Squash: Fix bugs

trunk/3rdparty/gperftools-2-fit/src/base/low_level_alloc.cc

@@ -0,0 +1,580 @@
+// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+/* Copyright (c) 2006, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// A low-level allocator that can be used by other low-level
+// modules without introducing dependency cycles.
+// This allocator is slow and wasteful of memory;
+// it should not be used when performance is key.
+
+#include "base/low_level_alloc.h"
+#include "base/dynamic_annotations.h"
+#include "base/spinlock.h"
+#include "base/logging.h"
+#include "malloc_hook-inl.h"
+#include <gperftools/malloc_hook.h>
+#include <errno.h>
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#ifdef HAVE_MMAP
+#include <sys/mman.h>
+#endif
+#include <new>                   // for placement-new
+
+// On systems (like freebsd) that don't define MAP_ANONYMOUS, use the old
+// form of the name instead.
+#ifndef MAP_ANONYMOUS
+# define MAP_ANONYMOUS MAP_ANON
+#endif
+
+// A first-fit allocator with amortized logarithmic free() time.
+
+LowLevelAlloc::PagesAllocator::~PagesAllocator() {
+}
+
+// ---------------------------------------------------------------------------
+static const int kMaxLevel = 30;
+
+// We put this class-only struct in a namespace to avoid polluting the
+// global namespace with this struct name (thus risking an ODR violation).
+namespace low_level_alloc_internal {
+  // This struct describes one allocated block, or one free block.
+  struct AllocList {
+    struct Header {
+      intptr_t size;  // size of entire region, including this field. Must be
+                      // first.  Valid in both allocated and unallocated blocks
+      intptr_t magic; // kMagicAllocated or kMagicUnallocated xor this
+      LowLevelAlloc::Arena *arena; // pointer to parent arena
+      void *dummy_for_alignment;   // aligns regions to 0 mod 2*sizeof(void*)
+    } header;
+
+    // Next two fields: in unallocated blocks: freelist skiplist data
+    //                  in allocated blocks: overlaps with client data
+    int levels;           // levels in skiplist used
+    AllocList *next[kMaxLevel];   // actually has levels elements.
+                                  // The AllocList node may not have room for
+                                  // all kMaxLevel entries.  See max_fit in
+                                  // LLA_SkiplistLevels()
+  };
+}
+using low_level_alloc_internal::AllocList;
+
+
+// ---------------------------------------------------------------------------
+// A trivial skiplist implementation.  This is used to keep the freelist
+// in address order while taking only logarithmic time per insert and delete.
+
+// An integer approximation of log2(size/base)
+// Requires size >= base.
+static int IntLog2(size_t size, size_t base) {
+  int result = 0;
+  for (size_t i = size; i > base; i >>= 1) { // i == floor(size/2**result)
+    result++;
+  }
+  //    floor(size / 2**result) <= base < floor(size / 2**(result-1))
+  // =>     log2(size/(base+1)) <= result < 1+log2(size/base)
+  // => result ~= log2(size/base)
+  return result;
+}
+
+// Return a random integer n:  p(n)=1/(2**n) if 1 <= n; p(n)=0 if n < 1.
+static int Random() {
+  static uint32 r = 1;         // no locking---it's not critical
+  int result = 1;
+  while ((((r = r*1103515245 + 12345) >> 30) & 1) == 0) {
+    result++;
+  }
+  return result;
+}
+
+// Return a number of skiplist levels for a node of size bytes, where
+// base is the minimum node size.  Compute level=log2(size / base)+n
+// where n is 1 if random is false and otherwise a random number generated with
+// the standard distribution for a skiplist:  See Random() above.
+// Bigger nodes tend to have more skiplist levels due to the log2(size / base)
+// term, so first-fit searches touch fewer nodes.  "level" is clipped so
+// level<kMaxLevel and next[level-1] will fit in the node.
