1//! Implementation of various bits and pieces of the `panic!` macro and
2//! associated runtime pieces.
3//!
4//! Specifically, this module contains the implementation of:
5//!
6//! * Panic hooks
7//! * Executing a panic up to doing the actual implementation
8//! * Shims around "try"
9
10#![deny(unsafe_op_in_unsafe_fn)]
11
12use crate::panic::BacktraceStyle;
13use core::panic::{Location, PanicInfo, PanicPayload};
14
15use crate::any::Any;
16use crate::fmt;
17use crate::intrinsics;
18use crate::mem::{self, ManuallyDrop};
19use crate::process;
20use crate::sync::atomic::{AtomicBool, Ordering};
21use crate::sync::{PoisonError, RwLock};
22use crate::sys::stdio::panic_output;
23use crate::sys_common::backtrace;
24use crate::sys_common::thread_info;
25use crate::thread;
26
27#[cfg(not(test))]
28use crate::io::set_output_capture;
29// make sure to use the stderr output configured
30// by libtest in the real copy of std
31#[cfg(test)]
32use realstd::io::set_output_capture;
33
34// Binary interface to the panic runtime that the standard library depends on.
35//
36// The standard library is tagged with `#![needs_panic_runtime]` (introduced in
37// RFC 1513) to indicate that it requires some other crate tagged with
38// `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
39// implement these symbols (with the same signatures) so we can get matched up
40// to them.
41//
42// One day this may look a little less ad-hoc with the compiler helping out to
43// hook up these functions, but it is not this day!
44#[allow(improper_ctypes)]
45extern "C" {
46 fn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static);
47}
48
49extern "Rust" {
50 /// `PanicPayload` lazily performs allocation only when needed (this avoids
51 /// allocations when using the "abort" panic runtime).
52 fn __rust_start_panic(payload: &mut dyn PanicPayload) -> u32;
53}
54
55/// This function is called by the panic runtime if FFI code catches a Rust
56/// panic but doesn't rethrow it. We don't support this case since it messes
57/// with our panic count.
58#[cfg(not(test))]
59#[rustc_std_internal_symbol]
60extern "C" fn __rust_drop_panic() -> ! {
61 rtabort!("Rust panics must be rethrown");
62}
63
64/// This function is called by the panic runtime if it catches an exception
65/// object which does not correspond to a Rust panic.
66#[cfg(not(test))]
67#[rustc_std_internal_symbol]
68extern "C" fn __rust_foreign_exception() -> ! {
69 rtabort!("Rust cannot catch foreign exceptions");
70}
71
72enum Hook {
73 Default,
74 Custom(Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>),
75}
76
77impl Hook {
78 #[inline]
79 fn into_box(self) -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
80 match self {
81 Hook::Default => Box::new(default_hook),
82 Hook::Custom(hook: Box) + Sync + Send>) => hook,
83 }
84 }
85}
86
87impl Default for Hook {
88 #[inline]
89 fn default() -> Hook {
90 Hook::Default
91 }
92}
93
94static HOOK: RwLock<Hook> = RwLock::new(Hook::Default);
95
96/// Registers a custom panic hook, replacing the previously registered hook.
97///
98/// The panic hook is invoked when a thread panics, but before the panic runtime
99/// is invoked. As such, the hook will run with both the aborting and unwinding
100/// runtimes.
101///
102/// The default hook, which is registered at startup, prints a message to standard error and
103/// generates a backtrace if requested. This behavior can be customized using the `set_hook` function.
104/// The current hook can be retrieved while reinstating the default hook with the [`take_hook`]
105/// function.
106///
107/// [`take_hook`]: ./fn.take_hook.html
108///
109/// The hook is provided with a `PanicInfo` struct which contains information
110/// about the origin of the panic, including the payload passed to `panic!` and
111/// the source code location from which the panic originated.
112///
113/// The panic hook is a global resource.
114///
115/// # Panics
116///
117/// Panics if called from a panicking thread.
