;
69}
70
71bool UnwindMapRemote::Build() {
72  return (unw_map_cursor_create(&map_cursor_, pid_) == 0) && GenerateMap();
73}
74
75UnwindMapLocal::UnwindMapLocal() : UnwindMap(getpid()), map_created_(false) {
76  pthread_rwlock_init(&map_lock_, nullptr);
77}
78
79UnwindMapLocal::~UnwindMapLocal() {
80  if (map_created_) {
81    unw_map_local_destroy();
82    unw_map_cursor_clear(&map_cursor_);
83  }
84}
85
86bool UnwindMapLocal::GenerateMap() {
87  // Lock so that multiple threads cannot modify the maps data at the
88  // same time.
89  pthread_rwlock_wrlock(&map_lock_);
90
91  // It's possible for the map to be regenerated while this loop is occurring.
92  // If that happens, get the map again, but only try at most three times
93  // before giving up.
94  bool generated = false;
95  for (int i = 0; i < 3; i++) {
96    maps_.clear();
97
98    // Save the map data retrieved so we can tell if it changes.
99    unw_map_local_cursor_get(&map_cursor_);
100
101    unw_map_t unw_map;
102    int ret;
103    while ((ret = unw_map_local_cursor_get_next(&map_cursor_, &unw_map)) > 0) {
104      backtrace_map_t map;
105
106      map.start = unw_map.start;
107      map.end = unw_map.end;
108      map.offset = unw_map.offset;
109      map.load_base = unw_map.load_base;
110      map.flags = unw_map.flags;
111      map.name = unw_map.path;
112
113      free(unw_map.path);
114
115      // The maps are in descending order, but we want them in ascending order.
116      maps_.push_front(map);
117    }
118    // Check to see if the map changed while getting the data.
119    if (ret != -UNW_EINVAL) {
120      generated = true;
121      break;
122    }
123  }
124
125  pthread_rwlock_unlock(&map_lock_);
126
127  if (!generated) {
128    BACK_LOGW("Unable to generate the map.");
129  }
130  return generated;
131}
132
133bool UnwindMapLocal::Build() {
134  return (map_created_ = (unw_map_local_create() == 0)) && GenerateMap();;
135}
136
137void UnwindMapLocal::FillIn(uintptr_t addr, backtrace_map_t* map) {
138  BacktraceMap::FillIn(addr, map);
139  if (!IsValid(*map)) {
140    // Check to see if the underlying map changed and regenerate the map
141    // if it did.
142    if (unw_map_local_cursor_valid(&map_cursor_) < 0) {
143      if (GenerateMap()) {
144        BacktraceMap::FillIn(addr, map);
145      }
146    }
147  }
148}
149
150//-------------------------------------------------------------------------
151// BacktraceMap create function.
152//-------------------------------------------------------------------------
153BacktraceMap* BacktraceMap::Create(pid_t pid, bool uncached) {
154  BacktraceMap* map;
155
156  if (uncached) {
157    // Force use of the base class to parse the maps when this call is made.
158    map = new BacktraceMap(pid);
159  } else if (pid == getpid()) {
160    map = new UnwindMapLocal();
161  } else {
162    map = new UnwindMapRemote(pid);
163  }
164  if (!map->Build()) {
165    delete map;
166    return nullptr;
167  }
168  return map;
169}
170