Linker errors with stdweb.

[kevincox]

I'm trying to set up cargo-fuzz for a web-based project. For production we deploy to wasm (using cargo-web) however we run are tests natively as well so the project runs just fine on x86. In fact we have AFL set up with a regular binary which works for fuzzing, however I figured I would try out libfuzzer as well.

When compiling with cargo fuzz run we get many linker errors such as in function <alloc::vec::IntoIter<T> as core::ops::drop::Drop>::drop': main.1d8o2qxf-cgu.0:(.text._ZN71_$LT$alloc..vec..IntoIter$LT$T$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h62c937e915a268ffE+0x316): undefined reference to emscripten_asm_const_int. Indicating that for some reason LLVM functions are being used even though they shouldn't be.

I have ensured that we are compiling with LTO however this doesn't seem to help.

Working bin target:

fn main() {
	onuw::fuzz::fuzz("binary", std::io::stdin().lock());
}

Failing cargo-fuzz target:

#![no_main]
use libfuzzer_sys::fuzz_target;

libfuzzer_sys::fuzz_target!(|data: &[u8]| {
	onuw::fuzz::fuzz("binary", data);
});

It would be really nice if this worked.

[kevincox]

It appears that the stdweb crate used by cargo-web is basically incompatible with cargo-fuzz.

Simply referencing a function such as console!(log, "Anything") is enough to break the build.

fuzz-web.tar.gz