gdb: Add a class to track last display symtab and line information

In stack.c we currently have a set of static global variables to track
the last displayed symtab and line.  This commit moves all of these
into a class and adds an instance of the class to track the same
information.

The API into stack.c is unchanged after this cleanup.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* stack.c (set_last_displayed_sal): Delete.
	(last_displayed_sal_valid): Delete.
	(last_displayed_pspace): Delete.
	(last_displayed_addr): Delete.
	(last_displayed_symtab): Delete.
	(last_displayed_line): Delete.
	(class last_displayed_symtab_info_type): New.
	(last_displayed_symtab_info): New static global variable.
	(print_frame_info): Call methods on last_displayed_symtab_info.
	(clear_last_displayed_sal): Update header comment, and make use of
	last_displayed_symtab_info.
	(last_displayed_sal_is_valid): Likewise.
	(get_last_displayed_pspace): Likewise.
	(get_last_displayed_addr): Likewise.
	(get_last_displayed_symtab): Likewise.
	(get_last_displayed_line): Likewise.
	(get_last_displayed_sal): Likewise.
	* stack.h (clear_last_displayed_sal): Update header comment.
	(last_displayed_sal_is_valid): Likewise.
	(get_last_displayed_pspace): Likewise.
	(get_last_displayed_addr): Likewise.
	(get_last_displayed_symtab): Likewise.
	(get_last_displayed_line): Likewise.
	(get_last_displayed_sal): Likewise.

Change-Id: Ia3dbfe267feec03108c5c8ed8bd94fc0a030c3ed

3 files changed, 148 insertions, 73 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 158af825020..06e5423fbeb 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,32 @@
 2019-11-10  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* stack.c (set_last_displayed_sal): Delete.
+	(last_displayed_sal_valid): Delete.
+	(last_displayed_pspace): Delete.
+	(last_displayed_addr): Delete.
+	(last_displayed_symtab): Delete.
+	(last_displayed_line): Delete.
+	(class last_displayed_symtab_info_type): New.
+	(last_displayed_symtab_info): New static global variable.
+	(print_frame_info): Call methods on last_displayed_symtab_info.
+	(clear_last_displayed_sal): Update header comment, and make use of
+	last_displayed_symtab_info.
+	(last_displayed_sal_is_valid): Likewise.
+	(get_last_displayed_pspace): Likewise.
+	(get_last_displayed_addr): Likewise.
+	(get_last_displayed_symtab): Likewise.
+	(get_last_displayed_line): Likewise.
+	(get_last_displayed_sal): Likewise.
+	* stack.h (clear_last_displayed_sal): Update header comment.
+	(last_displayed_sal_is_valid): Likewise.
+	(get_last_displayed_pspace): Likewise.
+	(get_last_displayed_addr): Likewise.
+	(get_last_displayed_symtab): Likewise.
+	(get_last_displayed_line): Likewise.
+	(get_last_displayed_sal): Likewise.
+
+2019-11-10  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* stack.c (frame_show_address): Convert return type to bool.
 	* stack.h (frame_show_address): Likewise, and update header
 	comment.
diff --git a/gdb/stack.c b/gdb/stack.c
index 5af00c708e4..b02f1779337 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -224,12 +224,6 @@ static void print_frame (const frame_print_options &opts,
 			 enum print_what print_what,  int print_args,
 			 struct symtab_and_line sal);
 
-static void set_last_displayed_sal (int valid,
-				    struct program_space *pspace,
-				    CORE_ADDR addr,
-				    struct symtab *symtab,
-				    int line);
-
 static struct frame_info *find_frame_for_function (const char *);
 static struct frame_info *find_frame_for_address (CORE_ADDR);
 
@@ -241,13 +235,79 @@ static struct frame_info *find_frame_for_address (CORE_ADDR);
 
 int annotation_level = 0;
 
