You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
91 lines
3.4 KiB
91 lines
3.4 KiB
1 year ago
|
# Debugging WebAssembly with Core Dumps
|
||
|
|
|
||
|
|
Wasmtime can be configured to generate [the standard Wasm core dump
|
||
|
|
format][spec] whenever guest Wasm programs trap. These core dumps can then be
|
||
|
|
consumed by external tooling (such as [`wasmgdb`][wasmgdb]) for post-mortem analysis.
|
||
|
|
|
||
|
|
This page focuses on generating and inspecting core dumps via the Wasmtime
|
||
|
|
command-line interface. For details on how to generate core dumps via the
|
||
|
|
`wasmtime` embedding API, see [Core Dumps in a Rust
|
||
|
|
Embedding](./examples-rust-core-dumps.md).
|
||
|
|
|
||
|
|
First, we need to compile some code to Wasm that can trap. Consider the
|
||
|
|
following Rust code:
|
||
|
|
|
||
|
|
```rust,no_run
|
||
|
|
// trap.rs
|
||
|
|
|
||
|
|
fn main() {
|
||
|
|
foo(42);
|
||
|
|
}
|
||
|
|
|
||
|
|
fn foo(x: u32) {
|
||
|
|
bar(x);
|
||
|
|
}
|
||
|
|
|
||
|
|
fn bar(x: u32) {
|
||
|
|
baz(x);
|
||
|
|
}
|
||
|
|
|
||
|
|
fn baz(x: u32) {
|
||
|
|
assert!(x != 42);
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
We can compile it to Wasm with the following command:
|
||
|
|
|
||
|
|
```shell-session
|
||
|
|
$ rustc --target wasm32-wasi -o ./trap.wasm ./trap.rs
|
||
|
|
```
|
||
|
|
|
||
|
|
Next, we can run it in Wasmtime and capture a core dump when it traps:
|
||
|
|
|
||
|
|
```shell-session
|
||
|
|
$ wasmtime -D coredump=./trap.coredump ./trap.wasm
|
||
|
|
thread 'main' panicked at /home/nick/scratch/trap.rs:14:5:
|
||
|
|
assertion failed: x != 42
|
||
|
|
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
|
||
|
|
Error: failed to run main module `/home/nick/scratch/trap.wasm`
|
||
|
|
|
||
|
|
Caused by:
|
||
|
|
0: core dumped at /home/nick/scratch/trap.coredump
|
||
|
|
1: failed to invoke command default
|
||
|
|
2: wasm coredump generated while executing store_name:
|
||
|
|
modules:
|
||
|
|
<module>
|
||
|
|
instances:
|
||
|
|
Instance(store=1, index=1)
|
||
|
|
memories:
|
||
|
|
Memory(store=1, index=1)
|
||
|
|
globals:
|
||
|
|
Global(store=1, index=0)
|
||
|
|
backtrace:
|
||
|
|
error while executing at wasm backtrace:
|
||
|
|
0: 0x5961 - <unknown>!__rust_start_panic
|
||
|
|
1: 0x562a - <unknown>!rust_panic
|
||
|
|
2: 0x555d - <unknown>!std::panicking::rust_panic_with_hook::h58e7d0b3d70e95b6
|
||
|
|
3: 0x485d - <unknown>!std::panicking::begin_panic_handler::{{closure}}::h1853004619879cfd
|
||
|
|
4: 0x47bd - <unknown>!std::sys_common::backtrace::__rust_end_short_backtrace::hed32bc5557405634
|
||
|
|
5: 0x4f02 - <unknown>!rust_begin_unwind
|
||
|
|
6: 0xac01 - <unknown>!core::panicking::panic_fmt::h53ca5bf48b428895
|
||
|
|
7: 0xb1c5 - <unknown>!core::panicking::panic::h62c2c2bb054da7e1
|
||
|
|
8: 0x661 - <unknown>!trap::baz::h859f39b65389c077
|
||
|
|
9: 0x616 - <unknown>!trap::bar::h7ad12f9c5b730d17
|
||
|
|
10: 0x60a - <unknown>!trap::foo::ha69c95723611c1a0
|
||
|
|
11: 0x5fe - <unknown>!trap::main::hdfcd9f2d150fc3dc
|
||
|
|
12: 0x434 - <unknown>!core::ops::function::FnOnce::call_once::h24336e950fb97d1e
|
||
|
|
13: 0x40b - <unknown>!std::sys_common::backtrace::__rust_begin_short_backtrace::h2b37384d2b1a57ff
|
||
|
|
14: 0x4ec - <unknown>!std::rt::lang_start::{{closure}}::he86eb1b6ac6d7501
|
||
|
|
15: 0x24f7 - <unknown>!std::rt::lang_start_internal::h21f6a1d8f3633b54
|
||
|
|
16: 0x497 - <unknown>!std::rt::lang_start::h7d256f21902ff32b
|
||
|
|
17: 0x687 - <unknown>!__main_void
|
||
|
|
18: 0x3e6 - <unknown>!_start
|
||
|
|
note: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information
|
||
|
|
```
|
||
|
|
|
||
|
|
You now have a core dump at `./trap.coredump` that can be consumed by external
|
||
|
|
tooling to do post-mortem analysis of the failure.
|
||
|
|
|
||
|
|
[spec]: https://github.com/WebAssembly/tool-conventions/blob/main/Coredump.md
|
||
|
|
[wasmgdb]: https://github.com/xtuc/wasm-coredump/blob/main/bin/wasmgdb/README.md
|