libc/bionic/malloc_debug_leak.cpp - platform/bionic - Git at Google

 /*
  * Copyright (C) 2008 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 <dlfcn.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <unwind.h>

 #include <arpa/inet.h>
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/system_properties.h>
 #include <sys/types.h>
 #include <sys/un.h>

 #include "dlmalloc.h"
 #include "logd.h"
 #include "malloc_debug_common.h"

 // This file should be included into the build only when
 // MALLOC_LEAK_CHECK, or MALLOC_QEMU_INSTRUMENT, or both
 // macros are defined.
 #ifndef MALLOC_LEAK_CHECK
 #error MALLOC_LEAK_CHECK is not defined.
 #endif  // !MALLOC_LEAK_CHECK

 // Global variables defined in malloc_debug_common.c
 extern int gMallocLeakZygoteChild;
 extern pthread_mutex_t gAllocationsMutex;
 extern HashTable gHashTable;

 // =============================================================================
 // stack trace functions
 // =============================================================================

 #ifndef MALLOC_ALIGNMENT
 #define MALLOC_ALIGNMENT    ((size_t)8U)
 #endif
 #define GUARD               0x48151642
 #define DEBUG               0

 // =============================================================================
 // Structures
 // =============================================================================

 struct AllocationEntry {
     HashEntry* entry;
     uint32_t guard;
 };

 static AllocationEntry* to_header(void* mem) {
   return reinterpret_cast<AllocationEntry*>(mem) - 1;
 }

 // =============================================================================
 // Hash Table functions
 // =============================================================================

 static uint32_t get_hash(intptr_t* backtrace, size_t numEntries) {
     if (backtrace == NULL) return 0;

     int hash = 0;
     size_t i;
     for (i = 0 ; i < numEntries ; i++) {
         hash = (hash * 33) + (backtrace[i] >> 2);
     }

     return hash;
 }

 static HashEntry* find_entry(HashTable* table, int slot,
         intptr_t* backtrace, size_t numEntries, size_t size) {
     HashEntry* entry = table->slots[slot];
     while (entry != NULL) {
         //debug_log("backtrace: %p, entry: %p entry->backtrace: %p\n",
         //        backtrace, entry, (entry != NULL) ? entry->backtrace : NULL);
         /*
          * See if the entry matches exactly.  We compare the "size" field,
          * including the flag bits.
          */
         if (entry->size == size && entry->numEntries == numEntries &&
                 !memcmp(backtrace, entry->backtrace, numEntries * sizeof(intptr_t))) {
             return entry;
         }

         entry = entry->next;
     }

     return NULL;
 }

 static HashEntry* record_backtrace(intptr_t* backtrace, size_t numEntries, size_t size) {
     size_t hash = get_hash(backtrace, numEntries);
     size_t slot = hash % HASHTABLE_SIZE;

     if (size & SIZE_FLAG_MASK) {
         debug_log("malloc_debug: allocation %zx exceeds bit width\n", size);
         abort();
     }

     if (gMallocLeakZygoteChild) {
         size |= SIZE_FLAG_ZYGOTE_CHILD;
     }

     HashEntry* entry = find_entry(&gHashTable, slot, backtrace, numEntries, size);

     if (entry != NULL) {
         entry->allocations++;
     } else {
         // create a new entry
         entry = static_cast<HashEntry*>(dlmalloc(sizeof(HashEntry) + numEntries*sizeof(intptr_t)));
         if (!entry) {
             return NULL;
         }
         entry->allocations = 1;
         entry->slot = slot;
         entry->prev = NULL;
         entry->next = gHashTable.slots[slot];
         entry->numEntries = numEntries;
         entry->size = size;

         memcpy(entry->backtrace, backtrace, numEntries * sizeof(intptr_t));

         gHashTable.slots[slot] = entry;

         if (entry->next != NULL) {
             entry->next->prev = entry;
         }

         // we just added an entry, increase the size of the hashtable
         gHashTable.count++;
     }

     return entry;
 }

 static int is_valid_entry(HashEntry* entry) {
     if (entry != NULL) {
         int i;
         for (i = 0 ; i < HASHTABLE_SIZE ; i++) {
             HashEntry* e1 = gHashTable.slots[i];

             while (e1 != NULL) {
                 if (e1 == entry) {
                     return 1;
                 }

                 e1 = e1->next;
             }
         }
     }

     return 0;
 }

 static void remove_entry(HashEntry* entry) {
     HashEntry* prev = entry->prev;
     HashEntry* next = entry->next;

     if (prev != NULL) entry->prev->next = next;
     if (next != NULL) entry->next->prev = prev;

     if (prev == NULL) {
         // we are the head of the list. set the head to be next
         gHashTable.slots[entry->slot] = entry->next;
     }