118///
119/// # Examples
120///
121/// The following will print "Custom panic hook":
122///
123/// ```should_panic
124/// use std::panic;
125///
126/// panic::set_hook(Box::new(|_| {
127/// println!("Custom panic hook");
128/// }));
129///
130/// panic!("Normal panic");
131/// ```
132#[stable(feature = "panic_hooks", since = "1.10.0")]
133pub fn set_hook(hook: Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>) {
134 if thread::panicking() {
135 panic!("cannot modify the panic hook from a panicking thread");
136 }
137
138 let new: Hook = Hook::Custom(hook);
139 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
140 let old: Hook = mem::replace(&mut *hook, src:new);
141 drop(hook);
142 // Only drop the old hook after releasing the lock to avoid deadlocking
143 // if its destructor panics.
144 drop(old);
145}
146
147/// Unregisters the current panic hook and returns it, registering the default hook
148/// in its place.
149///
150/// *See also the function [`set_hook`].*
151///
152/// [`set_hook`]: ./fn.set_hook.html
153///
154/// If the default hook is registered it will be returned, but remain registered.
155///
156/// # Panics
157///
158/// Panics if called from a panicking thread.
159///
160/// # Examples
161///
162/// The following will print "Normal panic":
163///
164/// ```should_panic
165/// use std::panic;
166///
167/// panic::set_hook(Box::new(|_| {
168/// println!("Custom panic hook");
169/// }));
170///
171/// let _ = panic::take_hook();
172///
173/// panic!("Normal panic");
174/// ```
175#[must_use]
176#[stable(feature = "panic_hooks", since = "1.10.0")]
177pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
178 if thread::panicking() {
179 panic!("cannot modify the panic hook from a panicking thread");
180 }
181
182 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
183 let old_hook: Hook = mem::take(&mut *hook);
184 drop(hook);
185
186 old_hook.into_box()
187}
188
189/// Atomic combination of [`take_hook`] and [`set_hook`]. Use this to replace the panic handler with
190/// a new panic handler that does something and then executes the old handler.
191///
192/// [`take_hook`]: ./fn.take_hook.html
193/// [`set_hook`]: ./fn.set_hook.html
194///
195/// # Panics
196///
197/// Panics if called from a panicking thread.
198///
199/// # Examples
200///
201/// The following will print the custom message, and then the normal output of panic.
202///
203/// ```should_panic
204/// #![feature(panic_update_hook)]
205/// use std::panic;
206///
207/// // Equivalent to
208/// // let prev = panic::take_hook();
209/// // panic::set_hook(move |info| {
210/// // println!("...");
211/// // prev(info);
212/// // );
213/// panic::update_hook(move |prev, info| {
214/// println!("Print custom message and execute panic handler as usual");
215/// prev(info);
216/// });
217///
218/// panic!("Custom and then normal");
219/// ```
220#[unstable(feature = "panic_update_hook", issue = "92649")]
221pub fn update_hook<F>(hook_fn: F)
222where
223 F: Fn(&(dyn Fn(&PanicInfo<'_>) + Send + Sync + 'static), &PanicInfo<'_>)
224 + Sync
225 + Send
226 + 'static,
227{
228 if thread::panicking() {
229 panic!("cannot modify the panic hook from a panicking thread");
230 }
231
232 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
233 let prev: Box) + Sync + Send> = mem::take(&mut *hook).into_box();
234 *hook = Hook::Custom(Box::new(move |info: &PanicInfo<'_>| hook_fn(&prev, info)));
235}
236
237/// The default panic handler.
238fn default_hook(info: &PanicInfo<'_>) {
239 // If this is a double panic, make sure that we print a backtrace
240 // for this panic. Otherwise only print it if logging is enabled.
241 let backtrace = if info.force_no_backtrace() {
242 None
243 } else if panic_count::get_count() >= 2 {
244 BacktraceStyle::full()
245 } else {
246 crate::panic::get_backtrace_style()
247 };
248
249 // The current implementation always returns `Some`.
