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+/* -*- 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__