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
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef CodeAddressService_h__
#define CodeAddressService_h__
#include "mozilla/Assertions.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/IntegerPrintfMacros.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Types.h"
#include "mozilla/StackWalk.h"
namespace mozilla {
// This class is used to print details about code locations.
//
// |StringTable| must implement an Intern() method that returns an interned
// copy of the string that was passed in, as well as a standard
// SizeOfExcludingThis() method.
//
// |StringAlloc| must implement |copy| and |free|. |copy| copies a string,
// while |free| is used to free strings created by |copy|.
//
// |DescribeCodeAddressLock| is needed when the callers may be holding a lock
// used by MozDescribeCodeAddress. |DescribeCodeAddressLock| must implement
// static methods IsLocked(), Unlock() and Lock().
template <class StringTable,
class StringAlloc,
class DescribeCodeAddressLock>
class CodeAddressService
{
// GetLocation() is the key function in this class. It's basically a wrapper
// around MozDescribeCodeAddress.
//
// However, MozDescribeCodeAddress is very slow on some platforms, and we
// have lots of repeated (i.e. same PC) calls to it. So we do some caching
// of results. Each cached result includes two strings (|mFunction| and
// |mLibrary|), so we also optimize them for space in the following ways.
//
// - The number of distinct library names is small, e.g. a few dozen. There
// is lots of repetition, especially of libxul. So we intern them in their
// own table, which saves space over duplicating them for each cache entry.
//
// - The number of distinct function names is much higher, so we duplicate
// them in each cache entry. That's more space-efficient than interning
// because entries containing single-occurrence function names are quickly
// overwritten, and their copies released. In addition, empty function
// names are common, so we use nullptr to represent them compactly.
StringTable mLibraryStrings;
struct Entry
{
const void* mPc;
char* mFunction; // owned by the Entry; may be null
const char* mLibrary; // owned by mLibraryStrings; never null
// in a non-empty entry is in use
ptrdiff_t mLOffset;
char* mFileName; // owned by the Entry; may be null
uint32_t mLineNo:31;
uint32_t mInUse:1; // is the entry used?
Entry()
: mPc(0), mFunction(nullptr), mLibrary(nullptr), mLOffset(0),
mFileName(nullptr), mLineNo(0), mInUse(0)
{}
~Entry()
{
// We don't free mLibrary because it's externally owned.
StringAlloc::free(mFunction);
StringAlloc::free(mFileName);
}
void Replace(const void* aPc, const char* aFunction,
const char* aLibrary, ptrdiff_t aLOffset,
const char* aFileName, unsigned long aLineNo)
{
mPc = aPc;
// Convert "" to nullptr. Otherwise, make a copy of the name.
StringAlloc::free(mFunction);
mFunction = !aFunction[0] ? nullptr : StringAlloc::copy(aFunction);
StringAlloc::free(mFileName);
mFileName = !aFileName[0] ? nullptr : StringAlloc::copy(aFileName);
mLibrary = aLibrary;
mLOffset = aLOffset;
mLineNo = aLineNo;
mInUse = 1;
}
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
// Don't measure mLibrary because it's externally owned.
size_t n = 0;
n += aMallocSizeOf(mFunction);
n += aMallocSizeOf(mFileName);
return n;
}
};
// A direct-mapped cache. When doing dmd::Analyze() just after starting
// desktop Firefox (which is similar to analyzing after a longer-running
// session, thanks to the limit on how many records we print), a cache with
// 2^24 entries (which approximates an infinite-entry cache) has a ~91% hit
// rate. A cache with 2^12 entries has a ~83% hit rate, and takes up ~85 KiB
// (on 32-bit platforms) or ~150 KiB (on 64-bit platforms).
static const size_t kNumEntries = 1 << 12;
static const size_t kMask = kNumEntries - 1;
Entry mEntries[kNumEntries];
size_t mNumCacheHits;
size_t mNumCacheMisses;
public:
CodeAddressService()
: mEntries(), mNumCacheHits(0), mNumCacheMisses(0)
{
}
void GetLocation(uint32_t aFrameNumber, const void* aPc, char* aBuf,
size_t aBufLen)
{
MOZ_ASSERT(DescribeCodeAddressLock::IsLocked());
uint32_t index = HashGeneric(aPc) & kMask;
MOZ_ASSERT(index < kNumEntries);
Entry& entry = mEntries[index];
if (!entry.mInUse || entry.mPc != aPc) {
mNumCacheMisses++;
// MozDescribeCodeAddress can (on Linux) acquire a lock inside
// the shared library loader. Another thread might call malloc
// while holding that lock (when loading a shared library). So
// we have to exit the lock around this call. For details, see
// https://bugzilla.mozilla.org/show_bug.cgi?id=363334#c3
MozCodeAddressDetails details;
{
DescribeCodeAddressLock::Unlock();
(void)MozDescribeCodeAddress(const_cast<void*>(aPc), &details);
DescribeCodeAddressLock::Lock();
}
const char* library = mLibraryStrings.Intern(details.library);
entry.Replace(aPc, details.function, library, details.loffset,
details.filename, details.lineno);
} else {
mNumCacheHits++;
}
MOZ_ASSERT(entry.mPc == aPc);
MozFormatCodeAddress(aBuf, aBufLen, aFrameNumber, entry.mPc,
entry.mFunction, entry.mLibrary, entry.mLOffset,
entry.mFileName, entry.mLineNo);
}
size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
size_t n = aMallocSizeOf(this);
for (uint32_t i = 0; i < kNumEntries; i++) {
n += mEntries[i].SizeOfExcludingThis(aMallocSizeOf);
}
n += mLibraryStrings.SizeOfExcludingThis(aMallocSizeOf);
return n;
}
size_t CacheCapacity() const { return kNumEntries; }
size_t CacheCount() const
{
size_t n = 0;
for (size_t i = 0; i < kNumEntries; i++) {
if (mEntries[i].mInUse) {
n++;
}
}
return n;
}
size_t NumCacheHits() const { return mNumCacheHits; }
size_t NumCacheMisses() const { return mNumCacheMisses; }
};
} // namespace mozilla
#endif // CodeAddressService_h__
|