250 let location = info.location().unwrap();
251
252 let msg = match info.payload().downcast_ref::<&'static str>() {
253 Some(s) => *s,
254 None => match info.payload().downcast_ref::<String>() {
255 Some(s) => &s[..],
256 None => "Box<dyn Any>",
257 },
258 };
259 let thread = thread_info::current_thread();
260 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
261
262 let write = |err: &mut dyn crate::io::Write| {
263 let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}");
264
265 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
266
267 match backtrace {
268 Some(BacktraceStyle::Short) => {
269 drop(backtrace::print(err, crate::backtrace_rs::PrintFmt::Short))
270 }
271 Some(BacktraceStyle::Full) => {
272 drop(backtrace::print(err, crate::backtrace_rs::PrintFmt::Full))
273 }
274 Some(BacktraceStyle::Off) => {
275 if FIRST_PANIC.swap(false, Ordering::SeqCst) {
276 let _ = writeln!(
277 err,
278 "note: run with `RUST_BACKTRACE=1` environment variable to display a \
279 backtrace"
280 );
281 }
282 }
283 // If backtraces aren't supported or are forced-off, do nothing.
284 None => {}
285 }
286 };
287
288 if let Some(local) = set_output_capture(None) {
289 write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()));
290 set_output_capture(Some(local));
291 } else if let Some(mut out) = panic_output() {
292 write(&mut out);
293 }
294}
295
296#[cfg(not(test))]
297#[doc(hidden)]
298#[cfg(feature = "panic_immediate_abort")]
299#[unstable(feature = "update_panic_count", issue = "none")]
300pub mod panic_count {
301 /// A reason for forcing an immediate abort on panic.
302 #[derive(Debug)]
303 pub enum MustAbort {
304 AlwaysAbort,
305 PanicInHook,
306 }
307
308 #[inline]
309 pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
310 None
311 }
312
313 #[inline]
314 pub fn finished_panic_hook() {}
315
316 #[inline]
317 pub fn decrease() {}
318
319 #[inline]
320 pub fn set_always_abort() {}
321
322 // Disregards ALWAYS_ABORT_FLAG
323 #[inline]
324 #[must_use]
325 pub fn get_count() -> usize {
326 0
327 }
328
329 #[must_use]
330 #[inline]
331 pub fn count_is_zero() -> bool {
332 true
333 }
334}
335
336#[cfg(not(test))]
337#[doc(hidden)]
338#[cfg(not(feature = "panic_immediate_abort"))]
339#[unstable(feature = "update_panic_count", issue = "none")]
340// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
341#[cfg_attr(not(bootstrap), allow(static_mut_refs))]
342pub mod panic_count {
343 use crate::cell::Cell;
344 use crate::sync::atomic::{AtomicUsize, Ordering};
345
346 const ALWAYS_ABORT_FLAG: usize = 1 << (usize::BITS - 1);
347
348 /// A reason for forcing an immediate abort on panic.
349 #[derive(Debug)]
350 pub enum MustAbort {
351 AlwaysAbort,
352 PanicInHook,
353 }
354
355 // Panic count for the current thread and whether a panic hook is currently
356 // being executed..
357 thread_local! {
358 static LOCAL_PANIC_COUNT: Cell<(usize, bool)> = const { Cell::new((0, false)) }
359 }
360
361 // Sum of panic counts from all threads. The purpose of this is to have
362 // a fast path in `count_is_zero` (which is used by `panicking`). In any particular
363 // thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
364 // then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
365 // and after increase and decrease, but not necessarily during their execution.
366 //
367 // Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG)
368 // records whether panic::always_abort() has been called. This can only be
369 // set, never cleared.
370 // panic::always_abort() is usually called to prevent memory allocations done by
371 // the panic handling in the child created by `libc::fork`.
372 // Memory allocations performed in a child created with `libc::fork` are undefined
373 // behavior in most operating systems.
374 // Accessing LOCAL_PANIC_COUNT in a child created by `libc::fork` would lead to a memory
375 // allocation. Only GLOBAL_PANIC_COUNT can be accessed in this situation. This is
376 // sufficient because a child process will always have exactly one thread only.
377 // See also #85261 for details.
378 //
379 // This could be viewed as a struct containing a single bit and an n-1-bit
380 // value, but if we wrote it like that it would be more than a single word,
381 // and even a newtype around usize would be clumsy because we need atomics.
382 // But we use such a tuple for the return type of increase().
383 //
384 // Stealing a bit is fine because it just amounts to assuming that each
385 // panicking thread consumes at least 2 bytes of address space.
