Fix glibc 2.34 ABI omission (missing GLIBC_2.34 in dynamic loader)

The glibc 2.34 release really should have added a GLIBC_2.34
symbol to the dynamic loader. With it, we could move functions such
as dlopen or pthread_key_create that work on process-global state
into the dynamic loader (once we have fixed a longstanding issue
with static linking).  Without the GLIBC_2.34 symbol, yet another
new symbol version would be needed because old glibc will fail to
load binaries due to the missing symbol version in ld.so that newly
linked programs will require.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/elf/dl-compat.c b/elf/dl-compat.c
new file mode 100644
index 0000000000..05c986a8be
--- /dev/null
+++ b/elf/dl-compat.c
@@ -0,0 +1,35 @@
+/* Placeholder compatibility symbols.
+   Copyright (C) 2022 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 <shlib-compat.h>
+#include <sys/cdefs.h>
+
+/* The GLIBC_2.35 symbol version is present naturally for later ports.
+   Use OTHER_SHLIB_COMPAT because the module is called rtld, but the
+   ABI version uses ld.  */
+#if OTHER_SHLIB_COMPAT (ld, GLIBC_2_0, GLIBC_2_35)
+void
+attribute_compat_text_section
+__attribute_used__
+__rtld_version_placeholder_1 (void)
+{
+}
+
+compat_symbol (ld, __rtld_version_placeholder_1,
+               __rtld_version_placeholder, GLIBC_2_34);
+#endif