Use unique_ptr for objfiles

A while back, I changed objfiles to be held via a shared_ptr.  The
idea at the time was that this was a step toward writing to the index
cache in the background, and this would let gdb keep a reference alive
to do so.  However, since then we've rewritten the DWARF reader, and
the new index can do this without requiring a shared pointer -- in
fact there are patches pending to implement this.

This patch switches objfile management to unique_ptr, which makes more
sense now.

Regression tested on x86-64 Fedora 34.

gdb/objfiles.c

@@ -468,9 +468,7 @@ objfile::make (bfd *bfd_, const char *name_, objfile_flags flags_,
   if (parent != nullptr)
     add_separate_debug_objfile (result, parent);
 
-  /* Using std::make_shared might be a bit nicer here, but that would
+  current_program_space->add_objfile (std::unique_ptr<objfile> (result),
-     require making the constructor public.  */
-  current_program_space->add_objfile (std::shared_ptr<objfile> (result),
 				      parent);
 
   /* Rebuild section map next time we need it.  */

gdb/objfiles.h

@@ -409,7 +409,7 @@ public:
      remove it from the program space's list.  In some cases, you may
      need to hold a reference to an objfile that is independent of its
      existence on the program space's list; for this case, the
-     destructor must be public so that shared_ptr can reference
+     destructor must be public so that unique_ptr can reference
      it.  */
   ~objfile ();
 

gdb/progspace.c

@@ -174,7 +174,7 @@ program_space::free_all_objfiles ()
 /* See progspace.h.  */
 
 void
-program_space::add_objfile (std::shared_ptr<objfile> &&objfile,
+program_space::add_objfile (std::unique_ptr<objfile> &&objfile,
 			    struct objfile *before)
 {
   if (before == nullptr)
@@ -182,7 +182,7 @@ program_space::add_objfile (std::shared_ptr<objfile> &&objfile,
   else
     {
       auto iter = std::find_if (objfiles_list.begin (), objfiles_list.end (),
-				[=] (const std::shared_ptr<::objfile> &objf)
+				[=] (const std::unique_ptr<::objfile> &objf)
 				{
 				  return objf.get () == before;
 				});
@@ -203,7 +203,7 @@ program_space::remove_objfile (struct objfile *objfile)
   reinit_frame_cache ();
 
   auto iter = std::find_if (objfiles_list.begin (), objfiles_list.end (),
-			    [=] (const std::shared_ptr<::objfile> &objf)
+			    [=] (const std::unique_ptr<::objfile> &objf)
 			    {
 			      return objf.get () == objfile;
 			    });

gdb/progspace.h

@@ -41,9 +41,9 @@ struct program_space_data;
 struct address_space_data;
 struct so_list;
 
-typedef std::list<std::shared_ptr<objfile>> objfile_list;
+typedef std::list<std::unique_ptr<objfile>> objfile_list;
 
-/* An iterator that wraps an iterator over std::shared_ptr<objfile>,
+/* An iterator that wraps an iterator over std::unique_ptr<objfile>,
    and dereferences the returned object.  This is useful for iterating
    over a list of shared pointers and returning raw pointers -- which
    helped avoid touching a lot of code when changing how objfiles are
@@ -234,7 +234,7 @@ struct program_space
   /* Add OBJFILE to the list of objfiles, putting it just before
      BEFORE.  If BEFORE is nullptr, it will go at the end of the
      list.  */
-  void add_objfile (std::shared_ptr<objfile> &&objfile,
+  void add_objfile (std::unique_ptr<objfile> &&objfile,
 		    struct objfile *before);
 
   /* Remove OBJFILE from the list of objfiles.  */
@@ -354,7 +354,7 @@ struct program_space
   struct objfile *symfile_object_file = NULL;
 
   /* All known objfiles are kept in a linked list.  */
-  std::list<std::shared_ptr<objfile>> objfiles_list;
+  std::list<std::unique_ptr<objfile>> objfiles_list;
 
   /* List of shared objects mapped into this space.  Managed by
      solib.c.  */