New approach

Author: hoodmane

Makefile.pre.in

@@ -3110,7 +3110,13 @@ Python/emscripten_trampoline_inner.wasm: $(srcdir)/Python/emscripten_trampoline_
 	# emcc has a path that ends with emsdk/upstream/emscripten/emcc, we're looking for emsdk/upstream/bin/clang.
 	$$(dirname $$(dirname $(CC)))/bin/clang -o $@ $< -mgc -O2 -Wl,--no-entry -Wl,--import-table -Wl,--import-memory -target wasm32-unknown-unknown -nostdlib
 
-Python/emscripten_trampoline.o: $(srcdir)/Python/emscripten_trampoline.c Python/emscripten_trampoline_inner.wasm
+Python/emscripten_trampoline_wasm.c: Python/emscripten_trampoline_inner.wasm
+	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/wasm/emscripten/prepare_wat.py $< $@ getWasmTrampolineModule
+
+Python/emscripten_trampoline_wasm.o: Python/emscripten_trampoline_wasm.c
+	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<
+
+Python/emscripten_trampoline.o: $(srcdir)/Python/emscripten_trampoline.c
 	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<
 
 JIT_DEPS = \

Python/emscripten_trampoline.c

@@ -8,72 +8,10 @@ typedef PyObject *(*TrampolineFunc)(int *success, PyCFunctionWithKeywords func,
                                     PyObject *arg1, PyObject *arg2,
                                     PyObject *arg3);
 
-EMSCRIPTEN_KEEPALIVE const char _PyEM_trampoline_inner_wasm[] = {
-#embed "Python/emscripten_trampoline_inner.wasm"
-};
-
-EMSCRIPTEN_KEEPALIVE const int _PyEM_trampoline_inner_wasm_length =
-    sizeof(trampoline_inner_wasm);
-
-// Offset of emscripten_count_args_function in _PyRuntimeState. There's a couple
-// of alternatives:
-// 1. Just make emscripten_count_args_function a real C global variable instead
-//    of a field of _PyRuntimeState. This would violate our rule against mutable
-//    globals.
-// 2. #define a preprocessor constant equal to a hard coded number and make a
-//    _Static_assert(offsetof(_PyRuntimeState, emscripten_count_args_function)
-//    == OURCONSTANT) This has the disadvantage that we have to update the hard
-//    coded constant when _PyRuntimeState changes
-//
-// So putting the mutable constant in _PyRuntime and using a immutable global to
-// record the offset so we can access it from JS is probably the best way.
-EMSCRIPTEN_KEEPALIVE const int _PyEM_EMSCRIPTEN_TRAMPOLINE_OFFSET =
-    offsetof(_PyRuntimeState, emscripten_trampoline);
-
-EM_JS(TrampolineFunc, _PyEM_GetTrampolinePtr, (void), {
-    return Module._PyEM_CountArgsPtr; // initialized below
-}
-
-function getPyEMTrampolinePtr() {
-    // Starting with iOS 18.3.1, WebKit on iOS has an issue with the garbage
-    // collector that breaks the call trampoline. See #130418 and
-    // https://bugs.webkit.org/show_bug.cgi?id=293113 for details.
-    let isIOS = globalThis.navigator && (
-        /iPad|iPhone|iPod/.test(navigator.userAgent) ||
-        // Starting with iPadOS 13, iPads might send a platform string that looks like a desktop Mac.
-        // To differentiate, we check if the platform is 'MacIntel' (common for Macs and newer iPads)
-        // AND if the device has multi-touch capabilities (navigator.maxTouchPoints > 1)
-        (navigator.platform === 'MacIntel' && typeof navigator.maxTouchPoints !== 'undefined' && navigator.maxTouchPoints > 1)
-    );
-    if (isIOS) {
-        return 0;
-    }
-    const code = HEAP8.subarray(
-        __PyEM_trampoline_inner_wasm,
-        __PyEM_trampoline_inner_wasm + HEAP32[__PyEM_trampoline_inner_wasm_length / 4]);
-    try {
-        const mod = new WebAssembly.Module(code);
-        const inst = new WebAssembly.Instance(mod, { e: { t: wasmTable } });
-        return addFunction(inst.exports.trampoline_call);
-    } catch (e) {
-        // If something goes wrong, we'll null out _PyEM_CountFuncParams and fall
-        // back to the JS trampoline.
-        return 0;
-    }
-}
-
-addOnPreRun(() => {
-    const ptr = getPyEMTrampolinePtr();
-    Module._PyEM_CountArgsPtr = ptr;
-    const offset = HEAP32[__PyEM_EMSCRIPTEN_TRAMPOLINE_OFFSET / 4];
-    HEAP32[(__PyRuntime + offset) / 4] = ptr;
-});
-);
 
 void
 _Py_EmscriptenTrampoline_Init(_PyRuntimeState *runtime)
 {
-    runtime->emscripten_trampoline = _PyEM_GetTrampolinePtr();
 }
 
