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