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 core::panic::{Location, PanicPayload};
13
14// make sure to use the stderr output configured
15// by libtest in the real copy of std
16#[cfg(test)]
17use realstd::io::try_set_output_capture;
18
19use crate::any::Any;
20#[cfg(not(test))]
21use crate::io::try_set_output_capture;
22use crate::mem::{self, ManuallyDrop};
23use crate::panic::{BacktraceStyle, PanicHookInfo};
24use crate::sync::atomic::{Atomic, AtomicBool, Ordering};
25use crate::sync::{PoisonError, RwLock};
26use crate::sys::backtrace;
27use crate::sys::stdio::panic_output;
28use crate::{fmt, intrinsics, process, thread};
29
30// This forces codegen of the function called by panic!() inside the std crate, rather than in
31// downstream crates. Primarily this is useful for rustc's codegen tests, which rely on noticing
32// complete removal of panic from generated IR. Since begin_panic is inline(never), it's only
33// codegen'd once per crate-graph so this pushes that to std rather than our codegen test crates.
34//
35// (See https://github.com/rust-lang/rust/pull/123244 for more info on why).
36//
37// If this is causing problems we can also modify those codegen tests to use a crate type like
38// cdylib which doesn't export "Rust" symbols to downstream linkage units.
39#[unstable(feature = "libstd_sys_internals", reason = "used by the panic! macro", issue = "none")]
40#[doc(hidden)]
41#[allow(dead_code)]
42#[used(compiler)]
43pub static EMPTY_PANIC: fn(&'static str) -> ! =
44 begin_panic::<&'static str> as fn(&'static str) -> !;
45
46// Binary interface to the panic runtime that the standard library depends on.
47//
48// The standard library is tagged with `#![needs_panic_runtime]` (introduced in
49// RFC 1513) to indicate that it requires some other crate tagged with
50// `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
51// implement these symbols (with the same signatures) so we can get matched up
52// to them.
53//
54// One day this may look a little less ad-hoc with the compiler helping out to
55// hook up these functions, but it is not this day!
56#[allow(improper_ctypes)]
57unsafe extern "C" {
58 #[rustc_std_internal_symbol]
59 unsafefn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static);
60}
61
62unsafe extern "Rust" {
63 /// `PanicPayload` lazily performs allocation only when needed (this avoids
64 /// allocations when using the "abort" panic runtime).
65 #[rustc_std_internal_symbol]
66 unsafefn __rust_start_panic(payload: &mut dyn PanicPayload) -> u32;
67}
68
69/// This function is called by the panic runtime if FFI code catches a Rust
70/// panic but doesn't rethrow it. We don't support this case since it messes
71/// with our panic count.
72#[cfg(not(test))]
73#[rustc_std_internal_symbol]
74extern "C" fn __rust_drop_panic() -> ! {
75 rtabort!("Rust panics must be rethrown");
76}
77
78/// This function is called by the panic runtime if it catches an exception
79/// object which does not correspond to a Rust panic.
80#[cfg(not(test))]
81#[rustc_std_internal_symbol]
82extern "C" fn __rust_foreign_exception() -> ! {
83 rtabort!("Rust cannot catch foreign exceptions");
84}
85
86#[derive(Default)]
87enum Hook {
88 #[default]
89 Default,
90 Custom(Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send>),
91}
92
93impl Hook {
94 #[inline]
95 fn into_box(self) -> Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send> {
96 match self {
97 Hook::Default => Box::new(default_hook),
98 Hook::Custom(hook: Box) + Send + Sync + 'static>) => hook,
99 }
100 }
101}
102
103static HOOK: RwLock<Hook> = RwLock::new(Hook::Default);
104
105/// Registers a custom panic hook, replacing the previously registered hook.
106///
107/// The panic hook is invoked when a thread panics, but before the panic runtime
108/// is invoked. As such, the hook will run with both the aborting and unwinding
109/// runtimes.
110///
111/// The default hook, which is registered at startup, prints a message to standard error and
112/// generates a backtrace if requested. This behavior can be customized using the `set_hook` function.