+// 0 < LLA_SkiplistLevels(x,y,false) <= LLA_SkiplistLevels(x,y,true) < kMaxLevel
+static int LLA_SkiplistLevels(size_t size, size_t base, bool random) {
+  // max_fit is the maximum number of levels that will fit in a node for the
+  // given size.   We can't return more than max_fit, no matter what the
+  // random number generator says.
+  int max_fit = (size-OFFSETOF_MEMBER(AllocList, next)) / sizeof (AllocList *);
+  int level = IntLog2(size, base) + (random? Random() : 1);
+  if (level > max_fit)     level = max_fit;
+  if (level > kMaxLevel-1) level = kMaxLevel - 1;
+  RAW_CHECK(level >= 1, "block not big enough for even one level");
+  return level;
+}
+
+// Return "atleast", the first element of AllocList *head s.t. *atleast >= *e.
+// For 0 <= i < head->levels, set prev[i] to "no_greater", where no_greater
+// points to the last element at level i in the AllocList less than *e, or is
+// head if no such element exists.
+static AllocList *LLA_SkiplistSearch(AllocList *head,
+                                     AllocList *e, AllocList **prev) {
+  AllocList *p = head;
+  for (int level = head->levels - 1; level >= 0; level--) {
+    for (AllocList *n; (n = p->next[level]) != 0 && n < e; p = n) {
+    }
+    prev[level] = p;
+  }
+  return (head->levels == 0) ?  0 : prev[0]->next[0];
+}
+
+// Insert element *e into AllocList *head.  Set prev[] as LLA_SkiplistSearch.
+// Requires that e->levels be previously set by the caller (using
+// LLA_SkiplistLevels())
+static void LLA_SkiplistInsert(AllocList *head, AllocList *e,
+                               AllocList **prev) {
+  LLA_SkiplistSearch(head, e, prev);
+  for (; head->levels < e->levels; head->levels++) { // extend prev pointers
+    prev[head->levels] = head;                       // to all *e's levels
+  }
+  for (int i = 0; i != e->levels; i++) { // add element to list
+    e->next[i] = prev[i]->next[i];
+    prev[i]->next[i] = e;
+  }
+}
+
+// Remove element *e from AllocList *head.  Set prev[] as LLA_SkiplistSearch().
+// Requires that e->levels be previous set by the caller (using
+// LLA_SkiplistLevels())
+static void LLA_SkiplistDelete(AllocList *head, AllocList *e,
+                               AllocList **prev) {
+  AllocList *found = LLA_SkiplistSearch(head, e, prev);
+  RAW_CHECK(e == found, "element not in freelist");
+  for (int i = 0; i != e->levels && prev[i]->next[i] == e; i++) {
+    prev[i]->next[i] = e->next[i];
+  }
+  while (head->levels > 0 && head->next[head->levels - 1] == 0) {
+    head->levels--;   // reduce head->levels if level unused
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Arena implementation
+
+struct LowLevelAlloc::Arena {
+  Arena() : mu(SpinLock::LINKER_INITIALIZED) {} // does nothing; for static init
+  explicit Arena(int) : pagesize(0) {}  // set pagesize to zero explicitly
+                                        // for non-static init
+
+  SpinLock mu;            // protects freelist, allocation_count,
+                          // pagesize, roundup, min_size
+  AllocList freelist;     // head of free list; sorted by addr (under mu)
+  int32 allocation_count; // count of allocated blocks (under mu)
+  int32 flags;            // flags passed to NewArena (ro after init)
+  size_t pagesize;        // ==getpagesize()  (init under mu, then ro)
+  size_t roundup;         // lowest power of 2 >= max(16,sizeof (AllocList))
+                          // (init under mu, then ro)
+  size_t min_size;        // smallest allocation block size
+                          // (init under mu, then ro)
+  PagesAllocator *allocator;
+};
+
+// The default arena, which is used when 0 is passed instead of an Arena
+// pointer.
+static struct LowLevelAlloc::Arena default_arena;
+
+// Non-malloc-hooked arenas: used only to allocate metadata for arenas that
+// do not want malloc hook reporting, so that for them there's no malloc hook
+// reporting even during arena creation.
