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panicking.rs
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panicking.rs
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//! Implementation of various bits and pieces of the `panic!` macro and
//! associated runtime pieces.
//!
//! Specifically, this module contains the implementation of:
//!
//! * Panic hooks
//! * Executing a panic up to doing the actual implementation
//! * Shims around "try"
#![deny(unsafe_op_in_unsafe_fn)]
use crate::panic::BacktraceStyle;
use core::panic::{Location, PanicInfo, PanicPayload};
use crate::any::Any;
use crate::fmt;
use crate::intrinsics;
use crate::mem::{self, ManuallyDrop};
use crate::process;
use crate::sync::atomic::{AtomicBool, Ordering};
use crate::sync::{PoisonError, RwLock};
use crate::sys::stdio::panic_output;
use crate::sys_common::backtrace;
use crate::sys_common::thread_info;
use crate::thread;
#[cfg(not(test))]
use crate::io::set_output_capture;
// make sure to use the stderr output configured
// by libtest in the real copy of std
#[cfg(test)]
use realstd::io::set_output_capture;
// Binary interface to the panic runtime that the standard library depends on.
//
// The standard library is tagged with `#![needs_panic_runtime]` (introduced in
// RFC 1513) to indicate that it requires some other crate tagged with
// `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
// implement these symbols (with the same signatures) so we can get matched up
// to them.
//
// One day this may look a little less ad-hoc with the compiler helping out to
// hook up these functions, but it is not this day!
#[allow(improper_ctypes)]
extern "C" {
fn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static);
}
extern "Rust" {
/// `PanicPayload` lazily performs allocation only when needed (this avoids
/// allocations when using the "abort" panic runtime).
fn __rust_start_panic(payload: &mut dyn PanicPayload) -> u32;
}
/// This function is called by the panic runtime if FFI code catches a Rust
/// panic but doesn't rethrow it. We don't support this case since it messes
/// with our panic count.
#[cfg(not(test))]
#[rustc_std_internal_symbol]
extern "C" fn __rust_drop_panic() -> ! {
rtabort!("Rust panics must be rethrown");
}
/// This function is called by the panic runtime if it catches an exception
/// object which does not correspond to a Rust panic.
#[cfg(not(test))]
#[rustc_std_internal_symbol]
extern "C" fn __rust_foreign_exception() -> ! {
rtabort!("Rust cannot catch foreign exceptions");
}
enum Hook {
Default,
Custom(Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>),
}
impl Hook {
#[inline]
fn into_box(self) -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
match self {
Hook::Default => Box::new(default_hook),
Hook::Custom(hook) => hook,
}
}
}
impl Default for Hook {
#[inline]
fn default() -> Hook {
Hook::Default
}
}
static HOOK: RwLock<Hook> = RwLock::new(Hook::Default);
/// Registers a custom panic hook, replacing the previously registered hook.
///
/// The panic hook is invoked when a thread panics, but before the panic runtime
/// is invoked. As such, the hook will run with both the aborting and unwinding
/// runtimes.
///
/// The default hook, which is registered at startup, prints a message to standard error and
/// generates a backtrace if requested. This behavior can be customized using the `set_hook` function.
/// The current hook can be retrieved while reinstating the default hook with the [`take_hook`]
/// function.
///
/// [`take_hook`]: ./fn.take_hook.html
///
/// The hook is provided with a `PanicInfo` struct which contains information
/// about the origin of the panic, including the payload passed to `panic!` and
/// the source code location from which the panic originated.
///
/// The panic hook is a global resource.
///
/// # Panics
///
/// Panics if called from a panicking thread.
///
/// # Examples
///
/// The following will print "Custom panic hook":
///
/// ```should_panic
/// use std::panic;
///
/// panic::set_hook(Box::new(|_| {
/// println!("Custom panic hook");
/// }));
///
/// panic!("Normal panic");
/// ```
#[stable(feature = "panic_hooks", since = "1.10.0")]
pub fn set_hook(hook: Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>) {
if thread::panicking() {
panic!("cannot modify the panic hook from a panicking thread");
}
let new = Hook::Custom(hook);
let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
let old = mem::replace(&mut *hook, new);
drop(hook);
// Only drop the old hook after releasing the lock to avoid deadlocking
// if its destructor panics.
drop(old);
}
/// Unregisters the current panic hook and returns it, registering the default hook
/// in its place.
