esp8266: When doing GC be sure to trace the memory holding native code.

Native code can hold pointers to objects on the heap, eg constant objects
like big integers.

esp8266/gccollect.c

@@ -46,6 +46,11 @@ void gc_collect(void) {
     // trace the stack, including the registers (since they live on the stack in this function)
     gc_collect_root((void**)sp, (STACK_END - sp) / sizeof(uint32_t));
 
+    #if MICROPY_EMIT_XTENSA || MICROPY_EMIT_INLINE_XTENSA
+    // trace any native code because it can contain pointers to the heap
+    esp_native_code_gc_collect();
+    #endif
+
     // end the GC
     gc_collect_end();
 }

esp8266/gccollect.h

@@ -38,3 +38,4 @@ extern uint32_t _heap_start;
 extern uint32_t _heap_end;
 
 void gc_collect(void);
+void esp_native_code_gc_collect(void);

esp8266/modesp.c

@@ -711,6 +711,8 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp_esf_free_bufs_obj, esp_esf_free_bufs);
 // esp.set_native_code_location() function; see below.  If flash is selected
 // then it is erased as needed.
 
+#include "gccollect.h"
+
 #define IRAM1_END (0x40108000)
 #define FLASH_START (0x40200000)
 #define FLASH_END (0x40300000)
@@ -734,6 +736,16 @@ void esp_native_code_init(void) {
     esp_native_code_erased = 0;
 }
 
+void esp_native_code_gc_collect(void) {
+    void *src;
+    if (esp_native_code_location == ESP_NATIVE_CODE_IRAM1) {
+        src = (void*)esp_native_code_start;
+    } else {
+        src = (void*)(FLASH_START + esp_native_code_start);
+    }
+    gc_collect_root(src, (esp_native_code_end - esp_native_code_start) / sizeof(uint32_t));
+}
+
 void *esp_native_code_commit(void *buf, size_t len) {
     //printf("COMMIT(buf=%p, len=%u, start=%08x, cur=%08x, end=%08x, erased=%08x)\n", buf, len, esp_native_code_start, esp_native_code_cur, esp_native_code_end, esp_native_code_erased);