Merge fd7bc4f12b into 7b050b366b

Although the original motivation given for the workaround[1] is correct,
nlr.o and nlrthumb.o are linked with a small enough distance that the
problem does not occur, and the workaround isn't necessary. The distance
between the b instruction and its target (nlr_push_tail) is just 64
bytes[2], well within the ±2046 byte range addressable by an
unconditional branch instruction in Thumb mode.

The workaround induces a relocation in the text section (textrel), which
isn't supported everywhere, notably not on musl-libc[3], where it causes
a crash on start-up. With the workaround removed, micropython works on an
ARMv5T Linux system built with musl-libc.

This commit changes nlrthumb.c to use a direct jump by default, but
leaves the long jump workaround as an option for those cases where it's
actually needed.

[1]: commit dd376a239d

Author: Damien George <damien.p.george@gmail.com>
Date:   Fri Sep 1 15:25:29 2017 +1000

    py/nlrthumb: Get working again on standard Thumb arch (ie not Thumb2).

    "b" on Thumb might not be long enough for the jump to nlr_push_tail so
    it must be done indirectly.

[2]: Excerpt from objdump -d micropython:

000095c4 <nlr_push_tail>:
    95c4:       b510            push    {r4, lr}
    95c6:       0004            movs    r4, r0
    95c8:       f02d fd42       bl      37050 <mp_thread_get_state>
    95cc:       6943            ldr     r3, [r0, #20]
    95ce:       6023            str     r3, [r4, #0]
    95d0:       6144            str     r4, [r0, #20]
    95d2:       2000            movs    r0, #0
    95d4:       bd10            pop     {r4, pc}

000095d6 <nlr_pop>:
    95d6:       b510            push    {r4, lr}
    95d8:       f02d fd3a       bl      37050 <mp_thread_get_state>
    95dc:       6943            ldr     r3, [r0, #20]
    95de:       681b            ldr     r3, [r3, #0]
    95e0:       6143            str     r3, [r0, #20]
    95e2:       bd10            pop     {r4, pc}

000095e4 <nlr_push>:
    95e4:       60c4            str     r4, [r0, #12]
    95e6:       6105            str     r5, [r0, #16]
    95e8:       6146            str     r6, [r0, #20]
    95ea:       6187            str     r7, [r0, #24]
    95ec:       4641            mov     r1, r8
    95ee:       61c1            str     r1, [r0, #28]
    95f0:       4649            mov     r1, r9
    95f2:       6201            str     r1, [r0, #32]
    95f4:       4651            mov     r1, sl
    95f6:       6241            str     r1, [r0, #36]   @ 0x24
    95f8:       4659            mov     r1, fp
    95fa:       6281            str     r1, [r0, #40]   @ 0x28
    95fc:       4669            mov     r1, sp
    95fe:       62c1            str     r1, [r0, #44]   @ 0x2c
    9600:       4671            mov     r1, lr
    9602:       6081            str     r1, [r0, #8]
    9604:       e7de            b.n     95c4 <nlr_push_tail>

[3]: https://www.openwall.com/lists/musl/2020/09/25/4

Signed-off-by: J. Neuschäfer <j.ne@posteo.net>

docs/library/builtins.rst

@@ -77,7 +77,7 @@ Functions and types
       In MicroPython, `byteorder` parameter must be positional (this is
       compatible with CPython).
 
-   .. method:: to_bytes(size, byteorder)
+   .. method:: to_bytes(size, byteorder, / signed=False)
 
       In MicroPython, `byteorder` parameter must be positional (this is
       compatible with CPython).

extmod/modasyncio.c

@@ -156,7 +156,7 @@ static MP_DEFINE_CONST_OBJ_TYPE(
 // Task class
 
 // This is the core asyncio context with cur_task, _task_queue and CancelledError.
-static mp_obj_t asyncio_context = MP_OBJ_NULL;
+mp_obj_t mp_asyncio_context = MP_OBJ_NULL;
 
 static mp_obj_t task_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     mp_arg_check_num(n_args, n_kw, 1, 2, false);
@@ -168,7 +168,7 @@ static mp_obj_t task_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     self->state = TASK_STATE_RUNNING_NOT_WAITED_ON;
     self->ph_key = MP_OBJ_NEW_SMALL_INT(0);
     if (n_args == 2) {
-        asyncio_context = args[1];
+        mp_asyncio_context = args[1];
     }
     return MP_OBJ_FROM_PTR(self);
 }
@@ -186,7 +186,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         return mp_const_false;
     }
     // Can't cancel self (not supported yet).
-    mp_obj_t cur_task = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+    mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
     if (self_in == cur_task) {
         mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT("can't cancel self"));
     }
@@ -195,7 +195,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         self = MP_OBJ_TO_PTR(self->data);
     }
 
-    mp_obj_t _task_queue = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR__task_queue));
+    mp_obj_t _task_queue = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR__task_queue));
 
     // Reschedule Task as a cancelled task.
     mp_obj_t dest[3];
@@ -218,7 +218,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         task_queue_push(2, dest);
     }
 
-    self->data = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_CancelledError));
+    self->data = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_CancelledError));
 
     return mp_const_true;
 }
@@ -278,7 +278,7 @@ static mp_obj_t task_iternext(mp_obj_t self_in) {
         nlr_raise(self->data);
     } else {
         // Put calling task on waiting queue.
-        mp_obj_t cur_task = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+        mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
         mp_obj_t args[2] = { self->state, cur_task };
         task_queue_push(2, args);
         // Set calling task's data to this task that it waits on, to double-link it.

ports/unix/modffi.c

@@ -442,7 +442,7 @@ static unsigned long long ffi_get_int_value(mp_obj_t o) {
         return MP_OBJ_SMALL_INT_VALUE(o);
     } else {
         unsigned long long res;
-        mp_obj_int_to_bytes_impl(o, MP_ENDIANNESS_BIG, sizeof(res), (byte *)&res);
+        mp_obj_int_to_bytes_impl(o, MP_ENDIANNESS_BIG, true, sizeof(res), (byte *)&res);
         return res;
     }
 }

ports/webassembly/Makefile

@@ -22,6 +22,9 @@ BUILD ?= build-$(VARIANT)
 include ../../py/mkenv.mk
 include $(VARIANT_DIR)/mpconfigvariant.mk
 
