elf: Allow dlopen of filter object to work [BZ #16272]

There are two fixes that are needed to be able to dlopen filter
objects. First _dl_map_object_deps cannot assume that map will be at
the beginning of l_searchlist.r_list[], as filtees are inserted before
map. Secondly dl_open_worker needs to ensure that filtees get
relocated.

In _dl_map_object_deps:

* avoiding removing relocation dependencies of map by setting
  l_reserved to 0 and otherwise processing the rest of the search
  list.

* ensure that map remains at the beginning of l_initfini - the list
  of things that need initialisation (and destruction). Do this by
  splitting the copy up. This may not be required, but matches the
  initialization order without dlopen.

Modify dl_open_worker to relocate the objects in new->l_inifini.
new->l_initfini is constructed in _dl_map_object_deps, and lists the
objects that need initialization and destruction. Originally the list
of objects in new->l_next are relocated. All of these objects should
also be included in new->l_initfini (both lists are populated with
dependencies in _dl_map_object_deps). We can't use new->l_prev to pick
up filtees, as during a recursive dlopen from an interposed malloc
call, l->prev can contain objects that are not ready for relocation.

Add tests to verify that symbols resolve to the filtee implementation
when auxiliary and filter objects are used, both as a normal link and
when dlopen'd.

Tested by running the testsuite on x86_64.

1 files changed, 42 insertions, 0 deletions

diff --git a/elf/tst-auxobj.c b/elf/tst-auxobj.c
new file mode 100644
index 0000000..bdc7713
--- /dev/null
+++ b/elf/tst-auxobj.c
@@ -0,0 +1,42 @@
+/* Test that symbols from auxiliary filter objects are resolved to the
+   filtee.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <support/check.h>
+#include "tst-filterobj-filtee.h"
+
+static int do_test (void)
+{
+  const char* text = get_text ();
+  printf ("%s\n", text);
+
+  /* Verify the text matches what we expect from the filtee */
+  TEST_COMPARE_STRING (text, "Hello from filtee (PASS)");
+
+  text = get_text2 ();
+  printf ("%s\n", text);
+
+  /* Verify the text matches what we expect from the auxiliary object */
+  TEST_COMPARE_STRING (text, "Hello from auxiliary filter object (PASS)");
+
+  return 0;
+}
+
+#include <support/test-driver.c>