Repository navigation
Preopen directories are not available in Wasm Reactors #79199
Description
It looks that preopen directories are not available in Wasm Reactors (i.e. when compiling crate as cdylib). Presumably, because __wasm_call_ctors and therefore __wasilibc_populate_preopens are not called.
It's also possible that I'm creating Wasm Reactors the wrong way, but I couldn't find any documentation, and this way seems to work fine, other than this particular issue.
cat Cargo.toml
[package]
name = "preopen"
version = "0.1.0"
edition = "2018"
[lib]
crate-type = ["cdylib"]Wasm Command:
cat src/main.rs
use std::fs;
use std::io::Read;
fn main() {
let mut file = fs::File::open("/etc/timezone").unwrap();
let mut contents = Vec::new();
file.read_to_end(&mut contents).unwrap();
println!("{}", std::str::from_utf8(&contents).unwrap());
}rm -rf target/; cargo build --release --target wasm32-wasi --bin preopen
wasm-objdump -x target/wasm32-wasi/release/*.wasm | awk '/Import/{p=1} /Function/{p=0} p' | cut -d"<" -f3-
Import[9]:
- wasi_snapshot_preview1.proc_exit
- wasi_snapshot_preview1.fd_close
- wasi_snapshot_preview1.fd_read
- wasi_snapshot_preview1.fd_write
- wasi_snapshot_preview1.path_open
- wasi_snapshot_preview1.environ_sizes_get
- wasi_snapshot_preview1.environ_get
- wasi_snapshot_preview1.fd_prestat_get
- wasi_snapshot_preview1.fd_prestat_dir_name
wasmtime --dir=/etc target/wasm32-wasi/release/preopen.wasm
Etc/UTC
Wasm Reactor:
cat src/lib.rs
use std::fs;
use std::io::Read;
#[no_mangle]
fn _initialize() {
let mut file = fs::File::open("/etc/timezone").unwrap();
let mut contents = Vec::new();
file.read_to_end(&mut contents).unwrap();
println!("{}", std::str::from_utf8(&contents).unwrap());
}rm -rf target/; cargo build --release --target wasm32-wasi --lib
wasm-objdump -x target/wasm32-wasi/release/*.wasm | awk '/Import/{p=1} /Function/{p=0} p' | cut -d"<" -f3-
Import[7]:
- wasi_snapshot_preview1.fd_close
- wasi_snapshot_preview1.fd_read
- wasi_snapshot_preview1.fd_write
- wasi_snapshot_preview1.path_open
- wasi_snapshot_preview1.environ_sizes_get
- wasi_snapshot_preview1.proc_exit
- wasi_snapshot_preview1.environ_get
(notice missing wasi_snapshot_preview1.fd_prestat_get and wasi_snapshot_preview1.fd_prestat_dir_name imports)
wasmtime --dir=/etc target/wasm32-wasi/release/preopen.wasm
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: Custom { kind: Other, error: "failed to find a pre-opened file descriptor through which \"/etc/timezone\" could be opened" }', src/lib.rs:6:52
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error: failed to run main module `target/wasm32-wasi/release/preopen.wasm`
Caused by:
0: failed to instantiate "target/wasm32-wasi/release/preopen.wasm"
1: calling the Reactor initialization function
2: wasm trap: unreachable
wasm backtrace:
0: 0x8199 - <unknown>!__rust_start_panic
1: 0x7fab - <unknown>!rust_panic
2: 0x7c21 - <unknown>!std::panicking::rust_panic_with_hook::h0b71fe06740b049c
3: 0x72ee - <unknown>!std::panicking::begin_panic_handler::{{closure}}::h5b60dc2bfcb2c446
4: 0x722f - <unknown>!std::sys_common::backtrace::__rust_end_short_backtrace::h3244caab767433b0
5: 0x7a27 - <unknown>!rust_begin_unwind
6: 0xd1e5 - <unknown>!core::panicking::panic_fmt::ha4cbfe39ae9ea3c9
7: 0xdd63 - <unknown>!core::option::expect_none_failed::h152d592dba3b4951
8: 0x573 - <unknown>!_initialize
rustc --version --verbose
rustc 1.50.0-nightly (825637983 2020-11-18)
binary: rustc
commit-hash: 8256379832b5ecb7f71e8c5e2018446482223c12
commit-date: 2020-11-18
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly
Activity
pengsrc commentedon Dec 11, 2020
Got the same error here.
Rollup merge of rust-lang#79997 - coolreader18:wasm-reactor, r=alexcr…