+# Use the default frozen manifest, variants may override this.
+FROZEN_MANIFEST ?= variants/manifest.py
+
 # Qstr definitions (must come before including py.mk).
 QSTR_DEFS = qstrdefsport.h
 

ports/webassembly/api.js

@@ -38,7 +38,7 @@ export async function loadMicroPython(options) {
         { heapsize: 1024 * 1024, linebuffer: true },
         options,
     );
-    const Module = {};
+    let Module = {};
     Module.locateFile = (path, scriptDirectory) =>
         url || scriptDirectory + path;
     Module._textDecoder = new TextDecoder();
@@ -83,11 +83,7 @@ export async function loadMicroPython(options) {
             Module.stderr = (c) => stderr(new Uint8Array([c]));
         }
     }
-    const moduleLoaded = new Promise((r) => {
-        Module.postRun = r;
-    });
-    _createMicroPythonModule(Module);
-    await moduleLoaded;
+    Module = await _createMicroPythonModule(Module);
     globalThis.Module = Module;
     proxy_js_init();
     const pyimport = (name) => {
@@ -131,23 +127,31 @@ export async function loadMicroPython(options) {
         },
         pyimport: pyimport,
         runPython(code) {
+            const len = Module.lengthBytesUTF8(code);
+            const buf = Module._malloc(len + 1);
+            Module.stringToUTF8(code, buf, len + 1);
             const value = Module._malloc(3 * 4);
             Module.ccall(
                 "mp_js_do_exec",
                 "number",
-                ["string", "pointer"],
-                [code, value],
+                ["pointer", "number", "pointer"],
+                [buf, len, value],
             );
+            Module._free(buf);
             return proxy_convert_mp_to_js_obj_jsside_with_free(value);
         },
         runPythonAsync(code) {
+            const len = Module.lengthBytesUTF8(code);
+            const buf = Module._malloc(len + 1);
+            Module.stringToUTF8(code, buf, len + 1);
             const value = Module._malloc(3 * 4);
             Module.ccall(
                 "mp_js_do_exec_async",
                 "number",
-                ["string", "pointer"],
-                [code, value],
+                ["pointer", "number", "pointer"],
+                [buf, len, value],
             );
+            Module._free(buf);
             return proxy_convert_mp_to_js_obj_jsside_with_free(value);
         },
         replInit() {
@@ -224,6 +228,16 @@ async function runCLI() {
             }
         });
     } else {
+        // If the script to run ends with a running of the asyncio main loop, then inject
+        // a simple `asyncio.run` hook that starts the main task.  This is primarily to
+        // support running the standard asyncio tests.
+        if (contents.endsWith("asyncio.run(main())\n")) {
+            const asyncio = mp.pyimport("asyncio");
+            asyncio.run = async (task) => {
+                await asyncio.create_task(task);
+            };
+        }
+
         try {
             mp.runPython(contents);
         } catch (error) {

ports/webassembly/asyncio/__init__.py

@@ -0,0 +1,9 @@
+# MicroPython asyncio module, for use with webassembly port
+# MIT license; Copyright (c) 2024 Damien P. George
+
+from .core import *
+from .funcs import wait_for, wait_for_ms, gather
+from .event import Event
+from .lock import Lock
+
+__version__ = (3, 0, 0)

