lib: newlib: Add malloc lock

This commit adds a lock implementation for the newlib heap memory
management functions (`malloc` and `free`).

The `__malloc_lock` and `__malloc_unlock` functions are called by the
newlib `malloc` and `free` functions to synchronise access to the heap
region.

Without this lock, making use of the `malloc` and `free` functions from
multiple threads will result in the corruption of the heap region.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

lib/libc/newlib/libc-hooks.c

@@ -16,6 +16,7 @@
 #include <app_memory/app_memdomain.h>
 #include <init.h>
 #include <sys/sem.h>
+#include <sys/mutex.h>
 #include <sys/mem_manage.h>
 
 #define LIBC_BSS	K_APP_BMEM(z_libc_partition)
@@ -291,6 +292,18 @@ void *_sbrk(intptr_t count)
 }
 __weak FUNC_ALIAS(_sbrk, sbrk, void *);
 
+static LIBC_DATA SYS_MUTEX_DEFINE(heap_mutex);
+
+void __malloc_lock(struct _reent *reent)
+{
+	sys_mutex_lock(&heap_mutex, K_FOREVER);
+}
+
+void __malloc_unlock(struct _reent *reent)
+{
+	sys_mutex_unlock(&heap_mutex);
+}
+
 __weak int *__errno(void)
 {
 	return z_errno();