386 static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0);
387
388 // Increases the global and local panic count, and returns whether an
389 // immediate abort is required.
390 //
391 // This also updates thread-local state to keep track of whether a panic
392 // hook is currently executing.
393 pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
394 let global_count = GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed);
395 if global_count & ALWAYS_ABORT_FLAG != 0 {
396 return Some(MustAbort::AlwaysAbort);
397 }
398
399 LOCAL_PANIC_COUNT.with(|c| {
400 let (count, in_panic_hook) = c.get();
401 if in_panic_hook {
402 return Some(MustAbort::PanicInHook);
403 }
404 c.set((count + 1, run_panic_hook));
405 None
406 })
407 }
408
409 pub fn finished_panic_hook() {
410 LOCAL_PANIC_COUNT.with(|c| {
411 let (count, _) = c.get();
412 c.set((count, false));
413 });
414 }
415
416 pub fn decrease() {
417 GLOBAL_PANIC_COUNT.fetch_sub(1, Ordering::Relaxed);
418 LOCAL_PANIC_COUNT.with(|c| {
419 let (count, _) = c.get();
420 c.set((count - 1, false));
421 });
422 }
423
424 pub fn set_always_abort() {
425 GLOBAL_PANIC_COUNT.fetch_or(ALWAYS_ABORT_FLAG, Ordering::Relaxed);
426 }
427
428 // Disregards ALWAYS_ABORT_FLAG
429 #[must_use]
430 pub fn get_count() -> usize {
431 LOCAL_PANIC_COUNT.with(|c| c.get().0)
432 }
433
434 // Disregards ALWAYS_ABORT_FLAG
435 #[must_use]
436 #[inline]
437 pub fn count_is_zero() -> bool {
438 if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) & !ALWAYS_ABORT_FLAG == 0 {
439 // Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads
440 // (including the current one) will have `LOCAL_PANIC_COUNT`
441 // equal to zero, so TLS access can be avoided.
442 //
443 // In terms of performance, a relaxed atomic load is similar to a normal
444 // aligned memory read (e.g., a mov instruction in x86), but with some
445 // compiler optimization restrictions. On the other hand, a TLS access
446 // might require calling a non-inlinable function (such as `__tls_get_addr`
447 // when using the GD TLS model).
448 true
449 } else {
450 is_zero_slow_path()
451 }
452 }
453
454 // Slow path is in a separate function to reduce the amount of code
455 // inlined from `count_is_zero`.
456 #[inline(never)]
457 #[cold]
458 fn is_zero_slow_path() -> bool {
459 LOCAL_PANIC_COUNT.with(|c| c.get().0 == 0)
460 }
461}
462
463#[cfg(test)]
464pub use realstd::rt::panic_count;
465
466/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
467#[cfg(feature = "panic_immediate_abort")]
468pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
469 Ok(f())
470}
471
472/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
473#[cfg(not(feature = "panic_immediate_abort"))]
474pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
475 union Data<F, R> {
476 f: ManuallyDrop<F>,
477 r: ManuallyDrop<R>,
478 p: ManuallyDrop<Box<dyn Any + Send>>,
479 }
480
481 // We do some sketchy operations with ownership here for the sake of
482 // performance. We can only pass pointers down to `do_call` (can't pass
483 // objects by value), so we do all the ownership tracking here manually
484 // using a union.
485 //
486 // We go through a transition where:
487 //
488 // * First, we set the data field `f` to be the argumentless closure that we're going to call.
489 // * When we make the function call, the `do_call` function below, we take
490 // ownership of the function pointer. At this point the `data` union is
491 // entirely uninitialized.
492 // * If the closure successfully returns, we write the return value into the
493 // data's return slot (field `r`).
494 // * If the closure panics (`do_catch` below), we write the panic payload into field `p`.
495 // * Finally, when we come back out of the `try` intrinsic we're
496 // in one of two states:
497 //
498 // 1. The closure didn't panic, in which case the return value was
499 // filled in. We move it out of `data.r` and return it.
500 // 2. The closure panicked, in which case the panic payload was
501 // filled in. We move it out of `data.p` and return it.
502 //
503 // Once we stack all that together we should have the "most efficient'
504 // method of calling a catch panic whilst juggling ownership.
