python
diff --git a/‎Programs/emscripten_beforemain.c‎
Lines changed: 41 additions & 20 deletions b/‎Programs/emscripten_beforemain.c‎
Lines changed: 41 additions & 20 deletions
diff --git a/‎Python/emscripten_syscalls.c‎
Lines changed: 13 additions & 0 deletions b/‎Python/emscripten_syscalls.c‎
Lines changed: 13 additions & 0 deletions
diff --git a/‎Python/emscripten_trampoline.c‎
Lines changed: 5 additions & 1 deletion b/‎Python/emscripten_trampoline.c‎
Lines changed: 5 additions & 1 deletion
diff --git a/‎configure‎
Lines changed: 9 additions & 1 deletion b/‎configure‎
Lines changed: 9 additions & 1 deletion
diff --git a/‎configure.ac‎
Lines changed: 6 additions & 1 deletion b/‎configure.ac‎
Lines changed: 6 additions & 1 deletion
diff --git a/‎pyconfig.h.in‎
Lines changed: 3 additions & 0 deletions b/‎pyconfig.h.in‎
Lines changed: 3 additions & 0 deletions
@@ -2,12 +2,31 @@
  * interpreter only, never into libpython.
  */
 
+#include "pyconfig.h"
+
 #include <emscripten.h>
 #include <errno.h>
 
 // Variant of EM_JS that does C preprocessor substitution on the body
 #define EM_JS_MACROS(ret, func_name, args, body...)                            \
   EM_JS(ret, func_name, args, body)
+
+#ifdef Py_EMSCRIPTEN_DYNAMIC_LINKING
+#define _Py_EM_WRAP_MAIN                                                       \
+    const origResolveGlobalSymbol = resolveGlobalSymbol;                       \
+    resolveGlobalSymbol = function (name, direct = false) {                    \
+        const orig = origResolveGlobalSymbol(name, direct);                    \
+        if (name === "main") {                                                 \
+            orig.sym = _PyEM_promising(orig.sym);                              \
+        }                                                                      \
+        return orig;                                                           \
+    };
+#else
+// wasmExports["main"], not _main: promising() rejects the export wrapper.
+#define _Py_EM_WRAP_MAIN                                                       \
+    _main = _PyEM_promising(wasmExports["main"]);
+#endif
+
 EM_JS_MACROS(void, _PyEmscripten_BeforeMain_js, (void), {
     // Define FS.createAsyncInputDevice(), This is quite similar to
     // FS.createDevice() defined here:
@@ -61,34 +80,36 @@ EM_JS_MACROS(void, _PyEmscripten_BeforeMain_js, (void), {
         // No stack switching support =(
         return;
     }
-    const origResolveGlobalSymbol = resolveGlobalSymbol;
     if (ENVIRONMENT_IS_NODE && !Module.onExit) {
         Module.onExit = (code) => process.exit(code);
     }
-    // * wrap the main symbol with WebAssembly.promising,
-    // * call exit_with_live_runtime() to prevent emscripten from shutting down
-    //   the runtime before the promise resolves,
-    // * call onExit / process.exit ourselves, since exit_with_live_runtime()
-    //   prevented Emscripten from calling it normally.
-    resolveGlobalSymbol = function (name, direct = false) {
-        const orig = origResolveGlobalSymbol(name, direct);
-        if (name === "main") {
-            const main = WebAssembly.promising(orig.sym);
-            orig.sym = (...args) => {
-                (async () => {
-                    const ret = await main(...args);
-                    Module.onExit?.(ret);
-                })();
-                _emscripten_exit_with_live_runtime();
-            };
-        }
-        return orig;
+    _Py_EM_WRAP_MAIN
+}
+// * wrap the entry point with WebAssembly.promising,
+// * call exit_with_live_runtime() to prevent emscripten from shutting down
+//   the runtime before the promise resolves,
+// * call onExit / process.exit ourselves, since exit_with_live_runtime()
+//   prevented Emscripten from calling it normally.
+function _PyEM_promising(orig) {
+    const main = WebAssembly.promising(orig);
+    return (...args) => {
+        (async () => {
+            const ret = await main(...args);
+            Module.onExit?.(ret);
+        })();
+        _emscripten_exit_with_live_runtime();
     };
-})
+}
+)
 