113/// The current hook can be retrieved while reinstating the default hook with the [`take_hook`]
114/// function.
115///
116/// [`take_hook`]: ./fn.take_hook.html
117///
118/// The hook is provided with a `PanicHookInfo` struct which contains information
119/// about the origin of the panic, including the payload passed to `panic!` and
120/// the source code location from which the panic originated.
121///
122/// The panic hook is a global resource.
123///
124/// # Panics
125///
126/// Panics if called from a panicking thread.
127///
128/// # Examples
129///
130/// The following will print "Custom panic hook":
131///
132/// ```should_panic
133/// use std::panic;
134///
135/// panic::set_hook(Box::new(|_| {
136/// println!("Custom panic hook");
137/// }));
138///
139/// panic!("Normal panic");
140/// ```
141#[stable(feature = "panic_hooks", since = "1.10.0")]
142pub fn set_hook(hook: Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send>) {
143 if thread::panicking() {
144 panic!("cannot modify the panic hook from a panicking thread");
145 }
146
147 let new: Hook = Hook::Custom(hook);
148 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
149 let old: Hook = mem::replace(&mut *hook, src:new);
150 drop(hook);
151 // Only drop the old hook after releasing the lock to avoid deadlocking
152 // if its destructor panics.
153 drop(old);
154}
155
156/// Unregisters the current panic hook and returns it, registering the default hook
157/// in its place.
158///
159/// *See also the function [`set_hook`].*
160///
161/// [`set_hook`]: ./fn.set_hook.html
162///
163/// If the default hook is registered it will be returned, but remain registered.
164///
165/// # Panics
166///
167/// Panics if called from a panicking thread.
168///
169/// # Examples
170///
171/// The following will print "Normal panic":
172///
173/// ```should_panic
174/// use std::panic;
175///
176/// panic::set_hook(Box::new(|_| {
177/// println!("Custom panic hook");
178/// }));
179///
180/// let _ = panic::take_hook();
181///
182/// panic!("Normal panic");
183/// ```
184#[must_use]
185#[stable(feature = "panic_hooks", since = "1.10.0")]
186pub fn take_hook() -> Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send> {
187 if thread::panicking() {
188 panic!("cannot modify the panic hook from a panicking thread");
189 }
190
191 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
192 let old_hook: Hook = mem::take(&mut *hook);
193 drop(hook);
194
195 old_hook.into_box()
196}
197
198/// Atomic combination of [`take_hook`] and [`set_hook`]. Use this to replace the panic handler with
199/// a new panic handler that does something and then executes the old handler.
200///
201/// [`take_hook`]: ./fn.take_hook.html
202/// [`set_hook`]: ./fn.set_hook.html
203///
204/// # Panics
205///
206/// Panics if called from a panicking thread.
207///
208/// # Examples
209///
210/// The following will print the custom message, and then the normal output of panic.
211///
212/// ```should_panic
213/// #![feature(panic_update_hook)]
214/// use std::panic;
215///
216/// // Equivalent to
217/// // let prev = panic::take_hook();
218/// // panic::set_hook(move |info| {
219/// // println!("...");
220/// // prev(info);
221/// // );
222/// panic::update_hook(move |prev, info| {
223/// println!("Print custom message and execute panic handler as usual");
224/// prev(info);
225/// });
226///
227/// panic!("Custom and then normal");
228/// ```
229#[unstable(feature = "panic_update_hook", issue = "92649")]
230pub fn update_hook<F>(hook_fn: F)
231where
232 F: Fn(&(dyn Fn(&PanicHookInfo<'_>) + Send + Sync + 'static), &PanicHookInfo<'_>)
233 + Sync
234 + Send
235 + 'static,
236{
237 if thread::panicking() {
238 panic!("cannot modify the panic hook from a panicking thread");
239 }
240
241 let mut hook: RwLockWriteGuard<'_, Hook> = HOOK.write().unwrap_or_else(op:PoisonError::into_inner);
242 let prev: Box) + Send + Sync + 'static> = mem::take(&mut *hook).into_box();
243 *hook = Hook::Custom(Box::new(move |info: &PanicHookInfo<'_>| hook_fn(&prev, info)));
244}
245
246/// The default panic handler.