ports/webassembly/asyncio/core.py

@@ -0,0 +1,249 @@
+# MicroPython asyncio module, for use with webassembly port
+# MIT license; Copyright (c) 2019-2024 Damien P. George
+
+from time import ticks_ms as ticks, ticks_diff, ticks_add
+import sys, js, jsffi
+
+# Import TaskQueue and Task from built-in C code.
+from _asyncio import TaskQueue, Task
+
+
+################################################################################
+# Exceptions
+
+
+class CancelledError(BaseException):
+    pass
+
+
+class TimeoutError(Exception):
+    pass
+
+
+# Used when calling Loop.call_exception_handler.
+_exc_context = {"message": "Task exception wasn't retrieved", "exception": None, "future": None}
+
+
+################################################################################
+# Sleep functions
+
+
+# "Yield" once, then raise StopIteration
+class SingletonGenerator:
+    def __init__(self):
+        self.state = None
+        self.exc = StopIteration()
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if self.state is not None:
+            _task_queue.push(cur_task, self.state)
+            self.state = None
+            return None
+        else:
+            self.exc.__traceback__ = None
+            raise self.exc
+
+
+# Pause task execution for the given time (integer in milliseconds, uPy extension)
+# Use a SingletonGenerator to do it without allocating on the heap
+def sleep_ms(t, sgen=SingletonGenerator()):
+    if cur_task is None:
+        # Support top-level asyncio.sleep, via a JavaScript Promise.
+        return jsffi.async_timeout_ms(t)
+    assert sgen.state is None
+    sgen.state = ticks_add(ticks(), max(0, t))
+    return sgen
+
+
+# Pause task execution for the given time (in seconds)
+def sleep(t):
+    return sleep_ms(int(t * 1000))
+
+
+################################################################################
+# Main run loop
+
+asyncio_timer = None
+
+
+class ThenableEvent:
+    def __init__(self, thenable):
+        self.result = None  # Result of the thenable
+        self.waiting = None  # Task waiting on completion of this thenable
+        thenable.then(self.set)
+
+    def set(self, value):
+        # Thenable/Promise is fulfilled, set result and schedule any waiting task.
+        self.result = value
+        if self.waiting:
+            _task_queue.push(self.waiting)
+            self.waiting = None
+            _schedule_run_iter(0)
+
+    def remove(self, task):
+        self.waiting = None
+
+    # async
+    def wait(self):
+        # Set the calling task as the task waiting on this thenable.
+        self.waiting = cur_task
+        # Set calling task's data to this object so it can be removed if needed.
+        cur_task.data = self
+        # Wait for the thenable to fulfill.
+        yield
+        # Return the result of the thenable.
+        return self.result
+
+
+# Ensure the awaitable is a task
+def _promote_to_task(aw):
+    return aw if isinstance(aw, Task) else create_task(aw)
+
+
+def _schedule_run_iter(dt):
+    global asyncio_timer
+    if asyncio_timer is not None:
+        js.clearTimeout(asyncio_timer)
+    asyncio_timer = js.setTimeout(_run_iter, dt)
+
+
+def _run_iter():
+    global cur_task
+    excs_all = (CancelledError, Exception)  # To prevent heap allocation in loop
+    excs_stop = (CancelledError, StopIteration)  # To prevent heap allocation in loop
+    while True:
+        # Wait until the head of _task_queue is ready to run
+        t = _task_queue.peek()
+        if t:
+            # A task waiting on _task_queue; "ph_key" is time to schedule task at
+            dt = max(0, ticks_diff(t.ph_key, ticks()))
+        else:
+            # No tasks can be woken so finished running
+            cur_task = None
+            return
+
+        if dt > 0:
+            # schedule to call again later
+            cur_task = None
+            _schedule_run_iter(dt)
+            return
+
+        # Get next task to run and continue it
+        t = _task_queue.pop()
+        cur_task = t
+        try:
+            # Continue running the coroutine, it's responsible for rescheduling itself
+            exc = t.data
+            if not exc:
+                t.coro.send(None)
+            else:
+                # If the task is finished and on the run queue and gets here, then it
+                # had an exception and was not await'ed on.  Throwing into it now will
+                # raise StopIteration and the code below will catch this and run the
+                # call_exception_handler function.
+                t.data = None
+                t.coro.throw(exc)
+        except excs_all as er:
+            # Check the task is not on any event queue
+            assert t.data is None
+            # This task is done.
+            if t.state:
+                # Task was running but is now finished.
+                waiting = False
+                if t.state is True:
+                    # "None" indicates that the task is complete and not await'ed on (yet).
+                    t.state = None
+                elif callable(t.state):
+                    # The task has a callback registered to be called on completion.
+                    t.state(t, er)
+                    t.state = False
+                    waiting = True
+                else:
+                    # Schedule any other tasks waiting on the completion of this task.
+                    while t.state.peek():
+                        _task_queue.push(t.state.pop())
+                        waiting = True
+                    # "False" indicates that the task is complete and has been await'ed on.
+                    t.state = False
+                if not waiting and not isinstance(er, excs_stop):
+                    # An exception ended this detached task, so queue it for later
+                    # execution to handle the uncaught exception if no other task retrieves
+                    # the exception in the meantime (this is handled by Task.throw).
+                    _task_queue.push(t)
+                # Save return value of coro to pass up to caller.
+                t.data = er
+            elif t.state is None:
+                # Task is already finished and nothing await'ed on the task,
+                # so call the exception handler.
+
+                # Save exception raised by the coro for later use.
+                t.data = exc
+
+                # Create exception context and call the exception handler.
+                _exc_context["exception"] = exc
+                _exc_context["future"] = t
+                Loop.call_exception_handler(_exc_context)
+
+
+# Create and schedule a new task from a coroutine.
+def create_task(coro):
+    if not hasattr(coro, "send"):
+        raise TypeError("coroutine expected")
+    t = Task(coro, globals())
+    _task_queue.push(t)
+    _schedule_run_iter(0)
+    return t
+
+
+################################################################################
+# Event loop wrapper
+
+
+cur_task = None
+
+
+class Loop:
+    _exc_handler = None
+
+    def create_task(coro):
+        return create_task(coro)
+
+    def close():
+        pass
+
+    def set_exception_handler(handler):
+        Loop._exc_handler = handler
+
+    def get_exception_handler():
+        return Loop._exc_handler
+
+    def default_exception_handler(loop, context):
+        print(context["message"], file=sys.stderr)
+        print("future:", context["future"], "coro=", context["future"].coro, file=sys.stderr)
+        sys.print_exception(context["exception"], sys.stderr)
+
+    def call_exception_handler(context):
+        (Loop._exc_handler or Loop.default_exception_handler)(Loop, context)
+
+
+def get_event_loop():
+    return Loop
+
+
+def current_task():
+    if cur_task is None:
+        raise RuntimeError("no running event loop")
+    return cur_task
+
+
+def new_event_loop():
+    global _task_queue
+    _task_queue = TaskQueue()  # TaskQueue of Task instances.
+    return Loop
+
+
+# Initialise default event loop.
+new_event_loop()

ports/webassembly/main.c

@@ -104,7 +104,7 @@ void mp_js_do_import(const char *name, uint32_t *out) {
     }
 }
 
-void mp_js_do_exec(const char *src, uint32_t *out) {
+void mp_js_do_exec(const char *src, size_t len, uint32_t *out) {
     // Collect at the top-level, where there are no root pointers from stack/registers.
     gc_collect_start();
     gc_collect_end();
@@ -112,7 +112,7 @@ void mp_js_do_exec(const char *src, uint32_t *out) {
     mp_parse_input_kind_t input_kind = MP_PARSE_FILE_INPUT;
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_lexer_t *lex = mp_lexer_new_from_str_len_dedent(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
+        mp_lexer_t *lex = mp_lexer_new_from_str_len_dedent(MP_QSTR__lt_stdin_gt_, src, len, 0);
         qstr source_name = lex->source_name;
         mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
         mp_obj_t module_fun = mp_compile(&parse_tree, source_name, false);
@@ -125,9 +125,9 @@ void mp_js_do_exec(const char *src, uint32_t *out) {
     }
 }
 
-void mp_js_do_exec_async(const char *src, uint32_t *out) {
+void mp_js_do_exec_async(const char *src, size_t len, uint32_t *out) {
     mp_compile_allow_top_level_await = true;
-    mp_js_do_exec(src, out);
+    mp_js_do_exec(src, len, out);
     mp_compile_allow_top_level_await = false;
 }
 

ports/webassembly/modjsffi.c

@@ -61,12 +61,27 @@ static mp_obj_t mp_jsffi_to_js(mp_obj_t arg) {
 }
 static MP_DEFINE_CONST_FUN_OBJ_1(mp_jsffi_to_js_obj, mp_jsffi_to_js);
 
+// *FORMAT-OFF*
+EM_JS(void, promise_with_timeout_ms, (double ms, uint32_t * out), {
+    const ret = new Promise((resolve) => setTimeout(resolve, ms));
+    proxy_convert_js_to_mp_obj_jsside(ret, out);
+});
+// *FORMAT-ON*
+
+static mp_obj_t mp_jsffi_async_timeout_ms(mp_obj_t arg) {
+    uint32_t out[PVN];
+    promise_with_timeout_ms(mp_obj_get_float_to_d(arg), out);
+    return proxy_convert_js_to_mp_obj_cside(out);
+}
+static MP_DEFINE_CONST_FUN_OBJ_1(mp_jsffi_async_timeout_ms_obj, mp_jsffi_async_timeout_ms);
+
 static const mp_rom_map_elem_t mp_module_jsffi_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_jsffi) },
 