505 let mut data = Data { f: ManuallyDrop::new(f) };
506
507 let data_ptr = &mut data as *mut _ as *mut u8;
508 // SAFETY:
509 //
510 // Access to the union's fields: this is `std` and we know that the `r#try`
511 // intrinsic fills in the `r` or `p` union field based on its return value.
512 //
513 // The call to `intrinsics::r#try` is made safe by:
514 // - `do_call`, the first argument, can be called with the initial `data_ptr`.
515 // - `do_catch`, the second argument, can be called with the `data_ptr` as well.
516 // See their safety preconditions for more information
517 unsafe {
518 return if intrinsics::r#try(do_call::<F, R>, data_ptr, do_catch::<F, R>) == 0 {
519 Ok(ManuallyDrop::into_inner(data.r))
520 } else {
521 Err(ManuallyDrop::into_inner(data.p))
522 };
523 }
524
525 // We consider unwinding to be rare, so mark this function as cold. However,
526 // do not mark it no-inline -- that decision is best to leave to the
527 // optimizer (in most cases this function is not inlined even as a normal,
528 // non-cold function, though, as of the writing of this comment).
529 #[cold]
530 unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send + 'static> {
531 // SAFETY: The whole unsafe block hinges on a correct implementation of
532 // the panic handler `__rust_panic_cleanup`. As such we can only
533 // assume it returns the correct thing for `Box::from_raw` to work
534 // without undefined behavior.
535 let obj = unsafe { Box::from_raw(__rust_panic_cleanup(payload)) };
536 panic_count::decrease();
537 obj
538 }
539
540 // SAFETY:
541 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
542 // Its must contains a valid `f` (type: F) value that can be use to fill
543 // `data.r`.
544 //
545 // This function cannot be marked as `unsafe` because `intrinsics::r#try`
546 // expects normal function pointers.
547 #[inline]
548 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
549 // SAFETY: this is the responsibility of the caller, see above.
550 unsafe {
551 let data = data as *mut Data<F, R>;
552 let data = &mut (*data);
553 let f = ManuallyDrop::take(&mut data.f);
554 data.r = ManuallyDrop::new(f());
555 }
556 }
557
558 // We *do* want this part of the catch to be inlined: this allows the
559 // compiler to properly track accesses to the Data union and optimize it
560 // away most of the time.
561 //
562 // SAFETY:
563 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
564 // Since this uses `cleanup` it also hinges on a correct implementation of
565 // `__rustc_panic_cleanup`.
566 //
567 // This function cannot be marked as `unsafe` because `intrinsics::r#try`
568 // expects normal function pointers.
569 #[inline]
570 #[rustc_nounwind] // `intrinsic::r#try` requires catch fn to be nounwind
571 fn do_catch<F: FnOnce() -> R, R>(data: *mut u8, payload: *mut u8) {
572 // SAFETY: this is the responsibility of the caller, see above.
573 //
574 // When `__rustc_panic_cleaner` is correctly implemented we can rely
575 // on `obj` being the correct thing to pass to `data.p` (after wrapping
576 // in `ManuallyDrop`).
577 unsafe {
578 let data = data as *mut Data<F, R>;
579 let data = &mut (*data);
580 let obj = cleanup(payload);
581 data.p = ManuallyDrop::new(obj);
582 }
583 }
584}
585
586/// Determines whether the current thread is unwinding because of panic.
587#[inline]
588pub fn panicking() -> bool {
589 !panic_count::count_is_zero()
590}
591
592/// Entry point of panics from the core crate (`panic_impl` lang item).
593#[cfg(not(any(test, doctest)))]
594#[panic_handler]
595pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
596 struct FormatStringPayload<'a> {
597 inner: &'a fmt::Arguments<'a>,
598 string: Option<String>,
599 }
600
601 impl<'a> FormatStringPayload<'a> {
602 fn new(inner: &'a fmt::Arguments<'a>) -> Self {
603 Self { inner, string: None }
604 }
605
606 fn fill(&mut self) -> &mut String {
607 use crate::fmt::Write;
608
609 let inner = self.inner;
610 // Lazily, the first time this gets called, run the actual string formatting.
