Implement native function pointer check, addr conversion and register, update documents (#185)

Modified WASM runtime API:
- wasm_runtime_module_malloc()
- wasm_runtime_lookup_function()
Introduced runtime API
- wasm_runtime_register_natives()

samples/littlevgl/vgl-wasm-runtime/src/platform/zephyr/iwasm_main.c

@@ -15,6 +15,9 @@
 #include "bi-inc/attr_container.h"
 #include "module_wasm_app.h"
 #include "wasm_export.h"
+#include "sensor_native_api.h"
+#include "connection_native_api.h"
+#include "display_indev.h"
 
 #include <zephyr.h>
 #include <drivers/uart.h>
@@ -30,7 +33,6 @@ int uart_char_cnt = 0;
 static void uart_irq_callback(struct device *dev)
 {
     unsigned char ch;
-    int size = 0;
 
     while (uart_poll_in(dev, &ch) == 0) {
         uart_char_cnt++;
@@ -77,11 +79,21 @@ timer_ctx_t timer_ctx;
 
 static char global_heap_buf[370 * 1024] = { 0 };
 
-extern void display_init(void);
+static NativeSymbol native_symbols[] = {
+    #include "runtime_sensor.inl"
+    #include "connection.inl"
+    EXPORT_WASM_API_WITH_SIG(display_input_read, "(*)i"),
+    EXPORT_WASM_API_WITH_SIG(display_flush, "(iiii*)"),
+    EXPORT_WASM_API_WITH_SIG(display_fill, "(iiii*)"),
+    EXPORT_WASM_API_WITH_SIG(display_vdb_write, "(*iii*i)"),
+    EXPORT_WASM_API_WITH_SIG(display_map, "(iiii*)"),
+    EXPORT_WASM_API_WITH_SIG(time_get_ms, "()i")
+};
 
 int iwasm_main()
 {
     korp_thread tid, tm_tid;
+    uint32 n_native_symbols;
 
     host_init();
 
@@ -95,6 +107,13 @@ int iwasm_main()
         goto fail1;
     }
 
+    /* Register native functions */
+    n_native_symbols = sizeof(native_symbols) / sizeof(NativeSymbol);
+    if (!wasm_runtime_register_natives("env",
+                                       native_symbols, n_native_symbols)) {
+        goto fail1;
+    }
+
     display_init();
 
     // timer manager