     { MP_ROM_QSTR(MP_QSTR_JsProxy), MP_ROM_PTR(&mp_type_jsproxy) },
     { MP_ROM_QSTR(MP_QSTR_create_proxy), MP_ROM_PTR(&mp_jsffi_create_proxy_obj) },
     { MP_ROM_QSTR(MP_QSTR_to_js), MP_ROM_PTR(&mp_jsffi_to_js_obj) },
+    { MP_ROM_QSTR(MP_QSTR_async_timeout_ms), MP_ROM_PTR(&mp_jsffi_async_timeout_ms_obj) },
 };
 static MP_DEFINE_CONST_DICT(mp_module_jsffi_globals, mp_module_jsffi_globals_table);
 

ports/webassembly/objjsproxy.c

@@ -346,6 +346,12 @@ typedef struct _jsproxy_gen_t {
 
 mp_vm_return_kind_t jsproxy_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t *ret_val) {
     jsproxy_gen_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (throw_value) {
+        *ret_val = throw_value;
+        return MP_VM_RETURN_EXCEPTION;
+    }
+
     switch (self->state) {
         case JSOBJ_GEN_STATE_WAITING:
             self->state = JSOBJ_GEN_STATE_COMPLETED;
@@ -468,9 +474,29 @@ static mp_obj_t jsproxy_new_gen(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
 
 /******************************************************************************/
 
+#if MICROPY_PY_ASYNCIO
+extern mp_obj_t mp_asyncio_context;
+#endif
+
 static mp_obj_t jsproxy_getiter(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
     mp_obj_jsproxy_t *self = MP_OBJ_TO_PTR(self_in);
     if (has_attr(self->ref, "then")) {
+        #if MICROPY_PY_ASYNCIO
+        // When asyncio is running and the caller here is a task, wrap the JavaScript
+        // thenable in a ThenableEvent, and get the task to wait on that event.  This
+        // decouples the task from the thenable and allows cancelling the task.
+        if (mp_asyncio_context != MP_OBJ_NULL) {
+            mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+            if (cur_task != mp_const_none) {
+                mp_obj_t thenable_event_class = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_ThenableEvent));
+                mp_obj_t thenable_event = mp_call_function_1(thenable_event_class, self_in);
+                mp_obj_t dest[2];
+                mp_load_method(thenable_event, MP_QSTR_wait, dest);
+                mp_obj_t wait_gen = mp_call_method_n_kw(0, 0, dest);
+                return mp_getiter(wait_gen, iter_buf);
+            }
+        }
+        #endif
         return jsproxy_new_gen(self_in, iter_buf);
     } else {
         return jsproxy_new_it(self_in, iter_buf);

ports/webassembly/proxy_c.c

@@ -296,10 +296,11 @@ EM_JS(void, js_then_resolve, (uint32_t * ret_value, uint32_t * resolve, uint32_t
     resolve_js(ret_value_js);
 });
 
-EM_JS(void, js_then_reject, (uint32_t * resolve, uint32_t * reject), {
+EM_JS(void, js_then_reject, (uint32_t * ret_value, uint32_t * resolve, uint32_t * reject), {
+    const ret_value_js = proxy_convert_mp_to_js_obj_jsside(ret_value);
     const resolve_js = proxy_convert_mp_to_js_obj_jsside(resolve);
     const reject_js = proxy_convert_mp_to_js_obj_jsside(reject);
-    reject_js(null);
+    reject_js(ret_value_js);
 });
 
 // *FORMAT-OFF*
@@ -307,14 +308,34 @@ EM_JS(void, js_then_continue, (int jsref, uint32_t * py_resume, uint32_t * resol
     const py_resume_js = proxy_convert_mp_to_js_obj_jsside(py_resume);
     const resolve_js = proxy_convert_mp_to_js_obj_jsside(resolve);
     const reject_js = proxy_convert_mp_to_js_obj_jsside(reject);
-    const ret = proxy_js_ref[jsref].then((x) => {py_resume_js(x, resolve_js, reject_js);}, reject_js);
+    const ret = proxy_js_ref[jsref].then(
+        (result) => {
+            // The Promise is fulfilled on the JavaScript side.  Take the result and
+            // send it to the encapsulating generator on the Python side, so it
+            // becomes the result of the "yield from" that deferred to this Promise.
+            py_resume_js(result, null, resolve_js, reject_js);
+        },
+        (reason) => {
+            // The Promise is rejected on the JavaScript side.  Take the reason and
+            // throw it into the encapsulating generator on the Python side.
+            py_resume_js(null, reason, resolve_js, reject_js);
+        },
+    );
     proxy_convert_js_to_mp_obj_jsside(ret, out);
 });
 // *FORMAT-ON*
 
-static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t value, mp_obj_t resolve, mp_obj_t reject) {
+static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t resolve, mp_obj_t reject) {
+    if (throw_value != MP_OBJ_NULL && throw_value != mp_const_none) {
+        if (send_value == mp_const_none) {
+            send_value = MP_OBJ_NULL;
+        }
+    } else {
+        throw_value = MP_OBJ_NULL;
+    }
+
     mp_obj_t ret_value;
-    mp_vm_return_kind_t ret_kind = mp_resume(self_in, value, MP_OBJ_NULL, &ret_value);
+    mp_vm_return_kind_t ret_kind = mp_resume(self_in, send_value, throw_value, &ret_value);
 
     uint32_t out_resolve[PVN];
     uint32_t out_reject[PVN];
@@ -335,17 +356,19 @@ static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t value, mp_obj_t
         uint32_t out[PVN];
         js_then_continue(ref, out_py_resume, out_resolve, out_reject, out);
         return proxy_convert_js_to_mp_obj_cside(out);
-    } else {
-        // MP_VM_RETURN_EXCEPTION;
-        js_then_reject(out_resolve, out_reject);
-        nlr_raise(ret_value);
+    } else { // ret_kind == MP_VM_RETURN_EXCEPTION;
+        // Pass the exception through as an object to reject the promise (don't raise/throw it).
+        uint32_t out_ret_value[PVN];
+        proxy_convert_mp_to_js_obj_cside(ret_value, out_ret_value);
+        js_then_reject(out_ret_value, out_resolve, out_reject);
+        return mp_const_none;
     }
 }
 
