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Cargo.toml
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@ -3,7 +3,11 @@ name = "panic-write"
version = "0.1.0"
authors = ["Robin Appelman <robin@icewind.nl>"]
edition = "2018"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
description = "Write panic messages to a core::fmt::Write and then halt"
license = "MIT OR Apache-2.0"
categories = ["embedded", "no-std"]
keywords = ["panic-handler"]
readme = "README.md"
documentation = "https://docs.rs/panic-write"
[dependencies]

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LICENSE-APACHE Normal file
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@ -0,0 +1,201 @@
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LICENSE-MIT Normal file
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Copyright 2019-2020 Robin Appelman
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32
README.md Normal file
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@ -0,0 +1,32 @@
# panic-write
Write panic messages to a `core::fmt::Write` and then halt, intended for bare metal development.
## Usage
```
#![no_std]
use panic_write::PanicHandler;
use core::fmt::Write;
let serial = ...;
// assign the handler to an unused variable to stop it from getting dropped
let _panic_handler = PanicHandler::new(serial);
```
The panic handler is un-registered when dropped, if no active panic handler is registered and the app panics, it will halt without printing anything.
Additionally, the panic handler can also be used in place of the original `Write` throughout the rest of the app.
```
#![no_std]
use panic_write::PanicHandler;
use core::fmt::Write;
let serial = ...;
let mut serial = PanicHandler::new(serial);
writeln!(&mut serial, "starting app");
```

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src/lib.rs
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@ -1,7 +1,98 @@
#[cfg(test)]
mod tests {
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
#![no_std]
use core::fmt::Write;
use core::marker::PhantomPinned;
use core::mem::{transmute, MaybeUninit};
use core::ops::DerefMut;
use core::panic::PanicInfo;
use core::pin::Pin;
use core::ptr::null_mut;
static mut PANIC_HANDLER_GETTER: Option<unsafe fn(handler: *mut (), info: &PanicInfo)> = None;
static mut PANIC_HANDLER: *mut () = null_mut();
/// Use monomorphization to "save" the type parameter of the static pointer
unsafe fn trampoline<W: Write>(ptr: *mut (), info: &PanicInfo) {
let handler: &mut PanicHandler<W> = transmute(ptr);
let _ = write!(handler.deref_mut(), "{}", info);
}
pub struct PanicHandler<W: Write> {
writer: MaybeUninit<W>,
_pin: PhantomPinned,
}
impl<W: Write> PanicHandler<W> {
/// Create a panic handler from a `core::fmt::Write`
///
/// Note that the returned handler is detached when it goes out of scope so in most cases it's
/// desired to keep the handler in scope for the full duration of the program.
///
/// Additionally, the panic handler implements `Deref` for the provided `Write` and can be used
/// in place of the original `Write` throughout the app.
#[must_use = "the panic handler must be kept in scope"]
pub fn new(writer: W) -> Pin<Self> {
let handler = unsafe {
Pin::new_unchecked(PanicHandler {
writer: MaybeUninit::new(writer),
_pin: PhantomPinned,
})
};
unsafe {
PANIC_HANDLER_GETTER = Some(trampoline::<W>);
PANIC_HANDLER = transmute(&handler);
}
handler
}
/// Detach this panic handler and return the underlying writer
pub fn detach(handler: Pin<Self>) -> W {
unsafe {
PANIC_HANDLER_GETTER = None;
PANIC_HANDLER = null_mut();
// unpin is safe because the pointer to the handler is removed
let mut handler = Pin::into_inner_unchecked(handler);
let writer = core::mem::replace(&mut handler.writer, MaybeUninit::uninit());
// safe because self.writer is only uninit during drop
writer.assume_init()
}
}
}
impl<W: Write> Drop for PanicHandler<W> {
fn drop(&mut self) {
unsafe {
PANIC_HANDLER_GETTER = None;
PANIC_HANDLER = null_mut();
}
}
}
impl<W: Write> core::ops::Deref for PanicHandler<W> {
type Target = W;
fn deref(&self) -> &Self::Target {
// safe because self.writer is only uninit during drop
unsafe { &*self.writer.as_ptr() }
}
}
impl<W: Write> core::ops::DerefMut for PanicHandler<W> {
fn deref_mut(&mut self) -> &mut Self::Target {
// safe because self.writer is only uninit during drop
unsafe { &mut *self.writer.as_mut_ptr() }
}
}
#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
unsafe {
if let Some(trampoline) = PANIC_HANDLER_GETTER {
trampoline(PANIC_HANDLER, info);
}
}
loop {}
}