nptl: Remove vfork IFUNC-based forwarder from libpthread [BZ #20188]

With commit f0b2132b35248c1f4a80f62a2c38cddcc802aa8c ("ld.so:
Support moving versioned symbols between sonames [BZ #24741]"), the
dynamic linker will find the definition of vfork in libc and binds
a vfork reference to that symbol, even if the soname in the version
reference says that the symbol should be located in libpthread.

As a result, the forwarder (whether it's IFUNC-based or a duplicate
of the libc implementation) is no longer necessary.

On older architectures, a placeholder symbol is required, to make sure
that the GLIBC_2.1.2 symbol version does not go away, or is turned in
to a weak symbol definition by the link editor.  (The symbol version
needs to preserved so that the symbol coverage check in
elf/dl-version.c does not fail for old binaries.)

mips32 is an outlier: It defined __vfork@@GLIBC_2.2, but the
baseline is GLIBC_2.0.  Since there are other @@GLIBC_2.2 symbols,
the placeholder symbol is not needed there.

1 files changed, 37 insertions, 0 deletions

diff --git a/nptl/libpthread-compat.c b/nptl/libpthread-compat.c
new file mode 100644
index 0000000..ea29e9f
--- /dev/null
+++ b/nptl/libpthread-compat.c
@@ -0,0 +1,37 @@
+/* Placeholder definitions to pull in removed symbol versions.
+   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/>.  */
+
+#include <shlib-compat.h>
+
+/* This is an unused compatibility symbol definition, to prevent ld
+   from creating a weak version definition for GLIBC_2.1.2.  (__vfork
+   used to be defined at that version, but it is now provided by libc,
+   and there are no versions left in libpthread for that symbol
+   version.)  If the ABI baseline for glibc is the GLIBC_2.2 symbol
+   version or later, the placeholder symbol is not needed because
+   there are plenty of other symbols which populate those later
+   versions.  */
+#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
+void
+attribute_compat_text_section
+__libpthread_version_placeholder (void)
+{
+}
+compat_symbol (libpthread, __libpthread_version_placeholder,
+               __libpthread_version_placeholder, GLIBC_2_1_2);
+#endif