///
/// *See also the function [`set_hook`].*
///
/// [`set_hook`]: ./fn.set_hook.html
///
/// If the default hook is registered it will be returned, but remain registered.
///
/// # Panics
///
/// Panics if called from a panicking thread.
///
/// # Examples
///
/// The following will print "Normal panic":
///
/// ```should_panic
/// use std::panic;
///
/// panic::set_hook(Box::new(|_| {
/// println!("Custom panic hook");
/// }));
///
/// let _ = panic::take_hook();
///
/// panic!("Normal panic");
/// ```
#[must_use]
#[stable(feature = "panic_hooks", since = "1.10.0")]
pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
if thread::panicking() {
panic!("cannot modify the panic hook from a panicking thread");
}
let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
let old_hook = mem::take(&mut *hook);
drop(hook);
old_hook.into_box()
}
/// Atomic combination of [`take_hook`] and [`set_hook`]. Use this to replace the panic handler with
/// a new panic handler that does something and then executes the old handler.
///
/// [`take_hook`]: ./fn.take_hook.html
/// [`set_hook`]: ./fn.set_hook.html
///
/// # Panics
///
/// Panics if called from a panicking thread.
///
/// # Examples
///
/// The following will print the custom message, and then the normal output of panic.
///
/// ```should_panic
/// #![feature(panic_update_hook)]
/// use std::panic;
///
/// // Equivalent to
/// // let prev = panic::take_hook();
/// // panic::set_hook(move |info| {
/// // println!("...");
/// // prev(info);
/// // );
/// panic::update_hook(move |prev, info| {
/// println!("Print custom message and execute panic handler as usual");
/// prev(info);
/// });
///
/// panic!("Custom and then normal");
/// ```
#[unstable(feature = "panic_update_hook", issue = "92649")]
pub fn update_hook<F>(hook_fn: F)
where
F: Fn(&(dyn Fn(&PanicInfo<'_>) + Send + Sync + 'static), &PanicInfo<'_>)
+ Sync
+ Send
+ 'static,
{
if thread::panicking() {
panic!("cannot modify the panic hook from a panicking thread");
}
let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
let prev = mem::take(&mut *hook).into_box();
*hook = Hook::Custom(Box::new(move |info| hook_fn(&prev, info)));
}
/// The default panic handler.
fn default_hook(info: &PanicInfo<'_>) {
// If this is a double panic, make sure that we print a backtrace
// for this panic. Otherwise only print it if logging is enabled.
let backtrace = if info.force_no_backtrace() {
None
} else if panic_count::get_count() >= 2 {
BacktraceStyle::full()
} else {
crate::panic::get_backtrace_style()
};
// The current implementation always returns `Some`.
let location = info.location().unwrap();
let msg = match info.payload().downcast_ref::<&'static str>() {
Some(s) => *s,
None => match info.payload().downcast_ref::<String>() {
Some(s) => &s[..],
None => "Box<dyn Any>",
},
};
let thread = thread_info::current_thread();
let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
let write = |err: &mut dyn crate::io::Write| {
let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
match backtrace {
Some(BacktraceStyle::Short) => {
drop(backtrace::print(err, crate::backtrace_rs::PrintFmt::Short))
}
Some(BacktraceStyle::Full) => {
drop(backtrace::print(err, crate::backtrace_rs::PrintFmt::Full))
}
Some(BacktraceStyle::Off) => {
if FIRST_PANIC.swap(false, Ordering::SeqCst) {
let _ = writeln!(
err,
"note: run with `RUST_BACKTRACE=1` environment variable to display a \
backtrace"
);
}
}
// If backtraces aren't supported or are forced-off, do nothing.
None => {}
}
};
if let Some(local) = set_output_capture(None) {
write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()));
set_output_capture(Some(local));
} else if let Some(mut out) = panic_output() {
write(&mut out);
}
}
#[cfg(not(test))]
#[doc(hidden)]
#[cfg(feature = "panic_immediate_abort")]
#[unstable(feature = "update_panic_count", issue = "none")]
pub mod panic_count {
/// A reason for forcing an immediate abort on panic.