-/* These variables hold the last symtab and line we displayed to the user.
- * This is where we insert a breakpoint or a skiplist entry by default.  */
-static int last_displayed_sal_valid = 0;
-static struct program_space *last_displayed_pspace = 0;
-static CORE_ADDR last_displayed_addr = 0;
-static struct symtab *last_displayed_symtab = 0;
-static int last_displayed_line = 0;
+/* Class used to manage tracking the last symtab we displayed.  */
+
+class last_displayed_symtab_info_type
+{
+public:
+  /* True if the cached information is valid.  */
+  bool is_valid () const
+  { return m_valid; }
+
+  /* Return the cached program_space.  If the cache is invalid nullptr is
+     returned.  */
+  struct program_space *pspace () const
+  { return m_pspace; }
+
+  /* Return the cached CORE_ADDR address.  If the cache is invalid 0 is
+     returned.  */
+  CORE_ADDR address () const
+  { return m_address; }
+
+  /* Return the cached symtab.  If the cache is invalid nullptr is
+     returned.  */
+  struct symtab *symtab () const
+  { return m_symtab; }
+
+  /* Return the cached line number.  If the cache is invalid 0 is
+     returned.  */
+  int line () const
+  { return m_line; }
+
+  /* Invalidate the cache, reset all the members to their default value.  */
+  void invalidate ()
+  {
+    m_valid = false;
+    m_pspace = nullptr;
+    m_address = 0;
+    m_symtab = nullptr;
+    m_line = 0;
+  }
+
+  /* Store a new set of values in the cache.  */
+  void set (struct program_space *pspace, CORE_ADDR address,
+	    struct symtab *symtab, int line)
+  {
+    gdb_assert (pspace != nullptr);
+
+    m_valid = true;
+    m_pspace = pspace;
+    m_address = address;
+    m_symtab = symtab;
+    m_line = line;
+  }
+
+private:
+  /* True when the cache is valid.  */
+  bool m_valid = false;
+
+  /* The last program space displayed.  */
+  struct program_space *m_pspace = nullptr;
+
+  /* The last address displayed.  */
+  CORE_ADDR m_address = 0;
+
+  /* The last symtab displayed.  */
+  struct symtab *m_symtab = nullptr;
+
+  /* The last line number displayed.  */
+  int m_line = 0;
+};
+
+/* An actual instance of the cache, holds information about the last symtab
+   displayed.  */
+static last_displayed_symtab_info_type last_displayed_symtab_info;
+
 
 
 /* See stack.h.  */
@@ -1105,9 +1165,9 @@ print_frame_info (const frame_print_options &fp_opts,
       CORE_ADDR pc;
 
       if (get_frame_pc_if_available (frame, &pc))
-	set_last_displayed_sal (1, sal.pspace, pc, sal.symtab, sal.line);
+	last_displayed_symtab_info.set (sal.pspace, pc, sal.symtab, sal.line);
       else
-	set_last_displayed_sal (0, 0, 0, 0, 0);
+	last_displayed_symtab_info.invalidate ();
     }
 
   annotate_frame_end ();
@@ -1115,103 +1175,67 @@ print_frame_info (const frame_print_options &fp_opts,
   gdb_flush (gdb_stdout);
 }
 
-/* Remember the last symtab and line we displayed, which we use e.g.
- * as the place to put a breakpoint when the `break' command is
- * invoked with no arguments.  */
-
-static void
-set_last_displayed_sal (int valid, struct program_space *pspace,
-			CORE_ADDR addr, struct symtab *symtab,
-			int line)
-{
-  last_displayed_sal_valid = valid;
-  last_displayed_pspace = pspace;
-  last_displayed_addr = addr;
-  last_displayed_symtab = symtab;
-  last_displayed_line = line;
-  if (valid && pspace == NULL)
-    {
-      clear_last_displayed_sal ();
-      internal_error (__FILE__, __LINE__,
-		      _("Trying to set NULL pspace."));
-    }
-}
-
-/* Forget the last sal we displayed.  */
+/* See stack.h.  */
 
 void
 clear_last_displayed_sal (void)
 {
-  last_displayed_sal_valid = 0;
-  last_displayed_pspace = 0;
-  last_displayed_addr = 0;
-  last_displayed_symtab = 0;
-  last_displayed_line = 0;
+  last_displayed_symtab_info.invalidate ();
 }
 