     // we just removed and entry, decrease the size of the hashtable
     gHashTable.count--;
 }

 // =============================================================================
 // malloc fill functions
 // =============================================================================

 #define CHK_FILL_FREE           0xef
 #define CHK_SENTINEL_VALUE      0xeb

 extern "C" void* fill_calloc(size_t n_elements, size_t elem_size) {
     return dlcalloc(n_elements, elem_size);
 }

 extern "C" void* fill_malloc(size_t bytes) {
     void* buffer = dlmalloc(bytes);
     if (buffer) {
         memset(buffer, CHK_SENTINEL_VALUE, bytes);
     }
     return buffer;
 }

 extern "C" void fill_free(void* mem) {
     size_t bytes = dlmalloc_usable_size(mem);
     memset(mem, CHK_FILL_FREE, bytes);
     dlfree(mem);
 }

 extern "C" void* fill_realloc(void* mem, size_t bytes) {
     void* buffer = fill_malloc(bytes);
     if (mem == NULL) {
         return buffer;
     }
     if (buffer) {
         size_t old_size = dlmalloc_usable_size(mem);
         size_t size = (bytes < old_size)?(bytes):(old_size);
         memcpy(buffer, mem, size);
         fill_free(mem);
     }
     return buffer;
 }

 extern "C" void* fill_memalign(size_t alignment, size_t bytes) {
     void* buffer = dlmemalign(alignment, bytes);
     if (buffer) {
         memset(buffer, CHK_SENTINEL_VALUE, bytes);
     }
     return buffer;
 }

 // =============================================================================
 // malloc leak functions
 // =============================================================================

 static void* MEMALIGN_GUARD = reinterpret_cast<void*>(0xA1A41520);

 extern __LIBC_HIDDEN__ int get_backtrace(intptr_t* addrs, size_t max_entries);

 extern "C" void* leak_malloc(size_t bytes) {
     // allocate enough space infront of the allocation to store the pointer for
     // the alloc structure. This will making free'ing the structer really fast!

     // 1. allocate enough memory and include our header
     // 2. set the base pointer to be right after our header

     size_t size = bytes + sizeof(AllocationEntry);
     if (size < bytes) { // Overflow.
         return NULL;
     }

     void* base = dlmalloc(size);
     if (base != NULL) {
         ScopedPthreadMutexLocker locker(&gAllocationsMutex);

         intptr_t backtrace[BACKTRACE_SIZE];
         size_t numEntries = get_backtrace(backtrace, BACKTRACE_SIZE);

         AllocationEntry* header = reinterpret_cast<AllocationEntry*>(base);
         header->entry = record_backtrace(backtrace, numEntries, bytes);
         header->guard = GUARD;

         // now increment base to point to after our header.
         // this should just work since our header is 8 bytes.
         base = reinterpret_cast<AllocationEntry*>(base) + 1;
     }

     return base;
 }

 extern "C" void leak_free(void* mem) {
     if (mem != NULL) {
         ScopedPthreadMutexLocker locker(&gAllocationsMutex);

         // check the guard to make sure it is valid
         AllocationEntry* header = to_header(mem);

         if (header->guard != GUARD) {
             // could be a memaligned block
             if (reinterpret_cast<void**>(mem)[-1] == MEMALIGN_GUARD) {
                 mem = reinterpret_cast<void**>(mem)[-2];
                 header = to_header(mem);
             }
         }

         if (header->guard == GUARD || is_valid_entry(header->entry)) {
             // decrement the allocations
             HashEntry* entry = header->entry;
             entry->allocations--;
             if (entry->allocations <= 0) {
                 remove_entry(entry);
                 dlfree(entry);
             }

