don't share per-BFD data if relocations are needed

Right now we always share per-BFD data across objfiles, if there is a
BFD.  This works fine.  However, we're going to start sharing more
data, and sometimes this data will come directly from sections of the
BFD.  If such a section has SEC_RELOC set, then the data coming from
that section will not be truly sharable -- the section will be
program-space-dependent, and re-read by gdb for each objfile.

This patch disallows per-BFD sharing in this case.  This is a bit
"heavy" in that we could in theory examine each bit of shared data for
suitability.  However, that is more complicated, and SEC_RELOC is rare
enough that I think we needn't bother.

Note that the "no sharing" case is equivalent to "gdb works as it
historically did".  That is, the sharing is a new(-ish) optimization.

Built and regtested on x86-64 Fedora 18.

	* gdb_bfd.c (struct gdb_bfd_data) <relocation_computed,
	needs_relocations>: New fields.
	(gdb_bfd_requires_relocations): New function.
	* gdb_bfd.h (gdb_bfd_requires_relocations): Declare.
	* objfiles.c (get_objfile_bfd_data): Disallow sharing if
	the BFD needs relocations applied.

1 files changed, 8 insertions, 4 deletions

diff --git a/gdb/objfiles.c b/gdb/objfiles.c
index b10f803..b9bcfd7 100644
--- a/gdb/objfiles.c
+++ b/gdb/objfiles.c
@@ -137,18 +137,22 @@ get_objfile_bfd_data (struct objfile *objfile, struct bfd *abfd)
 
   if (storage == NULL)
     {
-      if (abfd != NULL)
+      /* If the object requires gdb to do relocations, we simply fall
+	 back to not sharing data across users.  These cases are rare
+	 enough that this seems reasonable.  */
+      if (abfd != NULL && !gdb_bfd_requires_relocations (abfd))
 	{
 	  storage = bfd_zalloc (abfd, sizeof (struct objfile_per_bfd_storage));
 	  set_bfd_data (abfd, objfiles_bfd_data, storage);
-
-	  /* Look up the gdbarch associated with the BFD.  */
-	  storage->gdbarch = gdbarch_from_bfd (abfd);
 	}
       else
 	storage = OBSTACK_ZALLOC (&objfile->objfile_obstack,
 				  struct objfile_per_bfd_storage);
 
+      /* Look up the gdbarch associated with the BFD.  */
+      if (abfd != NULL)
+	storage->gdbarch = gdbarch_from_bfd (abfd);
+
       obstack_init (&storage->storage_obstack);
       storage->filename_cache = bcache_xmalloc (NULL, NULL);
       storage->macro_cache = bcache_xmalloc (NULL, NULL);