 static mp_obj_t resume_fun(size_t n_args, const mp_obj_t *args) {
-    return proxy_resume_execute(args[0], args[1], args[2], args[3]);
+    return proxy_resume_execute(args[0], args[1], args[2], args[3], args[4]);
 }
-static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(resume_obj, 4, 4, resume_fun);
+static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(resume_obj, 5, 5, resume_fun);
 
 void proxy_c_to_js_resume(uint32_t c_ref, uint32_t *args) {
     nlr_buf_t nlr;
@@ -353,7 +376,7 @@ void proxy_c_to_js_resume(uint32_t c_ref, uint32_t *args) {
         mp_obj_t obj = proxy_c_get_obj(c_ref);
         mp_obj_t resolve = proxy_convert_js_to_mp_obj_cside(args + 1 * 3);
         mp_obj_t reject = proxy_convert_js_to_mp_obj_cside(args + 2 * 3);
-        mp_obj_t ret = proxy_resume_execute(obj, mp_const_none, resolve, reject);
+        mp_obj_t ret = proxy_resume_execute(obj, mp_const_none, mp_const_none, resolve, reject);
         nlr_pop();
         return proxy_convert_mp_to_js_obj_cside(ret, args);
     } else {

ports/webassembly/variants/manifest.py

@@ -0,0 +1,24 @@
+# The asyncio package is built from the standard implementation but with the
+# core scheduler replaced with a custom scheduler that uses the JavaScript
+# runtime (with setTimeout an Promise's) to contrtol the scheduling.
+
+package(
+    "asyncio",
+    (
+        "event.py",
+        "funcs.py",
+        "lock.py",
+    ),
+    base_path="$(MPY_DIR)/extmod",
+    opt=3,
+)
+
+package(
+    "asyncio",
+    (
+        "__init__.py",
+        "core.py",
+    ),
+    base_path="$(PORT_DIR)",
+    opt=3,
+)

ports/webassembly/variants/pyscript/manifest.py

@@ -1,3 +1,5 @@
+include("$(PORT_DIR)/variants/manifest.py")
+
 require("abc")
 require("base64")
 require("collections")

py/binary.c

@@ -444,7 +444,7 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte *p
         default:
             #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
             if (mp_obj_is_exact_type(val_in, &mp_type_int)) {
-                mp_obj_int_to_bytes_impl(val_in, struct_type == '>', size, p);
+                mp_obj_int_to_bytes_impl(val_in, struct_type == '>', true, size, p);
                 return;
             }
             #endif
@@ -482,7 +482,7 @@ void mp_binary_set_val_array(char typecode, void *p, size_t index, mp_obj_t val_
             #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
             if (mp_obj_is_exact_type(val_in, &mp_type_int)) {
                 size_t size = mp_binary_get_size('@', typecode, NULL);
-                mp_obj_int_to_bytes_impl(val_in, MP_ENDIANNESS_BIG,
+                mp_obj_int_to_bytes_impl(val_in, MP_ENDIANNESS_BIG, true,
                     size, (uint8_t *)p + index * size);
                 return;
             }

py/misc.h

@@ -334,4 +334,45 @@ typedef const char *mp_rom_error_text_t;
 // For now, forward directly to MP_COMPRESSED_ROM_TEXT.
 #define MP_ERROR_TEXT(x) (mp_rom_error_text_t)MP_COMPRESSED_ROM_TEXT(x)
 
+// Macro and inline function to measure the length (in bytes) needed to hold an
+// unambiguous representation of a small (C representable) integer.
+//
+// Implemented inline as there's a lot the compiler can optimise based on the size of INT.
+#define MP_INT_REPR_LEN(INT, IS_SIGNED) mp_int_repr_len_helper(&(INT), sizeof(INT), IS_SIGNED)
+
+static inline int mp_int_repr_len_helper(void *pint, int size, bool is_signed) {
+    int i;
+    byte *b = (byte *)pint;
+    byte ext_byte = 0x00;
+    int result = size;
+    int msb_idx, step;
+
+    #if MP_ENDIANNESS_LITTLE
+    msb_idx = size - 1;
+    step = -1;
+    #else
+    msb_idx = 0;
+    step = 1;
+    #endif
+
+    if (is_signed && (b[msb_idx] & 0x80)) {
+        ext_byte = 0xFF; // Negative number
+    }
+
+    // Count down the number of most significant bytes that don't contain
+    // any significant values (i.e. equal to the extension byte).
+    for (i = msb_idx; i >= 0 && i <= size - 1; i += step) {
+        if (b[i] != ext_byte) {
+            if (is_signed && (b[i] & 0x80) != (ext_byte & 0x80)) {
+                // Add one additional byte to hold the sign bit
+                result++;
+            }
+            break;
+        }
+        result--;
+    }
+
+    return result;
+}
+
 #endif // MICROPY_INCLUDED_PY_MISC_H

py/mpconfig.h

@@ -587,6 +587,12 @@
 /*****************************************************************************/
 /* Python internal features                                                  */
 
+// Use a special long jump in nlrthumb.c, which may be necessary if nlr.o and
+// nlrthumb.o are linked far apart from each other.
+#ifndef MICROPY_NLR_THUMB_USE_LONG_JUMP
+#define MICROPY_NLR_THUMB_USE_LONG_JUMP (0)
+#endif
+
 // Whether to enable import of external modules
 // When disabled, only importing of built-in modules is supported
 // When enabled, a port must implement mp_import_stat (among other things)

py/mpz.c

@@ -1589,7 +1589,7 @@ bool mpz_as_uint_checked(const mpz_t *i, mp_uint_t *value) {
     return true;
 }
 
