elf: Make more functions available for binding during dlclose (bug 30425)

Previously, after destructors for a DSO have been invoked, ld.so refused
to bind against that DSO in all cases.  Relax this restriction somewhat
if the referencing object is itself a DSO that is being unloaded.  This
assumes that the symbol reference is not going to be stored anywhere.

The situation in the test case can arise fairly easily with C++ and
objects that are built with different optimization levels and therefore
define different functions with vague linkage.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c
new file mode 100644
index 0000000000..8439dc1925
--- /dev/null
+++ b/elf/tst-dlclose-lazy-mod1.c
@@ -0,0 +1,36 @@
+/* Lazy binding during dlclose.  Directly loaded module.
+   Copyright (C) 2023 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/>.  */
+
+/* This function is called from exported_function below.  It is only
+   defined in this module.  The weak attribute mimics how G++
+   implements vague linkage for C++.  */
+void __attribute__ ((weak))
+lazily_bound_exported_function (void)
+{
+}
+
+/* Called from tst-dlclose-lazy-mod2.so.  */
+void
+exported_function (int call_it)
+{
+  if (call_it)
+    /* Previous to the fix this would crash when called during dlclose
+       since symbols from the DSO were no longer available for binding
+       (bug 30425) after the DSO started being closed by dlclose.  */
+    lazily_bound_exported_function ();
+}