247#[optimize(size)]
248fn default_hook(info: &PanicHookInfo<'_>) {
249 // If this is a double panic, make sure that we print a backtrace
250 // for this panic. Otherwise only print it if logging is enabled.
251 let backtrace = if info.force_no_backtrace() {
252 None
253 } else if panic_count::get_count() >= 2 {
254 BacktraceStyle::full()
255 } else {
256 crate::panic::get_backtrace_style()
257 };
258
259 // The current implementation always returns `Some`.
260 let location = info.location().unwrap();
261
262 let msg = payload_as_str(info.payload());
263
264 let write = #[optimize(size)]
265 |err: &mut dyn crate::io::Write| {
266 // Use a lock to prevent mixed output in multithreading context.
267 // Some platforms also require it when printing a backtrace, like `SymFromAddr` on Windows.
268 let mut lock = backtrace::lock();
269
270 thread::with_current_name(|name| {
271 let name = name.unwrap_or("<unnamed>");
272
273 // Try to write the panic message to a buffer first to prevent other concurrent outputs
274 // interleaving with it.
275 let mut buffer = [0u8; 512];
276 let mut cursor = crate::io::Cursor::new(&mut buffer[..]);
277
278 let write_msg = |dst: &mut dyn crate::io::Write| {
279 // We add a newline to ensure the panic message appears at the start of a line.
280 writeln!(dst, "\nthread '{name}' panicked at {location}:\n{msg}")
281 };
282
283 if write_msg(&mut cursor).is_ok() {
284 let pos = cursor.position() as usize;
285 let _ = err.write_all(&buffer[0..pos]);
286 } else {
287 // The message did not fit into the buffer, write it directly instead.
288 let _ = write_msg(err);
289 };
290 });
291
292 static FIRST_PANIC: Atomic<bool> = AtomicBool::new(true);
293
294 match backtrace {
295 // SAFETY: we took out a lock just a second ago.
296 Some(BacktraceStyle::Short) => {
297 drop(lock.print(err, crate::backtrace_rs::PrintFmt::Short))
298 }
299 Some(BacktraceStyle::Full) => {
300 drop(lock.print(err, crate::backtrace_rs::PrintFmt::Full))
301 }
302 Some(BacktraceStyle::Off) => {
303 if FIRST_PANIC.swap(false, Ordering::Relaxed) {
304 let _ = writeln!(
305 err,
306 "note: run with `RUST_BACKTRACE=1` environment variable to display a \
307 backtrace"
308 );
309 if cfg!(miri) {
310 let _ = writeln!(
311 err,
312 "note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` \
313 for the environment variable to have an effect"
314 );
315 }
316 }
317 }
318 // If backtraces aren't supported or are forced-off, do nothing.
319 None => {}
320 }
321 };
322
323 if let Ok(Some(local)) = try_set_output_capture(None) {
324 write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()));
325 try_set_output_capture(Some(local)).ok();
326 } else if let Some(mut out) = panic_output() {
327 write(&mut out);
328 }
329}
330
331#[cfg(not(test))]
332#[doc(hidden)]
333#[cfg(feature = "panic_immediate_abort")]
334#[unstable(feature = "update_panic_count", issue = "none")]
335pub mod panic_count {
336 /// A reason for forcing an immediate abort on panic.
337 #[derive(Debug)]
338 pub enum MustAbort {
339 AlwaysAbort,
340 PanicInHook,
341 }
342
343 #[inline]
344 pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
345 None
346 }
347
348 #[inline]
349 pub fn finished_panic_hook() {}
350
351 #[inline]
352 pub fn decrease() {}
353
354 #[inline]
355 pub fn set_always_abort() {}
356
357 // Disregards ALWAYS_ABORT_FLAG
358 #[inline]
359 #[must_use]
360 pub fn get_count() -> usize {
361 0
362 }
363
364 #[must_use]
365 #[inline]
366 pub fn count_is_zero() -> bool {
367 true
368 }
369}
370
371#[cfg(not(test))]
372#[doc(hidden)]
373#[cfg(not(feature = "panic_immediate_abort"))]
374#[unstable(feature = "update_panic_count", issue = "none")]
375pub mod panic_count {
376 use crate::cell::Cell;
377 use crate::sync::atomic::{Atomic, AtomicUsize, Ordering};
378
379 const ALWAYS_ABORT_FLAG: usize = 1 << (usize::BITS - 1);
380
381 /// A reason for forcing an immediate abort on panic.
