* target.h (struct target_ops): Add new field to_get_ada_task_ptid.

        (target_get_ada_task_ptid): New macro.
        * target.c (default_get_ada_task_ptid): New function.
        (update_current_target): Inherit field default_get_ada_task_ptid.
        (update_current_target): Make default_get_ada_task_ptid the default
        value for field to_get_ada_task_ptid.
        * ada-lang.h (struct task_control_block): Delete. Never used.
        (struct task_ptid, task_ptid_t, struct task_entry, task_list):
        Likewise.
        (struct ada_task_info): New.
        (ada_task_is_alive, ada_find_printable_frame)
        (ada_task_list_iterator_ftype, iterate_over_live_ada_tasks): Add
        declarations.
        (ada_build_task_list): Update prototype.
        (init_task_list, ada_is_exception_breakpoint): Remove prototypes.
        * ada-lang.c (ada_find_printable_frame): Make non-static.
        * ada-tasks.c: New file.
        * Makefile.in (SFILES): Add ada-tasks.c.
        (COMMON_OBS): Add ada-tasks.o.
        * linux-thread-db.c (thread_db_find_thread_from_tid)
        (thread_db_get_ada_task_ptid): New functions.
        (init_thread_db_ops): Set thread_db_ops.to_get_ada_task_ptid.

1 files changed, 991 insertions, 0 deletions

diff --git a/gdb/ada-tasks.c b/gdb/ada-tasks.c
new file mode 100644
index 0000000..17671b3
--- /dev/null
+++ b/gdb/ada-tasks.c
@@ -0,0 +1,991 @@
+/* Copyright (C) 1992, 1993, 1994, 1997, 1998, 1999, 2000, 2003, 2004,
+   2005, 2007, 2008 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program 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 of the License, or
+   (at your option) any later version.
+
+   This program 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.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "observer.h"
+#include "gdbcmd.h"
+#include "target.h"
+#include "ada-lang.h"
+#include "gdbcore.h"
+#include "inferior.h"
+#include "gdbthread.h"
+
+/* The name of the array in the GNAT runtime where the Ada Task Control
+   Block of each task is stored.  */
+#define KNOWN_TASKS_NAME "system__tasking__debug__known_tasks"
+
+/* The maximum number of tasks known to the Ada runtime */
+static const int MAX_NUMBER_OF_KNOWN_TASKS = 1000;
+
+enum task_states
+{
+  Unactivated,
+  Runnable,
+  Terminated,
+  Activator_Sleep,
+  Acceptor_Sleep,
+  Entry_Caller_Sleep,
+  Async_Select_Sleep,
+  Delay_Sleep,
+  Master_Completion_Sleep,
+  Master_Phase_2_Sleep,
+  Interrupt_Server_Idle_Sleep,
+  Interrupt_Server_Blocked_Interrupt_Sleep,
+  Timer_Server_Sleep,
+  AST_Server_Sleep,
+  Asynchronous_Hold,
+  Interrupt_Server_Blocked_On_Event_Flag
+};
+
+/* A short description corresponding to each possible task state.  */
+static char *task_states[] = {
+  _("Unactivated"),
+  _("Runnable"),
+  _("Terminated"),
+  _("Child Activation Wait"),
+  _("Accept Statement"),
+  _("Waiting on entry call"),
+  _("Async Select Wait"),
+  _("Delay Sleep"),
+  _("Child Termination Wait"),
+  _("Wait Child in Term Alt"),
+  "",
+  "",
+  "",
+  "",
+  _("Asynchronous Hold"),
+  ""
+};
+
+/* A longer description corresponding to each possible task state.  */
+static char *long_task_states[] = {
+  _("Unactivated"),
+  _("Runnable"),
+  _("Terminated"),
+  _("Waiting for child activation"),
+  _("Blocked in accept statement"),
+  _("Waiting on entry call"),
+  _("Asynchronous Selective Wait"),
+  _("Delay Sleep"),
+  _("Waiting for children termination"),
+  _("Waiting for children in terminate alternative"),
+  "",
+  "",
+  "",
+  "",
+  _("Asynchronous Hold"),
+  ""
+};
+
+/* The index of certain important fields in the Ada Task Control Block
+   record and sub-records.  */
+
+struct tcb_fieldnos
+{
+  /* Fields in record Ada_Task_Control_Block.  */
+  int common;
+  int entry_calls;
+  int atc_nesting_level;
+
+  /* Fields in record Common_ATCB.  */
+  int state;
+  int parent;
+  int priority;
+  int image;
+  int image_len;     /* This field may be missing.  */
+  int call;
+  int ll;
+
+  /* Fields in Task_Primitives.Private_Data.  */
+  int ll_thread;
+  int ll_lwp;        /* This field may be missing.  */
+
+  /* Fields in Common_ATCB.Call.all.  */
+  int call_self;
+};
+
+/* The type description for the ATCB record and subrecords, and
+   the associated tcb_fieldnos. For efficiency reasons, these are made
+   static globals so that we can compute them only once the first time
+   and reuse them later.  Set to NULL if the types haven't been computed
+   yet, or if they may be obsolete (for instance after having loaded
+   a new binary).  */
+
+static struct type *atcb_type = NULL;
+static struct type *atcb_common_type = NULL;
+static struct type *atcb_ll_type = NULL;
+static struct type *atcb_call_type = NULL;
+static struct tcb_fieldnos fieldno;
+
+/* Set to 1 when the cached address of System.Tasking.Debug.Known_Tasks
+   might be stale and so needs to be recomputed.  */
+static int ada_tasks_check_symbol_table = 1;
+
+/* The list of Ada tasks.
