gcc/libgomp/target.c

/* Copyright (C) 2013-2015 Free Software Foundation, Inc.
   Contributed by Jakub Jelinek <jakub@redhat.com>.

   This file is part of the GNU OpenMP Library (libgomp).

   Libgomp is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This file contains the support of offloading.  */

#include "config.h"
#include "libgomp.h"
#include "libgomp_target.h"
#include <limits.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#ifdef PLUGIN_SUPPORT
#include <dlfcn.h>
#endif

static void gomp_target_init (void);

static pthread_once_t gomp_is_initialized = PTHREAD_ONCE_INIT;

/* Forward declaration for a node in the tree.  */
typedef struct splay_tree_node_s *splay_tree_node;
typedef struct splay_tree_s *splay_tree;
typedef struct splay_tree_key_s *splay_tree_key;

struct target_mem_desc {
  /* Reference count.  */
  uintptr_t refcount;
  /* All the splay nodes allocated together.  */
  splay_tree_node array;
  /* Start of the target region.  */
  uintptr_t tgt_start;
  /* End of the targer region.  */
  uintptr_t tgt_end;
  /* Handle to free.  */
  void *to_free;
  /* Previous target_mem_desc.  */
  struct target_mem_desc *prev;
  /* Number of items in following list.  */
  size_t list_count;

  /* Corresponding target device descriptor.  */
  struct gomp_device_descr *device_descr;

  /* List of splay keys to remove (or decrease refcount)
     at the end of region.  */
  splay_tree_key list[];
};

struct splay_tree_key_s {
  /* Address of the host object.  */
  uintptr_t host_start;
  /* Address immediately after the host object.  */
  uintptr_t host_end;
  /* Descriptor of the target memory.  */
  struct target_mem_desc *tgt;
  /* Offset from tgt->tgt_start to the start of the target object.  */
  uintptr_t tgt_offset;
  /* Reference count.  */
  uintptr_t refcount;
  /* True if data should be copied from device to host at the end.  */
  bool copy_from;
};

/* This structure describes an offload image.
   It contains type of the target device, pointer to host table descriptor, and
   pointer to target data.  */
struct offload_image_descr {
  enum offload_target_type type;
  void *host_table;
  void *target_data;
};

/* Array of descriptors of offload images.  */
static struct offload_image_descr *offload_images;

/* Total number of offload images.  */
static int num_offload_images;

/* Array of descriptors for all available devices.  */
static struct gomp_device_descr *devices;

/* Total number of available devices.  */
static int num_devices;

/* The comparison function.  */

static int
splay_compare (splay_tree_key x, splay_tree_key y)
{
  if (x->host_start == x->host_end
      && y->host_start == y->host_end)
    return 0;
  if (x->host_end <= y->host_start)
    return -1;
  if (x->host_start >= y->host_end)
    return 1;
  return 0;
}

#include "splay-tree.h"

/* This structure describes accelerator device.
   It contains ID-number of the device, its type, function handlers for
   interaction with the device, and information about mapped memory.  */
struct gomp_device_descr
{
  /* This is the ID number of device.  It could be specified in DEVICE-clause of
     TARGET construct.  */
  int id;

  /* This is the ID number of device among devices of the same type.  */
  int target_id;

  /* This is the TYPE of device.  */
  enum offload_target_type type;

  /* Set to true when device is initialized.  */
  bool is_initialized;

  /* Function handlers.  */
  int (*get_type_func) (void);
  int (*get_num_devices_func) (void);
  void (*register_image_func) (void *, void *);
  void (*init_device_func) (int);
  int (*get_table_func) (int, void *);
  void *(*alloc_func) (int, size_t);
  void (*free_func) (int, void *);
  void *(*host2dev_func) (int, void *, const void *, size_t);
  void *(*dev2host_func) (int, void *, const void *, size_t);
  void (*run_func) (int, void *, void *);

  /* Splay tree containing information about mapped memory regions.  */
  struct splay_tree_s dev_splay_tree;

