Wasm MEMORY64: RuntimeError: WebAssembly.instantiate(): table index is out of bounds

[juj]

STR:

a.c

void foo()
{
}

void js_callback(void (*callback)(void));

int main(int argc, char **argv)
{
  js_callback(foo);
}

lib_a.js

mergeInto(LibraryManager.library, {
  js_callback: function(foo) {}
});

Cmdline:

emcc -sMEMORY64 --js-library lib_a.js a.c -o a.html

Results in

during Wasm instantiation.

Attached Wast of generated a.wasm. There is a surprising (elem $0 (i64.const 2014339661825) $foo) in the code.

a.wast.txt

[sbc100]

When I build the same program I get (elem $0 (i64.const 1) $foo). Which version of emscripten and llvm are using?

$ emcc -sMEMORY64 --js-library lib_a.js test.c
$ wasm-dis a.out.wasm | grep elem
 (elem $0 (i64.const 1) $foo)

[juj]

I installed via emsdk install sdk-main-64bit, and reran that today to get latest git source to verify that I am on latest git main branch, and the issue reproduces.

[juj]

If I retry with

emsdk install latest
emsdk activate latest

then the problem does not reproduce. But with sdk-main-64bit it does.

[sbc100]

Can you try again with emsdk install tot which should even more recent?

If it still persists then we have some kind of strange difference between sdk-main-64bit (emsdk built from source) and the prebuilt binaries. My own personal build of llvm and binaryen from source also don't reproduce the issue.

Can you build with EMCC_DEBUG=1 and attach the resulting /tmp/emscripten_temp/emcc-00-base.wasm? It seems like the version of wasm-ld that you have built is doing something strange here.

[sbc100]

(I will also try to reproduce using sdk-main-64bit)

[juj]

The problem does not reproduce on emsdk install tot.

Issue seems to be some kind of uninitialized memory somewhere:

[juj]

1937030250497 = 0x1C3 0000 0001
2727304232961 = 0x27B 0000 0001
2491081031681 = 0x244 0000 0001
2843268349953 = 0x296 0000 0001

My bet goes to a sizeof(long) Windows vs Linux mismatch, which is only 32-bits even in 64-bit Visual Studio..

[juj]

The issue is already present in emcc-00-base.wasm:

C:\emsdk>emcc -sMEMORY64 --js-library lib_a.js a.c -o a.html && wasm-dis C:\Users\clb\AppData\Local\Temp\emscripten_temp\emcc-00-base.wasm | grep elem

...

 (elem $0 (i64.const 2757369004033) $foo)

[sbc100]

I was able to reproduce and have a fix in flight.

[juj]

Oh, splendid! 👍

[sbc100]

llvm/llvm-project#107780

[sbc100]

It was uninitialized stack data.. which I guess happened be a problem in the gcc build and not in the clang build perhaps?

[juj]

My build was with Visual Studio 2022 on Windows, which triggered it. In any case, emsdk install latest was a good workaround, and I was able to update juj/wasm_webgpu today to support Wasm64 with that. Thanks for the quick help!