+ 
+   Note: To each task we associate a number that the user can use to
+   reference it - this number is printed beside each task in the tasks
+   info listing displayed by "info tasks".  This number is equal to
+   its index in the vector + 1.  Reciprocally, to compute the index
+   of a task in the vector, we need to substract 1 from its number.  */
+typedef struct ada_task_info ada_task_info_s;
+DEF_VEC_O(ada_task_info_s);
+static VEC(ada_task_info_s) *task_list = NULL;
+
+/* When non-zero, this flag indicates that the current task_list
+   is obsolete, and should be recomputed before it is accessed.  */
+static int stale_task_list_p = 1;
+
+/* Return the task number of the task whose ptid is PTID, or zero
+   if the task could not be found.  */
+
+int
+ada_get_task_number (ptid_t ptid)
+{
+  int i;
+
+  for (i=0; i < VEC_length (ada_task_info_s, task_list); i++)
+    if (ptid_equal (VEC_index (ada_task_info_s, task_list, i)->ptid, ptid))
+      return i + 1;
+
+  return 0;  /* No matching task found.  */
+}
+
+/* Return the task number of the task that matches TASK_ID, or zero
+   if the task could not be found.  */
+ 
+static int
+get_task_number_from_id (CORE_ADDR task_id)
+{
+  int i;
+
+  for (i = 0; i < VEC_length (ada_task_info_s, task_list); i++)
+    {
+      struct ada_task_info *task_info =
+        VEC_index (ada_task_info_s, task_list, i);
+
+      if (task_info->task_id == task_id)
+        return i + 1;
+    }
+
+  /* Task not found.  Return 0.  */
+  return 0;
+}
+
+/* Return non-zero if TASK_NUM is a valid task number.  */
+
+int
+valid_task_id (int task_num)
+{
+  return (task_num > 0
+          && task_num <= VEC_length (ada_task_info_s, task_list));
+}
+
+/* Return the task info associated to the Environment Task.
+   This function assumes that the inferior does in fact use tasking.  */
+
+struct ada_task_info *
+ada_get_environment_task (void)
+{
+  ada_build_task_list (0);
+  gdb_assert (VEC_length (ada_task_info_s, task_list) > 0);
+
+  /* We use a little bit of insider knowledge to determine which task
+     is the Environment Task:  We know that this task is created first,
+     and thus should always be task #1, which is at index 0 of the
+     TASK_LIST.  */
+  return (VEC_index (ada_task_info_s, task_list, 0));
+}
+
+/* Call the ITERATOR function once for each Ada task that hasn't been
+   terminated yet.  */
+
+void
+iterate_over_live_ada_tasks (ada_task_list_iterator_ftype *iterator)
+{
+  int i, nb_tasks;
+  struct ada_task_info *task;
+
+  ada_build_task_list (0);
+  nb_tasks = VEC_length (ada_task_info_s, task_list);
+
+  for (i = 0; i < nb_tasks; i++)
+    {
+      task = VEC_index (ada_task_info_s, task_list, i);
+      if (!ada_task_is_alive (task))
+        continue;
+      iterator (task);
+    }
+}
+
+/* Extract the contents of the value as a string whose length is LENGTH,
+   and store the result in DEST.  */
+
+static void
+value_as_string (char *dest, struct value *val, int length)
+{
+  memcpy (dest, value_contents (val), length);
+  dest[length] = '\0';
+}
+
+/* Extract the string image from the fat string corresponding to VAL,
+   and store it in DEST.  If the string length is greater than MAX_LEN,
+   then truncate the result to the first MAX_LEN characters of the fat
+   string.  */
+
+static void
+read_fat_string_value (char *dest, struct value *val, int max_len)
+{
+  struct value *array_val;
+  struct value *bounds_val;
+  int len;
+
+  /* The following variables are made static to avoid recomputing them
+     each time this function is called.  */
+  static int initialize_fieldnos = 1;
+  static int array_fieldno;
+  static int bounds_fieldno;
+  static int upper_bound_fieldno;
+
+  /* Get the index of the fields that we will need to read in order
+     to extract the string from the fat string.  */
+  if (initialize_fieldnos)
+    {
+      struct type *type = value_type (val);
+      struct type *bounds_type;
+
+      array_fieldno = ada_get_field_index (type, "P_ARRAY", 0);
+      bounds_fieldno = ada_get_field_index (type, "P_BOUNDS", 0);
+
+      bounds_type = TYPE_FIELD_TYPE (type, bounds_fieldno);
+      if (TYPE_CODE (bounds_type) == TYPE_CODE_PTR)
+        bounds_type = TYPE_TARGET_TYPE (bounds_type);
+      if (TYPE_CODE (bounds_type) != TYPE_CODE_STRUCT)
+        error (_("Unknown task name format. Aborting"));
+      upper_bound_fieldno = ada_get_field_index (bounds_type, "UB0", 0);
+
+      initialize_fieldnos = 0;
+    }
+
+  /* Get the size of the task image by checking the value of the bounds.