382 #[derive(Debug)]
383 pub enum MustAbort {
384 AlwaysAbort,
385 PanicInHook,
386 }
387
388 // Panic count for the current thread and whether a panic hook is currently
389 // being executed..
390 thread_local! {
391 static LOCAL_PANIC_COUNT: Cell<(usize, bool)> = const { Cell::new((0, false)) }
392 }
393
394 // Sum of panic counts from all threads. The purpose of this is to have
395 // a fast path in `count_is_zero` (which is used by `panicking`). In any particular
396 // thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
397 // then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
398 // and after increase and decrease, but not necessarily during their execution.
399 //
400 // Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG)
401 // records whether panic::always_abort() has been called. This can only be
402 // set, never cleared.
403 // panic::always_abort() is usually called to prevent memory allocations done by
404 // the panic handling in the child created by `libc::fork`.
405 // Memory allocations performed in a child created with `libc::fork` are undefined
406 // behavior in most operating systems.
407 // Accessing LOCAL_PANIC_COUNT in a child created by `libc::fork` would lead to a memory
408 // allocation. Only GLOBAL_PANIC_COUNT can be accessed in this situation. This is
409 // sufficient because a child process will always have exactly one thread only.
410 // See also #85261 for details.
411 //
412 // This could be viewed as a struct containing a single bit and an n-1-bit
413 // value, but if we wrote it like that it would be more than a single word,
414 // and even a newtype around usize would be clumsy because we need atomics.
415 // But we use such a tuple for the return type of increase().
416 //
417 // Stealing a bit is fine because it just amounts to assuming that each
418 // panicking thread consumes at least 2 bytes of address space.
419 static GLOBAL_PANIC_COUNT: Atomic<usize> = AtomicUsize::new(0);
420
421 // Increases the global and local panic count, and returns whether an
422 // immediate abort is required.
423 //
424 // This also updates thread-local state to keep track of whether a panic
425 // hook is currently executing.
426 pub fn increase(run_panic_hook: bool) -> Option<MustAbort> {
427 let global_count = GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed);
428 if global_count & ALWAYS_ABORT_FLAG != 0 {
429 // Do *not* access thread-local state, we might be after a `fork`.
430 return Some(MustAbort::AlwaysAbort);
431 }
432
433 LOCAL_PANIC_COUNT.with(|c| {
434 let (count, in_panic_hook) = c.get();
435 if in_panic_hook {
436 return Some(MustAbort::PanicInHook);
437 }
438 c.set((count + 1, run_panic_hook));
439 None
440 })
441 }
442
443 pub fn finished_panic_hook() {
444 LOCAL_PANIC_COUNT.with(|c| {
445 let (count, _) = c.get();
446 c.set((count, false));
447 });
448 }
449
450 pub fn decrease() {
451 GLOBAL_PANIC_COUNT.fetch_sub(1, Ordering::Relaxed);
452 LOCAL_PANIC_COUNT.with(|c| {
453 let (count, _) = c.get();
454 c.set((count - 1, false));
455 });
456 }
457
458 pub fn set_always_abort() {
459 GLOBAL_PANIC_COUNT.fetch_or(ALWAYS_ABORT_FLAG, Ordering::Relaxed);
460 }
461
462 // Disregards ALWAYS_ABORT_FLAG
463 #[must_use]
464 pub fn get_count() -> usize {
465 LOCAL_PANIC_COUNT.with(|c| c.get().0)
466 }
467
468 // Disregards ALWAYS_ABORT_FLAG
469 #[must_use]
470 #[inline]
471 pub fn count_is_zero() -> bool {
472 if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) & !ALWAYS_ABORT_FLAG == 0 {
473 // Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads
474 // (including the current one) will have `LOCAL_PANIC_COUNT`
475 // equal to zero, so TLS access can be avoided.