611 self.string.get_or_insert_with(|| {
612 let mut s = String::new();
613 let _err = s.write_fmt(*inner);
614 s
615 })
616 }
617 }
618
619 unsafe impl<'a> PanicPayload for FormatStringPayload<'a> {
620 fn take_box(&mut self) -> *mut (dyn Any + Send) {
621 // We do two allocations here, unfortunately. But (a) they're required with the current
622 // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
623 // begin_panic below).
624 let contents = mem::take(self.fill());
625 Box::into_raw(Box::new(contents))
626 }
627
628 fn get(&mut self) -> &(dyn Any + Send) {
629 self.fill()
630 }
631 }
632
633 struct StaticStrPayload(&'static str);
634
635 unsafe impl PanicPayload for StaticStrPayload {
636 fn take_box(&mut self) -> *mut (dyn Any + Send) {
637 Box::into_raw(Box::new(self.0))
638 }
639
640 fn get(&mut self) -> &(dyn Any + Send) {
641 &self.0
642 }
643 }
644
645 let loc = info.location().unwrap(); // The current implementation always returns Some
646 let msg = info.message().unwrap(); // The current implementation always returns Some
647 crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
648 // FIXME: can we just pass `info` along rather than taking it apart here, only to have
649 // `rust_panic_with_hook` construct a new `PanicInfo`?
650 if let Some(msg) = msg.as_str() {
651 rust_panic_with_hook(
652 &mut StaticStrPayload(msg),
653 info.message(),
654 loc,
655 info.can_unwind(),
656 info.force_no_backtrace(),
657 );
658 } else {
659 rust_panic_with_hook(
660 &mut FormatStringPayload::new(msg),
661 info.message(),
662 loc,
663 info.can_unwind(),
664 info.force_no_backtrace(),
665 );
666 }
667 })
668}
669
670/// This is the entry point of panicking for the non-format-string variants of
671/// panic!() and assert!(). In particular, this is the only entry point that supports
672/// arbitrary payloads, not just format strings.
673#[unstable(feature = "libstd_sys_internals", reason = "used by the panic! macro", issue = "none")]
674#[cfg_attr(not(any(test, doctest)), lang = "begin_panic")]
675// lang item for CTFE panic support
676// never inline unless panic_immediate_abort to avoid code
677// bloat at the call sites as much as possible
678#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
679#[cfg_attr(feature = "panic_immediate_abort", inline)]
680#[track_caller]
681#[rustc_do_not_const_check] // hooked by const-eval
682pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
683 if cfg!(feature = "panic_immediate_abort") {
684 intrinsics::abort()
685 }
686
687 let loc = Location::caller();
688 return crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
689 rust_panic_with_hook(
690 &mut Payload::new(msg),
691 None,
692 loc,
693 /* can_unwind */ true,
694 /* force_no_backtrace */ false,
695 )
696 });
697
698 struct Payload<A> {
699 inner: Option<A>,
700 }
701
702 impl<A: Send + 'static> Payload<A> {
703 fn new(inner: A) -> Payload<A> {
704 Payload { inner: Some(inner) }
705 }
706 }
707
708 unsafe impl<A: Send + 'static> PanicPayload for Payload<A> {
709 fn take_box(&mut self) -> *mut (dyn Any + Send) {
710 // Note that this should be the only allocation performed in this code path. Currently
711 // this means that panic!() on OOM will invoke this code path, but then again we're not
712 // really ready for panic on OOM anyway. If we do start doing this, then we should
713 // propagate this allocation to be performed in the parent of this thread instead of the
714 // thread that's panicking.
715 let data = match self.inner.take() {
716 Some(a) => Box::new(a) as Box<dyn Any + Send>,
717 None => process::abort(),
718 };
719 Box::into_raw(data)
720 }
721
722 fn get(&mut self) -> &(dyn Any + Send) {
723 match self.inner {
724 Some(ref a) => a,
725 None => process::abort(),
726 }
727 }
728 }
729}
730
731/// Central point for dispatching panics.
732///
733/// Executes the primary logic for a panic, including checking for recursive
734/// panics, panic hooks, and finally dispatching to the panic runtime to either
735/// abort or unwind.
