Avoid rereading shared libraries that haven't changed.

[Pedro Alves <pedro at codesourcery dot com>]

Here's another patch in the same theme as the previous.

This avoids rereading shared libraries that haven't changed
when the user adds does "set sysroot", but also, and more
importantly, when the user adds new paths to the non-absolute
search path with "set solib-search-path".  On targets that
tend to have many dlls loaded, or when the search path
is pointing at loading the dlls straight from target memory,
always reloading all symbols can be slow.

-- 
Pedro Alves

2010-04-12  Daniel Jacobowitz  <dan@codesourcery.com>
	    Pedro Alves  <pedro@codesourcery.com>

	Avoid rereading shared libraries that haven't changed.

	* solib.c (free_so_symbols): New function, from ...
	(free_so): ... here.  Call it.
	(reload_shared_libraries_1): New.
	(reload_shared_libraries): Rewrite to not fetch the library list.

---
 gdb/solib.c |  142 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 123 insertions(+), 19 deletions(-)

Index: src/gdb/solib.c
===================================================================
--- src.orig/gdb/solib.c	2010-04-12 11:53:48.000000000 +0100
+++ src/gdb/solib.c	2010-04-12 11:53:50.000000000 +0100
@@ -422,6 +422,39 @@ solib_map_sections (void *arg)
   return (1);
 }
 
+/* Free symbol-file related contents of SO.  If we have opened a BFD
+   for SO, close it.  If we have placed SO's sections in some target's
+   section table, the caller is responsible for removing them.
+
+   This function doesn't mess with objfiles at all.  If there is an
+   objfile associated with SO that needs to be removed, the caller is
+   responsible for taking care of that.  */
+
+static void
+free_so_symbols (struct so_list *so)
+{
+  char *bfd_filename = 0;
+
+  if (so->sections)
+    {
+      xfree (so->sections);
+      so->sections = so->sections_end = NULL;
+    }
+
+  gdb_bfd_unref (so->abfd);
+  so->abfd = NULL;
+
+  /* Our caller closed the objfile, possibly via objfile_purge_solibs.  */
+  so->symbols_loaded = 0;
+  so->objfile = NULL;
+
+  so->addr_low = so->addr_high = 0;
+
+  /* Restore the target-supplied file name.  SO_NAME may be the path
+     of the symbol file.  */
+  strcpy (so->so_name, so->so_original_name);
+}
+
 /* LOCAL FUNCTION
 
    free_so --- free a `struct so_list' object
@@ -448,11 +481,7 @@ free_so (struct so_list *so)
 {
   struct target_so_ops *ops = solib_ops (target_gdbarch);
 
-  if (so->sections)
-    xfree (so->sections);
-
-  gdb_bfd_unref (so->abfd);
-
+  free_so_symbols (so);
   ops->free_so (so);
 
   xfree (so);
@@ -1124,11 +1153,84 @@ no_shared_libraries (char *ignored, int 
   objfile_purge_solibs ();
 }
 
+/* Reload shared libraries, but avoid reloading the same symbol file
+   we already have loaded.  Returns true if we've loaded or unloaded
+   new symbol file; that is, if something changed.  */
+
+static int
+reload_shared_libraries_1 (int from_tty)
+{
+  struct so_list *so;
+  int any_changed = 0;
+  struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
+
+  for (so = so_list_head; so != NULL; so = so->next)
+    {
+      char *filename, *found_pathname = NULL;
+      bfd *abfd;
+      int scratch_chan;
+      int was_loaded = so->symbols_loaded;
+      const int flags =
+	SYMFILE_DEFER_BP_RESET | (from_tty ? SYMFILE_VERBOSE : 0);
+
+      filename = tilde_expand (so->so_original_name);
+      abfd = solib_bfd_open (filename);
+      if (abfd != NULL)
+	{
+	  found_pathname = xstrdup (bfd_get_filename (abfd));
+	  make_cleanup (xfree, found_pathname);
+	  /* ref/unref so that we don't have to inline the warning
+	     within gdb_bfd_unref.  */
+	  gdb_bfd_ref (abfd);
+	  gdb_bfd_unref (abfd);
+	}
+
+      /* If this shared library is no longer associated with its previous
+	 symbol file, close that.  */
+      if ((found_pathname == NULL && was_loaded)
+	  || (found_pathname != NULL
+	      && strcmp (found_pathname, so->so_name) != 0))
+	{
+	  any_changed = 1;
+
+	  if (so->objfile && ! (so->objfile->flags & OBJF_USERLOADED))
+	    free_objfile (so->objfile);
+	  remove_target_sections (so->abfd);
+	  free_so_symbols (so);
+	}
+
+      /* If this shared library is now associated with a new symbol
+	 file, open it.  */
+      if (found_pathname != NULL
+	  && strcmp (found_pathname, so->so_name) != 0)
+	{
+	  volatile struct gdb_exception e;
+
+	  any_changed = 1;
+
+	  TRY_CATCH (e, RETURN_MASK_ERROR)
+	    solib_map_sections (so);
+
+	  if (e.reason < 0)
+	    exception_fprintf (gdb_stderr, e, _("\
+Error while mapping shared library sections:\n"));
+	  else if (auto_solib_add || libpthread_solib_p (so) || was_loaded)
+	    solib_read_symbols (so, flags);
+	}
+    }
+
+  do_cleanups (old_chain);
+
+  return any_changed;
+}
+
 static void
 reload_shared_libraries (char *ignored, int from_tty,
 			 struct cmd_list_element *e)
 {
-  no_shared_libraries (NULL, from_tty);
+  struct target_so_ops *ops;
+  int any_changed;
+
   /* Creating inferior hooks here has two purposes. First, if we reload 
      shared libraries then the address of solib breakpoint we've computed
      previously might be no longer valid.  For example, if we forgot to set
@@ -1147,20 +1249,22 @@ reload_shared_libraries (char *ignored, 
 #endif
     }
 
-  /* Sometimes the platform-specific hook loads initial shared
-     libraries, and sometimes it doesn't.  If it doesn't FROM_TTY will be
-     incorrectly 0 but such solib targets should be fixed anyway.  If we
-     made all the inferior hook methods consistent, this call could be
-     removed.  Call it only after the solib target has been initialized by
-     solib_create_inferior_hook.  */
-
-  solib_add (NULL, 0, NULL, auto_solib_add);
-
-  /* We have unloaded and then reloaded debug info for all shared libraries.
-     However, frames may still reference them, for example a frame's 
-     unwinder might still point of DWARF FDE structures that are now freed.
-     Reinit frame cache to avoid crashing.  */
+  any_changed = reload_shared_libraries_1 (from_tty);
+  if (!any_changed)
+    return;
+
+  breakpoint_re_set ();
+
+  ops = solib_ops (target_gdbarch);
+
+  /* We may have loaded or unloaded debug info for some (or all)
+     shared libraries.  However, frames may still reference them, for
+     example a frame's unwinder might still point of DWARF FDE
+     structures that are now freed.  Also, getting new symbols may
+     change our opinion about what is frameless.  */
   reinit_frame_cache ();
+
+  ops->special_symbol_handling ();
 }
 
 static void