Make main_ui be heap allocated

This is preparation for being able to create more than one UI object.

The change to gdb_main to stop using catch_errors is necessary because
catch_errors references current_uiout, which expands to
current_ui->m_current_ui, which would crash because current_ui is not
initialized yet at that point.  It didn't trigger earlier in the
series because before this patch, main_ui/current_ui always start out
non-NULL.

gdb/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* event-top.c (main_ui_): Delete.
	(main_ui, current_ui, ui_list): No longer initialize here.
	* main.c (captured_main): UI initialization code factored out to
	new new_ui function.
	(gdb_main): Wrap captured_main with TRY/CATCH instead of
	catch_errors.
	* top.c (highest_ui_num): New global.
	(new_ui): New function.
	* top.h (struct ui) <num>: New field.
	(new_ui): New declaration.

1 files changed, 6 insertions, 0 deletions

diff --git a/gdb/top.h b/gdb/top.h
index df96baa1672..9766cd58601 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -57,6 +57,9 @@ struct ui
   /* Pointer to next in singly-linked list.  */
   struct ui *next;
 
+  /* Convenient handle (UI number).  Unique across all UIs.  */
+  int num;
+
   /* The UI's command line buffer.  This is to used to accumulate
      input until we have a whole command line.  */
   struct buffer line_buffer;
@@ -170,6 +173,9 @@ extern void switch_thru_all_uis_next (struct switch_thru_all_uis *state);
 #define ALL_UIS(UI)				\
   for (UI = ui_list; UI; UI = UI->next)		\
 
+/* Create a new UI.  */
+extern struct ui *new_ui (FILE *instream, FILE *outstream, FILE *errstream);
+
 /* Cleanup that restores the current UI.  */
 extern void restore_ui_cleanup (void *data);