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27 lines
1.2 KiB
27 lines
1.2 KiB
5 years ago
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# Logging in the `wasmtime` CLI
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Wasmtime's libraries use Rust's [`log`] crate to log diagnostic
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information, and the `wasmtime` CLI executable uses [`pretty_env_logger`]
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by default for logging this information to the console.
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Basic logging is controlled by the `RUST_LOG` environment variable. For example,
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To enable logging of WASI system calls, similar to the `strace` command on Linux,
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set `RUST_LOG=wasi_common=trace`.
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```sh
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$ RUST_LOG=wasi_common=trace wasmtime hello.wasm
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[...]
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TRACE wasi_common::hostcalls_impl::fs > fd_write(fd=1, iovs_ptr=0x10408, iovs_len=1, nwritten=0x10404)
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Hello, world!
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TRACE wasi_common::hostcalls_impl::fs > | *nwritten=14
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TRACE wasi_common::hostcalls > | errno=ESUCCESS (No error occurred. System call completed successfully.)
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TRACE wasi_common::hostcalls_impl::misc > proc_exit(rval=1)
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```
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Wasmtime can also redirect the log messages into log files, with the
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`--log-to-files` option. It creates one file per thread within Wasmtime, with
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the files named `wasmtime.dbg.*`.
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[`log`]: https://crates.io/crates/log
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[`pretty_env_logger`]: https://crates.io/crates/pretty_env_logger
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