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.

4 files changed, 42 insertions, 70 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index de312b3..d23a235 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -120,7 +120,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      cancellation \
 		      lowlevellock \
 		      lll_timedlock_wait \
-		      pt-fork pt-vfork pt-fcntl \
+		      pt-fork pt-fcntl \
 		      $(pthread-compat-wrappers) \
 		      pt-raise pt-system \
 		      flockfile ftrylockfile funlockfile \
@@ -144,7 +144,8 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      mtx_destroy mtx_init mtx_lock mtx_timedlock \
 		      mtx_trylock mtx_unlock call_once cnd_broadcast \
 		      cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait \
-		      tss_create tss_delete tss_get tss_set pthread_mutex_conf
+		      tss_create tss_delete tss_get tss_set pthread_mutex_conf \
+		      libpthread-compat
 #		      pthread_setuid pthread_seteuid pthread_setreuid \
 #		      pthread_setresuid \
 #		      pthread_setgid pthread_setegid pthread_setregid \
diff --git a/nptl/Versions b/nptl/Versions
index e7f691d..6007fd0 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -36,7 +36,6 @@ libc {
     __libc_alloca_cutoff;
     # Internal libc interface to libpthread
     __libc_dl_error_tsd;
-    __libc_vfork;
     __libc_pthread_init;
     __libc_current_sigrtmin_private; __libc_current_sigrtmax_private;
     __libc_allocate_rtsig_private;
@@ -98,7 +97,7 @@ libpthread {
     sem_destroy; sem_getvalue; sem_init; sem_post; sem_trywait; sem_wait;
 
     # Special fork handling.
-    fork; __fork; vfork;
+    fork; __fork;
 
     # Cancellation points.
     close; __close; fcntl; __fcntl; read; __read; write; __write; accept;
@@ -152,7 +151,7 @@ libpthread {
   }
 
   GLIBC_2.1.2 {
-    __vfork;
+    __libpthread_version_placeholder;
   }
 
   GLIBC_2.2 {
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
diff --git a/nptl/pt-vfork.c b/nptl/pt-vfork.c
deleted file mode 100644
index 3676977..0000000
--- a/nptl/pt-vfork.c
+++ /dev/null
@@ -1,65 +0,0 @@
-/* vfork ABI-compatibility entry points for libpthread.
-   Copyright (C) 2014-2019 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 <unistd.h>
-#include <shlib-compat.h>
-
-/* libpthread used to have its own vfork implementation that differed
-   from libc's only in having a pointless micro-optimization.  There
-   is no longer any use to having a separate copy in libpthread, but
-   the historical ABI requires it.  For static linking, there is no
-   need to provide anything here--the libc version will be linked in.
-   For shared library ABI compatibility, there must be __vfork and
-   vfork symbols in libpthread.so; so we define them using IFUNC to
-   redirect to the libc function.  */
-
-/* Note! If the architecture doesn't support IFUNC, then we need an
-   alternate target-specific mechanism to implement this.  So we just
-   assume IFUNC here and require that the target override this file
-   if necessary.
-
-   If the architecture can assume all supported versions of gcc will
-   produce a tail-call to __libc_vfork, consider including the version
-   in sysdeps/unix/sysv/linux/aarch64/pt-vfork.c.  */
-
-#if !HAVE_IFUNC
-# error "must write pt-vfork for this machine or get IFUNC support"
-#endif
-
-#if (SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_20) \
-     || SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_20))
-
-extern __typeof (vfork) __libc_vfork;   /* Defined in libc.  */
-
-# undef INIT_ARCH
-# define INIT_ARCH()
-# define DEFINE_VFORK(name) libc_ifunc (name, &__libc_vfork)
-
-#endif
-
-#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_20)
-extern __typeof(vfork) vfork_ifunc;
-DEFINE_VFORK (vfork_ifunc)
-compat_symbol (libpthread, vfork_ifunc, vfork, GLIBC_2_0);
-#endif
-
-#if SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_20)
-extern __typeof(vfork) __vfork_ifunc;
-DEFINE_VFORK (__vfork_ifunc)
-compat_symbol (libpthread, __vfork_ifunc, __vfork, GLIBC_2_1_2);
-#endif