             // now free the memory!
             dlfree(header);
         } else {
             debug_log("WARNING bad header guard: '0x%x'! and invalid entry: %p\n",
                     header->guard, header->entry);
         }
     }
 }

 extern "C" void* leak_calloc(size_t n_elements, size_t elem_size) {
     /* Fail on overflow - just to be safe even though this code runs only
      * within the debugging C library, not the production one */
     if (n_elements && MAX_SIZE_T / n_elements < elem_size) {
         return NULL;
     }
     size_t size = n_elements * elem_size;
     void* ptr  = leak_malloc(size);
     if (ptr != NULL) {
         memset(ptr, 0, size);
     }
     return ptr;
 }

 extern "C" void* leak_realloc(void* oldMem, size_t bytes) {
     if (oldMem == NULL) {
         return leak_malloc(bytes);
     }
     void* newMem = NULL;
     AllocationEntry* header = to_header(oldMem);
     if (header && header->guard == GUARD) {
         size_t oldSize = header->entry->size & ~SIZE_FLAG_MASK;
         newMem = leak_malloc(bytes);
         if (newMem != NULL) {
             size_t copySize = (oldSize <= bytes) ? oldSize : bytes;
             memcpy(newMem, oldMem, copySize);
             leak_free(oldMem);
         }
     } else {
         newMem = dlrealloc(oldMem, bytes);
     }
     return newMem;
 }

 extern "C" void* leak_memalign(size_t alignment, size_t bytes) {
     // we can just use malloc
     if (alignment <= MALLOC_ALIGNMENT) {
         return leak_malloc(bytes);
     }

     // need to make sure it's a power of two
     if (alignment & (alignment-1)) {
         alignment = 1L << (31 - __builtin_clz(alignment));
     }

     // here, aligment is at least MALLOC_ALIGNMENT<<1 bytes
     // we will align by at least MALLOC_ALIGNMENT bytes
     // and at most alignment-MALLOC_ALIGNMENT bytes
     size_t size = (alignment-MALLOC_ALIGNMENT) + bytes;
     if (size < bytes) { // Overflow.
         return NULL;
     }

     void* base = leak_malloc(size);
     if (base != NULL) {
         intptr_t ptr = reinterpret_cast<intptr_t>(base);
         if ((ptr % alignment) == 0) {
             return base;
         }

         // align the pointer
         ptr += ((-ptr) % alignment);

         // there is always enough space for the base pointer and the guard
         reinterpret_cast<void**>(ptr)[-1] = MEMALIGN_GUARD;
         reinterpret_cast<void**>(ptr)[-2] = base;

         return reinterpret_cast<void*>(ptr);
     }
     return base;
 }
	/*
	* Copyright (C) 2008 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 <dlfcn.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <pthread.h>
	#include <stdarg.h>
	#include <stddef.h>
	#include <stdint.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <unistd.h>
	#include <unwind.h>

	#include <arpa/inet.h>
	#include <sys/select.h>
	#include <sys/socket.h>
	#include <sys/system_properties.h>
	#include <sys/types.h>
	#include <sys/un.h>

	#include "dlmalloc.h"
	#include "logd.h"
	#include "malloc_debug_common.h"

	// This file should be included into the build only when
	// MALLOC_LEAK_CHECK, or MALLOC_QEMU_INSTRUMENT, or both
	// macros are defined.
	#ifndef MALLOC_LEAK_CHECK
	#error MALLOC_LEAK_CHECK is not defined.
	#endif // !MALLOC_LEAK_CHECK

	// Global variables defined in malloc_debug_common.c
	extern int gMallocLeakZygoteChild;
	extern pthread_mutex_t gAllocationsMutex;
	extern HashTable gHashTable;

	// =============================================================================
	// stack trace functions
	// =============================================================================

	#ifndef MALLOC_ALIGNMENT
	#define MALLOC_ALIGNMENT ((size_t)8U)
	#endif
	#define GUARD 0x48151642
	#define DEBUG 0

	// =============================================================================
	// Structures
	// =============================================================================

	struct AllocationEntry {
	HashEntry* entry;
	uint32_t guard;
	};

	static AllocationEntry* to_header(void* mem) {
	return reinterpret_cast<AllocationEntry*>(mem) - 1;
	}

	// =============================================================================
	// Hash Table functions
	// =============================================================================

	static uint32_t get_hash(intptr_t* backtrace, size_t numEntries) {
	if (backtrace == NULL) return 0;

	int hash = 0;
	size_t i;
	for (i = 0 ; i < numEntries ; i++) {
	hash = (hash * 33) + (backtrace[i] >> 2);
	}

