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, 47 insertions, 0 deletions

diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c
new file mode 100644
index 0000000..976a6bb
--- /dev/null
+++ b/elf/tst-dlclose-lazy.c
@@ -0,0 +1,47 @@
+/* Test lazy binding during dlclose (bug 30425).
+   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 test re-creates a situation that can arise naturally for C++
+   applications due to the use of vague linkage and differences in the
+   set of compiler-emitted functions.  A function in
+   tst-dlclose-lazy-mod1.so (exported_function) interposes a function
+   in tst-dlclose-lazy-mod2.so.  This function is called from the
+   destructor in tst-dlclose-lazy-mod2.so, after the destructor for
+   tst-dlclose-lazy-mod1.so has already completed.  Prior to the fix
+   for bug 30425, this would lead to a lazy binding failure in
+   tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO
+   as unavailable for binding (by setting l_removed).  */
+
+#include <dlfcn.h>
+#include <support/xdlfcn.h>
+#include <support/check.h>
+
+int
+main (void)
+{
+  /* Load tst-dlclose-lazy-mod1.so, indirectly loading
+     tst-dlclose-lazy-mod2.so.  */
+  void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY);
+
+  /* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls
+     into tst-dlclose-lazy-mod1.so after its destructor has been
+     called.  */
+  xdlclose (handle);
+
+  return 0;
+}