elf: Support dlvsym within libc.so

This commit adds a new _dl_open_hook entry for dlvsym and implements the
function using the existing dl_lookup_symbol_x function supplied by the
dynamic loader.

A new hook variable, _dl_open_hook2, is introduced, which should make
this change suitable for backporting: For old statically linked
binaries, __libc_dlvsym will always return NULL.

1 files changed, 34 insertions, 0 deletions

diff --git a/elf/tst-libc_dlvsym.c b/elf/tst-libc_dlvsym.c
new file mode 100644
index 0000000000..864db4ee6a
--- /dev/null
+++ b/elf/tst-libc_dlvsym.c
@@ -0,0 +1,34 @@
+/* Compare dlvsym and __libc_dlvsym results.  Dynamic version.
+   Copyright (C) 2017 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include "tst-libc_dlvsym.h"
+
+static int
+do_test (void)
+{
+  compare_vsyms ();
+
+  void *handle = xdlopen ("tst-libc_dlvsym-dso.so", RTLD_LAZY);
+  void (*compare) (void) = xdlsym (handle, "compare_vsyms_global");
+  compare ();
+  xdlclose (handle);
+
+  return 0;
+}
+
+#include <support/test-driver.c>