-void mpz_as_bytes(const mpz_t *z, bool big_endian, size_t len, byte *buf) {
+bool mpz_as_bytes(const mpz_t *z, bool big_endian, bool as_signed, size_t len, byte *buf) {
     byte *b = buf;
     if (big_endian) {
         b += len;
@@ -1598,6 +1598,8 @@ void mpz_as_bytes(const mpz_t *z, bool big_endian, size_t len, byte *buf) {
     int bits = 0;
     mpz_dbl_dig_t d = 0;
     mpz_dbl_dig_t carry = 1;
+    size_t olen = len; // bytes in output buffer
+    bool ok = true;
     for (size_t zlen = z->len; zlen > 0; --zlen) {
         bits += DIG_SIZE;
         d = (d << DIG_SIZE) | *zdig++;
@@ -1607,28 +1609,32 @@ void mpz_as_bytes(const mpz_t *z, bool big_endian, size_t len, byte *buf) {
                 val = (~val & 0xff) + carry;
                 carry = val >> 8;
             }
+
+            if (!olen) {
+                // Buffer is full, only OK if all remaining bytes are zeroes
+                ok = ok && ((byte)val == 0);
+                continue;
+            }
+
             if (big_endian) {
                 *--b = val;
-                if (b == buf) {
-                    return;
-                }
             } else {
                 *b++ = val;
-                if (b == buf + len) {
-                    return;
-                }
             }
+            olen--;
         }
     }
 
-    // fill remainder of buf with zero/sign extension of the integer
-    if (big_endian) {
-        len = b - buf;
+    if (as_signed && olen == 0 && len > 0) {
+        // If output exhausted then ensure there was enough space for the sign bit
+        byte most_sig = big_endian ? buf[0] : buf[len - 1];
+        ok = ok && (bool)(most_sig & 0x80) == (bool)z->neg;
     } else {
-        len = buf + len - b;
-        buf = b;
+        // fill remainder of buf with zero/sign extension of the integer
+        memset(big_endian ? buf : b, z->neg ? 0xff : 0x00, olen);
     }
-    memset(buf, z->neg ? 0xff : 0x00, len);
+
+    return ok;
 }
 
 #if MICROPY_PY_BUILTINS_FLOAT

py/mpz.h

@@ -93,9 +93,9 @@ typedef int8_t mpz_dbl_dig_signed_t;
 typedef struct _mpz_t {
     // Zero has neg=0, len=0.  Negative zero is not allowed.
     size_t neg : 1;
-    size_t fixed_dig : 1;
-    size_t alloc : (8 * sizeof(size_t) - 2);
-    size_t len;
+    size_t fixed_dig : 1; // flag, 'dig' buffer cannot be reallocated
+    size_t alloc : (8 * sizeof(size_t) - 2); // number of entries allocated in 'dig'
+    size_t len; // number of entries used in 'dig'
     mpz_dig_t *dig;
 } mpz_t;
 
@@ -145,7 +145,8 @@ static inline size_t mpz_max_num_bits(const mpz_t *z) {
 mp_int_t mpz_hash(const mpz_t *z);
 bool mpz_as_int_checked(const mpz_t *z, mp_int_t *value);
 bool mpz_as_uint_checked(const mpz_t *z, mp_uint_t *value);
-void mpz_as_bytes(const mpz_t *z, bool big_endian, size_t len, byte *buf);
+// Returns true if 'z' fit into 'len' bytes of 'buf' without overflowing, 'buf' is truncated otherwise.
+bool mpz_as_bytes(const mpz_t *z, bool big_endian, bool as_signed, size_t len, byte *buf);
 #if MICROPY_PY_BUILTINS_FLOAT
 mp_float_t mpz_as_float(const mpz_t *z);
 #endif

py/nlrthumb.c

@@ -38,6 +38,14 @@
 
 __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
 
+    // If you get a linker error here, indicating that a relocation doesn't
+    // fit, try the following (in that order):
+    //
+    // 1. Ensure that nlr.o nlrthumb.o are linked closely together, i.e.
+    //    there aren't too many other files between them in the linker list
+    //    (PY_CORE_O_BASENAME in py/py.mk)
+    // 2. Set -DMICROPY_NLR_THUMB_USE_LONG_JUMP=1 during the build
+    //
     __asm volatile (
         "str    r4, [r0, #12]       \n" // store r4 into nlr_buf
         "str    r5, [r0, #16]       \n" // store r5 into nlr_buf
@@ -71,7 +79,7 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
         "str    lr, [r0, #8]        \n" // store lr into nlr_buf
         #endif
 
-        #if !defined(__thumb2__)
+        #if MICROPY_NLR_THUMB_USE_LONG_JUMP
         "ldr    r1, nlr_push_tail_var \n"
         "bx     r1                  \n" // do the rest in C
         ".align 2                   \n"

py/objint.c

@@ -420,35 +420,59 @@ static mp_obj_t int_from_bytes(size_t n_args, const mp_obj_t *args) {
 static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(int_from_bytes_fun_obj, 3, 4, int_from_bytes);
 static MP_DEFINE_CONST_CLASSMETHOD_OBJ(int_from_bytes_obj, MP_ROM_PTR(&int_from_bytes_fun_obj));
 
-static mp_obj_t int_to_bytes(size_t n_args, const mp_obj_t *args) {
-    // TODO: Support signed param (assumes signed=False)
-    (void)n_args;
+static mp_obj_t int_to_bytes(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    // Only supported kwarg is 'signed'
+    enum { ARG_signed };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_signed, MP_ARG_BOOL, {.u_bool = false} },
+    };
 
-    mp_int_t len = mp_obj_get_int(args[1]);
-    if (len < 0) {
+    // Parse positional args
+    mp_obj_t self = pos_args[0];
+    mp_int_t dlen = mp_obj_get_int(pos_args[1]);
+    if (dlen < 0) {
         mp_raise_ValueError(NULL);
     }
-    bool big_endian = args[2] != MP_OBJ_NEW_QSTR(MP_QSTR_little);
+    bool big_endian = pos_args[2] != MP_OBJ_NEW_QSTR(MP_QSTR_little);
+
+    // parse kwargs
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - 3, pos_args + 3, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+    bool as_signed = args[ARG_signed].u_bool;
+
+    bool overflow;
 
     vstr_t vstr;
-    vstr_init_len(&vstr, len);
+    vstr_init_len(&vstr, dlen);
     byte *data = (byte *)vstr.buf;
-    memset(data, 0, len);
 