+     The lower bound is always 1, so we only need to read the upper bound.  */
+  bounds_val = value_ind (value_field (val, bounds_fieldno));
+  len = value_as_long (value_field (bounds_val, upper_bound_fieldno));
+
+  /* Make sure that we do not read more than max_len characters...  */
+  if (len > max_len)
+    len = max_len;
+
+  /* Extract LEN characters from the fat string.  */
+  array_val = value_ind (value_field (val, array_fieldno));
+  read_memory (VALUE_ADDRESS (array_val), dest, len);
+
+  /* Add the NUL character to close the string.  */
+  dest[len] = '\0';
+}
+
+/* Return the address of the Known_Tasks array maintained in
+   the Ada Runtime.  Return NULL if the array could not be found,
+   meaning that the inferior program probably does not use tasking.
+
+   In order to provide a fast response time, this function caches
+   the Known_Tasks array address after the lookup during the first
+   call. Subsequent calls will simply return this cached address.  */
+
+static CORE_ADDR
+get_known_tasks_addr (void)
+{
+  static CORE_ADDR known_tasks_addr = 0;
+
+  if (ada_tasks_check_symbol_table)
+    {
+      struct symbol *sym;
+      struct minimal_symbol *msym;
+
+      msym = lookup_minimal_symbol (KNOWN_TASKS_NAME, NULL, NULL);
+      if (msym != NULL)
+        known_tasks_addr = SYMBOL_VALUE_ADDRESS (msym);
+      else
+        {
+          if (target_lookup_symbol (KNOWN_TASKS_NAME, &known_tasks_addr) != 0)
+            return 0;
+        }
+
+      /* FIXME: brobecker 2003-03-05: Here would be a much better place
+         to attach the ada-tasks observers, instead of doing this
+         unconditionaly in _initialize_tasks. This would avoid an
+         unecessary notification when the inferior does not use tasking
+         or as long as the user does not use the ada-tasks commands.
+         Unfortunately, this is not possible for the moment: the current
+         code resets ada__tasks_check_symbol_table back to 1 whenever
+         symbols for a new program are being loaded. If we place the
+         observers intialization here, we will end up adding new observers
+         everytime we do the check for Ada tasking-related symbols
+         above. This would currently have benign effects, but is still
+         undesirable. The cleanest approach is probably to create a new
+         observer to notify us when the user is debugging a new program.
+         We would then reset ada__tasks_check_symbol_table back to 1
+         during the notification, but also detach all observers.
+         BTW: observers are probably not reentrant, so detaching during
+         a notification may not be the safest thing to do... Sigh...
+         But creating the new observer would be a good idea in any case,
+         since this allow us to make ada__tasks_check_symbol_table
+         static, which is a good bonus.  */
+      ada_tasks_check_symbol_table = 0;
+    }
+
+  return known_tasks_addr;
+}
+
+/* Get from the debugging information the type description of all types
+   related to the Ada Task Control Block that will be needed in order to
+   read the list of known tasks in the Ada runtime.  Also return the
+   associated ATCB_FIELDNOS.
+
+   Error handling:  Any data missing from the debugging info will cause
+   an error to be raised, and none of the return values to be set.
