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use core::{intrinsics, any::Any, mem::ManuallyDrop};
use super::Box;
// extern crate unwind;
// use unwind as uw;
extern crate panic_unwind;
use panic_unwind::__rust_panic_cleanup;
pub mod personality;
// #[lang ="eh_personality"]
// pub extern "C" fn eh_personality(){super::println!("eh_personality called");}
/// a function just make linker happy.
#[cfg_attr(not(test), no_mangle)]
pub extern "C" fn __rust_foreign_exception()->!{super::println!("__rust_foreign_exception called, abort.");core::intrinsics::abort()}
/// a function just make linker happy.
#[cfg_attr(not(test), no_mangle)]
pub extern "C" fn __rust_drop_panic()->!{super::println!("__rust_drop_panic called, abort.");core::intrinsics::abort()}
/// almost the same impl in std crate.
pub unsafe fn catch_unwind<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
union Data<F, R> {
f: ManuallyDrop<F>,
r: ManuallyDrop<R>,
p: ManuallyDrop<Box<dyn Any + Send>>,
}
// We do some sketchy operations with ownership here for the sake of
// performance. We can only pass pointers down to `do_call` (can't pass
// objects by value), so we do all the ownership tracking here manually
// using a union.
//
// We go through a transition where:
//
// * First, we set the data field `f` to be the argumentless closure that we're going to call.
// * When we make the function call, the `do_call` function below, we take
// ownership of the function pointer. At this point the `data` union is
// entirely uninitialized.
// * If the closure successfully returns, we write the return value into the
// data's return slot (field `r`).
// * If the closure panics (`do_catch` below), we write the panic payload into field `p`.
// * Finally, when we come back out of the `try` intrinsic we're
// in one of two states:
//
// 1. The closure didn't panic, in which case the return value was
// filled in. We move it out of `data.r` and return it.
// 2. The closure panicked, in which case the panic payload was
// filled in. We move it out of `data.p` and return it.
//
// Once we stack all that together we should have the "most efficient'
// method of calling a catch panic whilst juggling ownership.
let mut data = Data { f: ManuallyDrop::new(f) };
let data_ptr = core::ptr::addr_of_mut!(data) as *mut u8;
// SAFETY:
//
// Access to the union's fields: this is `std` and we know that the `r#try`
// intrinsic fills in the `r` or `p` union field based on its return value.
//
// The call to `intrinsics::catch_unwind` is made safe by:
// - `do_call`, the first argument, can be called with the initial `data_ptr`.
// - `do_catch`, the second argument, can be called with the `data_ptr` as well.
// See their safety preconditions for more information
unsafe {
return if intrinsics::catch_unwind(do_call::<F, R>, data_ptr, do_catch::<F, R>) == 0 {
Ok(ManuallyDrop::into_inner(data.r))
} else {
Err(ManuallyDrop::into_inner(data.p))
};
}
// We consider unwinding to be rare, so mark this function as cold. However,
// do not mark it no-inline -- that decision is best to leave to the
// optimizer (in most cases this function is not inlined even as a normal,
// non-cold function, though, as of the writing of this comment).
#[cold]
unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send + 'static> {
// SAFETY: The whole unsafe block hinges on a correct implementation of
// the panic handler `__rust_panic_cleanup`. As such we can only
// assume it returns the correct thing for `Box::from_raw` to work
// without undefined behavior.
let obj = unsafe { Box::from_raw(__rust_panic_cleanup(payload)) };
// panic_count::decrease(); // there is no need to decrease the non-exist counter.
obj
}
// SAFETY:
// data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
// Its must contains a valid `f` (type: F) value that can be use to fill
// `data.r`.
//
// This function cannot be marked as `unsafe` because `intrinsics::catch_unwind`
// expects normal function pointers.
#[inline]
fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
// SAFETY: this is the responsibility of the caller, see above.
unsafe {
let data = data as *mut Data<F, R>;
let data = &mut (*data);
let f = ManuallyDrop::take(&mut data.f);
data.r = ManuallyDrop::new(f());
}
}
// We *do* want this part of the catch to be inlined: this allows the
// compiler to properly track accesses to the Data union and optimize it
// away most of the time.
//
// SAFETY:
// data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
// Since this uses `cleanup` it also hinges on a correct implementation of
// `__rustc_panic_cleanup`.
//
// This function cannot be marked as `unsafe` because `intrinsics::catch_unwind`
// expects normal function pointers.
#[inline]
#[rustc_nounwind] // `intrinsic::r#try` requires catch fn to be nounwind
fn do_catch<F: FnOnce() -> R, R>(data: *mut u8, payload: *mut u8) {
// SAFETY: this is the responsibility of the caller, see above.
//
// When `__rustc_panic_cleaner` is correctly implemented we can rely
// on `obj` being the correct thing to pass to `data.p` (after wrapping
// in `ManuallyDrop`).
unsafe {
let data = data as *mut Data<F, R>;
let data = &mut (*data);
let obj = cleanup(payload);
data.p = ManuallyDrop::new(obj);
}
}
}