     #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
-    if (!mp_obj_is_small_int(args[0])) {
-        mp_obj_int_to_bytes_impl(args[0], big_endian, len, data);
+    if (!mp_obj_is_small_int(self)) {
+        overflow = !mp_obj_int_to_bytes_impl(self, big_endian, as_signed, dlen, data);
     } else
     #endif
     {
-        mp_int_t val = MP_OBJ_SMALL_INT_VALUE(args[0]);
-        size_t l = MIN((size_t)len, sizeof(val));
-        mp_binary_set_int(l, big_endian, data + (big_endian ? (len - l) : 0), val);
+        mp_int_t val = MP_OBJ_SMALL_INT_VALUE(self);
+        if (val < 0 && !as_signed) {
+            mp_raise_msg(&mp_type_OverflowError, MP_ERROR_TEXT("can't convert negative int to unsigned"));
+        }
+        int slen = MP_INT_REPR_LEN(val, as_signed);
+        memset(data, val < 0 ? 0xFF : 0x00, dlen);
+        if (slen <= dlen) {
+            mp_binary_set_int(slen, big_endian, data + (big_endian ? (dlen - slen) : 0), val);
+            overflow = false;
+        } else {
+            overflow = true;
+        }
+    }
+
+    if (overflow) {
+        mp_raise_msg(&mp_type_OverflowError, MP_ERROR_TEXT("int too big to convert"));
     }
 
     return mp_obj_new_bytes_from_vstr(&vstr);
 }
-static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(int_to_bytes_obj, 3, 4, int_to_bytes);
+static MP_DEFINE_CONST_FUN_OBJ_KW(int_to_bytes_obj, 3, int_to_bytes);
 
 static const mp_rom_map_elem_t int_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_from_bytes), MP_ROM_PTR(&int_from_bytes_obj) },

py/objint.h

@@ -55,7 +55,8 @@ char *mp_obj_int_formatted_impl(char **buf, size_t *buf_size, size_t *fmt_size,
     int base, const char *prefix, char base_char, char comma);
 mp_int_t mp_obj_int_hash(mp_obj_t self_in);
 mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf);
-void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf);
+// Returns true if 'self_in' fit into 'len' bytes of 'buf' without overflowing, 'buf' is truncated otherwise.
+bool mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, bool as_signed, size_t len, byte *buf);
 int mp_obj_int_sign(mp_obj_t self_in);
 mp_obj_t mp_obj_int_unary_op(mp_unary_op_t op, mp_obj_t o_in);
 mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in);

py/objint_longlong.c

@@ -57,10 +57,12 @@ mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf
     return mp_obj_new_int_from_ll(value);
 }
 
-void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf) {
+bool mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, bool as_signed, size_t len, byte *buf) {
     assert(mp_obj_is_exact_type(self_in, &mp_type_int));
     mp_obj_int_t *self = self_in;
     long long val = self->val;
+    size_t slen = MP_INT_REPR_LEN(val, as_signed);
+    bool ok = slen <= len;
     if (big_endian) {
         byte *b = buf + len;
         while (b > buf) {
@@ -73,6 +75,7 @@ void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byt
             val >>= 8;
         }
     }
+    return ok;
 }
 
 int mp_obj_int_sign(mp_obj_t self_in) {

py/objint_mpz.c

@@ -112,10 +112,13 @@ mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf
     return MP_OBJ_FROM_PTR(o);
 }
 
-void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf) {
+bool mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, bool as_signed, size_t len, byte *buf) {
     assert(mp_obj_is_exact_type(self_in, &mp_type_int));
     mp_obj_int_t *self = MP_OBJ_TO_PTR(self_in);
-    mpz_as_bytes(&self->mpz, big_endian, len, buf);
+    if (self->mpz.neg && !as_signed) {
+        mp_raise_msg(&mp_type_OverflowError, MP_ERROR_TEXT("can't convert negative int to unsigned"));
+    }
+    return mpz_as_bytes(&self->mpz, big_endian, as_signed, len, buf);
 }
 
 int mp_obj_int_sign(mp_obj_t self_in) {

tests/basics/int_bytes.py

@@ -1,3 +1,5 @@
+import sys
+
 print((10).to_bytes(1, "little"))
 print((111111).to_bytes(4, "little"))
 print((100).to_bytes(10, "little"))
@@ -20,3 +22,63 @@ try:
     (1).to_bytes(-1, "little")
 except ValueError:
     print("ValueError")
+
+# zero byte destination should also raise an error
+try:
+    (1).to_bytes(0, "little")
+except OverflowError:
+    print("OverflowError")
+
+# except for converting 0 to a zero-length byte array
+print((0).to_bytes(0, "big"))
+
+# byte length can fit the integer directly
+print((0xFF).to_bytes(1, "little"))
+print((0xFF).to_bytes(1, "big"))
+print((0xEFF).to_bytes(2, "little"))
+print((0xEFF).to_bytes(2, "big"))
+print((0xCDEFF).to_bytes(3, "little"))
+print((0xCDEFF).to_bytes(3, "big"))
+
+# OverFlowError if not big enough
+
+try:
+    (0x123).to_bytes(1, "big")
+except OverflowError:
+    print("OverflowError")
+
+try:
+    (0x12345).to_bytes(2, "big")
+except OverflowError:
+    print("OverflowError")
+
+try:
+    (0x1234567).to_bytes(3, "big")
+except OverflowError:
+    print("OverflowError")
+
+
+# negative representations
+
+print((-1).to_bytes(1, "little", signed=True))
+print((-1).to_bytes(3, "little", signed=True))
+print((-1).to_bytes(1, "big", signed=True))
+print((-1).to_bytes(3, "big", signed=True))
+print((-128).to_bytes(1, "big", signed=True))
+print((-32768).to_bytes(2, "big", signed=True))
+print((-(1 << 23)).to_bytes(3, "big", signed=True))
+
+try:
+    print((-129).to_bytes(1, "big", signed=True))
+except OverflowError:
+    print("OverflowError")
+
+try:
+    print((-32769).to_bytes(2, "big", signed=True))
+except OverflowError:
+    print("OverflowError")
+
+try:
+    print(((-1 << 23) - 1).to_bytes(2, "big", signed=True))
+except OverflowError:
+    print("OverflowError")

