Pass thread_info pointer to various inferior control functions

[ Migrating this from Gerrit: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/321 ]

I noticed that some functions in infcmd and infrun call each other and
all call inferior_thread, while they could just get the thread_info
pointer from their caller.  That means less calls to inferior_thread, so
less reliance on global state, since inferior_thread reads
inferior_ptid.

The paths I am unsure about are:

  - fetch_inferior_event calls...
  - step_command_fsm::should_stop calls...
  - prepare_one_step

and

 - process_event_stop_test calls...
 - set_step_info

Before this patch, prepare_one_step gets the thread pointer using
inferior_thread.  After this patch, it gets it from the
execution_control_state structure in fetch_inferior_event.  Are we sure
that the thread from the execution_control_state structure is the same
as the one inferior_thread would return?  This code path is used when a
thread completes a step, but the user had specified a step count (e.g.
"step 5") so we decide to do one more step.  It would be strange (and
even a bug I suppose) if the thread in the ecs structure in
fetch_inferior_event was not the same thread that is prepared to stepped
by prepare_one_step.  So I believe passing the ecs thread is fine.

The same logic applies to process_event_stop_test calling
set_step_info.

gdb/ChangeLog:

	* infrun.h: Forward-declare thread_info.
	(set_step_info): Add thread_info parameter, add doc.
	* infrun.c (set_step_info): Add thread_info parameter, move doc
	to header.
	* infrun.c (process_event_stop_test): Pass thread to
	set_step_info call.
	* infcmd.c (set_step_frame): Add thread_info pointer, pass it to
	set_step_info.
	(prepare_one_step): Add thread_info parameter, pass it to
	set_step_frame and prepare_one_step (recursive) call.
	(step_1): Pass thread to prepare_one_step call.
	(step_command_fsm::should_stop): Pass thread to
	prepare_one_step.
	(until_next_fsm): Pass thread to set_step_frame call.
	(finish_command): Pass thread to set_step_info call.

gdb/ChangeLog

@@ -1,3 +1,21 @@
+2020-03-06  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* infrun.h: Forward-declare thread_info.
+	(set_step_info): Add thread_info parameter, add doc.
+	* infrun.c (set_step_info): Add thread_info parameter, move doc
+	to header.
+	* infrun.c (process_event_stop_test): Pass thread to
+	set_step_info call.
+	* infcmd.c (set_step_frame): Add thread_info pointer, pass it to
+	set_step_info.
+	(prepare_one_step): Add thread_info parameter, pass it to
+	set_step_frame and prepare_one_step (recursive) call.
+	(step_1): Pass thread to prepare_one_step call.
+	(step_command_fsm::should_stop): Pass thread to
+	prepare_one_step.
+	(until_next_fsm): Pass thread to set_step_frame call.
+	(finish_command): Pass thread to set_step_info call.
+
 2020-03-06  Hannes Domani  <ssbssa@yahoo.de>
 
 	* windows-tdep.c (windows_solib_create_inferior_hook):

gdb/infcmd.c

@@ -914,18 +914,21 @@ continue_command (const char *args, int from_tty)
   continue_1 (all_threads_p);
 }
 
-/* Record the starting point of a "step" or "next" command.  */
+/* Record in TP the starting point of a "step" or "next" command.  */
 
 static void
-set_step_frame (void)
+set_step_frame (thread_info *tp)
 {
+  /* This can be removed once this function no longer implicitly relies on the
+     inferior_ptid value.  */
+  gdb_assert (inferior_ptid == tp->ptid);
+
   frame_info *frame = get_current_frame ();
 
   symtab_and_line sal = find_frame_sal (frame);
-  set_step_info (frame, sal);
+  set_step_info (tp, frame, sal);
 
   CORE_ADDR pc = get_frame_pc (frame);
-  thread_info *tp = inferior_thread ();
   tp->control.step_start_function = find_pc_function (pc);
 }
 
@@ -1002,7 +1005,7 @@ step_command_fsm_prepare (struct step_command_fsm *sm,
   thread->control.stepping_command = 1;
 }
 