476 //
477 // In terms of performance, a relaxed atomic load is similar to a normal
478 // aligned memory read (e.g., a mov instruction in x86), but with some
479 // compiler optimization restrictions. On the other hand, a TLS access
480 // might require calling a non-inlinable function (such as `__tls_get_addr`
481 // when using the GD TLS model).
482 true
483 } else {
484 is_zero_slow_path()
485 }
486 }
487
488 // Slow path is in a separate function to reduce the amount of code
489 // inlined from `count_is_zero`.
490 #[inline(never)]
491 #[cold]
492 fn is_zero_slow_path() -> bool {
493 LOCAL_PANIC_COUNT.with(|c| c.get().0 == 0)
494 }
495}
496
497#[cfg(test)]
498pub use realstd::rt::panic_count;
499
500/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
501#[cfg(feature = "panic_immediate_abort")]
502pub unsafe fn catch_unwind<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
503 Ok(f())
504}
505
506/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
507#[cfg(not(feature = "panic_immediate_abort"))]
508pub unsafe fn catch_unwind<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
509 union Data<F, R> {
510 f: ManuallyDrop<F>,
511 r: ManuallyDrop<R>,
512 p: ManuallyDrop<Box<dyn Any + Send>>,
513 }
514
515 // We do some sketchy operations with ownership here for the sake of
516 // performance. We can only pass pointers down to `do_call` (can't pass
517 // objects by value), so we do all the ownership tracking here manually
518 // using a union.
519 //
520 // We go through a transition where:
521 //
522 // * First, we set the data field `f` to be the argumentless closure that we're going to call.
523 // * When we make the function call, the `do_call` function below, we take
524 // ownership of the function pointer. At this point the `data` union is
525 // entirely uninitialized.
526 // * If the closure successfully returns, we write the return value into the
527 // data's return slot (field `r`).
528 // * If the closure panics (`do_catch` below), we write the panic payload into field `p`.
529 // * Finally, when we come back out of the `try` intrinsic we're
530 // in one of two states:
531 //
532 // 1. The closure didn't panic, in which case the return value was
533 // filled in. We move it out of `data.r` and return it.
534 // 2. The closure panicked, in which case the panic payload was
535 // filled in. We move it out of `data.p` and return it.
536 //
537 // Once we stack all that together we should have the "most efficient'
538 // method of calling a catch panic whilst juggling ownership.
539 let mut data = Data { f: ManuallyDrop::new(f) };
540
541 let data_ptr = (&raw mut data) as *mut u8;
542 // SAFETY:
543 //
544 // Access to the union's fields: this is `std` and we know that the `catch_unwind`
545 // intrinsic fills in the `r` or `p` union field based on its return value.
546 //
547 // The call to `intrinsics::catch_unwind` is made safe by:
548 // - `do_call`, the first argument, can be called with the initial `data_ptr`.
549 // - `do_catch`, the second argument, can be called with the `data_ptr` as well.
550 // See their safety preconditions for more information
551 unsafe {
552 return if intrinsics::catch_unwind(do_call::<F, R>, data_ptr, do_catch::<F, R>) == 0 {
553 Ok(ManuallyDrop::into_inner(data.r))
554 } else {
555 Err(ManuallyDrop::into_inner(data.p))
556 };
557 }
558
559 // We consider unwinding to be rare, so mark this function as cold. However,
560 // do not mark it no-inline -- that decision is best to leave to the
561 // optimizer (in most cases this function is not inlined even as a normal,
562 // non-cold function, though, as of the writing of this comment).
563 #[cold]
564 #[optimize(size)]
565 unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send + 'static> {
566 // SAFETY: The whole unsafe block hinges on a correct implementation of
567 // the panic handler `__rust_panic_cleanup`. As such we can only
568 // assume it returns the correct thing for `Box::from_raw` to work
569 // without undefined behavior.
