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>

3 files changed, 39 insertions, 1 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 4f99af626f..d3e909637a 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -66,7 +66,8 @@ elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \
 # interpreter and operating independent of libc.
 rtld-routines	= rtld $(all-dl-routines) dl-sysdep dl-environ dl-minimal \
   dl-error-minimal dl-conflict dl-hwcaps dl-hwcaps_split dl-hwcaps-subdirs \
-  dl-usage dl-diagnostics dl-diagnostics-kernel dl-diagnostics-cpu
+  dl-usage dl-diagnostics dl-diagnostics-kernel dl-diagnostics-cpu \
+  dl-mutex
 all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)
 
 CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
diff --git a/elf/dl-mutex.c b/elf/dl-mutex.c
new file mode 100644
index 0000000000..2cd9d49c2e
--- /dev/null
+++ b/elf/dl-mutex.c
@@ -0,0 +1,19 @@
+/* Recursive locking implementation for the dynamic loader.  Generic 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/>.  */
+
+/* The generic version initialization happpens in dl_main.  */
diff --git a/elf/rtld.c b/elf/rtld.c
index ad325d4c10..a359167f8a 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -857,6 +857,14 @@ rtld_lock_default_unlock_recursive (void *lock)
   __rtld_lock_default_unlock_recursive (lock);
 }
 #endif
+#if PTHREAD_IN_LIBC
+/* Dummy implementation.  See __rtld_mutex_init.  */
+static int
+rtld_mutex_dummy (pthread_mutex_t *lock)
+{
+  return 0;
+}
+#endif
 
 
 static void
@@ -1148,6 +1156,10 @@ dl_main (const ElfW(Phdr) *phdr,
   GL(dl_rtld_lock_recursive) = rtld_lock_default_lock_recursive;
   GL(dl_rtld_unlock_recursive) = rtld_lock_default_unlock_recursive;
 #endif
+#if PTHREAD_IN_LIBC
+  ___rtld_mutex_lock = rtld_mutex_dummy;
+  ___rtld_mutex_unlock = rtld_mutex_dummy;
+#endif
 
   /* The explicit initialization here is cheaper than processing the reloc
      in the _rtld_local definition's initializer.  */
@@ -2363,6 +2375,9 @@ dl_main (const ElfW(Phdr) *phdr,
 	 loader.  */
       __rtld_malloc_init_real (main_map);
 
+      /* Likewise for the locking implementation.  */
+      __rtld_mutex_init ();
+
       /* Mark all the objects so we know they have been already relocated.  */
       for (struct link_map *l = main_map; l != NULL; l = l->l_next)
 	{
@@ -2468,6 +2483,9 @@ dl_main (const ElfW(Phdr) *phdr,
 	 at this point.  */
       __rtld_malloc_init_real (main_map);
 
+      /* Likewise for the locking implementation.  */
+      __rtld_mutex_init ();
+
       RTLD_TIMING_VAR (start);
       rtld_timer_start (&start);