 // We have to be careful to work correctly with memory snapshots. Even if we are
@@ -84,9 +22,17 @@ _Py_EmscriptenTrampoline_Init(_PyRuntimeState *runtime)
 /**
  * Backwards compatible trampoline works with all JS runtimes
  */
-EM_JS(PyObject*, _PyEM_TrampolineCall_JS, (PyCFunctionWithKeywords func, PyObject *arg1, PyObject *arg2, PyObject *arg3), {
+EM_JS(PyObject*, _PyEM_TrampolineCall_inner, (int* success, PyCFunctionWithKeywords func, PyObject *arg1, PyObject *arg2, PyObject *arg3), {
     return wasmTable.get(func)(arg1, arg2, arg3);
-});
+}
+try {
+  const trampolineModule = getWasmTrampolineModule();
+  const trampolineInstance = new WebAssembly.Instance(trampolineModule, {
+    env: { __indirect_function_table: wasmTable, memory: wasmMemory },
+  });
+  _PyEM_TrampolineCall_inner = trampolineInstance.exports.trampoline_call;
+} catch (e) {}
+);
 
 typedef PyObject* (*zero_arg)(void);
 typedef PyObject* (*one_arg)(PyObject*);
@@ -99,12 +45,8 @@ _PyEM_TrampolineCall(PyCFunctionWithKeywords func,
                      PyObject* args,
                      PyObject* kw)
 {
-    TrampolineFunc trampoline = _PyRuntime.emscripten_trampoline;
-    if (trampoline == 0) {
-        return _PyEM_TrampolineCall_JS(func, self, args, kw);
-    }
-    int success = 0;
-    PyObject *result = trampoline(&success, func, self, args, kw);
+    int success = 1;
+    PyObject *result = _PyEM_TrampolineCall_inner(&success, func, self, args, kw);
     if (!success) {
         PyErr_SetString(PyExc_SystemError, "Handler takes too many arguments");
     }

Tools/wasm/emscripten/prepare_wat.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+
+import argparse
+import sys
+from pathlib import Path
+from shutil import which
+
+JS_TEMPLATE = """
+#include "emscripten.h"
+
+EM_JS(void, {function_name}, (void), {{
+    return new WebAssembly.Module(hexStringToUTF8Array("{hex_string}"));
+}}
+function hexStringToUTF8Array(hex) {{
+  const bytes = [];
+  for (let i = 0; i < hex.length; i += 2) {{
+    bytes.push(parseInt(hex.substr(i, 2), 16));
+  }}
+  return new Uint8Array(bytes);
+}});
+"""
+
+
+def find_wasm_as():
+    emcc_path = which("emcc")
+    if not emcc_path:
+        print("Error: emcc not found in PATH", file=sys.stderr)
+        return None
+
+    wasm_as_path = Path(emcc_path).parents[1] / "bin/wasm-as"
+
+    if not wasm_as_path.exists():
+        print(f"Error: wasm-as not found at {wasm_as_path}", file=sys.stderr)
+        return None
+    return wasm_as_path
+
+
+def compile_wat(input_file, output_file, function_name):
+    # Read the compiled WASM as binary and convert to hex
+    wasm_bytes = Path(input_file).read_bytes()
+
+    hex_string = "".join(f"{byte:02x}" for byte in wasm_bytes)
+
+    # Generate JavaScript module
+    js_content = JS_TEMPLATE.format(
+        function_name=function_name, hex_string=hex_string
+    )
+    Path(output_file).write_text(js_content)
+
+    print(
+        f"Successfully compiled {input_file} and generated {output_file}"
+    )
+    return 0
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Compile WebAssembly text files using wasm-as"
+    )
+    parser.add_argument("input_file", help="Input .wat file to compile")
+    parser.add_argument("output_file", help="Output file name")
+    parser.add_argument("function_name", help="Name of the export function")
+
+    args = parser.parse_args()
+
+    return compile_wat(args.input_file, args.output_file, args.function_name)
+
+
+if __name__ == "__main__":
+    sys.exit(main())

configure

@@ -2336,7 +2336,7 @@ AS_CASE([$ac_sys_system],
     dnl Include file system support
     AS_VAR_APPEND([LINKFORSHARED], [" -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js"])
     AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV,HEAPU32,TTY"])
-    AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_TRAMPOLINE_OFFSET,_PyGILState_GetThisThreadState,__Py_DumpTraceback"])
+    AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,_PyGILState_GetThisThreadState,__Py_DumpTraceback"])
     AS_VAR_APPEND([LINKFORSHARED], [" -sSTACK_SIZE=5MB"])
     dnl Avoid bugs in JS fallback string decoding path
     AS_VAR_APPEND([LINKFORSHARED], [" -sTEXTDECODER=2"])
@@ -5139,7 +5139,7 @@ PLATFORM_OBJS=
 
 AS_CASE([$ac_sys_system],
   [Emscripten], [
-    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o Python/emscripten_syscalls.o'])
+    AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o Python/emscripten_trampoline_wasm.o Python/emscripten_syscalls.o'])
     AS_VAR_APPEND([PLATFORM_HEADERS], [' $(srcdir)/Include/internal/pycore_emscripten_signal.h $(srcdir)/Include/internal/pycore_emscripten_trampoline.h'])
   ],
 )