736fn rust_panic_with_hook(
737 payload: &mut dyn PanicPayload,
738 message: Option<&fmt::Arguments<'_>>,
739 location: &Location<'_>,
740 can_unwind: bool,
741 force_no_backtrace: bool,
742) -> ! {
743 let must_abort = panic_count::increase(true);
744
745 // Check if we need to abort immediately.
746 if let Some(must_abort) = must_abort {
747 match must_abort {
748 panic_count::MustAbort::PanicInHook => {
749 // Don't try to print the message in this case
750 // - perhaps that is causing the recursive panics.
751 rtprintpanic!("thread panicked while processing panic. aborting.\n");
752 }
753 panic_count::MustAbort::AlwaysAbort => {
754 // Unfortunately, this does not print a backtrace, because creating
755 // a `Backtrace` will allocate, which we must to avoid here.
756 let panicinfo = PanicInfo::internal_constructor(
757 message,
758 location,
759 can_unwind,
760 force_no_backtrace,
761 );
762 rtprintpanic!("{panicinfo}\npanicked after panic::always_abort(), aborting.\n");
763 }
764 }
765 crate::sys::abort_internal();
766 }
767
768 let mut info =
769 PanicInfo::internal_constructor(message, location, can_unwind, force_no_backtrace);
770 let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner);
771 match *hook {
772 // Some platforms (like wasm) know that printing to stderr won't ever actually
773 // print anything, and if that's the case we can skip the default
774 // hook. Since string formatting happens lazily when calling `payload`
775 // methods, this means we avoid formatting the string at all!
776 // (The panic runtime might still call `payload.take_box()` though and trigger
777 // formatting.)
778 Hook::Default if panic_output().is_none() => {}
779 Hook::Default => {
780 info.set_payload(payload.get());
781 default_hook(&info);
782 }
783 Hook::Custom(ref hook) => {
784 info.set_payload(payload.get());
785 hook(&info);
786 }
787 };
788 drop(hook);
789
790 // Indicate that we have finished executing the panic hook. After this point
791 // it is fine if there is a panic while executing destructors, as long as it
792 // it contained within a `catch_unwind`.
793 panic_count::finished_panic_hook();
794
795 if !can_unwind {
796 // If a thread panics while running destructors or tries to unwind
797 // through a nounwind function (e.g. extern "C") then we cannot continue
798 // unwinding and have to abort immediately.
799 rtprintpanic!("thread caused non-unwinding panic. aborting.\n");
800 crate::sys::abort_internal();
801 }
802
803 rust_panic(payload)
804}
805
806/// This is the entry point for `resume_unwind`.
807/// It just forwards the payload to the panic runtime.
808#[cfg_attr(feature = "panic_immediate_abort", inline)]
809pub fn rust_panic_without_hook(payload: Box<dyn Any + Send>) -> ! {
810 panic_count::increase(run_panic_hook:false);
811
812 struct RewrapBox(Box<dyn Any + Send>);
813
814 unsafe impl PanicPayload for RewrapBox {
815 fn take_box(&mut self) -> *mut (dyn Any + Send) {
816 Box::into_raw(mem::replace(&mut self.0, src:Box::new(())))
817 }
818
819 fn get(&mut self) -> &(dyn Any + Send) {
820 &*self.0
821 }
822 }
823
824 rust_panic(&mut RewrapBox(payload))
825}
826
827/// An unmangled function (through `rustc_std_internal_symbol`) on which to slap
828/// yer breakpoints.
829#[inline(never)]
830#[cfg_attr(not(test), rustc_std_internal_symbol)]
831#[cfg(not(feature = "panic_immediate_abort"))]
832fn rust_panic(msg: &mut dyn PanicPayload) -> ! {
833 let code: u32 = unsafe { __rust_start_panic(payload:msg) };
834 rtabort!("failed to initiate panic, error {code}")
835}
836
837#[cfg_attr(not(test), rustc_std_internal_symbol)]
838#[cfg(feature = "panic_immediate_abort")]
839fn rust_panic(_: &mut dyn PanicPayload) -> ! {
840 unsafe {
841 crate::intrinsics::abort();
842 }
843}
844