Add multiple-CPU support in ravenscar-thread.c

This patch reworks the ravenscar-thread layer to remove the
assumption that the target only has 1 CPU. In particular,
when connected to a QEMU target over the remote protocol,
QEMU reports each CPU as one thread. This patch adapts
the ravenscar-thread layer to this, and adds a large comment
explaining the general design of this unit.

gdb/ChangeLog:

        * ada-lang.h (ada_get_task_info_from_ptid): Add declaration.
        * ada-tasks.c (ada_get_task_info_from_ptid): New function.
        * ravenscar-thread.c: Add into comment.
        (base_magic_null_ptid): Delete.
        (base_ptid): Change documentation.
        (ravenscar_active_task): Renames ravenscar_running_thread.
        All callers updated throughout.
        (is_ravenscar_task, ravenscar_get_thread_base_cpu): New function.
        (ravenscar_task_is_currently_active): Likewise.
        (get_base_thread_from_ravenscar_task): Ditto.
        (ravenscar_update_inferior_ptid): Adjust to handle multiple CPUs.
        (ravenscar_runtime_initialized): Likewise.
        (get_running_thread_id): Add new parameter "cpu".  Adjust
        implementation to handle this new parameter.
        (ravenscar_fetch_registers): Small adjustment to use
        is_ravenscar_task and ravenscar_task_is_currently_active in
        order to decide whether to use the target beneath or this
        module's arch_ops.
        (ravenscar_store_registers, ravenscar_prepare_to_store): Likewise.
        (ravenscar_stopped_by_sw_breakpoint): Use
        get_base_thread_from_ravenscar_task to get the underlying
        thread, rather than using base_ptid.
        (ravenscar_stopped_by_hw_breakpoint, ravenscar_stopped_by_watchpoint)
        (ravenscar_stopped_data_address, ravenscar_core_of_thread):
        Likewise.
        (ravenscar_inferior_created): Do not set base_magic_null_ptid.

4 files changed, 191 insertions, 34 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 7300cdd..d7cf066 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,34 @@
 2017-11-21  Joel Brobecker  <brobecker@adacore.com>
 
+	* ada-lang.h (ada_get_task_info_from_ptid): Add declaration.
+	* ada-tasks.c (ada_get_task_info_from_ptid): New function.
+	* ravenscar-thread.c: Add into comment.
+	(base_magic_null_ptid): Delete.
+	(base_ptid): Change documentation.
+	(ravenscar_active_task): Renames ravenscar_running_thread.
+	All callers updated throughout.
+	(is_ravenscar_task, ravenscar_get_thread_base_cpu): New function.
+	(ravenscar_task_is_currently_active): Likewise.
+	(get_base_thread_from_ravenscar_task): Ditto.
+	(ravenscar_update_inferior_ptid): Adjust to handle multiple CPUs.
+	(ravenscar_runtime_initialized): Likewise.
+	(get_running_thread_id): Add new parameter "cpu".  Adjust
+	implementation to handle this new parameter.
+	(ravenscar_fetch_registers): Small adjustment to use
+	is_ravenscar_task and ravenscar_task_is_currently_active in
+	order to decide whether to use the target beneath or this
+	module's arch_ops.
+	(ravenscar_store_registers, ravenscar_prepare_to_store): Likewise.
+	(ravenscar_stopped_by_sw_breakpoint): Use
+	get_base_thread_from_ravenscar_task to get the underlying
+	thread, rather than using base_ptid.
+	(ravenscar_stopped_by_hw_breakpoint, ravenscar_stopped_by_watchpoint)
+	(ravenscar_stopped_data_address, ravenscar_core_of_thread):
+	Likewise.
+	(ravenscar_inferior_created): Do not set base_magic_null_ptid.
+
+2017-11-21  Joel Brobecker  <brobecker@adacore.com>
+
 	* ada-lang.h (struct ada_task_info) <base_cpu>: New field.
 	* ada-lang.c (struct atcb_fieldno) <base_cpu>: New field.
 	(get_tcb_types_info): Set fieldnos.base_cpu.
diff --git a/gdb/ada-lang.h b/gdb/ada-lang.h
index c11fb48..36a5820 100644
--- a/gdb/ada-lang.h
+++ b/gdb/ada-lang.h
@@ -401,6 +401,8 @@ extern std::vector<ada_exc_info> ada_exceptions_list (const char *regexp);
 
 extern int valid_task_id (int);
 