tests/basics/int_bytes_int64.py

@@ -0,0 +1,41 @@
+import sys
+
+# Depending on the port, the numbers in this test may be implemented as "small"
+# native 64 bit ints, arbitrary precision large ints, or large integers using 64-bit
+# long longs.
+
+try:
+    x = int.from_bytes(b"\x6F\xAB\xCD\x12\x34\x56\x78\xFB", "big")
+except OverflowError:
+    print("SKIP")  # Port can't represent this size of integer at all
+    raise SystemExit
+
+print(hex(x))
+b = x.to_bytes(8, "little")
+print(b)
+print(x.to_bytes(8, "big"))
+
+# padding in output
+print(x.to_bytes(20, "little"))
+print(x.to_bytes(20, "big"))
+
+# check that extra zero bytes don't change the internal int value
+print(int.from_bytes(b + bytes(10), "little") == x)
+
+# can't write to a zero-length bytes object
+try:
+    x.to_bytes(0, "little")
+except OverflowError:
+    print("OverflowError")
+
+# or one that it too short
+try:
+    x.to_bytes(7, "big")
+except OverflowError:
+    print("OverflowError")
+
+# negative representations
+
+print((-x).to_bytes(8, "little", signed=True))
+print((-x).to_bytes(20, "big", signed=True))
+print((-x).to_bytes(20, "little", signed=True))

tests/basics/int_bytes_intbig.py

@@ -1,3 +1,5 @@
+import sys
+
 print((2**64).to_bytes(9, "little"))
 print((2**64).to_bytes(9, "big"))
 
@@ -10,5 +12,40 @@ print(ib)
 print(il.to_bytes(20, "little"))
 print(ib.to_bytes(20, "big"))
 
+# check padding comes out correctly
+print(il.to_bytes(40, "little"))
+print(ib.to_bytes(40, "big"))
+
 # check that extra zero bytes don't change the internal int value
 print(int.from_bytes(b + bytes(10), "little") == int.from_bytes(b, "little"))
+
+# can't write to a zero-length bytes object
+try:
+    ib.to_bytes(0, "little")
+except OverflowError:
+    print("OverflowError")
+
+# or one that it too short
+try:
+    ib.to_bytes(18, "big")
+except OverflowError:
+    print("OverflowError")
+
+# negative representations
+
+print((-ib).to_bytes(20, "big", signed=True))
+print((ib * -ib).to_bytes(40, "big", signed=True))
+
+# case where an additional byte is needed for sign bit
+ib = (2**64) - 1
+print(ib.to_bytes(8, "little"))
+
+ib *= -1
+
+try:
+    print((ib).to_bytes(8, "little", signed=True))
+except OverflowError:
+    print("OverflowError")
+
+print((ib).to_bytes(9, "little", signed=True))
+print((ib).to_bytes(9, "big", signed=True))

tests/ports/webassembly/asyncio_create_task.mjs

@@ -0,0 +1,44 @@
+// Test asyncio.create_task(), and tasks waiting on a Promise.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+globalThis.p0 = new Promise((resolve, reject) => {
+    resolve(123);
+});
+
+globalThis.p1 = new Promise((resolve, reject) => {
+    setTimeout(() => {
+        console.log("setTimeout resolved");
+        resolve(456);
+    }, 200);
+});
+
+mp.runPython(`
+import js
+import asyncio
+
+async def task(id, promise):
+    print("task start", id)
+    print("task await", id, await promise)
+    print("task await", id, await promise)
+    print("task end", id)
+
+print("start")
+t1 = asyncio.create_task(task(1, js.p0))
+t2 = asyncio.create_task(task(2, js.p1))
+print("t1", t1.done(), t2.done())
+print("end")
+`);
+
+// Wait for p1 to fulfill so t2 can continue.
+await globalThis.p1;
+
+// Wait a little longer so t2 can complete.
+await new Promise((resolve, reject) => {
+    setTimeout(resolve, 10);
+});
+
+mp.runPython(`
+print("restart")
+print("t1", t1.done(), t2.done())
+`);

tests/ports/webassembly/asyncio_create_task.mjs.exp

@@ -0,0 +1,14 @@
+start
+t1 False False
+end
+task start 1
+task start 2
+task await 1 123
+task await 1 123
+task end 1
+setTimeout resolved
+task await 2 456
+task await 2 456
+task end 2
+restart
+t1 True True

tests/ports/webassembly/asyncio_sleep.mjs

@@ -0,0 +1,25 @@
+// Test asyncio.sleep(), both at the top level and within a task.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+await mp.runPythonAsync(`
+import time
+import asyncio
+
+print("main start")
+t0 = time.time()
+await asyncio.sleep(0.25)
+dt = time.time() - t0
+print(0.2 <= dt <= 0.3)
+
+async def task():
+    print("task start")
+    t0 = time.time()
+    await asyncio.sleep(0.25)
+    dt = time.time() - t0
+    print(0.2 <= dt <= 0.3)
+    print("task end")
+
+asyncio.create_task(task())
+print("main end")
+`);

tests/ports/webassembly/asyncio_sleep.mjs.exp

@@ -0,0 +1,6 @@
+main start
+True
+main end
+task start
+True
+task end

tests/run-tests.py

@@ -681,6 +681,17 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         elif args.target == "webassembly":
             skip_tests.add("basics/string_format_modulo.py")  # can't print nulls to stdout
             skip_tests.add("basics/string_strip.py")  # can't print nulls to stdout
+            skip_tests.add("extmod/asyncio_basic2.py")
+            skip_tests.add("extmod/asyncio_cancel_self.py")
+            skip_tests.add("extmod/asyncio_current_task.py")
+            skip_tests.add("extmod/asyncio_exception.py")
+            skip_tests.add("extmod/asyncio_gather_finished_early.py")
+            skip_tests.add("extmod/asyncio_get_event_loop.py")
+            skip_tests.add("extmod/asyncio_heaplock.py")
+            skip_tests.add("extmod/asyncio_loop_stop.py")
+            skip_tests.add("extmod/asyncio_new_event_loop.py")
+            skip_tests.add("extmod/asyncio_threadsafeflag.py")
+            skip_tests.add("extmod/asyncio_wait_for_fwd.py")
             skip_tests.add("extmod/binascii_a2b_base64.py")
             skip_tests.add("extmod/re_stack_overflow.py")
             skip_tests.add("extmod/time_res.py")