Build .wasm without dead code elimination? · general

I'm trying to ensure I've exhaustively covered all possible imports in a wasm program (the idea being that I build the program and use wasm-nm to list all imports) in a wrapper (using wasmtime-go) that I'm building. Does anyone know how I can disable dead code elimination or some other mechanism to get these imports? Such as querying a crate to find all extern "C" decls, or functions with a wasm link attr?

Alex Vidal (Nov 18 2020 at 02:00):

I suppose the list of imports doesn't change often, so it's not really a big deal to hand-write the list, but now I feel nerd baited

bjorn3 (Nov 19 2020 at 11:40):

Alex Vidal (Nov 19 2020 at 16:38):

Alex Vidal (Nov 19 2020 at 18:16):

Ok. Just did a minimal repro that defines three wasm imports. Compiling with rustc --target=wasm32-wasi -g ./src/main.rs -C link-dead-code=yes then running the result through wasm-nm, the result is that there's no import defined for functions that are not used in my main function

Alex Vidal (Nov 19 2020 at 18:24):

// Compile with:
// rustc --target=wasm32-unknown-unknown -g main.rs -C link-dead-code=yes
// Check with:
// wasm-nm -i main.wasm

#[link(wasm_import_module="math")]
extern "C" {
    #[link_name = "add"]
    pub fn add(a: i32, b: i32) -> i32;

    #[link_name = "mul"]
    pub fn mul(a: i32, b: i32) -> i32;
}

#[no_mangle]
extern "C" {
    pub fn top();
}

fn main() {
    println!("Hello, world!");

    // Comment this out and there's no `top` import in the wasm binary
    unsafe { top() };

    // Comment this out and there's no `add` import in the wasm binary
    call_add();
}

fn call_add() {
    unsafe { add(1, 2) };
}

// mul is never in the wasm binary because `call_mul` is never called
fn call_mul() {
    unsafe { mul(1, 2) };
}

Alex Vidal (Nov 19 2020 at 18:27):

bjorn3 (Nov 20 2020 at 20:58):

~~Executables only export the main function by default. The linker removes all functions that are not directly or indirectly used through an export.~~ Didn't notice which topic this is.

Stream: general

Topic: Build .wasm without dead code elimination?

Alex Vidal (Nov 18 2020 at 01:58):