Allow locking routine to be retargeted

At the moment when targeting bare-metal targets or systems without
definition for the locking primitives newlib, uses dummy empty macros.
This has the advantage of reduced size and faster implementation but
does not allow the application to retarget the locking routines.
Retargeting is useful for a single toolchain to support multiple systems
since then it's only at link time that you know which system you are
targeting.

This patch adds a new configure option
--enable-newlib-retargetable-locking to use dummy empty functions
instead of dummy empty macros. The default is to keep the current
behavior to not have any size or speed impact on targets not interested
in this feature. To allow for any size of lock, the _LOCK_T type is
changed into pointer to struct _lock and the _init function are tasked
with allocating the locks. The platform being targeted must provide the
static locks. A dummy implementation of the locking routines and static
lock is provided for single-threaded applications to link successfully
out of the box.

To ensure that the behavior is consistent (either no locking whatsoever
or working locking), the dummy implementation is strongly defined such
that a partial retargeting will cause a doubly defined link error.
Indeed, the linker will only pull in the file providing the dummy
implementation if it cannot find an implementation for one of the
routine or lock.

10 files changed, 316 insertions, 14 deletions

diff --git a/newlib/configure b/newlib/configure
index 2ac07fe06..de28c25b3 100755
--- a/newlib/configure
+++ b/newlib/configure
@@ -802,6 +802,7 @@ enable_newlib_nano_malloc
 enable_newlib_unbuf_stream_opt
 enable_lite_exit
 enable_newlib_nano_formatted_io
+enable_newlib_retargetable_locking
 enable_multilib
 enable_target_optspace
 enable_malloc_debugging
@@ -1473,6 +1474,7 @@ Optional Features:
   --disable-newlib-unbuf-stream-opt    disable unbuffered stream optimization in streamio
   --enable-lite-exit	enable light weight exit
   --enable-newlib-nano-formatted-io    Use nano version formatted IO
+  --enable-newlib-retargetable-locking    Allow locking routines to be retargeted at link time
   --enable-multilib         build many library versions (default)
   --enable-target-optspace  optimize for space
   --enable-malloc-debugging indicate malloc debugging requested
@@ -2474,6 +2476,18 @@ else
 fi
 
 
+# Check whether --enable-newlib-retargetable-locking was given.
+if test "${enable_newlib_retargetable_locking+set}" = set; then :
+  enableval=$enable_newlib_retargetable_locking; case "${enableval}" in
+   yes) newlib_retargetable_locking=yes ;;
+   no)  newlib_retargetable_locking=no ;;
+   *) as_fn_error $? "bad value ${enableval} for newlib-retargetable-locking" "$LINENO" 5 ;;
+ esac
+else
+  newlib_retargetable_locking=no
+fi
+
+
 
 # Make sure we can run config.sub.
 $SHELL "$ac_aux_dir/config.sub" sun4 >/dev/null 2>&1 ||
@@ -11780,7 +11794,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11783 "configure"
+#line 11797 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11886,7 +11900,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11889 "configure"
+#line 11903 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12455,6 +12469,13 @@ _ACEOF
 
 fi
 
+if test "${newlib_retargetable_locking}" = "yes"; then
+cat >>confdefs.h <<_ACEOF
+#define _RETARGETABLE_LOCKING 1
+_ACEOF
+
+fi
+
 
 if test "x${iconv_encodings}" != "x" \
    || test "x${iconv_to_encodings}" != "x" \
diff --git a/newlib/configure.in b/newlib/configure.in
index bfaf038c7..354c07ca5 100644
--- a/newlib/configure.in
+++ b/newlib/configure.in
@@ -218,6 +218,17 @@ AC_ARG_ENABLE(newlib_nano_formatted_io,
    *) AC_MSG_ERROR(bad value ${enableval} for newlib-nano-formatted-io) ;;
  esac],[newlib_nano_formatted_io=no])
 
+dnl Support --enable-retargetable-locking
+dnl This option is also read in libc/configure.in.  It is repeated
+dnl here so that it shows up in the help text.
+AC_ARG_ENABLE(newlib-retargetable-locking,
+[  --enable-newlib-retargetable-locking    Allow locking routines to be retargeted at link time],
+[case "${enableval}" in
+   yes) newlib_retargetable_locking=yes ;;
+   no)  newlib_retargetable_locking=no ;;
+   *) AC_MSG_ERROR(bad value ${enableval} for newlib-retargetable-locking) ;;
+ esac],[newlib_retargetable_locking=no])
+
 NEWLIB_CONFIGURE(.)
 