+   Users of this function can depend on the fact that all or none of the
+   return values will be set.  */
+
+static void
+get_tcb_types_info (struct type **atcb_type,
+                    struct type **atcb_common_type,
+                    struct type **atcb_ll_type,
+                    struct type **atcb_call_type,
+                    struct tcb_fieldnos *atcb_fieldnos)
+{
+  struct type *type;
+  struct type *common_type;
+  struct type *ll_type;
+  struct type *call_type;
+  struct tcb_fieldnos fieldnos;
+
+  const char *atcb_name = "system__tasking__ada_task_control_block___XVE";
+  const char *atcb_name_fixed = "system__tasking__ada_task_control_block";
+  const char *common_atcb_name = "system__tasking__common_atcb";
+  const char *private_data_name = "system__task_primitives__private_data";
+  const char *entry_call_record_name = "system__tasking__entry_call_record";
+
+  struct symbol *atcb_sym =
+    lookup_symbol (atcb_name, NULL, VAR_DOMAIN, NULL);
+  const struct symbol *common_atcb_sym =
+    lookup_symbol (common_atcb_name, NULL, VAR_DOMAIN, NULL);
+  const struct symbol *private_data_sym =
+    lookup_symbol (private_data_name, NULL, VAR_DOMAIN, NULL);
+  const struct symbol *entry_call_record_sym =
+    lookup_symbol (entry_call_record_name, NULL, VAR_DOMAIN, NULL);
+
+  if (atcb_sym == NULL || atcb_sym->type == NULL)
+    {
+      /* In Ravenscar run-time libs, the  ATCB does not have a dynamic
+         size, so the symbol name differs.  */
+      atcb_sym = lookup_symbol (atcb_name_fixed, NULL, VAR_DOMAIN, NULL);
+
+      if (atcb_sym == NULL || atcb_sym->type == NULL)
+        error (_("Cannot find Ada_Task_Control_Block type. Aborting"));
+
+      type = atcb_sym->type;
+    }
+  else
+    {
+      /* Get a static representation of the type record
+         Ada_Task_Control_Block.  */
+      type = atcb_sym->type;
+      type = ada_template_to_fixed_record_type_1 (type, NULL, 0, NULL, 0);
+    }
+
+  if (common_atcb_sym == NULL || common_atcb_sym->type == NULL)
+    error (_("Cannot find Common_ATCB type. Aborting"));
+  if (private_data_sym == NULL || private_data_sym->type == NULL)
+    error (_("Cannot find Private_Data type. Aborting"));
+  if (entry_call_record_sym == NULL || entry_call_record_sym->type == NULL)
+    error (_("Cannot find Entry_Call_Record type. Aborting"));
+
+  /* Get the type for Ada_Task_Control_Block.Common.  */
+  common_type = common_atcb_sym->type;
+
+  /* Get the type for Ada_Task_Control_Bloc.Common.Call.LL.  */
+  ll_type = private_data_sym->type;
+
+  /* Get the type for Common_ATCB.Call.all.  */
+  call_type = entry_call_record_sym->type;
+
+  /* Get the field indices.  */
+  fieldnos.common = ada_get_field_index (type, "common", 0);
+  fieldnos.entry_calls = ada_get_field_index (type, "entry_calls", 1);
+  fieldnos.atc_nesting_level =
+    ada_get_field_index (type, "atc_nesting_level", 1);
+  fieldnos.state = ada_get_field_index (common_type, "state", 0);
+  fieldnos.parent = ada_get_field_index (common_type, "parent", 1);
+  fieldnos.priority = ada_get_field_index (common_type, "base_priority", 0);
+  fieldnos.image = ada_get_field_index (common_type, "task_image", 1);
+  fieldnos.image_len = ada_get_field_index (common_type, "task_image_len", 1);
+  fieldnos.call = ada_get_field_index (common_type, "call", 1);
+  fieldnos.ll = ada_get_field_index (common_type, "ll", 0);
+  fieldnos.ll_thread = ada_get_field_index (ll_type, "thread", 0);
+  fieldnos.ll_lwp = ada_get_field_index (ll_type, "lwp", 1);
+  fieldnos.call_self = ada_get_field_index (call_type, "self", 0);
+
+  /* On certain platforms such as x86-windows, the "lwp" field has been
+     named "thread_id".  This field will likely be renamed in the future,
+     but we need to support both possibilities to avoid an unnecessary
+     dependency on a recent compiler.  We therefore try locating the
+     "thread_id" field in place of the "lwp" field if we did not find
+     the latter.  */
+  if (fieldnos.ll_lwp < 0)
+    fieldnos.ll_lwp = ada_get_field_index (ll_type, "thread_id", 1);
+
+  /* Set all the out parameters all at once, now that we are certain
+     that there are no potential error() anymore.  */
+  *atcb_type = type;
+  *atcb_common_type = common_type;
+  *atcb_ll_type = ll_type;
+  *atcb_call_type = call_type;
+  *atcb_fieldnos = fieldnos;
+}
+
+/* Build the PTID of the task from its COMMON_VALUE, which is the "Common"
+   component of its ATCB record.  This PTID needs to match the PTID used
+   by the thread layer.  */
+
+static ptid_t
+ptid_from_atcb_common (struct value *common_value)
+{
