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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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__
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