+extern struct ada_task_info *ada_get_task_info_from_ptid (ptid_t ptid);
+
 extern int ada_get_task_number (ptid_t);
 
 typedef void (ada_task_list_iterator_ftype) (struct ada_task_info *task);
diff --git a/gdb/ada-tasks.c b/gdb/ada-tasks.c
index e29b563..16cee35 100644
--- a/gdb/ada-tasks.c
+++ b/gdb/ada-tasks.c
@@ -353,6 +353,30 @@ ada_task_is_alive (struct ada_task_info *task_info)
   return (task_info->state != Terminated);
 }
 
+/* Search through the list of known tasks for the one whose ptid is
+   PTID, and return it.  Return NULL if the task was not found.  */
+
+struct ada_task_info *
+ada_get_task_info_from_ptid (ptid_t ptid)
+{
+  int i, nb_tasks;
+  struct ada_task_info *task;
+  struct ada_tasks_inferior_data *data;
+
+  ada_build_task_list ();
+  data = get_ada_tasks_inferior_data (current_inferior ());
+  nb_tasks = VEC_length (ada_task_info_s, data->task_list);
+
+  for (i = 0; i < nb_tasks; i++)
+    {
+      task = VEC_index (ada_task_info_s, data->task_list, i);
+      if (ptid_equal (task->ptid, ptid))
+	return task;
+    }
+
+  return NULL;
+}
+
 /* Call the ITERATOR function once for each Ada task that hasn't been
    terminated yet.  */
 
diff --git a/gdb/ravenscar-thread.c b/gdb/ravenscar-thread.c
index 7edfa29..83dfd9d 100644
--- a/gdb/ravenscar-thread.c
+++ b/gdb/ravenscar-thread.c
@@ -31,17 +31,41 @@
 #include "regcache.h"
 #include "objfiles.h"
 
+/* This module provides support for "Ravenscar" tasks (Ada) when
+   debugging on bare-metal targets.
+
+   The typical situation is when debugging a bare-metal target over
+   the remote protocol. In that situation, the system does not know
+   about high-level comcepts such as threads, only about some code
+   running on one or more CPUs. And since the remote protocol does not
+   provide any handling for CPUs, the de facto standard for handling
+   them is to have one thread per CPU, where the thread's ptid has
+   its lwp field set to the CPU number (eg: 1 for the first CPU,
+   2 for the second one, etc).  This module will make that assumption.
+
+   This module then creates and maintains the list of threads based
+   on the list of Ada tasks, with one thread per Ada tasks. The convention
+   is that threads corresponding to the CPUs (see assumption above)
+   have a ptid_t of the form (PID, LWP, 0), which threads corresponding
+   to our Ada tasks have a ptid_t of the form (PID, 0, TID) where TID
+   is the Ada task's ID as extracted from Ada runtime information.
+
+   Switching to a given Ada tasks (or its underlying thread) is performed
+   by fetching the registers of that tasks from the memory area where
+   the registers were saved.  For any of the other operations, the
+   operation is performed by first finding the CPU on which the task
+   is running, switching to its corresponding ptid, and then performing
+   the operation on that ptid using the target beneath us.  */
+
 /* If non-null, ravenscar task support is enabled.  */
 static int ravenscar_task_support = 1;
 
 /* This module's target-specific operations.  */
 static struct target_ops ravenscar_ops;
 
