sandbox: Improve/augment memory allocation functions

Implement realloc() and free() for sandbox, by adding a header to each
block which contains the block size.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>

include/os.h

@@ -106,6 +106,35 @@ void os_tty_raw(int fd);
  */
 void *os_malloc(size_t length);
 
+/**
+ * Free memory previous allocated with os_malloc()/os_realloc()
+ *
+ * This returns the memory to the OS.
+ *
+ * \param ptr		Pointer to memory block to free
+ */
+void *os_free(void *ptr);
+
+/**
+ * Reallocate previously-allocated memory to increase/decrease space
+ *
+ * This works in a similar way to the C library realloc() function. If
+ * length is 0, then ptr is freed. Otherwise the space used by ptr is
+ * expanded or reduced depending on whether length is larger or smaller
+ * than before.
+ *
+ * If ptr is NULL, then this is similar to calling os_malloc().
+ *
+ * This function may need to move the memory block to make room for any
+ * extra space, in which case the new pointer is returned.
+ *
+ * \param ptr		Pointer to memory block to reallocate
+ * \param length	New length for memory block
+ * \return pointer to new memory block, or NULL on failure or if length
+ *	is 0.
+ */
+void *os_realloc(void *ptr, size_t length);
+
 /**
  * Access to the usleep function of the os
  *