  /* Mutex for operating with the splay tree and other shared structures.  */
  gomp_mutex_t dev_env_lock;
};

attribute_hidden int
gomp_get_num_devices (void)
{
  (void) pthread_once (&gomp_is_initialized, gomp_target_init);
  return num_devices;
}

static struct gomp_device_descr *
resolve_device (int device_id)
{
  if (device_id == -1)
    {
      struct gomp_task_icv *icv = gomp_icv (false);
      device_id = icv->default_device_var;
    }

  if (device_id < 0 || device_id >= gomp_get_num_devices ())
    return NULL;

  return &devices[device_id];
}


/* Handle the case where splay_tree_lookup found oldn for newn.
   Helper function of gomp_map_vars.  */

static inline void
gomp_map_vars_existing (splay_tree_key oldn, splay_tree_key newn,
			unsigned char kind)
{
  if (oldn->host_start > newn->host_start
      || oldn->host_end < newn->host_end)
    gomp_fatal ("Trying to map into device [%p..%p) object when"
		"[%p..%p) is already mapped",
		(void *) newn->host_start, (void *) newn->host_end,
		(void *) oldn->host_start, (void *) oldn->host_end);
  oldn->refcount++;
}

static struct target_mem_desc *
gomp_map_vars (struct gomp_device_descr *devicep, size_t mapnum,
	       void **hostaddrs, size_t *sizes, unsigned char *kinds,
	       bool is_target)
{
  size_t i, tgt_align, tgt_size, not_found_cnt = 0;
  struct splay_tree_key_s cur_node;
  struct target_mem_desc *tgt
    = gomp_malloc (sizeof (*tgt) + sizeof (tgt->list[0]) * mapnum);
  tgt->list_count = mapnum;
  tgt->refcount = 1;
  tgt->device_descr = devicep;

  if (mapnum == 0)
    return tgt;

  tgt_align = sizeof (void *);
  tgt_size = 0;
  if (is_target)
    {
      size_t align = 4 * sizeof (void *);
      tgt_align = align;
      tgt_size = mapnum * sizeof (void *);
    }

  gomp_mutex_lock (&devicep->dev_env_lock);
  for (i = 0; i < mapnum; i++)
    {
      if (hostaddrs[i] == NULL)
	{
	  tgt->list[i] = NULL;
	  continue;
	}
      cur_node.host_start = (uintptr_t) hostaddrs[i];
      if ((kinds[i] & 7) != 4)
	cur_node.host_end = cur_node.host_start + sizes[i];
      else
	cur_node.host_end = cur_node.host_start + sizeof (void *);
      splay_tree_key n = splay_tree_lookup (&devicep->dev_splay_tree,
					    &cur_node);
      if (n)
	{
	  tgt->list[i] = n;
	  gomp_map_vars_existing (n, &cur_node, kinds[i]);
	}
      else
	{
	  size_t align = (size_t) 1 << (kinds[i] >> 3);
	  tgt->list[i] = NULL;
	  not_found_cnt++;
	  if (tgt_align < align)
	    tgt_align = align;
	  tgt_size = (tgt_size + align - 1) & ~(align - 1);
	  tgt_size += cur_node.host_end - cur_node.host_start;
	  if ((kinds[i] & 7) == 5)
	    {
	      size_t j;
	      for (j = i + 1; j < mapnum; j++)
		if ((kinds[j] & 7) != 4)
		  break;
		else if ((uintptr_t) hostaddrs[j] < cur_node.host_start
			 || ((uintptr_t) hostaddrs[j] + sizeof (void *)
			     > cur_node.host_end))
		  break;
		else
		  {
		    tgt->list[j] = NULL;
		    i++;
		  }
	    }
	}
    }

  if (not_found_cnt || is_target)
    {
      /* Allocate tgt_align aligned tgt_size block of memory.  */
      /* FIXME: Perhaps change interface to allocate properly aligned
	 memory.  */
      tgt->to_free = devicep->alloc_func (devicep->target_id,
					  tgt_size + tgt_align - 1);
      tgt->tgt_start = (uintptr_t) tgt->to_free;
      tgt->tgt_start = (tgt->tgt_start + tgt_align - 1) & ~(tgt_align - 1);
      tgt->tgt_end = tgt->tgt_start + tgt_size;
    }
  else
    {
      tgt->to_free = NULL;
      tgt->tgt_start = 0;
      tgt->tgt_end = 0;
    }

  tgt_size = 0;
  if (is_target)
    tgt_size = mapnum * sizeof (void *);

  tgt->array = NULL;
  if (not_found_cnt)
    {
      tgt->array = gomp_malloc (not_found_cnt * sizeof (*tgt->array));
      splay_tree_node array = tgt->array;
      size_t j;

