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gh-156780: Emscripten: move promising-main setup out of libpython
The FS.createAsyncInputDevice() definition and the resolveGlobalSymbol hook that wraps main() in WebAssembly.promising() only make sense when Python is the program, but they lived in libpython, so every embedder got them. PLATFORM_OBJS goes into LIBRARY_OBJS and so into libpython. Add PLATFORM_MAIN_OBJS for platform objects that belong to the interpreter alone, and move this setup to Programs/emscripten_beforemain.c. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
1 parent 465b3b8 commit c1d3f41

5 files changed

Lines changed: 108 additions & 88 deletions

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‎Makefile.pre.in‎

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -970,9 +970,12 @@ clinic: check-clean-src
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clinic-tests: check-clean-src $(srcdir)/Lib/test/clinic.test.c
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$(PYTHON_FOR_REGEN) $(srcdir)/Tools/clinic/clinic.py -f $(srcdir)/Lib/test/clinic.test.c
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# Objects linked into the interpreter only, not into libpython.
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PLATFORM_MAIN_OBJS= @PLATFORM_MAIN_OBJS@
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# Build the interpreter
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$(BUILDPYTHON): Programs/python.o $(LINK_PYTHON_DEPS)
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$(LINKCC) $(PY_CORE_EXE_LDFLAGS) $(LINKFORSHARED) -o $@ Programs/python.o $(LINK_PYTHON_OBJS) $(LIBS) $(MODLIBS) $(SYSLIBS)
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$(BUILDPYTHON): Programs/python.o $(PLATFORM_MAIN_OBJS) $(LINK_PYTHON_DEPS)
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$(LINKCC) $(PY_CORE_EXE_LDFLAGS) $(LINKFORSHARED) -o $@ Programs/python.o $(PLATFORM_MAIN_OBJS) $(LINK_PYTHON_OBJS) $(LIBS) $(MODLIBS) $(SYSLIBS)
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platform: $(PYTHON_FOR_BUILD_DEPS) pybuilddir.txt
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$(RUNSHARED) $(PYTHON_FOR_BUILD) -c 'import sys ; from sysconfig import get_platform ; print("%s-%d.%d" % (get_platform(), *sys.version_info[:2]))' >platform

‎Programs/emscripten_beforemain.c‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,95 @@
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/* Emscripten setup for when Python is the program. Linked into the
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* interpreter only, never into libpython.
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*/
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#include <emscripten.h>
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#include <errno.h>
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// Variant of EM_JS that does C preprocessor substitution on the body
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#define EM_JS_MACROS(ret, func_name, args, body...) \
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EM_JS(ret, func_name, args, body)
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EM_JS_MACROS(void, _PyEmscripten_BeforeMain_js, (void), {
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// Define FS.createAsyncInputDevice(), This is quite similar to
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// FS.createDevice() defined here:
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// https://github.com/emscripten-core/emscripten/blob/4.0.11/src/lib/libfs.js?plain=1#L1642
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// but instead of returning one byte at a time, the input() function should
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// return a Uint8Array. This makes the handler code simpler, the
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// `createAsyncInputDevice` simpler, and everything faster.
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FS.createAsyncInputDevice = function(parent, name, input) {
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parent = typeof parent == 'string' ? parent : FS.getPath(parent);
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var path = PATH.join2(parent, name);
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var mode = FS_getMode(true, false);
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FS.createDevice.major ||= 64;
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var dev = FS.makedev(FS.createDevice.major++, 0);
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async function getDataBuf() {
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var buf;
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try {
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buf = await input();
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} catch (e) {
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throw new FS.ErrnoError(EIO);
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}
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if (!buf?.byteLength) {
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throw new FS.ErrnoError(EAGAIN);
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}
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ops._dataBuf = buf;
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}
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var ops = {
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_dataBuf: new Uint8Array(0),
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open(stream) {
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stream.seekable = false;
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},
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async readAsync(stream, buffer, offset, length, pos /* ignored */) {
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buffer = buffer.subarray(offset, offset + length);
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if (!ops._dataBuf.byteLength) {
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await getDataBuf();
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}
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var toRead = Math.min(ops._dataBuf.byteLength, buffer.byteLength);
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buffer.subarray(0, toRead).set(ops._dataBuf);
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buffer = buffer.subarray(toRead);
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ops._dataBuf = ops._dataBuf.subarray(toRead);
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if (toRead) {
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stream.node.atime = Date.now();
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}
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return toRead;
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},
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};
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FS.registerDevice(dev, ops);
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return FS.mkdev(path, mode, dev);
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};
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if (!WebAssembly.promising) {
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// No stack switching support =(
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return;
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}
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const origResolveGlobalSymbol = resolveGlobalSymbol;
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if (ENVIRONMENT_IS_NODE && !Module.onExit) {
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Module.onExit = (code) => process.exit(code);
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}
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// * wrap the main symbol with WebAssembly.promising,
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// * call exit_with_live_runtime() to prevent emscripten from shutting down
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// the runtime before the promise resolves,
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// * call onExit / process.exit ourselves, since exit_with_live_runtime()
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// prevented Emscripten from calling it normally.
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resolveGlobalSymbol = function (name, direct = false) {
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const orig = origResolveGlobalSymbol(name, direct);
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if (name === "main") {
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const main = WebAssembly.promising(orig.sym);
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orig.sym = (...args) => {
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(async () => {
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const ret = await main(...args);
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Module.onExit?.(ret);
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})();
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_emscripten_exit_with_live_runtime();
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};
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}
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return orig;
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};
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})
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EM_JS_DEPS(_PyEmscripten_BeforeMain,
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"$FS,$PATH,$FS_getMode,$resolveGlobalSymbol,"
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"emscripten_exit_with_live_runtime");
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__attribute__((constructor)) void _PyEmscripten_BeforeMain(void) {
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_PyEmscripten_BeforeMain_js();
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}