-/* Is our record of the last sal we displayed valid?  If not,
- * the get_last_displayed_* functions will return NULL or 0, as
- * appropriate.  */
+/* See stack.h.  */
 
-int
+bool
 last_displayed_sal_is_valid (void)
 {
-  return last_displayed_sal_valid;
+  return last_displayed_symtab_info.is_valid ();
 }
 
-/* Get the pspace of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 struct program_space *
 get_last_displayed_pspace (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_pspace;
-  return 0;
+  return last_displayed_symtab_info.pspace ();
 }
 
-/* Get the address of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 CORE_ADDR
 get_last_displayed_addr (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_addr;
-  return 0;
+  return last_displayed_symtab_info.address ();
 }
 
-/* Get the symtab of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 struct symtab*
 get_last_displayed_symtab (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_symtab;
-  return 0;
+  return last_displayed_symtab_info.symtab ();
 }
 
-/* Get the line of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 int
 get_last_displayed_line (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_line;
-  return 0;
+  return last_displayed_symtab_info.line ();
 }
 
-/* Get the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 symtab_and_line
 get_last_displayed_sal ()
 {
   symtab_and_line sal;
 
-  if (last_displayed_sal_valid)
+  if (last_displayed_symtab_info.is_valid ())
     {
-      sal.pspace = last_displayed_pspace;
-      sal.pc = last_displayed_addr;
-      sal.symtab = last_displayed_symtab;
-      sal.line = last_displayed_line;
+      sal.pspace = last_displayed_symtab_info.pspace ();
+      sal.pc = last_displayed_symtab_info.address ();
+      sal.symtab = last_displayed_symtab_info.symtab ();
+      sal.line = last_displayed_symtab_info.line ();
     }
 
   return sal;
diff --git a/gdb/stack.h b/gdb/stack.h
index 28d22730b18..9b038f0948f 100644
--- a/gdb/stack.h
+++ b/gdb/stack.h
@@ -54,14 +54,38 @@ void get_user_print_what_frame_info (gdb::optional<enum print_what> *what);
 
 bool frame_show_address (struct frame_info *frame, struct symtab_and_line sal);
 
-/* Get or set the last displayed symtab and line, which is, e.g. where we set a
- * breakpoint when `break' is supplied with no arguments.  */
+/* Forget the last sal we displayed.  */
+
 void clear_last_displayed_sal (void);
-int last_displayed_sal_is_valid (void);
+
+/* Is our record of the last sal we displayed valid?  If not, the
+   get_last_displayed_* functions will return NULL or 0, as appropriate.  */
+
+bool last_displayed_sal_is_valid (void);
+
+/* Get the pspace of the last sal we displayed, if it's valid, otherwise
+   return nullptr.  */
+
 struct program_space* get_last_displayed_pspace (void);
+
+/* Get the address of the last sal we displayed, if it's valid, otherwise
+   return an address of 0.  */
+
 CORE_ADDR get_last_displayed_addr (void);
+
+/* Get the symtab of the last sal we displayed, if it's valid, otherwise
+   return nullptr.  */
+
 struct symtab* get_last_displayed_symtab (void);
+
+/* Get the line of the last sal we displayed, if it's valid, otherwise
+   return 0.  */
+
 int get_last_displayed_line (void);
+
+/* Get the last sal we displayed, if it's valid, otherwise return a
+   symtab_and_line constructed in its default state.  */
+
 symtab_and_line get_last_displayed_sal ();
 
 /* Completer for the "frame apply all" command.  */