+static struct LowLevelAlloc::Arena unhooked_arena;
+static struct LowLevelAlloc::Arena unhooked_async_sig_safe_arena;
+
+namespace {
+
+  class DefaultPagesAllocator : public LowLevelAlloc::PagesAllocator {
+  public:
+    virtual ~DefaultPagesAllocator() {};
+    virtual void *MapPages(int32 flags, size_t size);
+    virtual void UnMapPages(int32 flags, void *addr, size_t size);
+  };
+
+}
+
+// magic numbers to identify allocated and unallocated blocks
+static const intptr_t kMagicAllocated = 0x4c833e95;
+static const intptr_t kMagicUnallocated = ~kMagicAllocated;
+
+namespace {
+  class SCOPED_LOCKABLE ArenaLock {
+   public:
+    explicit ArenaLock(LowLevelAlloc::Arena *arena)
+        EXCLUSIVE_LOCK_FUNCTION(arena->mu)
+        : left_(false), mask_valid_(false), arena_(arena) {
+      if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
+      // We've decided not to support async-signal-safe arena use until
+      // there a demonstrated need.  Here's how one could do it though
+      // (would need to be made more portable).
+#if 0
+        sigset_t all;
+        sigfillset(&all);
+        this->mask_valid_ =
+            (pthread_sigmask(SIG_BLOCK, &all, &this->mask_) == 0);
+#else
+        RAW_CHECK(false, "We do not yet support async-signal-safe arena.");
+#endif
+      }
+      this->arena_->mu.Lock();
+    }
+    ~ArenaLock() { RAW_CHECK(this->left_, "haven't left Arena region"); }
+    void Leave() UNLOCK_FUNCTION() {
+      this->arena_->mu.Unlock();
+#if 0
+      if (this->mask_valid_) {
+        pthread_sigmask(SIG_SETMASK, &this->mask_, 0);
+      }
+#endif
+      this->left_ = true;
+    }
+   private:
+    bool left_;       // whether left region
+    bool mask_valid_;
+#if 0
+    sigset_t mask_;   // old mask of blocked signals
+#endif
+    LowLevelAlloc::Arena *arena_;
+    DISALLOW_COPY_AND_ASSIGN(ArenaLock);
+  };
+} // anonymous namespace
+
+// create an appropriate magic number for an object at "ptr"
+// "magic" should be kMagicAllocated or kMagicUnallocated
+inline static intptr_t Magic(intptr_t magic, AllocList::Header *ptr) {
+  return magic ^ reinterpret_cast<intptr_t>(ptr);
+}
+
+// Initialize the fields of an Arena
+static void ArenaInit(LowLevelAlloc::Arena *arena) {
+  if (arena->pagesize == 0) {
+    arena->pagesize = getpagesize();
+    // Round up block sizes to a power of two close to the header size.
+    arena->roundup = 16;
+    while (arena->roundup < sizeof (arena->freelist.header)) {
+      arena->roundup += arena->roundup;
+    }
+    // Don't allocate blocks less than twice the roundup size to avoid tiny
+    // free blocks.
+    arena->min_size = 2 * arena->roundup;
+    arena->freelist.header.size = 0;
+    arena->freelist.header.magic =
+        Magic(kMagicUnallocated, &arena->freelist.header);
+    arena->freelist.header.arena = arena;
+    arena->freelist.levels = 0;
+    memset(arena->freelist.next, 0, sizeof (arena->freelist.next));
+    arena->allocation_count = 0;
+    if (arena == &default_arena) {
+      // Default arena should be hooked, e.g. for heap-checker to trace
+      // pointer chains through objects in the default arena.
+      arena->flags = LowLevelAlloc::kCallMallocHook;
+    } else if (arena == &unhooked_async_sig_safe_arena) {
+      arena->flags = LowLevelAlloc::kAsyncSignalSafe;
+    } else {
+      arena->flags = 0;   // other arenas' flags may be overridden by client,
+                          // but unhooked_arena will have 0 in 'flags'.