‎Python/emscripten_syscalls.c‎

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Original file line numberDiff line numberDiff line change
@@ -54,92 +54,6 @@ __attribute__((constructor)) void __syscall_init_umask(void) {
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#define EM_JS_MACROS(ret, func_name, args, body...) \
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EM_JS(ret, func_name, args, body)
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EM_JS_MACROS(void, _emscripten_promising_main_js, (void), {
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// Define FS.createAsyncInputDevice(), This is quite similar to
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// FS.createDevice() defined here:
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// https://github.com/emscripten-core/emscripten/blob/4.0.11/src/lib/libfs.js?plain=1#L1642
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// but instead of returning one byte at a time, the input() function should
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// return a Uint8Array. This makes the handler code simpler, the
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// `createAsyncInputDevice` simpler, and everything faster.
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FS.createAsyncInputDevice = function(parent, name, input) {
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parent = typeof parent == 'string' ? parent : FS.getPath(parent);
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var path = PATH.join2(parent, name);
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var mode = FS_getMode(true, false);
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FS.createDevice.major ||= 64;
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var dev = FS.makedev(FS.createDevice.major++, 0);
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async function getDataBuf() {
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var buf;
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try {
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buf = await input();
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} catch (e) {
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throw new FS.ErrnoError(EIO);
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}
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if (!buf?.byteLength) {
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throw new FS.ErrnoError(EAGAIN);
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}
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ops._dataBuf = buf;
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}
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var ops = {
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_dataBuf: new Uint8Array(0),
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open(stream) {
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stream.seekable = false;
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},
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async readAsync(stream, buffer, offset, length, pos /* ignored */) {
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buffer = buffer.subarray(offset, offset + length);
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if (!ops._dataBuf.byteLength) {
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await getDataBuf();
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}
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var toRead = Math.min(ops._dataBuf.byteLength, buffer.byteLength);
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buffer.subarray(0, toRead).set(ops._dataBuf);
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buffer = buffer.subarray(toRead);
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ops._dataBuf = ops._dataBuf.subarray(toRead);
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if (toRead) {
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stream.node.atime = Date.now();
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}
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return toRead;
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},
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};
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FS.registerDevice(dev, ops);
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return FS.mkdev(path, mode, dev);
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};
106-
if (!WebAssembly.promising) {
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// No stack switching support =(
108-
return;
109-
}
110-
const origResolveGlobalSymbol = resolveGlobalSymbol;
111-
if (ENVIRONMENT_IS_NODE && !Module.onExit) {
112-
Module.onExit = (code) => process.exit(code);
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}
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// * wrap the main symbol with WebAssembly.promising,
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// * call exit_with_live_runtime() to prevent emscripten from shutting down
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// the runtime before the promise resolves,
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// * call onExit / process.exit ourselves, since exit_with_live_runtime()
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// prevented Emscripten from calling it normally.
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resolveGlobalSymbol = function (name, direct = false) {
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const orig = origResolveGlobalSymbol(name, direct);
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if (name === "main") {
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const main = WebAssembly.promising(orig.sym);
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orig.sym = (...args) => {
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(async () => {
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const ret = await main(...args);
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Module.onExit?.(ret);
127-
})();
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_emscripten_exit_with_live_runtime();
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};
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}
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return orig;
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};
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})
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EM_JS_DEPS(_emscripten_promising_main,
136-
"$FS,$PATH,$FS_getMode,$resolveGlobalSymbol,"
137-
"emscripten_exit_with_live_runtime");
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__attribute__((constructor)) void _emscripten_promising_main(void) {
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_emscripten_promising_main_js();
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}
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#define IOVEC_T_BUF_OFFSET 0
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#define IOVEC_T_BUF_LEN_OFFSET 4

‎configure‎

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‎configure.ac‎

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Original file line numberDiff line numberDiff line change
@@ -5427,9 +5427,12 @@ fi
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dnl Platform-specific C and header files.
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PLATFORM_HEADERS=
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PLATFORM_OBJS=
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dnl Objects linked into the interpreter only, not into libpython.
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PLATFORM_MAIN_OBJS=
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AS_CASE([$ac_sys_system],
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[Emscripten], [
5435+
AS_VAR_APPEND([PLATFORM_MAIN_OBJS], [' Programs/emscripten_beforemain.o'])
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AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_signal.o Python/emscripten_trampoline.o Python/emscripten_trampoline_wasm.o'])
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AS_VAR_IF([enable_emscripten_syscalls], [yes], [
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AS_VAR_APPEND([PLATFORM_OBJS], [' Python/emscripten_syscalls.o'])
@@ -5439,6 +5442,7 @@ AS_CASE([$ac_sys_system],
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)
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AC_SUBST([PLATFORM_HEADERS])
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AC_SUBST([PLATFORM_OBJS])
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AC_SUBST([PLATFORM_MAIN_OBJS])
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54435447
# -I${DLINCLDIR} is added to the compile rule for importdl.o
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AC_SUBST([DLINCLDIR])

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