RFC: fix archive refcounting in gdb

[Tom Tromey <tromey at redhat dot com>]

I just sent some BFD patches to fix some bugs in BFD regarding memory
management of archive member BFDs.

This patch changs gdb to follow the newly-documented best pratice for
such BFDs: if a member BFD is in use, the archive BFD must be kept
alive.  In gdb terms, this is easily implemented by having an archive
member BFD keep a reference to the archive BFD.

I'd like to check this in after the BFD patches go in.

	* gdb_bfd.c (struct gdb_bfd_data) <archive_bfd>: New field.
	(gdb_bfd_ref): Initialize new field.
	(gdb_bfd_unref): Unref the archive BFD.
	(gdb_bfd_openr_next_archived_file): Acquire a reference to the
	parent archive.
---
 gdb/gdb_bfd.c |   19 ++++++++++++++++++-
 1 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/gdb/gdb_bfd.c b/gdb/gdb_bfd.c
index 40e1c4d..266272d 100644
--- a/gdb/gdb_bfd.c
+++ b/gdb/gdb_bfd.c
@@ -81,6 +81,10 @@ struct gdb_bfd_data
 
   /* The mtime of the BFD at the point the cache entry was made.  */
   time_t mtime;
+
+  /* If the BFD comes from an archive, this points to the archive's
+     BFD.  Otherwise, this is NULL.  */
+  bfd *archive_bfd;
 };
 
 /* A hash table storing all the BFDs maintained in the cache.  */
@@ -249,6 +253,7 @@ gdb_bfd_ref (struct bfd *abfd)
   gdata = bfd_zalloc (abfd, sizeof (struct gdb_bfd_data));
   gdata->refc = 1;
   gdata->mtime = bfd_get_mtime (abfd);
+  gdata->archive_bfd = NULL;
   bfd_usrdata (abfd) = gdata;
 
   /* This is the first we've seen it, so add it to the hash table.  */
@@ -265,6 +270,7 @@ gdb_bfd_unref (struct bfd *abfd)
   struct gdb_bfd_data *gdata;
   struct gdb_bfd_cache_search search;
   void **slot;
+  bfd *archive_bfd;
 
   if (abfd == NULL)
     return;
@@ -276,6 +282,7 @@ gdb_bfd_unref (struct bfd *abfd)
   if (gdata->refc > 0)
     return;
 
+  archive_bfd = gdata->archive_bfd;
   search.filename = bfd_get_filename (abfd);
 
   if (gdb_bfd_cache && search.filename)
@@ -296,6 +303,8 @@ gdb_bfd_unref (struct bfd *abfd)
   htab_remove_elt (all_bfds, abfd);
 
   gdb_bfd_close_or_warn (abfd);
+
+  gdb_bfd_unref (archive_bfd);
 }
 
 /* A helper function that returns the section data descriptor
@@ -591,8 +600,16 @@ gdb_bfd_openr_next_archived_file (bfd *archive, bfd *previous)
 
   if (result)
     {
+      struct gdb_bfd_data *gdata;
+
       gdb_bfd_ref (result);
-      /* No need to stash the filename here.  */
+      /* No need to stash the filename here, because we also keep a
+	 reference on the parent archive.  */
+
+      gdata = bfd_usrdata (result);
+      gdb_assert (gdata->archive_bfd == NULL || gdata->archive_bfd == archive);
+      gdata->archive_bfd = archive;
+      gdb_bfd_ref (archive);
     }
 
   return result;
-- 
1.7.7.6