      for (i = 0; i < mapnum; i++)
	if (tgt->list[i] == NULL)
	  {
	    if (hostaddrs[i] == NULL)
	      continue;
	    splay_tree_key k = &array->key;
	    k->host_start = (uintptr_t) hostaddrs[i];
	    if ((kinds[i] & 7) != 4)
	      k->host_end = k->host_start + sizes[i];
	    else
	      k->host_end = k->host_start + sizeof (void *);
	    splay_tree_key n
	      = splay_tree_lookup (&devicep->dev_splay_tree, k);
	    if (n)
	      {
		tgt->list[i] = n;
		gomp_map_vars_existing (n, k, kinds[i]);
	      }
	    else
	      {
		size_t align = (size_t) 1 << (kinds[i] >> 3);
		tgt->list[i] = k;
		tgt_size = (tgt_size + align - 1) & ~(align - 1);
		k->tgt = tgt;
		k->tgt_offset = tgt_size;
		tgt_size += k->host_end - k->host_start;
		k->copy_from = false;
		if ((kinds[i] & 7) == 2 || (kinds[i] & 7) == 3)
		  k->copy_from = true;
		k->refcount = 1;
		tgt->refcount++;
		array->left = NULL;
		array->right = NULL;
		splay_tree_insert (&devicep->dev_splay_tree, array);
		switch (kinds[i] & 7)
		  {
		  case 0: /* ALLOC */
		  case 2: /* FROM */
		    break;
		  case 1: /* TO */
		  case 3: /* TOFROM */
		    /* FIXME: Perhaps add some smarts, like if copying
		       several adjacent fields from host to target, use some
		       host buffer to avoid sending each var individually.  */
		    devicep->host2dev_func (devicep->target_id,
					    (void *) (tgt->tgt_start
						      + k->tgt_offset),
					    (void *) k->host_start,
					    k->host_end - k->host_start);
		    break;
		  case 4: /* POINTER */
		    cur_node.host_start
		      = (uintptr_t) *(void **) k->host_start;
		    if (cur_node.host_start == (uintptr_t) NULL)
		      {
			cur_node.tgt_offset = (uintptr_t) NULL;
			devicep->host2dev_func (devicep->target_id,
						(void *) (tgt->tgt_start
							  + k->tgt_offset),
						(void *) &cur_node.tgt_offset,
						sizeof (void *));
			break;
		      }
		    /* Add bias to the pointer value.  */
		    cur_node.host_start += sizes[i];
		    cur_node.host_end = cur_node.host_start + 1;
		    n = splay_tree_lookup (&devicep->dev_splay_tree,
					   &cur_node);
		    if (n == NULL)
		      {
			/* Could be possibly zero size array section.  */
			cur_node.host_end--;
			n = splay_tree_lookup (&devicep->dev_splay_tree,
					       &cur_node);
			if (n == NULL)
			  {
			    cur_node.host_start--;
			    n = splay_tree_lookup (&devicep->dev_splay_tree,
						   &cur_node);
			    cur_node.host_start++;
			  }
		      }
		    if (n == NULL)
		      gomp_fatal ("Pointer target of array section "
				  "wasn't mapped");
		    cur_node.host_start -= n->host_start;
		    cur_node.tgt_offset = n->tgt->tgt_start + n->tgt_offset
					  + cur_node.host_start;
		    /* At this point tgt_offset is target address of the
		       array section.  Now subtract bias to get what we want
		       to initialize the pointer with.  */
		    cur_node.tgt_offset -= sizes[i];
		    devicep->host2dev_func (devicep->target_id,
					    (void *) (tgt->tgt_start
						      + k->tgt_offset),
					    (void *) &cur_node.tgt_offset,
					    sizeof (void *));
		    break;
		  case 5: /* TO_PSET */
		    devicep->host2dev_func (devicep->target_id,
					    (void *) (tgt->tgt_start
						      + k->tgt_offset),
					    (void *) k->host_start,
					    k->host_end - k->host_start);
		    for (j = i + 1; j < mapnum; j++)
		      if ((kinds[j] & 7) != 4)
			break;
		      else if ((uintptr_t) hostaddrs[j] < k->host_start
			       || ((uintptr_t) hostaddrs[j] + sizeof (void *)
				   > k->host_end))
			break;
		      else
			{
			  tgt->list[j] = k;
			  k->refcount++;
			  cur_node.host_start
			    = (uintptr_t) *(void **) hostaddrs[j];
			  if (cur_node.host_start == (uintptr_t) NULL)
			    {
			      cur_node.tgt_offset = (uintptr_t) NULL;
			      devicep->host2dev_func (devicep->target_id,
				 (void *) (tgt->tgt_start + k->tgt_offset
					   + ((uintptr_t) hostaddrs[j]
					      - k->host_start)),
				 (void *) &cur_node.tgt_offset,
				 sizeof (void *));
			      i++;
			      continue;
			    }
			  /* Add bias to the pointer value.  */
			  cur_node.host_start += sizes[j];
			  cur_node.host_end = cur_node.host_start + 1;
			  n = splay_tree_lookup (&devicep->dev_splay_tree,
						 &cur_node);
			  if (n == NULL)
			    {
			      /* Could be possibly zero size array section.  */
			      cur_node.host_end--;
			      n = splay_tree_lookup (&devicep->dev_splay_tree,
						     &cur_node);
			      if (n == NULL)
				{
				  cur_node.host_start--;
				  n = splay_tree_lookup
					(&devicep->dev_splay_tree, &cur_node);
				  cur_node.host_start++;
				}
			    }
			  if (n == NULL)
			    gomp_fatal ("Pointer target of array section "
					"wasn't mapped");
			  cur_node.host_start -= n->host_start;
			  cur_node.tgt_offset = n->tgt->tgt_start
						+ n->tgt_offset
						+ cur_node.host_start;
			  /* At this point tgt_offset is target address of the
			     array section.  Now subtract bias to get what we
			     want to initialize the pointer with.  */
			  cur_node.tgt_offset -= sizes[j];
			  devicep->host2dev_func (devicep->target_id,
			     (void *) (tgt->tgt_start + k->tgt_offset
				       + ((uintptr_t) hostaddrs[j]
					  - k->host_start)),
			     (void *) &cur_node.tgt_offset,
			     sizeof (void *));
			  i++;
			}
		      break;
		  }
		array++;
	      }
	  }
    }
  if (is_target)
    {
      for (i = 0; i < mapnum; i++)
	{
	  if (tgt->list[i] == NULL)
	    cur_node.tgt_offset = (uintptr_t) NULL;
	  else
	    cur_node.tgt_offset = tgt->list[i]->tgt->tgt_start
				  + tgt->list[i]->tgt_offset;
	  devicep->host2dev_func (devicep->target_id,
				  (void *) (tgt->tgt_start
					    + i * sizeof (void *)),
				  (void *) &cur_node.tgt_offset,
				  sizeof (void *));
	}
    }