+  long thread = 0;
+  CORE_ADDR lwp = 0;
+  struct value *ll_value;
+  ptid_t ptid;
+
+  ll_value = value_field (common_value, fieldno.ll);
+
+  if (fieldno.ll_lwp >= 0)
+    lwp = value_as_address (value_field (ll_value, fieldno.ll_lwp));
+  thread = value_as_long (value_field (ll_value, fieldno.ll_thread));
+
+  ptid = target_get_ada_task_ptid (lwp, thread);
+
+  return ptid;
+}
+
+/* Read the ATCB data of a given task given its TASK_ID (which is in practice
+   the address of its assocated ATCB record), and store the result inside
+   TASK_INFO.  */
+
+static void
+read_atcb (CORE_ADDR task_id, struct ada_task_info *task_info)
+{
+  struct value *tcb_value;
+  struct value *common_value;
+  struct value *atc_nesting_level_value;
+  struct value *entry_calls_value;
+  struct value *entry_calls_value_element;
+  int called_task_fieldno = -1;
+  const char ravenscar_task_name[] = "Ravenscar task";
+
+  if (atcb_type == NULL)
+    get_tcb_types_info (&atcb_type, &atcb_common_type, &atcb_ll_type,
+                        &atcb_call_type, &fieldno);
+
+  tcb_value = value_from_contents_and_address (atcb_type, NULL, task_id);
+  common_value = value_field (tcb_value, fieldno.common);
+
+  /* Fill in the task_id.  */
+
+  task_info->task_id = task_id;
+
+  /* Compute the name of the task.
+
+     Depending on the GNAT version used, the task image is either a fat
+     string, or a thin array of characters.  Older versions of GNAT used
+     to use fat strings, and therefore did not need an extra field in
+     the ATCB to store the string length. For efficiency reasons, newer
+     versions of GNAT replaced the fat string by a static buffer, but this
+     also required the addition of a new field named "Image_Len" containing
+     the length of the task name. The method used to extract the task name
+     is selected depending on the existence of this field.
+
+     In some run-time libs (e.g. Ravenscar), the name is not in the ATCB;
+     we may want to get it from the first user frame of the stack. For now,
+     we just give a dummy name.  */
+
+  if (fieldno.image_len == -1)
+    {
+      if (fieldno.image >= 0)
+        read_fat_string_value (task_info->name,
+                               value_field (common_value, fieldno.image),
+                               sizeof (task_info->name) - 1);
+      else
+        strcpy (task_info->name, ravenscar_task_name);
+    }
+  else
+    {
+      int len = value_as_long (value_field (common_value, fieldno.image_len));
+
+      value_as_string (task_info->name,
+                       value_field (common_value, fieldno.image), len);
+    }
+
+  /* Compute the task state and priority.  */
+
+  task_info->state = value_as_long (value_field (common_value, fieldno.state));
+  task_info->priority =
+    value_as_long (value_field (common_value, fieldno.priority));
+
+  /* If the ATCB contains some information about the parent task,
+     then compute it as well.  Otherwise, zero.  */
+
+  if (fieldno.parent >= 0)
+    task_info->parent =
+      value_as_address (value_field (common_value, fieldno.parent));
+  else
+    task_info->parent = 0;
+  
+
+  /* If the ATCB contains some information about entry calls, then
+     compute the "called_task" as well.  Otherwise, zero.  */
+
+  if (fieldno.atc_nesting_level > 0 && fieldno.entry_calls > 0) 
+    {
+      /* Let My_ATCB be the Ada task control block of a task calling the
+         entry of another task; then the Task_Id of the called task is
+         in My_ATCB.Entry_Calls (My_ATCB.ATC_Nesting_Level).Called_Task.  */
+      atc_nesting_level_value = value_field (tcb_value,
+                                             fieldno.atc_nesting_level);
+      entry_calls_value =
+        ada_coerce_to_simple_array_ptr (value_field (tcb_value,
+                                                     fieldno.entry_calls));
+      entry_calls_value_element =
+        value_subscript (entry_calls_value, atc_nesting_level_value);
+      called_task_fieldno =
+        ada_get_field_index (value_type (entry_calls_value_element),
+                             "called_task", 0);
+      task_info->called_task =
+        value_as_address (value_field (entry_calls_value_element,
+                                       called_task_fieldno));
+    }
+  else
+    {
+      task_info->called_task = 0;
+    }
+
+  /* If the ATCB cotnains some information about RV callers,
+     then compute the "caller_task".  Otherwise, zero.  */
+
+  task_info->caller_task = 0;
+  if (fieldno.call >= 0)
+    {
+      /* Get the ID of the caller task from Common_ATCB.Call.all.Self.
