2 * Copyright 2017 Facebook, Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
19 #include <climits> // for PATH_MAX
24 #include <unordered_map>
27 #include <boost/container/flat_map.hpp>
28 #include <boost/intrusive/list.hpp>
29 #include <boost/operators.hpp>
30 #include <glog/logging.h>
32 #include <folly/Hash.h>
33 #include <folly/Range.h>
34 #include <folly/experimental/symbolizer/Elf.h>
36 namespace folly { namespace symbolizer {
39 * Number of ELF files loaded by the dynamic loader.
41 size_t countLoadedElfFiles();
45 virtual std::shared_ptr<ElfFile> getFile(StringPiece path) = 0;
46 virtual ~ElfCacheBase() { }
50 * Cache ELF files. Async-signal-safe: does memory allocation upfront.
52 * Will not grow; once the capacity is reached, lookups for files that
53 * aren't already in the cache will fail (return nullptr).
55 * Not MT-safe. May not be used concurrently from multiple threads.
57 * NOTE that async-signal-safety is preserved only as long as the
58 * SignalSafeElfCache object exists; after the SignalSafeElfCache object
59 * is destroyed, destroying returned shared_ptr<ElfFile> objects may
60 * cause ElfFile objects to be destroyed, and that's not async-signal-safe.
62 class SignalSafeElfCache : public ElfCacheBase {
64 explicit SignalSafeElfCache(size_t capacity);
66 std::shared_ptr<ElfFile> getFile(StringPiece path) override;
69 // We can't use std::string (allocating memory is bad!) so we roll our
70 // own wrapper around a fixed-size, null-terminated string.
71 class Path : private boost::totally_ordered<Path> {
74 assign(folly::StringPiece());
77 explicit Path(StringPiece s) {
81 void assign(StringPiece s) {
82 DCHECK_LE(s.size(), kMaxSize);
84 memcpy(data_, s.data(), s.size());
86 data_[s.size()] = '\0';
89 bool operator<(const Path& other) const {
90 return strcmp(data_, other.data_) < 0;
93 bool operator==(const Path& other) const {
94 return strcmp(data_, other.data_) == 0;
97 const char* data() const {
101 static constexpr size_t kMaxSize = PATH_MAX - 1;
104 char data_[kMaxSize + 1];
107 Path scratchpad_; // Preallocated key for map_ lookups.
108 boost::container::flat_map<Path, int> map_;
109 std::vector<std::shared_ptr<ElfFile>> slots_;
113 * General-purpose ELF file cache.
115 * LRU of given capacity. MT-safe (uses locking). Not async-signal-safe.
117 class ElfCache : public ElfCacheBase {
119 explicit ElfCache(size_t capacity);
121 std::shared_ptr<ElfFile> getFile(StringPiece path) override;
126 typedef boost::intrusive::list_member_hook<> LruLink;
134 static std::shared_ptr<ElfFile> filePtr(const std::shared_ptr<Entry>& e);
137 std::unordered_map<StringPiece, std::shared_ptr<Entry>, Hash> files_;
139 typedef boost::intrusive::list<
141 boost::intrusive::member_hook<Entry, LruLink, &Entry::lruLink>,
142 boost::intrusive::constant_time_size<false>> LruList;