  gomp_mutex_unlock (&devicep->dev_env_lock);
  return tgt;
}

static void
gomp_unmap_tgt (struct target_mem_desc *tgt)
{
  /* Deallocate on target the tgt->tgt_start .. tgt->tgt_end region.  */
  if (tgt->tgt_end)
    tgt->device_descr->free_func (tgt->device_descr->target_id, tgt->to_free);

  free (tgt->array);
  free (tgt);
}

static void
gomp_unmap_vars (struct target_mem_desc *tgt)
{
  struct gomp_device_descr *devicep = tgt->device_descr;

  if (tgt->list_count == 0)
    {
      free (tgt);
      return;
    }

  size_t i;
  gomp_mutex_lock (&devicep->dev_env_lock);
  for (i = 0; i < tgt->list_count; i++)
    if (tgt->list[i] == NULL)
      ;
    else if (tgt->list[i]->refcount > 1)
      tgt->list[i]->refcount--;
    else
      {
	splay_tree_key k = tgt->list[i];
	if (k->copy_from)
	  devicep->dev2host_func (devicep->target_id, (void *) k->host_start,
				  (void *) (k->tgt->tgt_start + k->tgt_offset),
				  k->host_end - k->host_start);
	splay_tree_remove (&devicep->dev_splay_tree, k);
	if (k->tgt->refcount > 1)
	  k->tgt->refcount--;
	else
	  gomp_unmap_tgt (k->tgt);
      }

  if (tgt->refcount > 1)
    tgt->refcount--;
  else
    gomp_unmap_tgt (tgt);
  gomp_mutex_unlock (&devicep->dev_env_lock);
}