+#ifdef Py_EMSCRIPTEN_DYNAMIC_LINKING
 EM_JS_DEPS(_PyEmscripten_BeforeMain,
            "$FS,$PATH,$FS_getMode,$resolveGlobalSymbol,"
            "emscripten_exit_with_live_runtime");
+#else
+EM_JS_DEPS(_PyEmscripten_BeforeMain,
+           "$FS,$PATH,$FS_getMode,emscripten_exit_with_live_runtime");
+#endif
 
 __attribute__((constructor)) void _PyEmscripten_BeforeMain(void) {
     _PyEmscripten_BeforeMain_js();
 
@@ -161,6 +161,19 @@ EM_JS_MACROS(__externref_t, __maybe_poll_async, (intptr_t fds, int nfds, int tim
     if (!WebAssembly.promising) {
         return null;
     }
+    // Suspending at all requires a promising stack, so do not if there is
+    // nothing to await.
+    var async = false;
+    for (var i = 0; i < nfds; i++) {
+        var s = FS.getStream(HEAP32[(fds + POLLFD_SIZE * i + POLLFD_FD)/4]);
+        if (s && s.stream_ops.pollAsync) {
+            async = true;
+            break;
+        }
+    }
+    if (!async) {
+        return null;
+    }
     return (async function() {
         try {
             var nonzero = 0;
 
@@ -47,6 +47,10 @@ typedef PyObject* (*TrampolineFunc)(int* success,
                                     PyObject* args,
                                     PyObject* kw);
 
+// The JS glue only binds _PyRuntime if it is exported, which an embedder
+// linking libpython does not do.
+EMSCRIPTEN_KEEPALIVE _PyRuntimeState *const _PyEM_runtime = &_PyRuntime;
+
 /**
  * Backwards compatible trampoline works with all JS runtimes
  */
@@ -90,7 +94,7 @@ function getPyEMTrampolinePtr() {
 addOnPreRun(function setEmscriptenTrampoline() {
     const ptr = getPyEMTrampolinePtr();
     const offset = HEAP32[__PyEM_EMSCRIPTEN_TRAMPOLINE_OFFSET / 4];
-    HEAP32[(__PyRuntime + offset) / 4] = ptr;
+    HEAP32[(HEAPU32[__PyEM_runtime / 4] + offset) / 4] = ptr;
 });
 );
 
 
@@ -2446,6 +2446,11 @@ AS_CASE([$ac_sys_system],
 
     AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
       AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE"])
+      AC_DEFINE([Py_EMSCRIPTEN_DYNAMIC_LINKING], [1],
+                [Define if the Emscripten build is linked with -sMAIN_MODULE.])
+    ], [
+      dnl Implied by MAIN_MODULE; the call trampoline's addFunction() needs it.
+      AS_VAR_APPEND([LINKFORSHARED], [" -sALLOW_TABLE_GROWTH"])
     ])
 
     AS_VAR_IF([enable_wasm_pthreads], [yes], [
@@ -5406,8 +5411,8 @@ PLATFORM_MAIN_OBJS=
 
 AS_CASE([$ac_sys_system],
   [Emscripten], [
-    AS_VAR_APPEND([PLATFORM_MAIN_OBJS], [' Programs/emscripten_beforemain.o'])
     AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o Python/emscripten_trampoline_wasm.o'])
+    AS_VAR_APPEND([PLATFORM_MAIN_OBJS], [' Programs/emscripten_beforemain.o'])
     AS_VAR_IF([enable_emscripten_syscalls], [yes], [
       AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_syscalls.o'])
     ])
 
@@ -1898,6 +1898,9 @@
 /* Define if you want to build an interpreter with many run-time checks. */
 #undef Py_DEBUG
 
+/* Define if the Emscripten build is linked with -sMAIN_MODULE. */
+#undef Py_EMSCRIPTEN_DYNAMIC_LINKING
+
 /* Defined if Python is built as a shared library. */
 #undef Py_ENABLE_SHARED