+    }
+    arena->allocator = LowLevelAlloc::GetDefaultPagesAllocator();
+  }
+}
+
+// L < meta_data_arena->mu
+LowLevelAlloc::Arena *LowLevelAlloc::NewArena(int32 flags,
+                                              Arena *meta_data_arena) {
+  return NewArenaWithCustomAlloc(flags, meta_data_arena, NULL);
+}
+
+// L < meta_data_arena->mu
+LowLevelAlloc::Arena *LowLevelAlloc::NewArenaWithCustomAlloc(int32 flags,
+                                                             Arena *meta_data_arena,
+                                                             PagesAllocator *allocator) {
+  RAW_CHECK(meta_data_arena != 0, "must pass a valid arena");
+  if (meta_data_arena == &default_arena) {
+    if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
+      meta_data_arena = &unhooked_async_sig_safe_arena;
+    } else if ((flags & LowLevelAlloc::kCallMallocHook) == 0) {
+      meta_data_arena = &unhooked_arena;
+    }
+  }
+  // Arena(0) uses the constructor for non-static contexts
+  Arena *result =
+    new (AllocWithArena(sizeof (*result), meta_data_arena)) Arena(0);
+  ArenaInit(result);
+  result->flags = flags;
+  if (allocator) {
+    result->allocator = allocator;
+  }
+  return result;
+}
+
+// L < arena->mu, L < arena->arena->mu
+bool LowLevelAlloc::DeleteArena(Arena *arena) {
+  RAW_CHECK(arena != 0 && arena != &default_arena && arena != &unhooked_arena,
+            "may not delete default arena");
+  ArenaLock section(arena);
+  bool empty = (arena->allocation_count == 0);
+  section.Leave();
+  if (empty) {
+    while (arena->freelist.next[0] != 0) {
+      AllocList *region = arena->freelist.next[0];
+      size_t size = region->header.size;
+      arena->freelist.next[0] = region->next[0];
+      RAW_CHECK(region->header.magic ==
+                Magic(kMagicUnallocated, &region->header),
+                "bad magic number in DeleteArena()");
+      RAW_CHECK(region->header.arena == arena,
+                "bad arena pointer in DeleteArena()");
+      RAW_CHECK(size % arena->pagesize == 0,
+                "empty arena has non-page-aligned block size");
+      RAW_CHECK(reinterpret_cast<intptr_t>(region) % arena->pagesize == 0,
+                "empty arena has non-page-aligned block");
+      int munmap_result;
+      if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
+        munmap_result = munmap(region, size);
+      } else {
+        munmap_result = MallocHook::UnhookedMUnmap(region, size);
+      }
+      RAW_CHECK(munmap_result == 0,
+                "LowLevelAlloc::DeleteArena:  munmap failed address");
+    }
+    Free(arena);
+  }
+  return empty;
+}
+
+// ---------------------------------------------------------------------------
+
+// Return value rounded up to next multiple of align.
+// align must be a power of two.
+static intptr_t RoundUp(intptr_t addr, intptr_t align) {
+  return (addr + align - 1) & ~(align - 1);
+}
+
+// Equivalent to "return prev->next[i]" but with sanity checking
+// that the freelist is in the correct order, that it
+// consists of regions marked "unallocated", and that no two regions
+// are adjacent in memory (they should have been coalesced).
+// L < arena->mu
+static AllocList *Next(int i, AllocList *prev, LowLevelAlloc::Arena *arena) {
+  RAW_CHECK(i < prev->levels, "too few levels in Next()");
+  AllocList *next = prev->next[i];
+  if (next != 0) {
+    RAW_CHECK(next->header.magic == Magic(kMagicUnallocated, &next->header),
+              "bad magic number in Next()");
+    RAW_CHECK(next->header.arena == arena,
+              "bad arena pointer in Next()");
+    if (prev != &arena->freelist) {
+      RAW_CHECK(prev < next, "unordered freelist");
+      RAW_CHECK(reinterpret_cast<char *>(prev) + prev->header.size <
+                reinterpret_cast<char *>(next), "malformed freelist");
+    }
+  }
+  return next;
+}
+
+// Coalesce list item "a" with its successor if they are adjacent.