static void
gomp_update (struct gomp_device_descr *devicep, size_t mapnum,
	     void **hostaddrs, size_t *sizes, unsigned char *kinds)
{
  size_t i;
  struct splay_tree_key_s cur_node;

  if (!devicep)
    return;

  if (mapnum == 0)
    return;

  gomp_mutex_lock (&devicep->dev_env_lock);
  for (i = 0; i < mapnum; i++)
    if (sizes[i])
      {
	cur_node.host_start = (uintptr_t) hostaddrs[i];
	cur_node.host_end = cur_node.host_start + sizes[i];
	splay_tree_key n = splay_tree_lookup (&devicep->dev_splay_tree,
					      &cur_node);
	if (n)
	  {
	    if (n->host_start > cur_node.host_start
		|| n->host_end < cur_node.host_end)
	      gomp_fatal ("Trying to update [%p..%p) object when"
			  "only [%p..%p) is mapped",
			  (void *) cur_node.host_start,
			  (void *) cur_node.host_end,
			  (void *) n->host_start,
			  (void *) n->host_end);
	    if ((kinds[i] & 7) == 1)
	      devicep->host2dev_func (devicep->target_id,
				      (void *) (n->tgt->tgt_start
						+ n->tgt_offset
						+ cur_node.host_start
						- n->host_start),
				      (void *) cur_node.host_start,
				      cur_node.host_end - cur_node.host_start);
	    else if ((kinds[i] & 7) == 2)
	      devicep->dev2host_func (devicep->target_id,
				      (void *) cur_node.host_start,
				      (void *) (n->tgt->tgt_start
						+ n->tgt_offset
						+ cur_node.host_start
						- n->host_start),
				      cur_node.host_end - cur_node.host_start);
	  }
	else
	  gomp_fatal ("Trying to update [%p..%p) object that is not mapped",
		      (void *) cur_node.host_start,
		      (void *) cur_node.host_end);
      }
  gomp_mutex_unlock (&devicep->dev_env_lock);
}

/* This function should be called from every offload image.
   It gets the descriptor of the host func and var tables HOST_TABLE, TYPE of
   the target, and TARGET_DATA needed by target plugin.  */

void
GOMP_offload_register (void *host_table, enum offload_target_type target_type,
		       void *target_data)
{
  offload_images = gomp_realloc (offload_images,
				 (num_offload_images + 1)
				 * sizeof (struct offload_image_descr));

  offload_images[num_offload_images].type = target_type;
  offload_images[num_offload_images].host_table = host_table;
  offload_images[num_offload_images].target_data = target_data;

  num_offload_images++;
}

/* This function initializes the target device, specified by DEVICEP.  */

static void
gomp_init_device (struct gomp_device_descr *devicep)
{
  devicep->init_device_func (devicep->target_id);

  /* Get address mapping table for device.  */
  struct mapping_table *table = NULL;
  int num_entries = devicep->get_table_func (devicep->target_id, &table);

  /* Insert host-target address mapping into dev_splay_tree.  */
  int i;
  for (i = 0; i < num_entries; i++)
    {
      struct target_mem_desc *tgt = gomp_malloc (sizeof (*tgt));
      tgt->refcount = 1;
      tgt->array = gomp_malloc (sizeof (*tgt->array));
      tgt->tgt_start = table[i].tgt_start;
      tgt->tgt_end = table[i].tgt_end;
      tgt->to_free = NULL;
      tgt->list_count = 0;
      tgt->device_descr = devicep;
      splay_tree_node node = tgt->array;
      splay_tree_key k = &node->key;
      k->host_start = table[i].host_start;
      k->host_end = table[i].host_end;
      k->tgt_offset = 0;
      k->refcount = 1;
      k->copy_from = false;
      k->tgt = tgt;
      node->left = NULL;
      node->right = NULL;
      splay_tree_insert (&devicep->dev_splay_tree, node);
    }

  free (table);
  devicep->is_initialized = true;
}

/* Called when encountering a target directive.  If DEVICE
   is -1, it means use device-var ICV.  If it is -2 (or any other value
   larger than last available hw device, use host fallback.
   FN is address of host code, OPENMP_TARGET contains value of the
   __OPENMP_TARGET__ symbol in the shared library or binary that invokes
   GOMP_target.  HOSTADDRS, SIZES and KINDS are arrays
   with MAPNUM entries, with addresses of the host objects,
   sizes of the host objects (resp. for pointer kind pointer bias
   and assumed sizeof (void *) size) and kinds.  */

