diff --git a/libc/malloc_debug/MapData.cpp b/libc/malloc_debug/MapData.cpp
new file mode 100644
index 0000000..ce2b999
--- /dev/null
+++ b/libc/malloc_debug/MapData.cpp
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ * 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.
+ *
+ * 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.
+ */
+
+#include <ctype.h>
+#include <elf.h>
+#include <inttypes.h>
+#include <link.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include <vector>
+
+#include "debug_disable.h"
+#include "MapData.h"
+
+// Format of /proc/<PID>/maps:
+//   6f000000-6f01e000 rwxp 00000000 00:0c 16389419   /system/lib/libcomposer.so
+static MapEntry* parse_line(char* line) {
+  uintptr_t start;
+  uintptr_t end;
+  uintptr_t offset;
+  char permissions[4];
+  int name_pos;
+  if (sscanf(line, "%" PRIxPTR "-%" PRIxPTR " %4s %" PRIxPTR " %*x:%*x %*d %n", &start,
+             &end, permissions, &offset, &name_pos) < 2) {
+    return nullptr;
+  }
+
+  const char* name = line + name_pos;
+  size_t name_len = strlen(name);
+  if (name_len && name[name_len - 1] == '\n') {
+    name_len -= 1;
+  }
+
+  MapEntry* entry = new MapEntry(start, end, offset, name, name_len);
+  if (permissions[0] != 'r') {
+    // Any unreadable map will just get a zero load base.
+    entry->load_base = 0;
+    entry->load_base_read = true;
+  }
+  return entry;
+}
+
+template<typename T>
+static inline bool get_val(MapEntry* entry, uintptr_t addr, T* store) {
+  if (addr < entry->start || addr + sizeof(T) > entry->end) {
+    return false;
+  }
+  // Make sure the address is aligned properly.
+  if (addr & (sizeof(T)-1)) {
+    return false;
+  }
+  *store = *reinterpret_cast<T*>(addr);
+  return true;
+}
+
+static void read_loadbase(MapEntry* entry) {
+  entry->load_base = 0;
+  entry->load_base_read = true;
+  uintptr_t addr = entry->start;
+  ElfW(Ehdr) ehdr;
+  if (!get_val<ElfW(Half)>(entry, addr + offsetof(ElfW(Ehdr), e_phnum), &ehdr.e_phnum)) {
+    return;
+  }
+  if (!get_val<ElfW(Off)>(entry, addr + offsetof(ElfW(Ehdr), e_phoff), &ehdr.e_phoff)) {
+    return;
+  }
+  addr += ehdr.e_phoff;
+  for (size_t i = 0; i < ehdr.e_phnum; i++) {
+    ElfW(Phdr) phdr;
+    if (!get_val<ElfW(Word)>(entry, addr + offsetof(ElfW(Phdr), p_type), &phdr.p_type)) {
+      return;
+    }
+    if (!get_val<ElfW(Off)>(entry, addr + offsetof(ElfW(Phdr), p_offset), &phdr.p_offset)) {
+      return;
+    }
+    if (phdr.p_type == PT_LOAD && phdr.p_offset == entry->offset) {
+      if (!get_val<ElfW(Addr)>(entry, addr + offsetof(ElfW(Phdr), p_vaddr), &phdr.p_vaddr)) {
+        return;
+      }
+      entry->load_base = phdr.p_vaddr;
+      return;
+    }
+    addr += sizeof(phdr);
+  }
+}
+
+bool MapData::Initialize() {
+  ScopedDisableDebugCalls disable;
+
+  FILE* fp = fopen("/proc/self/maps", "re");
+  if (fp == nullptr) {
+    return false;
+  }
+
+  std::vector<char> buffer(1024);
+  while (fgets(buffer.data(), buffer.size(), fp) != nullptr) {
+    MapEntry* entry = parse_line(buffer.data());
+    if (entry == nullptr) {
+      return false;
+    }
+    entries_.push_back(entry);
+  }
+  fclose(fp);
+  return true;
+}
+
+MapData* MapData::Create() {
+  MapData* maps = new MapData();
+  if (!maps->Initialize()) {
+    delete maps;
+    return nullptr;
+  }
+  return maps;
+}
+
+MapData::~MapData() {
+  ScopedDisableDebugCalls disable;
+
+  for (auto* entry : entries_) {
+    delete entry;
+  }
+  entries_.clear();
+}
+
+// Find the containing map info for the PC.
+const MapEntry* MapData::find(uintptr_t pc, uintptr_t* rel_pc) {
+  for (auto* entry : entries_) {
+    if ((pc >= entry->start) && (pc < entry->end)) {
+      if (!entry->load_base_read) {
+        read_loadbase(entry);
+      }
+      if (rel_pc) {
+        *rel_pc = pc - entry->start + entry->load_base;
+      }
+      return entry;
+    }
+  }
+  if (rel_pc) {
+    *rel_pc = pc;
+  }
+  return nullptr;
+}