+static void Coalesce(AllocList *a) {
+  AllocList *n = a->next[0];
+  if (n != 0 && reinterpret_cast<char *>(a) + a->header.size ==
+                    reinterpret_cast<char *>(n)) {
+    LowLevelAlloc::Arena *arena = a->header.arena;
+    a->header.size += n->header.size;
+    n->header.magic = 0;
+    n->header.arena = 0;
+    AllocList *prev[kMaxLevel];
+    LLA_SkiplistDelete(&arena->freelist, n, prev);
+    LLA_SkiplistDelete(&arena->freelist, a, prev);
+    a->levels = LLA_SkiplistLevels(a->header.size, arena->min_size, true);
+    LLA_SkiplistInsert(&arena->freelist, a, prev);
+  }
+}
+
+// Adds block at location "v" to the free list
+// L >= arena->mu
+static void AddToFreelist(void *v, LowLevelAlloc::Arena *arena) {
+  AllocList *f = reinterpret_cast<AllocList *>(
+                        reinterpret_cast<char *>(v) - sizeof (f->header));
+  RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header),
+            "bad magic number in AddToFreelist()");
+  RAW_CHECK(f->header.arena == arena,
+            "bad arena pointer in AddToFreelist()");
+  f->levels = LLA_SkiplistLevels(f->header.size, arena->min_size, true);
+  AllocList *prev[kMaxLevel];
+  LLA_SkiplistInsert(&arena->freelist, f, prev);
+  f->header.magic = Magic(kMagicUnallocated, &f->header);
+  Coalesce(f);                  // maybe coalesce with successor
+  Coalesce(prev[0]);            // maybe coalesce with predecessor
+}
+
+// Frees storage allocated by LowLevelAlloc::Alloc().
+// L < arena->mu
+void LowLevelAlloc::Free(void *v) {
+  if (v != 0) {
+    AllocList *f = reinterpret_cast<AllocList *>(
+                        reinterpret_cast<char *>(v) - sizeof (f->header));
+    RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header),
+              "bad magic number in Free()");
+    LowLevelAlloc::Arena *arena = f->header.arena;
+    if ((arena->flags & kCallMallocHook) != 0) {
+      MallocHook::InvokeDeleteHook(v);
+    }
+    ArenaLock section(arena);
+    AddToFreelist(v, arena);
+    RAW_CHECK(arena->allocation_count > 0, "nothing in arena to free");
+    arena->allocation_count--;
+    section.Leave();
+  }
+}
+
+// allocates and returns a block of size bytes, to be freed with Free()
+// L < arena->mu
+static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
+  void *result = 0;
+  if (request != 0) {
+    AllocList *s;       // will point to region that satisfies request
+    ArenaLock section(arena);
+    ArenaInit(arena);
+    // round up with header
+    size_t req_rnd = RoundUp(request + sizeof (s->header), arena->roundup);
+    for (;;) {      // loop until we find a suitable region
+      // find the minimum levels that a block of this size must have
+      int i = LLA_SkiplistLevels(req_rnd, arena->min_size, false) - 1;
+      if (i < arena->freelist.levels) {   // potential blocks exist
+        AllocList *before = &arena->freelist;  // predecessor of s
+        while ((s = Next(i, before, arena)) != 0 && s->header.size < req_rnd) {
+          before = s;
+        }
+        if (s != 0) {       // we found a region
+          break;
+        }
+      }
+      // we unlock before mmap() both because mmap() may call a callback hook,
+      // and because it may be slow.
