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// Copyright 2022 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//! A panic handler for better crash signatures for rust apps.
use std::fmt::Write;
use std::fs::File;
use std::io;
use std::mem;
use std::panic;
use std::process::abort;
use crate::SafeDescriptor;
use crate::SharedMemory;
// TODO(b/309651697): This was written to be compatible with existing PanicInfo formatting, but it
// should probably be made more stable.
fn format_panic_info(panic_info: &panic::PanicInfo<'_>) -> String {
// 128 is arbitrary, but should be enough to cover most cases.
let mut result = String::with_capacity(128);
result += "panicked at '";
result += panic_info
.downcast_ref::<&'static str>()
result += ", ";
// At the time of writing, `PanicInfo::location()` cannot return `None`.
match panic_info.location() {
Some(location) => {
let _ = write!(&mut result, "{}", location);
None => {
result += "no location info";
/// Inserts a panic handler that writes the panic info to a memfd called
/// "RUST_PANIC_SIG" before calling the original panic handler. This
/// makes it possible for external crash handlers to recover the panic info.
pub fn install_memfd_handler() {
let hook = panic::take_hook();
panic::set_hook(Box::new(move |p| {
let panic_info = format_panic_info(p);
let panic_bytes = panic_info.as_bytes();
// On failure, ignore the error and call the original handler.
if let Ok(panic_memfd) = SharedMemory::new(PANIC_MEMFD_NAME, panic_bytes.len() as u64) {
let mut panic_memfd = File::from(SafeDescriptor::from(panic_memfd));
io::Write::write_all(&mut panic_memfd, panic_bytes).ok();
// Intentionally leak panic_memfd so it is picked up by the crash handler.
// If this is a multithreaded program, a panic in one thread will not kill the whole
// process. Abort so the entire process gets killed and produces a core dump.