esp32/main: Store native code as linked list instead of list on GC heap.

Finalisers that run during `gc_sweep_all()` may run native code, for
example if an open file is closed and the underlying block device is
implemented in native code, then the filesystem driver (eg FAT) may call
into the native code.

Therefore, native code must be freed after the call to `gc_sweep_all()`.
That can only be achieved if the GC heap is not used to store the list of
allocated native code blocks.  Instead, this commit makes the native code
blocks a linked list.
Signed-off-by: Damien George <damien@micropython.org>

ports/esp32/main.c

@@ -78,6 +78,15 @@
 #define MP_TASK_STACK_LIMIT_MARGIN (1024)
 #endif
 
+typedef struct _native_code_node_t {
+    struct _native_code_node_t *next;
+    uint32_t data[];
+} native_code_node_t;
+
+static native_code_node_t *native_code_head = NULL;
+
+static void esp_native_code_free_all(void);
+
 int vprintf_null(const char *format, va_list ap) {
     // do nothing: this is used as a log target during raw repl mode
     return 0;
@@ -130,8 +139,6 @@ soft_reset:
     mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_lib));
     readline_init0();
 
-    MP_STATE_PORT(native_code_pointers) = MP_OBJ_NULL;
-
     // initialise peripherals
     machine_pins_init();
     #if MICROPY_PY_MACHINE_I2S
@@ -182,18 +189,11 @@ soft_reset_exit:
     mp_thread_deinit();
     #endif
 
-    // Free any native code pointers that point to iRAM.
-    if (MP_STATE_PORT(native_code_pointers) != MP_OBJ_NULL) {
-        size_t len;
-        mp_obj_t *items;
-        mp_obj_list_get(MP_STATE_PORT(native_code_pointers), &len, &items);
-        for (size_t i = 0; i < len; ++i) {
-            heap_caps_free(MP_OBJ_TO_PTR(items[i]));
-        }
-    }
-
     gc_sweep_all();
 
+    // Free any native code pointers that point to iRAM.
+    esp_native_code_free_all();
+
     mp_hal_stdout_tx_str("MPY: soft reboot\r\n");
 
     // deinitialise peripherals
@@ -232,21 +232,27 @@ void nlr_jump_fail(void *val) {
     esp_restart();
 }
 
+static void esp_native_code_free_all(void) {
+    while (native_code_head != NULL) {
+        native_code_node_t *next = native_code_head->next;
+        heap_caps_free(native_code_head);
+        native_code_head = next;
+    }
+}
+
 void *esp_native_code_commit(void *buf, size_t len, void *reloc) {
     len = (len + 3) & ~3;
-    uint32_t *p = heap_caps_malloc(len, MALLOC_CAP_EXEC);
-    if (p == NULL) {
-        m_malloc_fail(len);
-    }
-    if (MP_STATE_PORT(native_code_pointers) == MP_OBJ_NULL) {
-        MP_STATE_PORT(native_code_pointers) = mp_obj_new_list(0, NULL);
+    size_t len_node = sizeof(native_code_node_t) + len;
+    native_code_node_t *node = heap_caps_malloc(len_node, MALLOC_CAP_EXEC);
+    if (node == NULL) {
+        m_malloc_fail(len_node);
     }
-    mp_obj_list_append(MP_STATE_PORT(native_code_pointers), MP_OBJ_TO_PTR(p));
+    node->next = native_code_head;
+    native_code_head = node;
+    void *p = node->data;
     if (reloc) {
         mp_native_relocate(reloc, buf, (uintptr_t)p);
     }
     memcpy(p, buf, len);
     return p;
 }
-
-MP_REGISTER_ROOT_POINTER(mp_obj_t native_code_pointers);