	return hash;
	}

	static HashEntry* find_entry(HashTable* table, int slot,
	intptr_t* backtrace, size_t numEntries, size_t size) {
	HashEntry* entry = table->slots[slot];
	while (entry != NULL) {
	//debug_log("backtrace: %p, entry: %p entry->backtrace: %p\n",
	// backtrace, entry, (entry != NULL) ? entry->backtrace : NULL);
	/*
	* See if the entry matches exactly. We compare the "size" field,
	* including the flag bits.
	*/
	if (entry->size == size && entry->numEntries == numEntries &&
	!memcmp(backtrace, entry->backtrace, numEntries * sizeof(intptr_t))) {
	return entry;
	}

	entry = entry->next;
	}

	return NULL;
	}

	static HashEntry* record_backtrace(intptr_t* backtrace, size_t numEntries, size_t size) {
	size_t hash = get_hash(backtrace, numEntries);
	size_t slot = hash % HASHTABLE_SIZE;

	if (size & SIZE_FLAG_MASK) {
	debug_log("malloc_debug: allocation %zx exceeds bit width\n", size);
	abort();
	}

	if (gMallocLeakZygoteChild) {
	size \|= SIZE_FLAG_ZYGOTE_CHILD;
	}

	HashEntry* entry = find_entry(&gHashTable, slot, backtrace, numEntries, size);

	if (entry != NULL) {
	entry->allocations++;
	} else {
	// create a new entry
	entry = static_cast<HashEntry>(dlmalloc(sizeof(HashEntry) + numEntriessizeof(intptr_t)));
	if (!entry) {
	return NULL;
	}
	entry->allocations = 1;
	entry->slot = slot;
	entry->prev = NULL;
	entry->next = gHashTable.slots[slot];
	entry->numEntries = numEntries;
	entry->size = size;

	memcpy(entry->backtrace, backtrace, numEntries * sizeof(intptr_t));

	gHashTable.slots[slot] = entry;

	if (entry->next != NULL) {
	entry->next->prev = entry;
	}

	// we just added an entry, increase the size of the hashtable
	gHashTable.count++;
	}

	return entry;
	}

	static int is_valid_entry(HashEntry* entry) {
	if (entry != NULL) {
	int i;
	for (i = 0 ; i < HASHTABLE_SIZE ; i++) {
	HashEntry* e1 = gHashTable.slots[i];

	while (e1 != NULL) {
	if (e1 == entry) {
	return 1;
	}

	e1 = e1->next;
	}
	}
	}

	return 0;
	}

	static void remove_entry(HashEntry* entry) {
	HashEntry* prev = entry->prev;
	HashEntry* next = entry->next;

	if (prev != NULL) entry->prev->next = next;
	if (next != NULL) entry->next->prev = prev;

	if (prev == NULL) {
	// we are the head of the list. set the head to be next
	gHashTable.slots[entry->slot] = entry->next;
	}

	// we just removed and entry, decrease the size of the hashtable
	gHashTable.count--;
	}

	// =============================================================================
	// malloc fill functions
	// =============================================================================

	#define CHK_FILL_FREE 0xef
	#define CHK_SENTINEL_VALUE 0xeb

	extern "C" void* fill_calloc(size_t n_elements, size_t elem_size) {
	return dlcalloc(n_elements, elem_size);
	}

	extern "C" void* fill_malloc(size_t bytes) {
	void* buffer = dlmalloc(bytes);
	if (buffer) {
	memset(buffer, CHK_SENTINEL_VALUE, bytes);
	}
	return buffer;
	}

	extern "C" void fill_free(void* mem) {
	size_t bytes = dlmalloc_usable_size(mem);
	memset(mem, CHK_FILL_FREE, bytes);
	dlfree(mem);
	}

	extern "C" void* fill_realloc(void* mem, size_t bytes) {
	void* buffer = fill_malloc(bytes);
	if (mem == NULL) {
	return buffer;
	}
	if (buffer) {
	size_t old_size = dlmalloc_usable_size(mem);
	size_t size = (bytes < old_size)?(bytes):(old_size);
	memcpy(buffer, mem, size);
	fill_free(mem);
	}
	return buffer;
	}

	extern "C" void* fill_memalign(size_t alignment, size_t bytes) {
	void* buffer = dlmemalign(alignment, bytes);
	if (buffer) {
	memset(buffer, CHK_SENTINEL_VALUE, bytes);
	}
	return buffer;
	}

	// =============================================================================
	// malloc leak functions
	// =============================================================================

	static void* MEMALIGN_GUARD = reinterpret_cast<void*>(0xA1A41520);

	extern __LIBC_HIDDEN__ int get_backtrace(intptr_t* addrs, size_t max_entries);

	extern "C" void* leak_malloc(size_t bytes) {
	// allocate enough space infront of the allocation to store the pointer for
	// the alloc structure. This will making free'ing the structer really fast!