-/* Some base target uses a special value for the null PID (exempli gratia
-   remote).  */
-static ptid_t base_magic_null_ptid;
-
-/* Ptid of the inferior as seen by the process stratum.  */
+/* PTID of the last thread that received an event.
+   This can be useful to determine the associated task that received
+   the event, to make it the current task.  */
 static ptid_t base_ptid;
 
 static const char running_thread_name[] = "__gnat_running_thread_table";
@@ -53,7 +77,7 @@ static const char ravenscar_runtime_initializer[] =
   "system__bb__threads__initialize";
 
 static void ravenscar_update_thread_list (struct target_ops *ops);
-static ptid_t ravenscar_running_thread (void);
+static ptid_t ravenscar_active_task (int cpu);
 static const char *ravenscar_extra_thread_info (struct target_ops *self,
 						struct thread_info *tp);
 static int ravenscar_thread_alive (struct target_ops *ops, ptid_t ptid);
@@ -72,22 +96,100 @@ static int ravenscar_runtime_initialized (void);
 static void ravenscar_inferior_created (struct target_ops *target,
 					int from_tty);
 
+/* Return nonzero iff PTID corresponds to a ravenscar task.  */
+
+static int
+is_ravenscar_task (ptid_t ptid)
+{
+  /* By construction, ravenscar tasks have their LWP set to zero.  */
+  return ptid_get_lwp (ptid) == 0;
+}
+
+/* Given PTID, which can be either a ravenscar task or a CPU thread,
+   return which CPU that ptid is running on.
+
+   This assume that PTID is a valid ptid_t.  Otherwise, a gdb_assert
+   will be triggered.  */
+
+static int
+ravenscar_get_thread_base_cpu (ptid_t ptid)
+{
+  int base_cpu;
+
+  if (is_ravenscar_task (ptid))
+    {
+      struct ada_task_info *task_info = ada_get_task_info_from_ptid (ptid);
+
+      gdb_assert (task_info != NULL);
+      base_cpu = task_info->base_cpu;
+    }
+  else
+    {
+      /* We assume that the LWP of the PTID is equal to the CPU number.  */
+      base_cpu = ptid_get_lwp (ptid);
+    }
+
+  return base_cpu;
+}
+
+/* Given a ravenscar task (identified by its ptid_t PTID), return nonzero
+   if this task is the currently active task on the cpu that task is
+   running on.
+
+   In other words, this function determine which CPU this task is
+   currently running on, and then return nonzero if the CPU in question
+   is executing the code for that task.  If that's the case, then
+   that task's registers are in the CPU bank.  Otherwise, the task
+   is currently suspended, and its registers have been saved in memory.  */
+
+static int
+ravenscar_task_is_currently_active (ptid_t ptid)
+{
+  ptid_t active_task_ptid
+    = ravenscar_active_task (ravenscar_get_thread_base_cpu (ptid));
+
+  return ptid_equal (ptid, active_task_ptid);
+}
+
+/* Return the CPU thread (as a ptid_t) on which the given ravenscar
+   task is running.
+
+   This is the thread that corresponds to the CPU on which the task
+   is running.  */
+
+static ptid_t
+get_base_thread_from_ravenscar_task (ptid_t ptid)
+{
+  int base_cpu;
+
+  if (!is_ravenscar_task (ptid))
+    return ptid;
+
+  base_cpu = ravenscar_get_thread_base_cpu (ptid);
+  return ptid_build (ptid_get_pid (ptid), base_cpu, 0);
+}
+
 /* Fetch the ravenscar running thread from target memory and
    update inferior_ptid accordingly.  */
 
 static void
 ravenscar_update_inferior_ptid (void)
 {
+  int base_cpu;
+
   base_ptid = inferior_ptid;
 
+  gdb_assert (!is_ravenscar_task (inferior_ptid));
+  base_cpu = ravenscar_get_thread_base_cpu (base_ptid);
+
   /* If the runtime has not been initialized yet, the inferior_ptid is
      the only ptid that there is.  */
   if (!ravenscar_runtime_initialized ())
     return;
 