#[derive(Debug)]
pub enum MustAbort {
AlwaysAbort,
PanicInHook,
}
#[inline]
pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
None
}
#[inline]
pub fn finished_panic_hook() {}
#[inline]
pub fn decrease() {}
#[inline]
pub fn set_always_abort() {}
// Disregards ALWAYS_ABORT_FLAG
#[inline]
#[must_use]
pub fn get_count() -> usize {
0
}
#[must_use]
#[inline]
pub fn count_is_zero() -> bool {
true
}
}
#[cfg(not(test))]
#[doc(hidden)]
#[cfg(not(feature = "panic_immediate_abort"))]
#[unstable(feature = "update_panic_count", issue = "none")]
pub mod panic_count {
use crate::cell::Cell;
use crate::sync::atomic::{AtomicUsize, Ordering};
const ALWAYS_ABORT_FLAG: usize = 1 << (usize::BITS - 1);
/// A reason for forcing an immediate abort on panic.
#[derive(Debug)]
pub enum MustAbort {
AlwaysAbort,
PanicInHook,
}
// Panic count for the current thread and whether a panic hook is currently
// being executed..
thread_local! {
static LOCAL_PANIC_COUNT: Cell<(usize, bool)> = const { Cell::new((0, false)) }
}
// Sum of panic counts from all threads. The purpose of this is to have
// a fast path in `count_is_zero` (which is used by `panicking`). In any particular
// thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
// then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
// and after increase and decrease, but not necessarily during their execution.
//
// Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG)
// records whether panic::always_abort() has been called. This can only be
// set, never cleared.
// panic::always_abort() is usually called to prevent memory allocations done by
// the panic handling in the child created by `libc::fork`.
// Memory allocations performed in a child created with `libc::fork` are undefined
// behavior in most operating systems.
// Accessing LOCAL_PANIC_COUNT in a child created by `libc::fork` would lead to a memory
// allocation. Only GLOBAL_PANIC_COUNT can be accessed in this situation. This is
// sufficient because a child process will always have exactly one thread only.
// See also #85261 for details.
//
// This could be viewed as a struct containing a single bit and an n-1-bit
// value, but if we wrote it like that it would be more than a single word,
// and even a newtype around usize would be clumsy because we need atomics.
// But we use such a tuple for the return type of increase().
//
// Stealing a bit is fine because it just amounts to assuming that each
// panicking thread consumes at least 2 bytes of address space.
static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0);
// Increases the global and local panic count, and returns whether an
// immediate abort is required.
//
// This also updates thread-local state to keep track of whether a panic
// hook is currently executing.
pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
let global_count = GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed);
if global_count & ALWAYS_ABORT_FLAG != 0 {
return Some(MustAbort::AlwaysAbort);
}
LOCAL_PANIC_COUNT.with(|c| {
let (count, in_panic_hook) = c.get();
if in_panic_hook {
return Some(MustAbort::PanicInHook);
}
c.set((count + 1, run_panic_hook));
None
})
}
pub fn finished_panic_hook() {
LOCAL_PANIC_COUNT.with(|c| {
let (count, _) = c.get();
c.set((count, false));
});
}
pub fn decrease() {
GLOBAL_PANIC_COUNT.fetch_sub(1, Ordering::Relaxed);
LOCAL_PANIC_COUNT.with(|c| {
let (count, _) = c.get();
c.set((count - 1, false));
});
}
pub fn set_always_abort() {
GLOBAL_PANIC_COUNT.fetch_or(ALWAYS_ABORT_FLAG, Ordering::Relaxed);
}
// Disregards ALWAYS_ABORT_FLAG
#[must_use]
pub fn get_count() -> usize {
LOCAL_PANIC_COUNT.with(|c| c.get().0)
}
// Disregards ALWAYS_ABORT_FLAG
#[must_use]
#[inline]
pub fn count_is_zero() -> bool {
if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) & !ALWAYS_ABORT_FLAG == 0 {
// Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads
// (including the current one) will have `LOCAL_PANIC_COUNT`
// equal to zero, so TLS access can be avoided.
//
// In terms of performance, a relaxed atomic load is similar to a normal
// aligned memory read (e.g., a mov instruction in x86), but with some
// compiler optimization restrictions. On the other hand, a TLS access
// might require calling a non-inlinable function (such as `__tls_get_addr`
// when using the GD TLS model).
true
} else {
is_zero_slow_path()
}
}
// Slow path is in a separate function to reduce the amount of code
// inlined from `count_is_zero`.