+         If Common_ATCB.Call is null, then there is no caller.  */
+      const CORE_ADDR call =
+        value_as_address (value_field (common_value, fieldno.call));
+      struct value *call_val;
+
+      if (call != 0)
+        {
+          call_val =
+            value_from_contents_and_address (atcb_call_type, NULL, call);
+          task_info->caller_task =
+            value_as_address (value_field (call_val, fieldno.call_self));
+        }
+    }
+
+  /* And finally, compute the task ptid.  */
+
+  if (ada_task_is_alive (task_info))
+    task_info->ptid = ptid_from_atcb_common (common_value);
+  else
+    task_info->ptid = null_ptid;
+}
+
+/* Read the ATCB info of the given task (identified by TASK_ID), and
+   add the result to the TASK_LIST.  */
+
+static void
+add_ada_task (CORE_ADDR task_id)
+{
+  struct ada_task_info task_info;
+
+  read_atcb (task_id, &task_info);
+  VEC_safe_push (ada_task_info_s, task_list, &task_info);
+}
+
+/* Read the Known_Tasks array from the inferior memory, and store
+   it in TASK_LIST.  Return non-zero upon success.  */
+
+static int
+read_known_tasks_array (void)
+{
+  const int target_ptr_byte =
+    gdbarch_ptr_bit (current_gdbarch) / TARGET_CHAR_BIT;
+  const CORE_ADDR known_tasks_addr = get_known_tasks_addr ();
+  const int known_tasks_size = target_ptr_byte * MAX_NUMBER_OF_KNOWN_TASKS;
+  gdb_byte *known_tasks = alloca (known_tasks_size);
+  int i;
+
+  /* Step 1: Clear the current list, if necessary.  */
+  VEC_truncate (ada_task_info_s, task_list, 0);
+
+  /* If the application does not use task, then no more needs to be done.
+     It is important to have the task list cleared (see above) before we
+     return, as we don't want a stale task list to be used...  This can
+     happen for instance when debugging a non-multitasking program after
+     having debugged a multitasking one.  */
+  if (known_tasks_addr == 0)
+    return 0;
+
+  /* Step 2: Build a new list by reading the ATCBs from the Known_Tasks
+     array in the Ada runtime.  */
+  read_memory (known_tasks_addr, known_tasks, known_tasks_size);
+  for (i = 0; i < MAX_NUMBER_OF_KNOWN_TASKS; i++)
+    {
+      struct type *data_ptr_type =
+        builtin_type (current_gdbarch)->builtin_data_ptr;
+      CORE_ADDR task_id =
+        extract_typed_address (known_tasks + i * target_ptr_byte,
+			       data_ptr_type);
+
+      if (task_id != 0)
+        add_ada_task (task_id);
+    }
+
+  /* Step 3: Unset stale_task_list_p, to avoid re-reading the Known_Tasks
+     array unless needed.  Then report a success.  */
+  stale_task_list_p = 0;
+
+  return 1;
+}
+
+/* Builds the task_list by reading the Known_Tasks array from
+   the inferior.  Prints an appropriate message and returns non-zero
+   if it failed to build this list.  */
+
+int
+ada_build_task_list (int warn_if_null)
+{
+  if (!target_has_stack)
+    error (_("Cannot inspect Ada tasks when program is not running"));
+
+  if (stale_task_list_p)
+    read_known_tasks_array ();
+
+  if (task_list == NULL)
+    {
+      if (warn_if_null)
+        printf_filtered (_("Your application does not use any Ada tasks.\n"));
+      return 0;
+    }
+
+  return 1;
+}
+
+/* Return non-zero iff the task STATE corresponds to a non-terminated
+   task state.  */
+
+int
+ada_task_is_alive (struct ada_task_info *task_info)
+{
+  return (task_info->state != Terminated);
+}
+
+/* Print a one-line description of the task whose number is TASKNO.