+      arena->mu.Unlock();
+      // mmap generous 64K chunks to decrease
+      // the chances/impact of fragmentation:
+      size_t new_pages_size = RoundUp(req_rnd, arena->pagesize * 16);
+      void *new_pages = arena->allocator->MapPages(arena->flags, new_pages_size);
+      arena->mu.Lock();
+      s = reinterpret_cast<AllocList *>(new_pages);
+      s->header.size = new_pages_size;
+      // Pretend the block is allocated; call AddToFreelist() to free it.
+      s->header.magic = Magic(kMagicAllocated, &s->header);
+      s->header.arena = arena;
+      AddToFreelist(&s->levels, arena);  // insert new region into free list
+    }
+    AllocList *prev[kMaxLevel];
+    LLA_SkiplistDelete(&arena->freelist, s, prev);    // remove from free list
+    // s points to the first free region that's big enough
+    if (req_rnd + arena->min_size <= s->header.size) {  // big enough to split
+      AllocList *n = reinterpret_cast<AllocList *>
+                        (req_rnd + reinterpret_cast<char *>(s));
+      n->header.size = s->header.size - req_rnd;
+      n->header.magic = Magic(kMagicAllocated, &n->header);
+      n->header.arena = arena;
+      s->header.size = req_rnd;
+      AddToFreelist(&n->levels, arena);
+    }
+    s->header.magic = Magic(kMagicAllocated, &s->header);
+    RAW_CHECK(s->header.arena == arena, "");
+    arena->allocation_count++;
+    section.Leave();
+    result = &s->levels;
+  }
+  return result;
+}
+
+void *LowLevelAlloc::Alloc(size_t request) {
+  void *result = DoAllocWithArena(request, &default_arena);
+  if ((default_arena.flags & kCallMallocHook) != 0) {
+    // this call must be directly in the user-called allocator function
+    // for MallocHook::GetCallerStackTrace to work properly
+    MallocHook::InvokeNewHook(result, request);
+  }
+  return result;
+}
+
+void *LowLevelAlloc::AllocWithArena(size_t request, Arena *arena) {
+  RAW_CHECK(arena != 0, "must pass a valid arena");
+  void *result = DoAllocWithArena(request, arena);
+  if ((arena->flags & kCallMallocHook) != 0) {
+    // this call must be directly in the user-called allocator function
+    // for MallocHook::GetCallerStackTrace to work properly
+    MallocHook::InvokeNewHook(result, request);
+  }
+  return result;
+}
+
+LowLevelAlloc::Arena *LowLevelAlloc::DefaultArena() {
+  return &default_arena;
+}
+
+static DefaultPagesAllocator *default_pages_allocator;
+static union {
+  char chars[sizeof(DefaultPagesAllocator)];
+  void *ptr;
+} debug_pages_allocator_space;
+
+LowLevelAlloc::PagesAllocator *LowLevelAlloc::GetDefaultPagesAllocator(void) {
+  if (default_pages_allocator) {
+    return default_pages_allocator;
+  }
+  default_pages_allocator = new (debug_pages_allocator_space.chars) DefaultPagesAllocator();
+  return default_pages_allocator;
+}
+
+void *DefaultPagesAllocator::MapPages(int32 flags, size_t size) {
+  void *new_pages;
+  if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
+    new_pages = MallocHook::UnhookedMMap(0, size,
+                                         PROT_WRITE|PROT_READ,
+                                         MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+  } else {
+    new_pages = mmap(0, size,
+                     PROT_WRITE|PROT_READ,
+                     MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+  }
+  RAW_CHECK(new_pages != MAP_FAILED, "mmap error");
+
+  return new_pages;
+}
+
+void DefaultPagesAllocator::UnMapPages(int32 flags, void *region, size_t size) {
+  int munmap_result;
+  if ((flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
+    munmap_result = munmap(region, size);
+  } else {
+    munmap_result = MallocHook::UnhookedMUnmap(region, size);
+  }
+  RAW_CHECK(munmap_result == 0,
+            "LowLevelAlloc::DeleteArena: munmap failed address");
+}