#[inline(never)]
#[cold]
fn is_zero_slow_path() -> bool {
LOCAL_PANIC_COUNT.with(|c| c.get().0 == 0)
}
}
#[cfg(test)]
pub use realstd::rt::panic_count;
/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
#[cfg(feature = "panic_immediate_abort")]
pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
Ok(f())
}
/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
#[cfg(not(feature = "panic_immediate_abort"))]
pub unsafe fn r#try<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();
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);
}
}
}
/// Determines whether the current thread is unwinding because of panic.
#[inline]
pub fn panicking() -> bool {
!panic_count::count_is_zero()
}
/// Entry point of panics from the core crate (`panic_impl` lang item).
#[cfg(not(any(test, doctest)))]
#[panic_handler]
pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
struct FormatStringPayload<'a> {
inner: &'a fmt::Arguments<'a>,
string: Option<String>,
}
impl<'a> FormatStringPayload<'a> {
fn new(inner: &'a fmt::Arguments<'a>) -> Self {
Self { inner, string: None }
}
fn fill(&mut self) -> &mut String {
use crate::fmt::Write;
let inner = self.inner;
// Lazily, the first time this gets called, run the actual string formatting.
self.string.get_or_insert_with(|| {
let mut s = String::new();
let _err = s.write_fmt(*inner);
s
})
}
}
unsafe impl<'a> PanicPayload for FormatStringPayload<'a> {
fn take_box(&mut self) -> *mut (dyn Any + Send) {
// We do two allocations here, unfortunately. But (a) they're required with the current
// scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
// begin_panic below).
let contents = mem::take(self.fill());
Box::into_raw(Box::new(contents))
}
fn get(&mut self) -> &(dyn Any + Send) {
self.fill()
}
}
struct StaticStrPayload(&'static str);
unsafe impl PanicPayload for StaticStrPayload {
fn take_box(&mut self) -> *mut (dyn Any + Send) {
Box::into_raw(Box::new(self.0))
}
fn get(&mut self) -> &(dyn Any + Send) {
&self.0
}
}
let loc = info.location().unwrap(); // The current implementation always returns Some
let msg = info.message().unwrap(); // The current implementation always returns Some
crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
// FIXME: can we just pass `info` along rather than taking it apart here, only to have
// `rust_panic_with_hook` construct a new `PanicInfo`?
if let Some(msg) = msg.as_str() {
rust_panic_with_hook(
&mut StaticStrPayload(msg),
info.message(),
loc,
info.can_unwind(),
info.force_no_backtrace(),
);
} else {
rust_panic_with_hook(
&mut FormatStringPayload::new(msg),
info.message(),
loc,
info.can_unwind(),
info.force_no_backtrace(),
);
}
})
}
/// This is the entry point of panicking for the non-format-string variants of
/// panic!() and assert!(). In particular, this is the only entry point that supports
/// arbitrary payloads, not just format strings.
#[unstable(feature = "libstd_sys_internals", reason = "used by the panic! macro", issue = "none")]
#[cfg_attr(not(any(test, doctest)), lang = "begin_panic")]
// lang item for CTFE panic support
// never inline unless panic_immediate_abort to avoid code
// bloat at the call sites as much as possible
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[track_caller]
#[rustc_do_not_const_check] // hooked by const-eval
pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
if cfg!(feature = "panic_immediate_abort") {
intrinsics::abort()
}
let loc = Location::caller();
return crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
rust_panic_with_hook(
&mut Payload::new(msg),
None,
loc,
/* can_unwind */ true,
/* force_no_backtrace */ false,
)
});
struct Payload<A> {
inner: Option<A>,
}
impl<A: Send + 'static> Payload<A> {
fn new(inner: A) -> Payload<A> {
Payload { inner: Some(inner) }
}
}
unsafe impl<A: Send + 'static> PanicPayload for Payload<A> {
fn take_box(&mut self) -> *mut (dyn Any + Send) {
// Note that this should be the only allocation performed in this code path. Currently
// this means that panic!() on OOM will invoke this code path, but then again we're not
// really ready for panic on OOM anyway. If we do start doing this, then we should
// propagate this allocation to be performed in the parent of this thread instead of the
// thread that's panicking.
let data = match self.inner.take() {
Some(a) => Box::new(a) as Box<dyn Any + Send>,
None => process::abort(),
};
Box::into_raw(data)
}
fn get(&mut self) -> &(dyn Any + Send) {
match self.inner {
Some(ref a) => a,
None => process::abort(),
}
}
}
}
/// Central point for dispatching panics.
