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.

1 files changed, 4 insertions, 1 deletions

diff --git a/gdb/infrun.h b/gdb/infrun.h
index 625c53a..9808541 100644
--- a/gdb/infrun.h
+++ b/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