570 let obj = unsafe { Box::from_raw(__rust_panic_cleanup(payload)) };
571 panic_count::decrease();
572 obj
573 }
574
575 // SAFETY:
576 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
577 // Its must contains a valid `f` (type: F) value that can be use to fill
578 // `data.r`.
579 //
580 // This function cannot be marked as `unsafe` because `intrinsics::catch_unwind`
581 // expects normal function pointers.
582 #[inline]
583 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
584 // SAFETY: this is the responsibility of the caller, see above.
585 unsafe {
586 let data = data as *mut Data<F, R>;
587 let data = &mut (*data);
588 let f = ManuallyDrop::take(&mut data.f);
589 data.r = ManuallyDrop::new(f());
590 }
591 }
592
593 // We *do* want this part of the catch to be inlined: this allows the
594 // compiler to properly track accesses to the Data union and optimize it
595 // away most of the time.
596 //
597 // SAFETY:
598 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>`
599 // Since this uses `cleanup` it also hinges on a correct implementation of
600 // `__rustc_panic_cleanup`.
601 //
602 // This function cannot be marked as `unsafe` because `intrinsics::catch_unwind`
603 // expects normal function pointers.
604 #[inline]
605 #[rustc_nounwind] // `intrinsic::catch_unwind` requires catch fn to be nounwind
606 fn do_catch<F: FnOnce() -> R, R>(data: *mut u8, payload: *mut u8) {
607 // SAFETY: this is the responsibility of the caller, see above.
608 //
609 // When `__rustc_panic_cleaner` is correctly implemented we can rely
610 // on `obj` being the correct thing to pass to `data.p` (after wrapping
611 // in `ManuallyDrop`).
612 unsafe {
613 let data = data as *mut Data<F, R>;
614 let data = &mut (*data);
615 let obj = cleanup(payload);
616 data.p = ManuallyDrop::new(obj);
617 }
618 }
619}
620
621/// Determines whether the current thread is unwinding because of panic.
622#[inline]
623pub fn panicking() -> bool {
624 !panic_count::count_is_zero()
625}
626
627/// Entry point of panics from the core crate (`panic_impl` lang item).
628#[cfg(not(any(test, doctest)))]
629#[panic_handler]
630pub fn begin_panic_handler(info: &core::panic::PanicInfo<'_>) -> ! {
631 struct FormatStringPayload<'a> {
632 inner: &'a core::panic::PanicMessage<'a>,
633 string: Option<String>,
634 }
635
636 impl FormatStringPayload<'_> {
637 fn fill(&mut self) -> &mut String {
638 let inner = self.inner;
639 // Lazily, the first time this gets called, run the actual string formatting.
640 self.string.get_or_insert_with(|| {
641 let mut s = String::new();
642 let mut fmt = fmt::Formatter::new(&mut s, fmt::FormattingOptions::new());
643 let _err = fmt::Display::fmt(&inner, &mut fmt);
644 s
645 })
646 }
647 }
648
649 unsafe impl PanicPayload for FormatStringPayload<'_> {
650 fn take_box(&mut self) -> *mut (dyn Any + Send) {
651 // We do two allocations here, unfortunately. But (a) they're required with the current
652 // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
653 // begin_panic below).