 dnl We have to enable libtool after NEWLIB_CONFIGURE because if we try and
@@ -458,6 +469,10 @@ if test "${newlib_nano_formatted_io}" = "yes"; then
 AC_DEFINE_UNQUOTED(_NANO_FORMATTED_IO)
 fi
 
+if test "${newlib_retargetable_locking}" = "yes"; then
+AC_DEFINE_UNQUOTED(_RETARGETABLE_LOCKING)
+fi
+
 dnl
 dnl Parse --enable-newlib-iconv-encodings option argument
 dnl
diff --git a/newlib/libc/configure b/newlib/libc/configure
index 4dc4d1bf7..dabe44fd9 100755
--- a/newlib/libc/configure
+++ b/newlib/libc/configure
@@ -751,6 +751,8 @@ build
 newlib_basedir
 MAY_SUPPLY_SYSCALLS_FALSE
 MAY_SUPPLY_SYSCALLS_TRUE
+NEWLIB_RETARGETABLE_LOCKING_FALSE
+NEWLIB_RETARGETABLE_LOCKING_TRUE
 NEWLIB_NANO_FORMATTED_IO_FALSE
 NEWLIB_NANO_FORMATTED_IO_TRUE
 target_alias
@@ -797,6 +799,7 @@ enable_option_checking
 enable_newlib_io_pos_args
 enable_newlib_nano_malloc
 enable_newlib_nano_formatted_io
+enable_newlib_retargetable_locking
 enable_multilib
 enable_target_optspace
 enable_malloc_debugging
@@ -1448,6 +1451,7 @@ Optional Features:
   --enable-newlib-io-pos-args enable printf-family positional arg support
   --enable-newlib-nano-malloc    Use small-footprint nano-malloc implementation
   --enable-newlib-nano-formatted-io    Use small-footprint nano-formatted-IO implementation
+  --enable-newlib-retargetable-locking    Allow locking routines to be retargeted at link time
   --enable-multilib         build many library versions (default)
   --enable-target-optspace  optimize for space
   --enable-malloc-debugging indicate malloc debugging requested
@@ -2252,6 +2256,26 @@ else
 fi
 
 
+# Check whether --enable-newlib-retargetable-locking was given.
+if test "${enable_newlib_retargetable_locking+set}" = set; then :
+  enableval=$enable_newlib_retargetable_locking; case "${enableval}" in
+   yes) newlib_retargetable_locking=yes ;;
+   no)  newlib_retargetable_lock=no ;;
+   *) as_fn_error $? "bad value ${enableval} for newlib-retargetable-locking" "$LINENO" 5 ;;
+ esac
+else
+  newlib_retargetable_locking=no
+fi
+
+ if test x$newlib_retargetable_locking = xyes; then
+  NEWLIB_RETARGETABLE_LOCKING_TRUE=
+  NEWLIB_RETARGETABLE_LOCKING_FALSE='#'
+else
+  NEWLIB_RETARGETABLE_LOCKING_TRUE='#'
+  NEWLIB_RETARGETABLE_LOCKING_FALSE=
+fi
+
+
 
 # Make sure we can run config.sub.
 $SHELL "$ac_aux_dir/config.sub" sun4 >/dev/null 2>&1 ||
@@ -11525,7 +11549,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11528 "configure"
+#line 11552 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11631,7 +11655,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11634 "configure"
+#line 11658 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12248,6 +12272,10 @@ if test -z "${NEWLIB_NANO_FORMATTED_IO_TRUE}" && test -z "${NEWLIB_NANO_FORMATTE
   as_fn_error $? "conditional \"NEWLIB_NANO_FORMATTED_IO\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
 fi
+if test -z "${NEWLIB_RETARGETABLE_LOCKING_TRUE}" && test -z "${NEWLIB_RETARGETABLE_LOCKING_FALSE}"; then
+  as_fn_error $? "conditional \"NEWLIB_RETARGETABLE_LOCKING\" was never defined.
+Usually this means the macro was only invoked conditionally." "$LINENO" 5
+fi
 if test -z "${MAY_SUPPLY_SYSCALLS_TRUE}" && test -z "${MAY_SUPPLY_SYSCALLS_FALSE}"; then
   as_fn_error $? "conditional \"MAY_SUPPLY_SYSCALLS\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
diff --git a/newlib/libc/configure.in b/newlib/libc/configure.in
index 0a7bb8815..ac25a3933 100644
--- a/newlib/libc/configure.in
+++ b/newlib/libc/configure.in
@@ -36,6 +36,16 @@ AC_ARG_ENABLE(newlib_nano_formatted_io,
  esac],[newlib_nano_formatted_io=no])
 AM_CONDITIONAL(NEWLIB_NANO_FORMATTED_IO, test x$newlib_nano_formatted_io = xyes)
 