///
/// Executes the primary logic for a panic, including checking for recursive
/// panics, panic hooks, and finally dispatching to the panic runtime to either
/// abort or unwind.
fn rust_panic_with_hook(
payload: &mut dyn PanicPayload,
message: Option<&fmt::Arguments<'_>>,
location: &Location<'_>,
can_unwind: bool,
force_no_backtrace: bool,
) -> ! {
let must_abort = panic_count::increase(true);
// Check if we need to abort immediately.
if let Some(must_abort) = must_abort {
match must_abort {
panic_count::MustAbort::PanicInHook => {
// Don't try to print the message in this case
// - perhaps that is causing the recursive panics.
rtprintpanic!("thread panicked while processing panic. aborting.\n");
}
panic_count::MustAbort::AlwaysAbort => {
// Unfortunately, this does not print a backtrace, because creating
// a `Backtrace` will allocate, which we must to avoid here.
let panicinfo = PanicInfo::internal_constructor(
message,
location,
can_unwind,
force_no_backtrace,
);
rtprintpanic!("{panicinfo}\npanicked after panic::always_abort(), aborting.\n");
}
}
crate::sys::abort_internal();
}
let mut info =
PanicInfo::internal_constructor(message, location, can_unwind, force_no_backtrace);
let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner);
match *hook {
// Some platforms (like wasm) know that printing to stderr won't ever actually
// print anything, and if that's the case we can skip the default
// hook. Since string formatting happens lazily when calling `payload`
// methods, this means we avoid formatting the string at all!
// (The panic runtime might still call `payload.take_box()` though and trigger
// formatting.)
Hook::Default if panic_output().is_none() => {}
Hook::Default => {
info.set_payload(payload.get());
default_hook(&info);
}
Hook::Custom(ref hook) => {
info.set_payload(payload.get());
hook(&info);
}
};
drop(hook);
// Indicate that we have finished executing the panic hook. After this point
// it is fine if there is a panic while executing destructors, as long as it
// it contained within a `catch_unwind`.
panic_count::finished_panic_hook();
if !can_unwind {
// If a thread panics while running destructors or tries to unwind
// through a nounwind function (e.g. extern "C") then we cannot continue
// unwinding and have to abort immediately.
rtprintpanic!("thread caused non-unwinding panic. aborting.\n");
crate::sys::abort_internal();
}
rust_panic(payload)
}
/// This is the entry point for `resume_unwind`.
/// It just forwards the payload to the panic runtime.
#[cfg_attr(feature = "panic_immediate_abort", inline)]
pub fn rust_panic_without_hook(payload: Box<dyn Any + Send>) -> ! {
panic_count::increase(false);
struct RewrapBox(Box<dyn Any + Send>);
unsafe impl PanicPayload for RewrapBox {
fn take_box(&mut self) -> *mut (dyn Any + Send) {
Box::into_raw(mem::replace(&mut self.0, Box::new(())))
}
fn get(&mut self) -> &(dyn Any + Send) {
&*self.0
}
}
rust_panic(&mut RewrapBox(payload))
}
/// An unmangled function (through `rustc_std_internal_symbol`) on which to slap
/// yer breakpoints.
#[inline(never)]
#[cfg_attr(not(test), rustc_std_internal_symbol)]
#[cfg(not(feature = "panic_immediate_abort"))]
fn rust_panic(msg: &mut dyn PanicPayload) -> ! {
let code = unsafe { __rust_start_panic(msg) };
rtabort!("failed to initiate panic, error {code}")
}
#[cfg_attr(not(test), rustc_std_internal_symbol)]
#[cfg(feature = "panic_immediate_abort")]
fn rust_panic(_: &mut dyn PanicPayload) -> ! {
unsafe {
crate::intrinsics::abort();
}
}