654 let contents = mem::take(self.fill());
655 Box::into_raw(Box::new(contents))
656 }
657
658 fn get(&mut self) -> &(dyn Any + Send) {
659 self.fill()
660 }
661 }
662
663 impl fmt::Display for FormatStringPayload<'_> {
664 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
665 if let Some(s) = &self.string {
666 f.write_str(s)
667 } else {
668 fmt::Display::fmt(&self.inner, f)
669 }
670 }
671 }
672
673 struct StaticStrPayload(&'static str);
674
675 unsafe impl PanicPayload for StaticStrPayload {
676 fn take_box(&mut self) -> *mut (dyn Any + Send) {
677 Box::into_raw(Box::new(self.0))
678 }
679
680 fn get(&mut self) -> &(dyn Any + Send) {
681 &self.0
682 }
683
684 fn as_str(&mut self) -> Option<&str> {
685 Some(self.0)
686 }
687 }
688
689 impl fmt::Display for StaticStrPayload {
690 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
691 f.write_str(self.0)
692 }
693 }
694
695 let loc = info.location().unwrap(); // The current implementation always returns Some
696 let msg = info.message();
697 crate::sys::backtrace::__rust_end_short_backtrace(move || {
698 if let Some(s) = msg.as_str() {
699 rust_panic_with_hook(
700 &mut StaticStrPayload(s),
701 loc,
702 info.can_unwind(),
703 info.force_no_backtrace(),
704 );
705 } else {
706 rust_panic_with_hook(
707 &mut FormatStringPayload { inner: &msg, string: None },
708 loc,
709 info.can_unwind(),
710 info.force_no_backtrace(),
711 );
712 }
713 })
714}
715
716/// This is the entry point of panicking for the non-format-string variants of
717/// panic!() and assert!(). In particular, this is the only entry point that supports
718/// arbitrary payloads, not just format strings.
719#[unstable(feature = "libstd_sys_internals", reason = "used by the panic! macro", issue = "none")]
720#[cfg_attr(not(any(test, doctest)), lang = "begin_panic")]
721// lang item for CTFE panic support
722// never inline unless panic_immediate_abort to avoid code
723// bloat at the call sites as much as possible
724#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
725#[cfg_attr(feature = "panic_immediate_abort", inline)]
726#[track_caller]
727#[rustc_do_not_const_check] // hooked by const-eval
728pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
729 if cfg!(feature = "panic_immediate_abort") {
730 intrinsics::abort()
731 }
732
733 struct Payload<A> {
734 inner: Option<A>,
735 }
736
737 unsafe impl<A: Send + 'static> PanicPayload for Payload<A> {
738 fn take_box(&mut self) -> *mut (dyn Any + Send) {
739 // Note that this should be the only allocation performed in this code path. Currently
740 // this means that panic!() on OOM will invoke this code path, but then again we're not
741 // really ready for panic on OOM anyway. If we do start doing this, then we should
742 // propagate this allocation to be performed in the parent of this thread instead of the
743 // thread that's panicking.
744 let data = match self.inner.take() {
745 Some(a) => Box::new(a) as Box<dyn Any + Send>,
746 None => process::abort(),
747 };
748 Box::into_raw(data)
749 }
750
751 fn get(&mut self) -> &(dyn Any + Send) {
752 match self.inner {
753 Some(ref a) => a,
754 None => process::abort(),
755 }
756 }
757 }
758
759 impl<A: 'static> fmt::Display for Payload<A> {
760 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
761 match &self.inner {
762 Some(a) => f.write_str(payload_as_str(a)),
763 None => process::abort(),
764 }
765 }
766 }
767
768 let loc = Location::caller();
769 crate::sys::backtrace::__rust_end_short_backtrace(move || {
770 rust_panic_with_hook(
771 &mut Payload { inner: Some(msg) },
772 loc,
773 /* can_unwind */ true,
774 /* force_no_backtrace */ false,
775 )
776 })
777}
778
779fn payload_as_str(payload: &dyn Any) -> &str {
780 if let Some(&s: &str) = payload.downcast_ref::<&'static str>() {
781 s
782 } else if let Some(s: &String) = payload.downcast_ref::<String>() {
783 s.as_str()
784 } else {
785 "Box<dyn Any>"
786 }
787}
788
789/// Central point for dispatching panics.
790///
791/// Executes the primary logic for a panic, including checking for recursive
792/// panics, panic hooks, and finally dispatching to the panic runtime to either
793/// abort or unwind.
794#[optimize(size)]
795fn rust_panic_with_hook(
796 payload: &mut dyn PanicPayload,
797 location: &Location<'_>,
798 can_unwind: bool,
799 force_no_backtrace: bool,
800) -> ! {
801 let must_abort = panic_count::increase(true);
802
803 // Check if we need to abort immediately.
