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gh-128627: Emscripten: Fix address calculation for wasm-gc trampoline #128782

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merged 3 commits into from
Jan 23, 2025
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gh-128627: Emscripten: Fix address calculation for wasm-gc trampoline #128782

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gh-128627: Emscripten: Fix address calculation for wasm-gc trampoline
hoodmane Jan 13, 2025
55260c3
Add comment about branch of wabt that supports ref.test
hoodmane Jan 13, 2025
932f896
Add _PyRuntime and _PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET to exports
hoodmane Jan 13, 2025
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16 changes: 7 additions & 9 deletions Python/emscripten_trampoline.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,11 +26,9 @@ EM_JS(CountArgsFunc, _PyEM_GetCountArgsPtr, (), {
// Binary module for the checks. It has to be done in web assembly because
// clang/llvm have no support yet for the reference types yet. In fact, the wasm
// binary toolkit doesn't yet support the ref.test instruction either. To
// convert the following module to the binary, my approach is to find and
// replace "ref.test $type" -> "drop i32.const n" on the source text. This
// results in the bytes "0x1a, 0x41, n" where we need the bytes "0xfb, 0x14, n"
// so doing a find and replace on the output from "0x1a, 0x41" -> "0xfb, 0x14"
// gets us the output we need.
// convert the following textual wasm to a binary, you can build wabt from this
// branch: https://github.com/WebAssembly/wabt/pull/2529 and then use that
// wat2wasm binary.
//
// (module
// (type $type0 (func (param) (result i32)))
Expand Down Expand Up @@ -154,15 +152,15 @@ addOnPreRun(() => {
let ptr = 0;
try {
const mod = new WebAssembly.Module(code);
const inst = new WebAssembly.Instance(mod, {e: {t: wasmTable}});
const inst = new WebAssembly.Instance(mod, { e: { t: wasmTable } });
ptr = addFunction(inst.exports.f);
} catch(e) {
} catch (e) {
// If something goes wrong, we'll null out _PyEM_CountFuncParams and fall
// back to the JS trampoline.
}
Module._PyEM_CountArgsPtr = ptr;
const offset = HEAP32[__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET/4];
HEAP32[__PyRuntime/4 + offset] = ptr;
const offset = HEAP32[__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET / 4];
HEAP32[(__PyRuntime + offset) / 4] = ptr;
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This line is the only change: base/4 + offset ==> (base + offset)/4.

});
);

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2 changes: 1 addition & 1 deletion configure
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2 changes: 1 addition & 1 deletion configure.ac
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Expand Up @@ -2369,7 +2369,7 @@ 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"])
AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version"])
AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET"])
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This doesn't appear to be related to code formatting or the correction to memory address calculation - is it intentional?

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Yeah, __PyRuntime and __PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET are accessed from JS and that won't work without this.

AS_VAR_APPEND([LINKFORSHARED], [" -sSTACK_SIZE=5MB"])

AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
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