-static int prepare_one_step (struct step_command_fsm *sm);
+static int prepare_one_step (thread_info *, struct step_command_fsm *sm);
 
 static void
 step_1 (int skip_subroutines, int single_inst, const char *count_string)
@@ -1040,7 +1043,7 @@ step_1 (int skip_subroutines, int single_inst, const char *count_string)
      loop.  Let the continuation figure out how many other steps we
      need to do, and handle them one at the time, through
      step_once.  */
-  if (!prepare_one_step (step_sm))
+  if (!prepare_one_step (thr, step_sm))
     proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
   else
     {
@@ -1070,7 +1073,7 @@ step_command_fsm::should_stop (struct thread_info *tp)
       /* There are more steps to make, and we did stop due to
 	 ending a stepping range.  Do another step.  */
       if (--count > 0)
-	return prepare_one_step (this);
+	return prepare_one_step (tp, this);
 
       set_finished ();
     }
@@ -1102,19 +1105,17 @@ step_command_fsm::do_async_reply_reason ()
    resumed.  */
 
 static int
-prepare_one_step (struct step_command_fsm *sm)
+prepare_one_step (thread_info *tp, struct step_command_fsm *sm)
 {
+  /* This can be removed once this function no longer implicitly relies on the
+     inferior_ptid value.  */
+  gdb_assert (inferior_ptid == tp->ptid);
+
   if (sm->count > 0)
     {
       struct frame_info *frame = get_current_frame ();
 
-      /* Don't assume THREAD is a valid thread id.  It is set to -1 if
+      set_step_frame (tp);
-	 the longjmp breakpoint was not required.  Use the
-	 INFERIOR_PTID thread instead, which is the same thread when
-	 THREAD is set.  */
-      struct thread_info *tp = inferior_thread ();
-
-      set_step_frame ();
 
       if (!sm->single_inst)
 	{
@@ -1146,7 +1147,7 @@ prepare_one_step (struct step_command_fsm *sm)
 		  || !function_name_is_marked_for_skip (fn, sal))
 		{
 		  sm->count--;
-		  return prepare_one_step (sm);
+		  return prepare_one_step (tp, sm);
 		}
 	    }
 
@@ -1488,7 +1489,7 @@ until_next_command (int from_tty)
   struct until_next_fsm *sm;
 
   clear_proceed_status (0);
-  set_step_frame ();
+  set_step_frame (tp);
 
   frame = get_current_frame ();
 
@@ -1945,7 +1946,7 @@ finish_command (const char *arg, int from_tty)
 	 called by that frame.  We don't use the magic "1" value for
 	 step_range_end, because then infrun will think this is nexti,
 	 and not step over the rest of this inlined function call.  */
-      set_step_info (frame, {});
+      set_step_info (tp, frame, {});
       tp->control.step_range_start = get_frame_pc (frame);
       tp->control.step_range_end = tp->control.step_range_start;
       tp->control.step_over_calls = STEP_OVER_ALL;

gdb/infrun.c

@@ -4102,11 +4102,15 @@ fetch_inferior_event (void *client_data)
     printf_unfiltered (_("completed.\n"));
 }
 
-/* Record the frame and location we're currently stepping through.  */
+/* See infrun.h.  */
+
 void
-set_step_info (struct frame_info *frame, struct symtab_and_line sal)
+set_step_info (thread_info *tp, struct frame_info *frame,
+	       struct symtab_and_line sal)
 {
-  struct thread_info *tp = inferior_thread ();
+  /* This can be removed once this function no longer implicitly relies on the
+     inferior_ptid value.  */
+  gdb_assert (inferior_ptid == tp->ptid);
 
   tp->control.step_frame_id = get_frame_id (frame);
   tp->control.step_stack_frame_id = get_stack_frame_id (frame);
@@ -7200,7 +7204,7 @@ process_event_stop_test (struct execution_control_state *ecs)
   ecs->event_thread->control.step_range_start = stop_pc_sal.pc;
   ecs->event_thread->control.step_range_end = stop_pc_sal.end;
   ecs->event_thread->control.may_range_step = 1;
-  set_step_info (frame, stop_pc_sal);
+  set_step_info (ecs->event_thread, frame, stop_pc_sal);
 
   if (debug_infrun)
      fprintf_unfiltered (gdb_stdlog, "infrun: keep going\n");

gdb/infrun.h

@@ -26,6 +26,7 @@ struct frame_info;
 struct address_space;
 struct return_value_info;
 struct process_stratum_target;
+struct thread_info;
 
 /* True if we are debugging run control.  */
 extern unsigned int debug_infrun;
@@ -150,7 +151,9 @@ extern int thread_is_stepping_over_breakpoint (int thread);
    triggers a non-steppable watchpoint.  */
 extern int stepping_past_nonsteppable_watchpoint (void);
 
-extern void set_step_info (struct frame_info *frame,
+/* Record in TP the frame and location we're currently stepping through.  */
+extern void set_step_info (thread_info *tp,
+			   struct frame_info *frame,
 			   struct symtab_and_line sal);
 
 /* Several print_*_reason helper functions to print why the inferior