804 if let Some(must_abort) = must_abort {
805 match must_abort {
806 panic_count::MustAbort::PanicInHook => {
807 // Don't try to format the message in this case, perhaps that is causing the
808 // recursive panics. However if the message is just a string, no user-defined
809 // code is involved in printing it, so that is risk-free.
810 let message: &str = payload.as_str().unwrap_or_default();
811 rtprintpanic!(
812 "panicked at {location}:\n{message}\nthread panicked while processing panic. aborting.\n"
813 );
814 }
815 panic_count::MustAbort::AlwaysAbort => {
816 // Unfortunately, this does not print a backtrace, because creating
817 // a `Backtrace` will allocate, which we must avoid here.
818 rtprintpanic!("aborting due to panic at {location}:\n{payload}\n");
819 }
820 }
821 crate::sys::abort_internal();
822 }
823
824 match *HOOK.read().unwrap_or_else(PoisonError::into_inner) {
825 // Some platforms (like wasm) know that printing to stderr won't ever actually
826 // print anything, and if that's the case we can skip the default
827 // hook. Since string formatting happens lazily when calling `payload`
828 // methods, this means we avoid formatting the string at all!
829 // (The panic runtime might still call `payload.take_box()` though and trigger
830 // formatting.)
831 Hook::Default if panic_output().is_none() => {}
832 Hook::Default => {
833 default_hook(&PanicHookInfo::new(
834 location,
835 payload.get(),
836 can_unwind,
837 force_no_backtrace,
838 ));
839 }
840 Hook::Custom(ref hook) => {
841 hook(&PanicHookInfo::new(location, payload.get(), can_unwind, force_no_backtrace));
842 }
843 }
844
845 // Indicate that we have finished executing the panic hook. After this point
846 // it is fine if there is a panic while executing destructors, as long as it
847 // it contained within a `catch_unwind`.
848 panic_count::finished_panic_hook();
849
850 if !can_unwind {
851 // If a thread panics while running destructors or tries to unwind
852 // through a nounwind function (e.g. extern "C") then we cannot continue
853 // unwinding and have to abort immediately.
854 rtprintpanic!("thread caused non-unwinding panic. aborting.\n");
855 crate::sys::abort_internal();
856 }
857
858 rust_panic(payload)
859}
860
861/// This is the entry point for `resume_unwind`.
862/// It just forwards the payload to the panic runtime.
863#[cfg_attr(feature = "panic_immediate_abort", inline)]
864pub fn rust_panic_without_hook(payload: Box<dyn Any + Send>) -> ! {
865 panic_count::increase(run_panic_hook:false);
866
867 struct RewrapBox(Box<dyn Any + Send>);
868
869 unsafe impl PanicPayload for RewrapBox {
870 fn take_box(&mut self) -> *mut (dyn Any + Send) {
871 Box::into_raw(mem::replace(&mut self.0, src:Box::new(())))
872 }
873
874 fn get(&mut self) -> &(dyn Any + Send) {
875 &*self.0
876 }
877 }
878
879 impl fmt::Display for RewrapBox {
880 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
881 f.write_str(data:payload_as_str(&self.0))
882 }
883 }
884
885 rust_panic(&mut RewrapBox(payload))
886}
887
888/// An unmangled function (through `rustc_std_internal_symbol`) on which to slap
889/// yer breakpoints.
890#[inline(never)]
891#[cfg_attr(not(test), rustc_std_internal_symbol)]
892#[cfg(not(feature = "panic_immediate_abort"))]
893fn rust_panic(msg: &mut dyn PanicPayload) -> ! {
894 let code: u32 = unsafe { __rust_start_panic(payload:msg) };
895 rtabort!("failed to initiate panic, error {code}")
896}
897
898#[cfg_attr(not(test), rustc_std_internal_symbol)]
899#[cfg(feature = "panic_immediate_abort")]
900fn rust_panic(_: &mut dyn PanicPayload) -> ! {
901 unsafe {
902 crate::intrinsics::abort();
903 }
904}
905

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