+dnl Support --enable-retargetable-locking used by libc/sys
+AC_ARG_ENABLE(newlib-retargetable-locking,
+[  --enable-newlib-retargetable-locking    Allow locking routines to be retargeted at link time],
+[case "${enableval}" in
+   yes) newlib_retargetable_locking=yes ;;
+   no)  newlib_retargetable_lock=no ;;
+   *) AC_MSG_ERROR(bad value ${enableval} for newlib-retargetable-locking) ;;
+ esac],[newlib_retargetable_locking=no])
+AM_CONDITIONAL(NEWLIB_RETARGETABLE_LOCKING, test x$newlib_retargetable_locking = xyes)
+
 NEWLIB_CONFIGURE(..)
 
 AM_CONDITIONAL(NEWLIB_NANO_MALLOC, test x$newlib_nano_malloc = xyes)
diff --git a/newlib/libc/include/sys/lock.h b/newlib/libc/include/sys/lock.h
index 9075e35c9..42f9c4cd9 100644
--- a/newlib/libc/include/sys/lock.h
+++ b/newlib/libc/include/sys/lock.h
@@ -3,10 +3,13 @@
 
 /* dummy lock routines for single-threaded aps */
 
+#include <newlib.h>
+#include <_ansi.h>
+
+#if !defined(_RETARGETABLE_LOCKING)
+
 typedef int _LOCK_T;
 typedef int _LOCK_RECURSIVE_T;
- 
-#include <_ansi.h>
 
 #define __LOCK_INIT(class,lock) static int lock = 0;
 #define __LOCK_INIT_RECURSIVE(class,lock) static int lock = 0;
@@ -21,4 +24,46 @@ typedef int _LOCK_RECURSIVE_T;
 #define __lock_release(lock) (_CAST_VOID 0)
 #define __lock_release_recursive(lock) (_CAST_VOID 0)
 
+#else
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct __lock;
+typedef struct __lock * _LOCK_T;
+#define _LOCK_RECURSIVE_T _LOCK_T
+
+#define __LOCK_INIT(class,lock) extern struct __lock __lock_ ## lock; \
+	class _LOCK_T lock = &__lock_ ## lock
+#define __LOCK_INIT_RECURSIVE(class,lock) __LOCK_INIT(class,lock)
+
+extern void __retarget_lock_init(_LOCK_T *lock);
+#define __lock_init(lock) __retarget_lock_init(&lock)
+extern void __retarget_lock_init_recursive(_LOCK_T *lock);
+#define __lock_init_recursive(lock) __retarget_lock_init_recursive(&lock)
+extern void __retarget_lock_close(_LOCK_T lock);
+#define __lock_close(lock) __retarget_lock_close(lock)
+extern void __retarget_lock_close_recursive(_LOCK_T lock);
+#define __lock_close_recursive(lock) __retarget_lock_close_recursive(lock)
+extern void __retarget_lock_acquire(_LOCK_T lock);
+#define __lock_acquire(lock) __retarget_lock_acquire(lock)
+extern void __retarget_lock_acquire_recursive(_LOCK_T lock);
+#define __lock_acquire_recursive(lock) __retarget_lock_acquire_recursive(lock)
+extern int __retarget_lock_try_acquire(_LOCK_T lock);
+#define __lock_try_acquire(lock) __retarget_lock_try_acquire(lock)
+extern int __retarget_lock_try_acquire_recursive(_LOCK_T lock);
+#define __lock_try_acquire_recursive(lock) \
+  __retarget_lock_try_acquire_recursive(lock)
+extern void __retarget_lock_release(_LOCK_T lock);
+#define __lock_release(lock) __retarget_lock_release(lock)
+extern void __retarget_lock_release_recursive(_LOCK_T lock);
+#define __lock_release_recursive(lock) __retarget_lock_release_recursive(lock)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !defined(_RETARGETABLE_LOCKING) */
+
 #endif /* __SYS_LOCK_H__ */
diff --git a/newlib/libc/misc/Makefile.am b/newlib/libc/misc/Makefile.am
index 3fe8e55f5..7571ef263 100644
--- a/newlib/libc/misc/Makefile.am
+++ b/newlib/libc/misc/Makefile.am
@@ -6,6 +6,11 @@ INCLUDES = $(NEWLIB_CFLAGS) $(CROSS_CFLAGS) $(TARGET_CFLAGS)
 
