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.

1 files changed, 47 insertions, 2 deletions

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__ */