diff --git a/src/mi/mempool.c b/src/mi/mempool.c
index e69de29b..2ff2f479 100644
--- a/src/mi/mempool.c
+++ b/src/mi/mempool.c
@@ -0,0 +1,205 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2002-2003 Hewlett-Packard Co
+	Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/mman.h>
+
+#include "libunwind.h"
+#include "mempool.h"
+
+#define MAX_ALIGN	(sizeof (long double))
+#define SOS_MEMORY_SIZE	16384
+
+static char sos_memory[SOS_MEMORY_SIZE];
+static char *sos_memp;
+static size_t pg_size;
+
+HIDDEN void *
+sos_alloc (size_t size)
+{
+  char *mem;
+
+#ifdef HAVE_CMPXCHG
+  char *old_mem;
+
+  size = (size + MAX_ALIGN - 1) & -MAX_ALIGN;
+  if (!sos_memp)
+    cmpxchg_ptr (&sos_memp, 0, sos_memory);
+  do
+    {
+      old_mem = sos_memp;
+
+      mem = (char *) (((unsigned long) old_mem + MAX_ALIGN - 1) & -MAX_ALIGN);
+      mem += size;
+      if (mem >= sos_memory + sizeof (sos_memory))
+	abort ();
+    }
+  while (!cmpxchg_ptr (&sos_memp, old_mem, mem));
+#else
+  static pthread_mutex_t sos_lock = PTHREAD_MUTEX_INITIALIZER;
+  sigset_t saved_sigmask;
+
+  size = (size + MAX_ALIGN - 1) & -MAX_ALIGN;
+
+  sigprocmask (SIG_SETMASK, &unwi_full_sigmask, &saved_sigmask);
+  mutex_lock(&sos_lock);
+  {
+    if (!sos_memp)
+      sos_memp = sos_memory;
+
+    mem = (char *) (((unsigned long) sos_memp + MAX_ALIGN - 1) & -MAX_ALIGN);
+    mem += size;
+    if (mem >= sos_memory + sizeof (sos_memory))
+      abort ();
+    sos_memp = mem;
+  }
+  mutex_unlock(&sos_lock);
+  sigprocmask (SIG_SETMASK, &saved_sigmask, NULL);
+#endif
+  return mem;
+}
+
+static void *
+alloc_memory (size_t size)
+{
+  /* Hopefully, mmap() goes straight through to a system call stub...  */
+  void *mem = mmap (0, size, PROT_READ | PROT_WRITE,
+		    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (mem == MAP_FAILED)
+    return NULL;
+
+  return mem;
+}
+
+/* Must be called while holding the mempool lock. */
+
+static void
+free_object (struct mempool *pool, void *object)
+{
+  struct object *obj = object;
+
+  obj->next = pool->free_list;
+  pool->free_list = obj;
+  ++pool->num_free;
+}
+
+static void
+add_memory (struct mempool *pool, char *mem, size_t size, size_t obj_size)
+{
+  char *obj;
+
+  for (obj = mem; obj + obj_size <= mem + size; obj += obj_size)
+    free_object (pool, obj);
+}
+
+static void
+expand (struct mempool *pool)
+{
+  size_t size;
+  char *mem;
+
+  size = pool->chunk_size;
+  mem = alloc_memory (size);
+  if (!mem)
+    {
+      size = (pool->obj_size + pg_size - 1) & -pg_size;
+      mem = alloc_memory (size);
+      if (!mem)
+	{
+	  /* last chance: try to allocate one object from the SOS memory */
+	  size = pool->obj_size;
+	  mem = sos_alloc (size);
+	}
+    }
+  add_memory (pool, mem, size, pool->obj_size);
+}
+
+HIDDEN void
+mempool_init (struct mempool *pool, size_t obj_size, size_t reserve)
+{
+  if (pg_size == 0)
+    pg_size = getpagesize ();
+
+  memset (pool, 0, sizeof (*pool));
+
+  mutex_init (&pool->lock);
+
+  /* round object-size up to integer multiple of MAX_ALIGN */
+  obj_size = (obj_size + MAX_ALIGN - 1) & -MAX_ALIGN;
+
+  if (!reserve)
+    {
+      reserve = pg_size / obj_size / 2;
+      if (!reserve)
+	reserve = 16;
+    }
+
+  pool->obj_size = obj_size;
+  pool->reserve = reserve;
+  pool->chunk_size = (2*reserve*obj_size + pg_size - 1) & -pg_size;
+
+  expand (pool);
+}
+
+HIDDEN void *
+mempool_alloc (struct mempool *pool)
+{
+  sigset_t saved_sigmask;
+  struct object *obj;
+
+  sigprocmask (SIG_SETMASK, &unwi_full_sigmask, &saved_sigmask);
+  mutex_lock(&pool->lock);
+  {
+    if (pool->num_free <= pool->reserve)
+      expand (pool);
+
+    assert (pool->num_free > 0);
+
+    --pool->num_free;
+    obj = pool->free_list;
+    pool->free_list = obj->next;
+  }
+  mutex_unlock(&pool->lock);
+  sigprocmask (SIG_SETMASK, &saved_sigmask, NULL);
+  return obj;
+}
+
+HIDDEN void
+mempool_free (struct mempool *pool, void *object)
+{
+  sigset_t saved_sigmask;
+
+  sigprocmask (SIG_SETMASK, &unwi_full_sigmask, &saved_sigmask);
+  mutex_lock(&pool->lock);
+  {
+    free_object (pool, object);
+  }
+  mutex_unlock(&pool->lock);
+  sigprocmask (SIG_SETMASK, &saved_sigmask, NULL);
+}