	// 1. allocate enough memory and include our header
	// 2. set the base pointer to be right after our header

	size_t size = bytes + sizeof(AllocationEntry);
	if (size < bytes) { // Overflow.
	return NULL;
	}

	void* base = dlmalloc(size);
	if (base != NULL) {
	ScopedPthreadMutexLocker locker(&gAllocationsMutex);

	intptr_t backtrace[BACKTRACE_SIZE];
	size_t numEntries = get_backtrace(backtrace, BACKTRACE_SIZE);

	AllocationEntry* header = reinterpret_cast<AllocationEntry*>(base);
	header->entry = record_backtrace(backtrace, numEntries, bytes);
	header->guard = GUARD;

	// now increment base to point to after our header.
	// this should just work since our header is 8 bytes.
	base = reinterpret_cast<AllocationEntry*>(base) + 1;
	}

	return base;
	}

	extern "C" void leak_free(void* mem) {
	if (mem != NULL) {
	ScopedPthreadMutexLocker locker(&gAllocationsMutex);

	// check the guard to make sure it is valid
	AllocationEntry* header = to_header(mem);

	if (header->guard != GUARD) {
	// could be a memaligned block
	if (reinterpret_cast<void**>(mem)[-1] == MEMALIGN_GUARD) {
	mem = reinterpret_cast<void**>(mem)[-2];
	header = to_header(mem);
	}
	}

	if (header->guard == GUARD \|\| is_valid_entry(header->entry)) {
	// decrement the allocations
	HashEntry* entry = header->entry;
	entry->allocations--;
	if (entry->allocations <= 0) {
	remove_entry(entry);
	dlfree(entry);
	}

	// now free the memory!
	dlfree(header);
	} else {
	debug_log("WARNING bad header guard: '0x%x'! and invalid entry: %p\n",
	header->guard, header->entry);
	}
	}
	}

	extern "C" void* leak_calloc(size_t n_elements, size_t elem_size) {
	/* Fail on overflow - just to be safe even though this code runs only
	* within the debugging C library, not the production one */
	if (n_elements && MAX_SIZE_T / n_elements < elem_size) {
	return NULL;
	}
	size_t size = n_elements * elem_size;
	void* ptr = leak_malloc(size);
	if (ptr != NULL) {
	memset(ptr, 0, size);
	}
	return ptr;
	}

	extern "C" void* leak_realloc(void* oldMem, size_t bytes) {
	if (oldMem == NULL) {
	return leak_malloc(bytes);
	}
	void* newMem = NULL;
	AllocationEntry* header = to_header(oldMem);
	if (header && header->guard == GUARD) {
	size_t oldSize = header->entry->size & ~SIZE_FLAG_MASK;
	newMem = leak_malloc(bytes);
	if (newMem != NULL) {
	size_t copySize = (oldSize <= bytes) ? oldSize : bytes;
	memcpy(newMem, oldMem, copySize);
	leak_free(oldMem);
	}
	} else {
	newMem = dlrealloc(oldMem, bytes);
	}
	return newMem;
	}

	extern "C" void* leak_memalign(size_t alignment, size_t bytes) {
	// we can just use malloc
	if (alignment <= MALLOC_ALIGNMENT) {
	return leak_malloc(bytes);
	}

	// need to make sure it's a power of two
	if (alignment & (alignment-1)) {
	alignment = 1L << (31 - __builtin_clz(alignment));
	}

	// here, aligment is at least MALLOC_ALIGNMENT<<1 bytes
	// we will align by at least MALLOC_ALIGNMENT bytes
	// and at most alignment-MALLOC_ALIGNMENT bytes
	size_t size = (alignment-MALLOC_ALIGNMENT) + bytes;
	if (size < bytes) { // Overflow.
	return NULL;
	}

	void* base = leak_malloc(size);
	if (base != NULL) {
	intptr_t ptr = reinterpret_cast<intptr_t>(base);
	if ((ptr % alignment) == 0) {
	return base;
	}

	// align the pointer
	ptr += ((-ptr) % alignment);

	// there is always enough space for the base pointer and the guard
	reinterpret_cast<void**>(ptr)[-1] = MEMALIGN_GUARD;
	reinterpret_cast<void**>(ptr)[-2] = base;

	return reinterpret_cast<void*>(ptr);
	}
	return base;
	}