ld.so: Support moving versioned symbols between sonames [BZ #24741]

This change should be fully backwards-compatible because the old
code aborted the load if a soname mismatch was encountered
(instead of searching further for a matching symbol).  This means
that no different symbols are found.

The soname check was explicitly disabled for the skip_map != NULL
case.  However, this only happens with dl(v)sym and RTLD_NEXT,
and those lookups do not come with a verneed entry that could be used
for the check.

The error check was already explicitly disabled for the skip_map !=
NULL case, that is, when dl(v)sym was called with RTLD_NEXT.  But
_dl_vsym always sets filename in the struct r_found_version argument
to NULL, so the check was not active anyway.  This means that
symbol lookup results for the skip_map != NULL case do not change,
either.

1 files changed, 41 insertions, 0 deletions

diff --git a/elf/tst-sonamemove-link.c b/elf/tst-sonamemove-link.c
new file mode 100644
index 0000000..4bc3bf3
--- /dev/null
+++ b/elf/tst-sonamemove-link.c
@@ -0,0 +1,41 @@
+/* Check that a versioned symbol can move from one library to another.
+   Copyright (C) 2019 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/>.  */
+
+/* At link time, moved_function is bound to the symbol version
+   SONAME_MOVE in tst-sonamemove-runmod1.so, using the
+   tst-sonamemove-linkmod1.so stub object.
+
+   At run time, the process loads the real tst-sonamemove-runmod1.so,
+   which depends on tst-sonamemove-runmod2.so.
+   tst-sonamemove-runmod1.so does not define moved_function, but
+   tst-sonamemove-runmod2.so does.
+
+   The net effect is that the versioned symbol
+   moved_function@SONAME_MOVE moved from the soname
+   tst-sonamemove-linkmod1.so at link time to the soname
+   tst-sonamemove-linkmod2.so at run time. */
+void moved_function (void);
+
+static int
+do_test (void)
+{
+  moved_function ();
+  return 0;
+}
+
+#include <support/test-driver.c>