[PATCH 1/2] gdb: call frame unwinders' dealloc_cache methods through destroying the frame cache

[Simon Marchi <simon.marchi@efficios.com>]

Currently, some frame resources are deallocated by iterating on the
frame chain (starting from the sentinel), calling dealloc_cache.  The
problem is that user-created frames are not part of that chain, so we
never call dealloc_cache for them.

I propose to make it so the dealloc_cache callbacks are called when the
frames are removed from the frame_stash hash table, by registering a
deletion function to the hash table.  This happens when
frame_stash_invalidate is called by reinit_frame_cache.  This way, all
frames registered in the cache will get their unwinder's dealloc_cache
callbacks called.

Note that at the moment, the sentinel frames are not registered in the
cache, so we won't call dealloc_cache for them.  However, it's just a
theoritical problem, because the sentinel frame unwinder does not
provide this callback.  Also, a subsequent patch will change things so
that sentinel frames are registered to the cache.

I moved the obstack_free / obstack_init pair below the
frame_stash_invalidate call in reinit_frame_cache, because I assumed
that some dealloc_cache would need to access some data on that obstack,
so it would be better to free it after clearing the hash table.

Change-Id: If4f9b38266b458c4e2f7eb43e933090177c22190
---
 gdb/frame.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/gdb/frame.c b/gdb/frame.c
index a08a8f47ebc4..fed961b2a8df 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -259,6 +259,22 @@ frame_addr_hash_eq (const void *a, const void *b)
   return f_entry->this_id.value == f_element->this_id.value;
 }
 
+/* Deletion function for the frame cache hash table.  */
+
+static void
+frame_info_del (void *frame_v)
+{
+  frame_info *frame = (frame_info *) frame_v;
+
+  if (frame->prologue_cache != nullptr
+      && frame->unwind->dealloc_cache != nullptr)
+    frame->unwind->dealloc_cache (frame, frame->prologue_cache);
+
+  if (frame->base_cache != nullptr
+      && frame->base->unwind->dealloc_cache != nullptr)
+    frame->base->unwind->dealloc_cache (frame, frame->base_cache);
+}
+
 /* Internal function to create the frame_stash hash table.  100 seems
    to be a good compromise to start the hash table at.  */
 
@@ -268,7 +284,7 @@ frame_stash_create (void)
   frame_stash = htab_create (100,
 			     frame_addr_hash,
 			     frame_addr_hash_eq,
-			     NULL);
+			     frame_info_del);
 }
 
 /* Internal function to add a frame to the frame_stash hash table.
@@ -2048,26 +2064,19 @@ reinit_frame_cache (void)
 {
   ++frame_cache_generation;
 
-  /* Tear down all frame caches.  */
-  for (frame_info *fi = sentinel_frame; fi != NULL; fi = fi->prev)
-    {
-      if (fi->prologue_cache && fi->unwind->dealloc_cache)
-	fi->unwind->dealloc_cache (fi, fi->prologue_cache);
-      if (fi->base_cache && fi->base->unwind->dealloc_cache)
-	fi->base->unwind->dealloc_cache (fi, fi->base_cache);
-    }
-
-  /* Since we can't really be sure what the first object allocated was.  */
-  obstack_free (&frame_cache_obstack, 0);
-  obstack_init (&frame_cache_obstack);
-
   if (sentinel_frame != NULL)
     annotate_frames_invalid ();
 
-  sentinel_frame = NULL;		/* Invalidate cache */
   invalidate_selected_frame ();
+
+  /* Invalidate cache.  */
+  sentinel_frame = NULL;
   frame_stash_invalidate ();
 
+  /* Since we can't really be sure what the first object allocated was.  */
+  obstack_free (&frame_cache_obstack, 0);
+  obstack_init (&frame_cache_obstack);
+
   for (frame_info_ptr &iter : frame_info_ptr::frame_list)
     iter.invalidate ();
 
-- 
2.39.1