[scudo][standalone] Introduce the SizeClassMap

[cryptoad]

Summary

As with the sanitizer_common allocator, the SCM allows for efficient
mapping between sizes and size-classes, table-free.

It doesn't depart significantly from the original, except that we
allow the use of size-class 0 for other purposes (as opposed to
chunks of size 0). The Primary will use it to hold TransferBatches.

[cryptoad]

Correct comment & a format string.

lib/scudo/standalone/CMakeLists.txt

set(SCUDO_HEADERS
   interface.h
   internal_defs.h
   linux.h
   list.h
   mutex.h
   platform.h
   report.h
   secondary.h
+  size_class_map.h
   stats.h
   string_utils.h
   vector.h)
 
 if(COMPILER_RT_HAS_SCUDO_STANDALONE)
   add_compiler_rt_object_libraries(RTScudoStandalone
     ARCHS ${SCUDO_STANDALONE_SUPPORTED_ARCH}
     SOURCES ${SCUDO_SOURCES}

lib/scudo/standalone/common.h

INLINE uptr roundUpToPowerOfTwo(uptr Size) {
   const uptr Up = getMostSignificantSetBitIndex(Size);
   DCHECK_LT(Size, (1UL << (Up + 1)));
   DCHECK_GT(Size, (1UL << Up));
   return 1UL << (Up + 1);
 }
 
 INLINE uptr getLeastSignificantSetBitIndex(uptr X) {
   DCHECK_NE(X, 0U);
-  return static_cast<uptr>(__builtin_ctzll(X));
+  return static_cast<uptr>(__builtin_ctzl(X));
 }
 
 INLINE uptr getLog2(uptr X) {
   DCHECK(isPowerOfTwo(X));
   return getLeastSignificantSetBitIndex(X);
 }
 
 INLINE u32 getRandomU32(u32 *State) {

lib/scudo/standalone/size_class_map.h

+//===-- size_class_map.h ----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_SIZE_CLASS_MAP_H_
+#define SCUDO_SIZE_CLASS_MAP_H_
+
+#include "common.h"
+#include "string_utils.h"
+
+namespace scudo {
+
+// SizeClassMap maps allocation sizes into size classes and back, in an
+// efficient table-free manner.
+//
+// Class 0 is a special class that doesn't abide by the same rules as other
+// classes. The allocator uses it to hold batches.
+//
+// The other sizes are controlled by the template parameters:
+// - MinSizeLog: defines the first class as 2^MinSizeLog bytes.
+// - MaxSizeLog: defines the last class as 2^MaxSizeLog bytes.
+// - MidSizeLog: classes increase with step 2^MinSizeLog from 2^MinSizeLog to
+//               2^MidSizeLog bytes.
+// - NumBits: the number of non-zero bits in sizes after 2^MidSizeLog.
+//            eg. with NumBits==3 all size classes after 2^MidSizeLog look like
+//            0b1xx0..0 (where x is either 0 or 1).
+//
+// This class also gives a hint to a thread-caching allocator about the amount
+// of chunks that can be cached per-thread:
+//  - MaxNumCachedHint is a hint for the max number of chunks cached per class.
+//  - 2^MaxBytesCachedLog is the max number of bytes cached per class.
+
+template <u8 NumBits, u8 MinSizeLog, u8 MidSizeLog, u8 MaxSizeLog,
+          u32 MaxNumCachedHintT, u8 MaxBytesCachedLog>
+class SizeClassMap {
+  static const uptr MinSize = 1UL << MinSizeLog;
+  static const uptr MidSize = 1UL << MidSizeLog;
+  static const uptr MidClass = MidSize / MinSize;
+  static const u8 S = NumBits - 1;
+  static const uptr M = (1UL << S) - 1;
+
+public:
+  static const u32 MaxNumCachedHint = MaxNumCachedHintT;
+
+  static const uptr MaxSize = 1UL << MaxSizeLog;
+  static const uptr NumClasses =
+      MidClass + ((MaxSizeLog - MidSizeLog) << S) + 1;
+  COMPILER_CHECK(NumClasses <= 256);
+  static const uptr LargestClassId = NumClasses - 1;
+  static const uptr BatchClassId = 0;
+
+  static uptr getSizeByClassId(uptr ClassId) {
+    DCHECK_NE(ClassId, BatchClassId);
+    if (ClassId <= MidClass)
+      return ClassId << MinSizeLog;
+    ClassId -= MidClass;
+    const uptr T = MidSize << (ClassId >> S);
+    return T + (T >> S) * (ClassId & M);
+  }
+
+  static uptr getClassIdBySize(uptr Size) {
+    DCHECK_LE(Size, MaxSize);
+    if (Size <= MidSize)
+      return (Size + MinSize - 1) >> MinSizeLog;
+    const uptr L = getMostSignificantSetBitIndex(Size);
+    const uptr HBits = (Size >> (L - S)) & M;
+    const uptr LBits = Size & ((1UL << (L - S)) - 1);
+    const uptr L1 = L - MidSizeLog;
+    return MidClass + (L1 << S) + HBits + (LBits > 0);
+  }
+
+  static u32 getMaxCachedHint(uptr Size) {
+    DCHECK_LE(Size, MaxSize);
+    DCHECK_NE(Size, 0);
+    u32 N;
+    // Force a 32-bit division if the template parameters allow for it.
+    if (MaxBytesCachedLog > 31 || MaxSizeLog > 31)
+      N = static_cast<u32>((1UL << MaxBytesCachedLog) / Size);
+    else
+      N = (1U << MaxBytesCachedLog) / static_cast<u32>(Size);
+    return Max(1U, Min(MaxNumCachedHint, N));
+  }
+
+  static void print() {
+    uptr PrevS = 0;
+    uptr TotalCached = 0;
+    for (uptr I = 0; I < NumClasses; I++) {
+      if (I == BatchClassId)
+        continue;
+      const uptr S = getSizeByClassId(I);
+      if (S >= MidSize / 2 && (S & (S - 1)) == 0)
+        Printf("\n");
+      const uptr D = S - PrevS;
+      const uptr P = PrevS ? (D * 100 / PrevS) : 0;
+      const uptr L = S ? getMostSignificantSetBitIndex(S) : 0;
+      const uptr Cached = getMaxCachedHint(S) * S;
+      Printf(
+          "C%02zu => S: %zu diff: +%zu %02zu%% L %zu Cached: %zu %zu; id %zu\n",
+          I, getSizeByClassId(I), D, P, L, getMaxCachedHint(S), Cached,
+          getClassIdBySize(S));
+      TotalCached += Cached;
+      PrevS = S;
+    }
+    Printf("Total Cached: %zu\n", TotalCached);
+  }
+
+  static void validate() {
+    for (uptr C = 0; C < NumClasses; C++) {
+      if (C == BatchClassId)
+        continue;
+      const uptr S = getSizeByClassId(C);
+      CHECK_NE(S, 0U);
+      CHECK_EQ(getClassIdBySize(S), C);
+      if (C < LargestClassId)
+        CHECK_EQ(getClassIdBySize(S + 1), C + 1);
+      CHECK_EQ(getClassIdBySize(S - 1), C);
+      CHECK_GT(getSizeByClassId(C), getSizeByClassId(C - 1));
+    }
+    // Do not perform the loop if the maximum size is too large.
+    if (MaxSizeLog > 19)
+      return;
+    for (uptr S = 1; S <= MaxSize; S++) {
+      const uptr C = getClassIdBySize(S);
+      CHECK_LT(C, NumClasses);
+      CHECK_GE(getSizeByClassId(C), S);
+      if (C > 0)
+        CHECK_LT(getSizeByClassId(C - 1), S);
+    }
+  }
+};
+
+typedef SizeClassMap<3, 5, 8, 17, 8, 10> DefaultSizeClassMap;
+
+// TODO(kostyak): further tune class maps for Android & Fuchsia.
+#if SCUDO_WORDSIZE == 64U
+typedef SizeClassMap<3, 5, 8, 15, 8, 10> SvelteSizeClassMap;
+typedef SizeClassMap<3, 5, 8, 16, 14, 12> AndroidSizeClassMap;
+#else
+typedef SizeClassMap<3, 4, 7, 15, 8, 10> SvelteSizeClassMap;
+typedef SizeClassMap<3, 4, 7, 16, 14, 12> AndroidSizeClassMap;
+#endif
+
+} // namespace scudo
+
+#endif // SCUDO_SIZE_CLASS_MAP_H_