void
GOMP_target (int device, void (*fn) (void *), const void *openmp_target,
	     size_t mapnum, void **hostaddrs, size_t *sizes,
	     unsigned char *kinds)
{
  struct gomp_device_descr *devicep = resolve_device (device);
  if (devicep == NULL)
    {
      /* Host fallback.  */
      struct gomp_thread old_thr, *thr = gomp_thread ();
      old_thr = *thr;
      memset (thr, '\0', sizeof (*thr));
      if (gomp_places_list)
	{
	  thr->place = old_thr.place;
	  thr->ts.place_partition_len = gomp_places_list_len;
	}
      fn (hostaddrs);
      gomp_free_thread (thr);
      *thr = old_thr;
      return;
    }

  gomp_mutex_lock (&devicep->dev_env_lock);
  if (!devicep->is_initialized)
    gomp_init_device (devicep);

  struct splay_tree_key_s k;
  k.host_start = (uintptr_t) fn;
  k.host_end = k.host_start + 1;
  splay_tree_key tgt_fn = splay_tree_lookup (&devicep->dev_splay_tree, &k);
  if (tgt_fn == NULL)
    gomp_fatal ("Target function wasn't mapped");
  gomp_mutex_unlock (&devicep->dev_env_lock);

  struct target_mem_desc *tgt_vars
    = gomp_map_vars (devicep, mapnum, hostaddrs, sizes, kinds, true);
  struct gomp_thread old_thr, *thr = gomp_thread ();
  old_thr = *thr;
  memset (thr, '\0', sizeof (*thr));
  if (gomp_places_list)
    {
      thr->place = old_thr.place;
      thr->ts.place_partition_len = gomp_places_list_len;
    }
  devicep->run_func (devicep->target_id, (void *) tgt_fn->tgt->tgt_start,
		     (void *) tgt_vars->tgt_start);
  gomp_free_thread (thr);
  *thr = old_thr;
  gomp_unmap_vars (tgt_vars);
}

void
GOMP_target_data (int device, const void *openmp_target, size_t mapnum,
		  void **hostaddrs, size_t *sizes, unsigned char *kinds)
{
  struct gomp_device_descr *devicep = resolve_device (device);
  if (devicep == NULL)
    {
      /* Host fallback.  */
      struct gomp_task_icv *icv = gomp_icv (false);
      if (icv->target_data)
	{
	  /* Even when doing a host fallback, if there are any active
	     #pragma omp target data constructs, need to remember the
	     new #pragma omp target data, otherwise GOMP_target_end_data
	     would get out of sync.  */
	  struct target_mem_desc *tgt
	    = gomp_map_vars (NULL, 0, NULL, NULL, NULL, false);
	  tgt->prev = icv->target_data;
	  icv->target_data = tgt;
	}
      return;
    }

  gomp_mutex_lock (&devicep->dev_env_lock);
  if (!devicep->is_initialized)
    gomp_init_device (devicep);
  gomp_mutex_unlock (&devicep->dev_env_lock);

  struct target_mem_desc *tgt
    = gomp_map_vars (devicep, mapnum, hostaddrs, sizes, kinds, false);
  struct gomp_task_icv *icv = gomp_icv (true);
  tgt->prev = icv->target_data;
  icv->target_data = tgt;
}

void
GOMP_target_end_data (void)
{
  struct gomp_task_icv *icv = gomp_icv (false);
  if (icv->target_data)
    {
      struct target_mem_desc *tgt = icv->target_data;
      icv->target_data = tgt->prev;
      gomp_unmap_vars (tgt);
    }
}

void
GOMP_target_update (int device, const void *openmp_target, size_t mapnum,
		    void **hostaddrs, size_t *sizes, unsigned char *kinds)
{
  struct gomp_device_descr *devicep = resolve_device (device);
  if (devicep == NULL)
    return;

  gomp_mutex_lock (&devicep->dev_env_lock);
  if (!devicep->is_initialized)
    gomp_init_device (devicep);
  gomp_mutex_unlock (&devicep->dev_env_lock);

  gomp_update (devicep, mapnum, hostaddrs, sizes, kinds);
}

void
GOMP_teams (unsigned int num_teams, unsigned int thread_limit)
{
  if (thread_limit)
    {
      struct gomp_task_icv *icv = gomp_icv (true);
      icv->thread_limit_var
	= thread_limit > INT_MAX ? UINT_MAX : thread_limit;
    }
  (void) num_teams;
}