 LIB_SOURCES = __dprintf.c unctrl.c ffs.c init.c fini.c
 
+if NEWLIB_RETARGETABLE_LOCKING
+LIB_SOURCES += \
+	lock.c
+endif
+
 libmisc_la_LDFLAGS = -Xcompiler -nostdlib
 
 if USE_LIBTOOL
@@ -21,5 +26,5 @@ endif # USE_LIBTOOL
 
 include $(srcdir)/../../Makefile.shared
 
-CHEWOUT_FILES = unctrl.def ffs.def
+CHEWOUT_FILES = unctrl.def lock.def ffs.def
 CHAPTERS = misc.tex
diff --git a/newlib/libc/misc/Makefile.in b/newlib/libc/misc/Makefile.in
index 0ada8de34..e7925231c 100644
--- a/newlib/libc/misc/Makefile.in
+++ b/newlib/libc/misc/Makefile.in
@@ -53,6 +53,9 @@ PRE_UNINSTALL = :
 POST_UNINSTALL = :
 build_triplet = @build@
 host_triplet = @host@
+@NEWLIB_RETARGETABLE_LOCKING_TRUE@am__append_1 = \
+@NEWLIB_RETARGETABLE_LOCKING_TRUE@	lock.c
+
 DIST_COMMON = $(srcdir)/../../Makefile.shared $(srcdir)/Makefile.in \
 	$(srcdir)/Makefile.am
 subdir = misc
@@ -72,14 +75,19 @@ LIBRARIES = $(noinst_LIBRARIES)
 ARFLAGS = cru
 lib_a_AR = $(AR) $(ARFLAGS)
 lib_a_LIBADD =
-am__objects_1 = lib_a-__dprintf.$(OBJEXT) lib_a-unctrl.$(OBJEXT) \
-	lib_a-ffs.$(OBJEXT) lib_a-init.$(OBJEXT) lib_a-fini.$(OBJEXT)
-@USE_LIBTOOL_FALSE@am_lib_a_OBJECTS = $(am__objects_1)
+@NEWLIB_RETARGETABLE_LOCKING_TRUE@am__objects_1 =  \
+@NEWLIB_RETARGETABLE_LOCKING_TRUE@	lib_a-lock.$(OBJEXT)
+am__objects_2 = lib_a-__dprintf.$(OBJEXT) lib_a-unctrl.$(OBJEXT) \
+	lib_a-ffs.$(OBJEXT) lib_a-init.$(OBJEXT) lib_a-fini.$(OBJEXT) \
+	$(am__objects_1)
+@USE_LIBTOOL_FALSE@am_lib_a_OBJECTS = $(am__objects_2)
 lib_a_OBJECTS = $(am_lib_a_OBJECTS)
 LTLIBRARIES = $(noinst_LTLIBRARIES)
 libmisc_la_LIBADD =
-am__objects_2 = __dprintf.lo unctrl.lo ffs.lo init.lo fini.lo
-@USE_LIBTOOL_TRUE@am_libmisc_la_OBJECTS = $(am__objects_2)
+@NEWLIB_RETARGETABLE_LOCKING_TRUE@am__objects_3 = lock.lo
+am__objects_4 = __dprintf.lo unctrl.lo ffs.lo init.lo fini.lo \
+	$(am__objects_3)
+@USE_LIBTOOL_TRUE@am_libmisc_la_OBJECTS = $(am__objects_4)
 libmisc_la_OBJECTS = $(am_libmisc_la_OBJECTS)
 libmisc_la_LINK = $(LIBTOOL) --tag=CC $(AM_LIBTOOLFLAGS) \
 	$(LIBTOOLFLAGS) --mode=link $(CCLD) $(AM_CFLAGS) $(CFLAGS) \
@@ -252,7 +260,7 @@ top_builddir = @top_builddir@
 top_srcdir = @top_srcdir@
 AUTOMAKE_OPTIONS = cygnus
 INCLUDES = $(NEWLIB_CFLAGS) $(CROSS_CFLAGS) $(TARGET_CFLAGS)
-LIB_SOURCES = __dprintf.c unctrl.c ffs.c init.c fini.c
+LIB_SOURCES = __dprintf.c unctrl.c ffs.c init.c fini.c $(am__append_1)
 libmisc_la_LDFLAGS = -Xcompiler -nostdlib
 @USE_LIBTOOL_TRUE@noinst_LTLIBRARIES = libmisc.la
 @USE_LIBTOOL_TRUE@libmisc_la_SOURCES = $(LIB_SOURCES)
@@ -271,7 +279,7 @@ DOCBOOK_CHEW = ${top_srcdir}/../doc/makedocbook.py
 DOCBOOK_OUT_FILES = $(CHEWOUT_FILES:.def=.xml)
 DOCBOOK_CHAPTERS = $(CHAPTERS:.tex=.xml)
 CLEANFILES = $(CHEWOUT_FILES) $(CHEWOUT_FILES:.def=.ref) $(DOCBOOK_OUT_FILES)
-CHEWOUT_FILES = unctrl.def ffs.def
+CHEWOUT_FILES = unctrl.def lock.def ffs.def
 CHAPTERS = misc.tex
 all: all-am
 