lib/scudo/standalone/tests/CMakeLists.txt

set(SCUDO_UNIT_TEST_SOURCES
   bytemap_test.cc
   checksum_test.cc
   flags_test.cc
   list_test.cc
   map_test.cc
   mutex_test.cc
   report_test.cc
   secondary_test.cc
+  size_class_map_test.cc
   stats_test.cc
   strings_test.cc
   vector_test.cc
   scudo_unit_test_main.cc)
 
 add_scudo_unittest(ScudoUnitTest
   SOURCES ${SCUDO_UNIT_TEST_SOURCES})

lib/scudo/standalone/tests/size_class_map_test.cc

+//===-- size_class_map_test.cc ----------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "scudo/standalone/size_class_map.h"
+#include "gtest/gtest.h"
+
+template <class SizeClassMap> void testSizeClassMap() {
+  typedef SizeClassMap SCMap;
+  SCMap::print();
+  SCMap::validate();
+}
+
+TEST(ScudoSizeClassMapTest, DefaultSizeClassMap) {
+  testSizeClassMap<scudo::DefaultSizeClassMap>();
+}
+
+TEST(ScudoSizeClassMapTest, SvelteSizeClassMap) {
+  testSizeClassMap<scudo::SvelteSizeClassMap>();
+}
+
+TEST(ScudoSizeClassMapTest, AndroidSizeClassMap) {
+  testSizeClassMap<scudo::AndroidSizeClassMap>();
+}
+
+TEST(ScudoSizeClassMapTest, OneClassSizeClassMap) {
+  testSizeClassMap<scudo::SizeClassMap<1, 5, 5, 5, 0, 0>>();
+}
+
+#if SCUDO_CAN_USE_PRIMARY64
+TEST(ScudoSizeClassMapTest, LargeMaxSizeClassMap) {
+  testSizeClassMap<scudo::SizeClassMap<3, 4, 8, 63, 128, 16>>();
+}
+#endif