+   The formatting should fit the "info tasks" array.  */
+
+static void
+short_task_info (int taskno)
+{
+  const struct ada_task_info *const task_info =
+    VEC_index (ada_task_info_s, task_list, taskno - 1);
+  int active_task_p;
+
+  gdb_assert (task_info != NULL);
+
+  /* Print a star if this task is the current task (or the task currently
+     selected).  */
+
+  active_task_p = ptid_equal (task_info->ptid, inferior_ptid);
+  if (active_task_p)
+    printf_filtered ("*");
+  else
+    printf_filtered (" ");
+
+  /* Print the task number.  */
+  printf_filtered ("%3d", taskno);
+
+  /* Print the Task ID.  */
+  printf_filtered (" %9lx", (long) task_info->task_id);
+
+  /* Print the Task ID of the task parent.  */
+  printf_filtered (" %4d", get_task_number_from_id (task_info->parent));
+
+  /* Print the base priority of the task.  */
+  printf_filtered (" %3d", task_info->priority);
+
+  /* Print the task current state.  */
+  if (task_info->caller_task)
+    printf_filtered (_(" Accepting RV with %-4d"),
+                     get_task_number_from_id (task_info->caller_task));
+  else if (task_info->state == Entry_Caller_Sleep && task_info->called_task)
+    printf_filtered (_(" Waiting on RV with %-3d"),
+                     get_task_number_from_id (task_info->called_task));
+  else if (task_info->state == Runnable && active_task_p)
+    /* Replace "Runnable" by "Running" since this is the active task.  */
+    printf_filtered (" %-22s", "Running");
+  else
+    printf_filtered (" %-22s", task_states[task_info->state]);
+
+  /* Finally, print the task name.  */
+  if (task_info->name[0] != '\0')
+    printf_filtered (" %s\n", task_info->name);
+  else
+    printf_filtered (_(" <no name>\n"));
+}
+
+/* Print a list containing a short description of all Ada tasks.  */
+/* FIXME: Shouldn't we be using ui_out??? */
+
+static void
+info_tasks (int from_tty)
+{
+  int taskno;
+  const int nb_tasks = VEC_length (ada_task_info_s, task_list);
+
+  printf_filtered (_("  ID       TID P-ID Pri State                  Name\n"));
+  
+  for (taskno = 1; taskno <= nb_tasks; taskno++)
+    short_task_info (taskno);
+}
+
+/* Print a detailed description of the Ada task whose ID is TASKNO_STR.  */
+
+static void
+info_task (char *taskno_str, int from_tty)
+{
+  const int taskno = value_as_long (parse_and_eval (taskno_str));
+  struct ada_task_info *task_info;
+  int parent_taskno = 0;
+
+  if (taskno <= 0 || taskno > VEC_length (ada_task_info_s, task_list))
+    error (_("Task ID %d not known.  Use the \"info tasks\" command to\n"
+             "see the IDs of currently known tasks"), taskno);
+  task_info = VEC_index (ada_task_info_s, task_list, taskno - 1);
+
+  /* Print the Ada task ID.  */
+  printf_filtered (_("Ada Task: %s\n"), paddr_nz (task_info->task_id));
+
+  /* Print the name of the task.  */
+  if (task_info->name[0] != '\0')
+    printf_filtered (_("Name: %s\n"), task_info->name);
+  else
+    printf_filtered (_("<no name>\n"));
+
+  /* Print the TID and LWP.  */
+  printf_filtered (_("Thread: %#lx\n"), ptid_get_tid (task_info->ptid));
+  printf_filtered (_("LWP: %#lx\n"), ptid_get_lwp (task_info->ptid));
+
+  /* Print who is the parent (if any).  */
+  if (task_info->parent != 0)
+    parent_taskno = get_task_number_from_id (task_info->parent);
+  if (parent_taskno)
+    {
+      struct ada_task_info *parent =
+        VEC_index (ada_task_info_s, task_list, parent_taskno - 1);
+
+      printf_filtered (_("Parent: %d"), parent_taskno);
+      if (parent->name[0] != '\0')
+        printf_filtered (" (%s)", parent->name);
+      printf_filtered ("\n");
+    }
+  else
+    printf_filtered (_("No parent\n"));
+
+  /* Print the base priority.  */
+  printf_filtered (_("Base Priority: %d\n"), task_info->priority);
+
+  /* print the task current state.  */
+  {
+    int target_taskno = 0;
+
+    if (task_info->caller_task)
+      {
+        target_taskno = get_task_number_from_id (task_info->caller_task);
+        printf_filtered (_("State: Accepting rendezvous with %d"),
+                         target_taskno);
+      }
+    else if (task_info->state == Entry_Caller_Sleep && task_info->called_task)
+      {
+        target_taskno = get_task_number_from_id (task_info->called_task);
+        printf_filtered (_("State: Waiting on task %d's entry"),
+                         target_taskno);
+      }
+    else
+      printf_filtered ("State: %s", long_task_states[task_info->state]);
+
+    if (target_taskno)
+      {
+        struct ada_task_info *target_task_info =
+          VEC_index (ada_task_info_s, task_list, target_taskno - 1);
+
+        if (target_task_info->name[0] != '\0')
+          printf_filtered (" (%s)", target_task_info->name);
+      }
+
+    printf_filtered ("\n");
+  }
+}
+
+/* If ARG is empty or null, then print a list of all Ada tasks.