@@ -372,6 +380,12 @@ lib_a-fini.o: fini.c
 lib_a-fini.obj: fini.c
 	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-fini.obj `if test -f 'fini.c'; then $(CYGPATH_W) 'fini.c'; else $(CYGPATH_W) '$(srcdir)/fini.c'; fi`
 
+lib_a-lock.o: lock.c
+	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-lock.o `test -f 'lock.c' || echo '$(srcdir)/'`lock.c
+
+lib_a-lock.obj: lock.c
+	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-lock.obj `if test -f 'lock.c'; then $(CYGPATH_W) 'lock.c'; else $(CYGPATH_W) '$(srcdir)/lock.c'; fi`
+
 mostlyclean-libtool:
 	-rm -f *.lo
 
diff --git a/newlib/libc/misc/lock.c b/newlib/libc/misc/lock.c
new file mode 100644
index 000000000..a76317668
--- /dev/null
+++ b/newlib/libc/misc/lock.c
@@ -0,0 +1,157 @@
+/*
+FUNCTION
+<<__retarget_lock_init>>, <<__retarget_lock_init_recursive>>, <<__retarget_lock_close>>, <<__retarget_lock_close_recursive>>, <<__retarget_lock_acquire>>, <<__retarget_lock_acquire_recursive>>, <<__retarget_lock_try_acquire>>, <<__retarget_lock_try_acquire_recursive>>, <<__retarget_lock_release>>, <<__retarget_lock_release_recursive>>---locking routines
+
+INDEX
+	__lock___sinit_recursive_mutex
+INDEX
+	__lock___sfp_recursive_mutex
+INDEX
+	__lock___atexit_recursive_mutex
+INDEX
+	__lock___at_quick_exit_mutex
+INDEX
+	__lock___malloc_recursive_mutex
+INDEX
+	__lock___env_recursive_mutex
+INDEX
+	__lock___tz_mutex
+INDEX
+	__lock___dd_hash_mutex
+INDEX
+	__lock___arc4random_mutex
+
+INDEX
+	__retarget_lock_init
+INDEX
+	__retarget_lock_init_recursive
+INDEX
+	__retarget_lock_close
+INDEX
+	__retarget_lock_close_recursive
+INDEX
+	__retarget_lock_acquire
+INDEX
+	__retarget_lock_acquire_recursive
+INDEX
+	__retarget_lock_try_acquire
+INDEX
+	__retarget_lock_try_acquire_recursive
+INDEX
+	__retarget_lock_release
+INDEX
+	__retarget_lock_release_recursive
+
+ANSI_SYNOPSIS
+	#include <lock.h>
+	struct __lock __lock___sinit_recursive_mutex;
+	struct __lock __lock___sfp_recursive_mutex;
+	struct __lock __lock___atexit_recursive_mutex;
+	struct __lock __lock___at_quick_exit_mutex;
+	struct __lock __lock___malloc_recursive_mutex;
+	struct __lock __lock___env_recursive_mutex;
+	struct __lock __lock___tz_mutex;
+	struct __lock __lock___dd_hash_mutex;
+	struct __lock __lock___arc4random_mutex;
+
+	void __retarget_lock_init (_LOCK_T * <[lock_ptr]>);
+	void __retarget_lock_init_recursive (_LOCK_T * <[lock_ptr]>);
+	void __retarget_lock_close (_LOCK_T <[lock]>);
+	void __retarget_lock_close_recursive (_LOCK_T <[lock]>);
+	void __retarget_lock_acquire (_LOCK_T <[lock]>);
+	void __retarget_lock_acquire_recursive (_LOCK_T <[lock]>);
+	int __retarget_lock_try_acquire (_LOCK_T <[lock]>);
+	int __retarget_lock_try_acquire_recursive (_LOCK_T <[lock]>);
+	void __retarget_lock_release (_LOCK_T <[lock]>);
+	void __retarget_lock_release_recursive (_LOCK_T <[lock]>);
+
+DESCRIPTION
+Newlib was configured to allow the target platform to provide the locking
