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gh-161782: Emscripten: support builds without reference types #161783

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gh-161782: Emscripten: support builds without reference types #161783

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Emscripten/2026-11-10-14-09-19.gh-issue-161782.SkRhn8.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix compilation of Emscripten syscall wrappers when WebAssembly reference
types are disabled using ``-mno-reference-types``. Synchronous system calls
remain available without JSPI stack switching.
10 changes: 10 additions & 0 deletions Python/emscripten_syscalls.c
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Expand Up @@ -54,6 +54,7 @@ __attribute__((constructor)) void __syscall_init_umask(void) {
#define EM_JS_MACROS(ret, func_name, args, body...) \
EM_JS(ret, func_name, args, body)

#ifdef __wasm_reference_types__
EM_JS(void, _PyEmscripten_BeforeMain_js, (void), {
if (!WebAssembly.promising) {
// No stack switching support =(
Expand All @@ -80,6 +81,12 @@ EM_JS(void, _PyEmscripten_BeforeMain_js, (void), {
})

EM_JS_DEPS(_PyEmscripten_BeforeMain, "emscripten_exit_with_live_runtime");
#else
void
_PyEmscripten_BeforeMain_js(void)
{
}
#endif

// Define FS.createAsyncInputDevice(), This is quite similar to
// FS.createDevice() defined here:
Expand Down Expand Up @@ -138,6 +145,8 @@ __attribute__((constructor)) void __fs_init_async_input_device(void) {
__fs_init_async_input_device_js();
}

// JSPI syscall wrappers require reference types even when unused at runtime.
#ifdef __wasm_reference_types__
#define IOVEC_T_BUF_OFFSET 0
#define IOVEC_T_BUF_LEN_OFFSET 4
#define IOVEC_T_SIZE 8
Expand Down Expand Up @@ -304,6 +313,7 @@ int __syscall_poll(intptr_t fds, int nfds, int timeout) {
}
return __block_for_int(p);
}
#endif // __wasm_reference_types__

#include <sys/ioctl.h>

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