-  /* Make sure we set base_ptid before calling ravenscar_running_thread
+  /* Make sure we set base_ptid before calling ravenscar_active_task
      as the latter relies on it.  */
-  inferior_ptid = ravenscar_running_thread ();
+  inferior_ptid = ravenscar_active_task (base_cpu);
   gdb_assert (!ptid_equal (inferior_ptid, null_ptid));
 
   /* The running thread may not have been added to
@@ -144,14 +246,14 @@ has_ravenscar_runtime (void)
 static int
 ravenscar_runtime_initialized (void)
 {
-  return (!(ptid_equal (ravenscar_running_thread (), null_ptid)));
+  return (!(ptid_equal (ravenscar_active_task (1), null_ptid)));
 }
 
 /* Return the ID of the thread that is currently running.
    Return 0 if the ID could not be determined.  */
 
 static CORE_ADDR
-get_running_thread_id (void)
+get_running_thread_id (int cpu)
 {
   struct bound_minimal_symbol object_msym = get_running_thread_msymbol ();
   int object_size;
@@ -164,8 +266,9 @@ get_running_thread_id (void)
   if (!object_msym.minsym)
     return 0;
 
-  object_addr = BMSYMBOL_VALUE_ADDRESS (object_msym);
   object_size = TYPE_LENGTH (builtin_type_void_data_ptr);
+  object_addr = (BMSYMBOL_VALUE_ADDRESS (object_msym)
+		 + (cpu - 1) * object_size);
   buf_size = object_size;
   buf = (gdb_byte *) alloca (buf_size);
   read_memory (object_addr, buf, buf_size);
@@ -231,9 +334,9 @@ ravenscar_update_thread_list (struct target_ops *ops)
 }
 
 static ptid_t
-ravenscar_running_thread (void)
+ravenscar_active_task (int cpu)
 {
-  CORE_ADDR tid = get_running_thread_id ();
+  CORE_ADDR tid = get_running_thread_id (cpu);
 
   if (tid == 0)
     return null_ptid;
@@ -270,11 +373,9 @@ ravenscar_fetch_registers (struct target_ops *ops,
   struct target_ops *beneath = find_target_beneath (ops);
   ptid_t ptid = regcache_get_ptid (regcache);
 
-  if (!ravenscar_runtime_initialized ()
-      || ptid_equal (ptid, base_magic_null_ptid)
-      || ptid_equal (ptid, ravenscar_running_thread ()))
-    beneath->to_fetch_registers (beneath, regcache, regnum);
-  else
+  if (ravenscar_runtime_initialized ()
+      && is_ravenscar_task (ptid)
+      && !ravenscar_task_is_currently_active (ptid))
     {
       struct gdbarch *gdbarch = regcache->arch ();
       struct ravenscar_arch_ops *arch_ops
@@ -282,6 +383,8 @@ ravenscar_fetch_registers (struct target_ops *ops,
 
       arch_ops->to_fetch_registers (regcache, regnum);
     }
+  else
+    beneath->to_fetch_registers (beneath, regcache, regnum);
 }
 
 static void
@@ -291,11 +394,9 @@ ravenscar_store_registers (struct target_ops *ops,
   struct target_ops *beneath = find_target_beneath (ops);
   ptid_t ptid = regcache_get_ptid (regcache);
 
-  if (!ravenscar_runtime_initialized ()
-      || ptid_equal (ptid, base_magic_null_ptid)
-      || ptid_equal (ptid, ravenscar_running_thread ()))
-    beneath->to_store_registers (beneath, regcache, regnum);
-  else
+  if (ravenscar_runtime_initialized ()
+      && is_ravenscar_task (ptid)
+      && !ravenscar_task_is_currently_active (ptid))
     {
       struct gdbarch *gdbarch = regcache->arch ();
       struct ravenscar_arch_ops *arch_ops
@@ -303,6 +404,8 @@ ravenscar_store_registers (struct target_ops *ops,
 
       arch_ops->to_store_registers (regcache, regnum);
     }
+  else
+    beneath->to_store_registers (beneath, regcache, regnum);
 }
 
 static void
@@ -312,11 +415,9 @@ ravenscar_prepare_to_store (struct target_ops *self,
   struct target_ops *beneath = find_target_beneath (self);
   ptid_t ptid = regcache_get_ptid (regcache);
 
