elf, nptl: Resolve recursive lock implementation early

If libpthread is included in libc, it is not necessary to delay
initialization of the lock/unlock function pointers until libpthread
is loaded.  This eliminates two unprotected function pointers
from _rtld_global and removes some initialization code from
libpthread.

Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/sysdeps/nptl/dl-mutex.c b/sysdeps/nptl/dl-mutex.c
new file mode 100644
index 0000000..08b71dc
--- /dev/null
+++ b/sysdeps/nptl/dl-mutex.c
@@ -0,0 +1,53 @@
+/* Recursive locking implementation for the dynamic loader.  NPTL version.
+   Copyright (C) 2021 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/>.  */
+
+/* Use the mutex implementation in libc (assuming PTHREAD_IN_LIBC).  */
+
+#include <assert.h>
+#include <first-versions.h>
+#include <ldsodefs.h>
+
+__typeof (pthread_mutex_lock) *___rtld_mutex_lock attribute_relro;
+__typeof (pthread_mutex_unlock) *___rtld_mutex_unlock attribute_relro;
+
+void
+__rtld_mutex_init (void)
+{
+  /* There is an implicit assumption here that the lock counters are
+     zero and this function is called while nothing is locked.  For
+     early initialization of the mutex functions this is true because
+     it happens directly in dl_main in elf/rtld.c, and not some ELF
+     constructor while holding loader locks.  */
+
+  struct link_map *libc_map = GL (dl_ns)[LM_ID_BASE].libc_map;
+
+  const ElfW(Sym) *sym
+    = _dl_lookup_direct (libc_map, "pthread_mutex_lock",
+                         0x4f152227, /* dl_new_hash output.  */
+                         FIRST_VERSION_libc_pthread_mutex_lock_STRING,
+                         FIRST_VERSION_libc_pthread_mutex_lock_HASH);
+  assert (sym != NULL);
+  ___rtld_mutex_lock = DL_SYMBOL_ADDRESS (libc_map, sym);
+
+  sym = _dl_lookup_direct (libc_map, "pthread_mutex_unlock",
+                           0x7dd7aaaa, /* dl_new_hash output.  */
+                           FIRST_VERSION_libc_pthread_mutex_unlock_STRING,
+                           FIRST_VERSION_libc_pthread_mutex_unlock_HASH);
+  assert (sym != NULL);
+  ___rtld_mutex_unlock = DL_SYMBOL_ADDRESS (libc_map, sym);
+}