Dynamic linking: emscripten_get_now.sig is undefined

[hoodmane]

I am running into the following issue when building the cryptography PyO3 module:

RuntimeError: abort(Assertion failed: bad export type for `_emscripten_get_now`: undefined). Build with -s ASSERTIONS=1 for more info.
    at abort (http://127.0.0.1:32797/pyodide.asm.js:10:234384)
    at assert (http://127.0.0.1:32797/pyodide.asm.js:10:224838)
    at Object.reportUndefinedSymbols (http://127.0.0.1:32797/pyodide.asm.js:10:319214)

wasm-objdump shows that we are trying to import emscripten_get_now:

$ cryptography_rust.so -j Import -x | grep emscripten_get_now
 - func[62] sig=57 <env._emscripten_get_now> <- env._emscripten_get_now
 - global[57] i32 mutable=1 <- GOT.func._emscripten_get_now

but resolveGlobalSymbol("emscripten_get_now") returns undefined and so we get an error from reportUndefinedSymbols.

Adding the lines

Module["__emscripten_get_now"] = Module["_emscripten_get_now"];
Module["__emscripten_get_now"].sig = "d";

fixes the problem.

cf pyodide/pyodide#2378

[sbc100]

It looks like that side module is trying to import this symbol with an _ prefix. But that symbols doesn't start with and underscore:

emscripten/system/include/emscripten/emscripten.h

Line 86 in 922cf56

double emscripten_get_now(void);

Do you know where the _emscripten_get_now symbol is coming from? Which object contains that reference? In the native object files non of the symbols should have an _ prefix.

[sbc100]

(perhaps somewhere in the source code that symbols is incorrectly being forward declared with a leading underscore?)

[hoodmane]

The problem is here:
https://github.com/sebcrozet/instant/blob/master/src/wasm.rs

[hoodmane]

Even if I fix that, there is still an error because there is a GOT entry for emscripten_get_now but Module.resolveGlobalSymbol("emscripten_get_now").sig is undefined:

TypeError: Cannot read properties of undefined (reading 'slice')
    at convertJsFunctionToWasm (pyodide.asm.js:9356:24)
    at addFunctionWasm (pyodide.asm.js:9480:23)
    at Object.reportUndefinedSymbols (pyodide.asm.js:14952:34)

[sbc100]

That sounds like a real bug. Feel free to send a PR adding a __sig attribute to emscripten_get_now (if you don't have time someone else will get it).

[sbc100]

Can you re-title this bug (or open a new one)?