-  if (!ravenscar_runtime_initialized ()
-      || ptid_equal (ptid, base_magic_null_ptid)
-      || ptid_equal (ptid, ravenscar_running_thread ()))
-    beneath->to_prepare_to_store (beneath, regcache);
-  else
+  if (ravenscar_runtime_initialized ()
+      && is_ravenscar_task (ptid)
+      && !ravenscar_task_is_currently_active (ptid))
     {
       struct gdbarch *gdbarch = regcache->arch ();
       struct ravenscar_arch_ops *arch_ops
@@ -324,6 +425,8 @@ ravenscar_prepare_to_store (struct target_ops *self,
 
       arch_ops->to_prepare_to_store (regcache);
     }
+  else
+    beneath->to_prepare_to_store (beneath, regcache);
 }
 
 /* Implement the to_stopped_by_sw_breakpoint target_ops "method".  */
@@ -335,7 +438,7 @@ ravenscar_stopped_by_sw_breakpoint (struct target_ops *ops)
   struct target_ops *beneath = find_target_beneath (ops);
   int result;
 
-  inferior_ptid = base_ptid;
+  inferior_ptid = get_base_thread_from_ravenscar_task (saved_ptid);
   result = beneath->to_stopped_by_sw_breakpoint (beneath);
   inferior_ptid = saved_ptid;
   return result;
@@ -350,7 +453,7 @@ ravenscar_stopped_by_hw_breakpoint (struct target_ops *ops)
   struct target_ops *beneath = find_target_beneath (ops);
   int result;
 
-  inferior_ptid = base_ptid;
+  inferior_ptid = get_base_thread_from_ravenscar_task (saved_ptid);
   result = beneath->to_stopped_by_hw_breakpoint (beneath);
   inferior_ptid = saved_ptid;
   return result;
@@ -365,7 +468,7 @@ ravenscar_stopped_by_watchpoint (struct target_ops *ops)
   struct target_ops *beneath = find_target_beneath (ops);
   int result;
 
-  inferior_ptid = base_ptid;
+  inferior_ptid = get_base_thread_from_ravenscar_task (saved_ptid);
   result = beneath->to_stopped_by_watchpoint (beneath);
   inferior_ptid = saved_ptid;
   return result;
@@ -380,7 +483,7 @@ ravenscar_stopped_data_address (struct target_ops *ops, CORE_ADDR *addr_p)
   struct target_ops *beneath = find_target_beneath (ops);
   int result;
 
-  inferior_ptid = base_ptid;
+  inferior_ptid = get_base_thread_from_ravenscar_task (saved_ptid);
   result = beneath->to_stopped_data_address (beneath, addr_p);
   inferior_ptid = saved_ptid;
   return result;
@@ -405,7 +508,7 @@ ravenscar_core_of_thread (struct target_ops *ops, ptid_t ptid)
   struct target_ops *beneath = find_target_beneath (ops);
   int result;
 
-  inferior_ptid = base_ptid;
+  inferior_ptid = get_base_thread_from_ravenscar_task (saved_ptid);
   result = beneath->to_core_of_thread (beneath, inferior_ptid);
   inferior_ptid = saved_ptid;
   return result;
@@ -422,7 +525,6 @@ ravenscar_inferior_created (struct target_ops *target, int from_tty)
       || !has_ravenscar_runtime ())
     return;
 
-  base_magic_null_ptid = inferior_ptid;
   ravenscar_update_inferior_ptid ();
   push_target (&ravenscar_ops);
 }