Unexpected exit code with std::process::ExitCode when compiling wasm32-wasip1

[peterschwarz]

When compiled as a standard binary on the host system, the exit codes are returned as expected. When compiled with wasm32-wasip1, the use of ExitCode results in the exit code of 1, regardless of the value provided to ExitCode::from.

The following are the minimal examples used while reproducing the bug:

/// This example main uses [`std::process::exit`], which works as expected when compiled against the
/// `wasm32-wasip1` target.
fn main() {
    println!("Exiting with code 10");
    std::process::exit(10);
}

The above example produces the expected error code of 10 when compiling for the the host system and wasm32-wasi (executed with wasmtime 24.0.0).

/// This example main uses [`std::process::ExitCode`], which does not work as expected when
/// compiled using the `wasm32-wasip1` target.
use std::process::ExitCode;

fn main() -> ExitCode {
    println!("Exiting with code 11`");
    ExitCode::from(11)
}

The above example produces the exit code 11 when compiled for the host system but returns exit code 1 when compiled with wasm32-wasi (again run in wasmtime 24.0.0).

Investigative Details

Looking at the resulting WASM (decompiled to WAT) we see the main function returns a i32.const 1 (here compiled with #[no_mangle] for ease of searching):

(func $main (type 0) (result i32)
  (local i32)
  global.get $__stack_pointer
  ;; ...
  global.set $__stack_pointer
  i32.const 1)

For source code of the reproducer, see: peterschwarz/wasm32-wasip-exit-code-reproducer

Meta

Tested against stable, beta and nightly.

rustc --version --verbose:

rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7

rustc +beta --version --verbose

rustc 1.82.0-beta.3 (4976ae480 2024-09-09)
binary: rustc
commit-hash: 4976ae480e2b29cc46f44e1b9914469cc384fcc9
commit-date: 2024-09-09
host: x86_64-unknown-linux-gnu
release: 1.82.0-beta.3
LLVM version: 19.1.0

rustc +nightly --version --verbose

rustc 1.83.0-nightly (28e8f01c2 2024-09-17)
binary: rustc
commit-hash: 28e8f01c2a2f33fb4214925a704e3223b372cad5
commit-date: 2024-09-17
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0

[workingjubilee]

It seems that we just call libc::exit?

rust/library/std/src/sys/pal/wasi/os.rs

Lines 274 to 276 in f79a912

	pub fn exit(code: i32) -> ! {
	unsafe { libc::exit(code) }
	}

[ShE3py]

Minimized:

#![crate_type = "cdylib"]

use std::process::ExitCode;

#[no_mangle]
pub fn fun() -> ExitCode {
    ExitCode::from(2)
}

(func $fun (;0;) (type 0) (result i32)
  i32.const 1
)

rust/library/std/src/sys/pal/unsupported/process.rs

Lines 271 to 278 in eeb90cd

	impl From<u8> for ExitCode {
	fn from(code: u8) -> Self {
	match code {
	0 => Self::SUCCESS,
	1..=255 => Self::FAILURE,
	}
	}
	}

@rustbot claim
@rustbot label -O-wasi

[workingjubilee]

Oh, "cool"!

[peterschwarz]

@ShE3py that is so concise! Thanks.

I’d also be very interested in getting some insight on where to look in the code base for this sort of thing.

[ShE3py]

I’d also be very interested in getting some insight on where to look in the code base for this sort of thing.

I'm kinda just abusing my IDE (RustRover)’s Go To Declaration & Find Usages shortcuts, you may need to tell yours to use the wasm target for name resolution/code indexing instead of your OS’ default one.