+   Otherwise, print detailed information about the task whose ID
+   is ARG.
+   
+   Does nothing if the program doesn't use Ada tasking.  */
+
+static void
+info_tasks_command (char *arg, int from_tty)
+{
+  const int task_list_built = ada_build_task_list (1);
+
+  if (!task_list_built)
+    return;
+
+  if (arg == NULL || *arg == '\0')
+    info_tasks (from_tty);
+  else
+    info_task (arg, from_tty);
+}
+
+/* Print a message telling the user id of the current task.
+   This function assumes that tasking is in use in the inferior.  */
+
+static void
+display_current_task_id (void)
+{
+  const int current_task = ada_get_task_number (inferior_ptid);
+
+  if (current_task == 0)
+    printf_filtered (_("[Current task is unknown]\n"));
+  else
+    printf_filtered (_("[Current task is %d]\n"), current_task);
+}
+
+/* Parse and evaluate TIDSTR into a task id, and try to switch to
+   that task.  Print an error message if the task switch failed.  */
+
+static void
+task_command_1 (char *taskno_str, int from_tty)
+{
+  const int taskno = value_as_long (parse_and_eval (taskno_str));
+  struct ada_task_info *task_info;
+
+  if (taskno <= 0 || taskno > VEC_length (ada_task_info_s, task_list))
+    error (_("Task ID %d not known.  Use the \"info tasks\" command to\n"
+             "see the IDs of currently known tasks"), taskno);
+  task_info = VEC_index (ada_task_info_s, task_list, taskno - 1);
+
+  if (!ada_task_is_alive (task_info))
+    error (_("Cannot switch to task %d: Task is no longer running"), taskno);
+   
+  switch_to_thread (task_info->ptid);
+  ada_find_printable_frame (get_selected_frame (NULL));
+  printf_filtered (_("[Switching to task %d]\n"), taskno);
+  print_stack_frame (get_selected_frame (NULL),
+                     frame_relative_level (get_selected_frame (NULL)), 1);
+}
+
+
+/* Print the ID of the current task if TASKNO_STR is empty or NULL.
+   Otherwise, switch to the task indicated by TASKNO_STR.  */
+
+static void
+task_command (char *taskno_str, int from_tty)
+{
+  const int task_list_built = ada_build_task_list (1);
+
+  if (!task_list_built)
+    return;
+
+  if (taskno_str == NULL || taskno_str[0] == '\0')
+    display_current_task_id ();
+  else
+    {
+      /* Task switching in core files doesn't work, either because:
+           1. Thread support is not implemented with core files
+           2. Thread support is implemented, but the thread IDs created
+              after having read the core file are not the same as the ones
+              that were used during the program life, before the crash.
+              As a consequence, there is no longer a way for the debugger
+              to find the associated thead ID of any given Ada task.
+         So, instead of attempting a task switch without giving the user
+         any clue as to what might have happened, just error-out with
+         a message explaining that this feature is not supported.  */
+      if (!target_has_execution)
+        error (_("\
+Task switching not supported when debugging from core files\n\
+(use thread support instead)"));
+      task_command_1 (taskno_str, from_tty);
+    }
+}
+
+/* Indicate that the task list may have changed, so invalidate the cache.  */
+
+void
+ada_task_list_changed (void)
+{
+  stale_task_list_p = 1;  
+}
+
+/* The 'normal_stop' observer notification callback.  */
+
+static void
+ada_normal_stop_observer (struct bpstats *unused_args)
+{
+  /* The inferior has been resumed, and just stopped. This means that
+     our task_list needs to be recomputed before it can be used again.  */
+  ada_task_list_changed ();
+}
+
+/* A routine to be called when the objfiles have changed.  */
+
+void
+ada_new_objfile_observer (struct objfile *objfile)
+{
+  /* Invalidate all cached data that were extracted from an objfile.  */
+
+  atcb_type = NULL;
+  atcb_common_type = NULL;
+  atcb_ll_type = NULL;
+  atcb_call_type = NULL;
+
+  ada_tasks_check_symbol_table = 1;
+}
+
+void
+_initialize_tasks (void)
+{
+  /* Attach various observers.  */
+  observer_attach_normal_stop (ada_normal_stop_observer);
+  observer_attach_new_objfile (ada_new_objfile_observer);
+
+  /* Some new commands provided by this module.  */
+  add_info ("tasks", info_tasks_command,
+            _("Provide information about all known Ada tasks"));
+  add_cmd ("task", class_run, task_command,
+           _("Use this command to switch between Ada tasks.\n\
+Without argument, this command simply prints the current task ID"),
+           &cmdlist);
+}
+