#ifdef PLUGIN_SUPPORT

/* This function tries to load a plugin for DEVICE.  Name of plugin is passed
   in PLUGIN_NAME.
   The handles of the found functions are stored in the corresponding fields
   of DEVICE.  The function returns TRUE on success and FALSE otherwise.  */

static bool
gomp_load_plugin_for_device (struct gomp_device_descr *device,
			     const char *plugin_name)
{
  void *plugin_handle = dlopen (plugin_name, RTLD_LAZY);
  if (!plugin_handle)
    return false;

  /* Check if all required functions are available in the plugin and store
     their handlers.  */
#define DLSYM(f)						    \
  do								    \
    {								    \
      device->f##_func = dlsym (plugin_handle, "GOMP_OFFLOAD_"#f);  \
      if (!device->f##_func)					    \
	return false;						    \
    }								    \
  while (0)
  DLSYM (get_type);
  DLSYM (get_num_devices);
  DLSYM (register_image);
  DLSYM (init_device);
  DLSYM (get_table);
  DLSYM (alloc);
  DLSYM (free);
  DLSYM (dev2host);
  DLSYM (host2dev);
  DLSYM (run);
#undef DLSYM

  return true;
}

/* This function finds OFFLOAD_IMAGES corresponding to DEVICE type, and
   registers them in the plugin.  */

static void
gomp_register_images_for_device (struct gomp_device_descr *device)
{
  int i;
  for (i = 0; i < num_offload_images; i++)
    {
      struct offload_image_descr *image = &offload_images[i];
      if (image->type == device->type)
	device->register_image_func (image->host_table, image->target_data);
    }
}

/* This function initializes the runtime needed for offloading.
   It parses the list of offload targets and tries to load the plugins for these
   targets.  Result of the function is properly initialized variable NUM_DEVICES
   and array DEVICES, containing descriptors for corresponding devices.  */

static void
gomp_target_init (void)
{
  const char *prefix ="libgomp-plugin-";
  const char *suffix = ".so.1";
  const char *cur, *next;
  char *plugin_name;
  int i, new_num_devices;

  num_devices = 0;
  devices = NULL;

  cur = OFFLOAD_TARGETS;
  if (*cur)
    do
      {
	struct gomp_device_descr current_device;

	next = strchr (cur, ',');

	plugin_name = (char *) malloc (1 + (next ? next - cur : strlen (cur))
				       + strlen (prefix) + strlen (suffix));
	if (!plugin_name)
	  {
	    num_devices = 0;
	    break;
	  }

	strcpy (plugin_name, prefix);
	strncat (plugin_name, cur, next ? next - cur : strlen (cur));
	strcat (plugin_name, suffix);

	if (gomp_load_plugin_for_device (&current_device, plugin_name))
	  {
	    new_num_devices = current_device.get_num_devices_func ();
	    if (new_num_devices >= 1)
	      {
		devices = realloc (devices, (num_devices + new_num_devices)
				   * sizeof (struct gomp_device_descr));
		if (!devices)
		  {
		    num_devices = 0;
		    free (plugin_name);
		    break;
		  }

		current_device.type = current_device.get_type_func ();
		current_device.is_initialized = false;
		current_device.dev_splay_tree.root = NULL;
		gomp_register_images_for_device (&current_device);
		for (i = 0; i < new_num_devices; i++)
		  {
		    current_device.id = num_devices + 1;
		    current_device.target_id = i;
		    devices[num_devices] = current_device;
		    gomp_mutex_init (&devices[num_devices].dev_env_lock);
		    num_devices++;
		  }
	      }
	  }

	free (plugin_name);
	cur = next + 1;
      }
    while (next);

  free (offload_images);
  offload_images = NULL;
  num_offload_images = 0;
}

#else /* PLUGIN_SUPPORT */
/* If dlfcn.h is unavailable we always fallback to host execution.
   GOMP_target* routines are just stubs for this case.  */
static void
gomp_target_init (void)
{
}
#endif /* PLUGIN_SUPPORT */