+routines and static locks at link time.  As such, a dummy default
+implementation of these routines and static locks is provided for
+single-threaded application to link successfully out of the box on bare-metal
+systems.
+
+For multi-threaded applications the target platform is required to provide
+an implementation for @strong{all} these routines and static locks.  If some
+routines or static locks are missing, the link will fail with doubly defined
+symbols.
+
+PORTABILITY
+These locking routines and static lock are newlib-specific.  Supporting OS
+subroutines are required for linking multi-threaded applications.
+*/
+
+/* dummy lock routines and static locks for single-threaded apps */
+
+#ifndef __SINGLE_THREAD__
+
+#include <sys/lock.h>
+
+struct __lock {
+  char unused;
+};
+
+struct __lock __lock___sinit_recursive_mutex;
+struct __lock __lock___sfp_recursive_mutex;
+struct __lock __lock___atexit_recursive_mutex;
+struct __lock __lock___at_quick_exit_mutex;
+struct __lock __lock___malloc_recursive_mutex;
+struct __lock __lock___env_recursive_mutex;
+struct __lock __lock___tz_mutex;
+struct __lock __lock___dd_hash_mutex;
+struct __lock __lock___arc4random_mutex;
+
+void
+__retarget_lock_init (_LOCK_T *lock)
+{
+}
+
+void
+__retarget_lock_init_recursive(_LOCK_T *lock)
+{
+}
+
+void
+__retarget_lock_close(_LOCK_T lock)
+{
+}
+
+void
+__retarget_lock_close_recursive(_LOCK_T lock)
+{
+}
+
+void
+__retarget_lock_acquire (_LOCK_T lock)
+{
+}
+
+void
+__retarget_lock_acquire_recursive (_LOCK_T lock)
+{
+}
+
+int
+__retarget_lock_try_acquire(_LOCK_T lock)
+{
+  return 1;
+}
+
+int
+__retarget_lock_try_acquire_recursive(_LOCK_T lock)
+{
+  return 1;
+}
+
+void
+__retarget_lock_release (_LOCK_T lock)
+{
+}
+
+void
+__retarget_lock_release_recursive (_LOCK_T lock)
+{
+}
+
+#endif /* !defined(__SINGLE_THREAD__) */
diff --git a/newlib/libc/misc/misc.tex b/newlib/libc/misc/misc.tex
index 22c313eb1..248243b53 100644
--- a/newlib/libc/misc/misc.tex
+++ b/newlib/libc/misc/misc.tex
@@ -4,6 +4,7 @@ This chapter describes miscellaneous routines not covered elsewhere.
 
 @menu 
 * ffs::      Return first bit set in a word
+* __retarget_lock_init::     Retargetable locking routines
 * unctrl::   Return printable representation of a character
 @end menu
 
@@ -11,4 +12,7 @@ This chapter describes miscellaneous routines not covered elsewhere.
 @include misc/ffs.def
 
 @page
+@include misc/lock.def
+
+@page
 @include misc/unctrl.def
diff --git a/newlib/newlib.hin b/newlib/newlib.hin
index d03dfac0e..397bc9b96 100644
--- a/newlib/newlib.hin
+++ b/newlib/newlib.hin
@@ -82,6 +82,9 @@
 /* Define if small footprint nano-formatted-IO implementation used.  */
 #undef _NANO_FORMATTED_IO
 
+/* Define if using retargetable functions for default lock routines.  */
+#undef _RETARGETABLE_LOCKING
+
 /*
  * Iconv encodings enabled ("to" direction)
  */