1 //! Implementation of various bits and pieces of the `panic!` macro and
2 //! associated runtime pieces.
4 //! Specifically, this module contains the implementation of:
7 //! * Executing a panic up to doing the actual implementation
8 //! * Shims around "try"
10 use core::panic::{BoxMeUp, PanicInfo, Location};
14 use crate::intrinsics;
15 use crate::mem::{self, ManuallyDrop};
17 use crate::sync::atomic::{AtomicBool, Ordering};
18 use crate::sys::stdio::panic_output;
19 use crate::sys_common::rwlock::RWLock;
20 use crate::sys_common::{thread_info, util};
21 use crate::sys_common::backtrace::{self, RustBacktrace};
26 use crate::io::set_panic;
27 // make sure to use the stderr output configured
28 // by libtest in the real copy of std
30 use realstd::io::set_panic;
32 // Binary interface to the panic runtime that the standard library depends on.
34 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in
35 // RFC 1513) to indicate that it requires some other crate tagged with
36 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
37 // implement these symbols (with the same signatures) so we can get matched up
40 // One day this may look a little less ad-hoc with the compiler helping out to
41 // hook up these functions, but it is not this day!
42 #[allow(improper_ctypes)]
44 fn __rust_maybe_catch_panic(f: fn(*mut u8),
47 vtable_ptr: *mut usize) -> u32;
49 /// `payload` is actually a `*mut &mut dyn BoxMeUp` but that would cause FFI warnings.
51 fn __rust_start_panic(payload: usize) -> u32;
54 #[derive(Copy, Clone)]
57 Custom(*mut (dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send)),
60 static HOOK_LOCK: RWLock = RWLock::new();
61 static mut HOOK: Hook = Hook::Default;
63 /// Registers a custom panic hook, replacing any that was previously registered.
65 /// The panic hook is invoked when a thread panics, but before the panic runtime
66 /// is invoked. As such, the hook will run with both the aborting and unwinding
67 /// runtimes. The default hook prints a message to standard error and generates
68 /// a backtrace if requested, but this behavior can be customized with the
69 /// `set_hook` and [`take_hook`] functions.
71 /// [`take_hook`]: ./fn.take_hook.html
73 /// The hook is provided with a `PanicInfo` struct which contains information
74 /// about the origin of the panic, including the payload passed to `panic!` and
75 /// the source code location from which the panic originated.
77 /// The panic hook is a global resource.
81 /// Panics if called from a panicking thread.
85 /// The following will print "Custom panic hook":
90 /// panic::set_hook(Box::new(|_| {
91 /// println!("Custom panic hook");
94 /// panic!("Normal panic");
96 #[stable(feature = "panic_hooks", since = "1.10.0")]
97 pub fn set_hook(hook: Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>) {
98 if thread::panicking() {
99 panic!("cannot modify the panic hook from a panicking thread");
105 HOOK = Hook::Custom(Box::into_raw(hook));
106 HOOK_LOCK.write_unlock();
108 if let Hook::Custom(ptr) = old_hook {
109 #[allow(unused_must_use)] {
116 /// Unregisters the current panic hook, returning it.
118 /// *See also the function [`set_hook`].*
120 /// [`set_hook`]: ./fn.set_hook.html
122 /// If no custom hook is registered, the default hook will be returned.
126 /// Panics if called from a panicking thread.
130 /// The following will print "Normal panic":
135 /// panic::set_hook(Box::new(|_| {
136 /// println!("Custom panic hook");
139 /// let _ = panic::take_hook();
141 /// panic!("Normal panic");
143 #[stable(feature = "panic_hooks", since = "1.10.0")]
144 pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
145 if thread::panicking() {
146 panic!("cannot modify the panic hook from a panicking thread");
152 HOOK = Hook::Default;
153 HOOK_LOCK.write_unlock();
156 Hook::Default => Box::new(default_hook),
157 Hook::Custom(ptr) => Box::from_raw(ptr),
162 fn default_hook(info: &PanicInfo<'_>) {
163 // If this is a double panic, make sure that we print a backtrace
164 // for this panic. Otherwise only print it if logging is enabled.
165 let backtrace_env = if update_panic_count(0) >= 2 {
166 RustBacktrace::Print(backtrace_rs::PrintFmt::Full)
168 backtrace::rust_backtrace_env()
171 // The current implementation always returns `Some`.
172 let location = info.location().unwrap();
174 let msg = match info.payload().downcast_ref::<&'static str>() {
176 None => match info.payload().downcast_ref::<String>() {
181 let thread = thread_info::current_thread();
182 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
184 let write = |err: &mut dyn crate::io::Write| {
185 let _ = writeln!(err, "thread '{}' panicked at '{}', {}",
186 name, msg, location);
188 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
190 match backtrace_env {
191 RustBacktrace::Print(format) => drop(backtrace::print(err, format)),
192 RustBacktrace::Disabled => {}
193 RustBacktrace::RuntimeDisabled => {
194 if FIRST_PANIC.swap(false, Ordering::SeqCst) {
195 let _ = writeln!(err, "note: run with `RUST_BACKTRACE=1` \
196 environment variable to display a backtrace.");
202 if let Some(mut local) = set_panic(None) {
203 // NB. In `cfg(test)` this uses the forwarding impl
204 // for `Box<dyn (::realstd::io::Write) + Send>`.
206 set_panic(Some(local));
207 } else if let Some(mut out) = panic_output() {
215 #[unstable(feature = "update_panic_count", issue = "0")]
216 pub fn update_panic_count(amt: isize) -> usize {
217 use crate::cell::Cell;
218 thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
220 PANIC_COUNT.with(|c| {
221 let next = (c.get() as isize + amt) as usize;
228 pub use realstd::rt::update_panic_count;
230 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
231 pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
237 // We do some sketchy operations with ownership here for the sake of
238 // performance. We can only pass pointers down to
239 // `__rust_maybe_catch_panic` (can't pass objects by value), so we do all
240 // the ownership tracking here manually using a union.
242 // We go through a transition where:
244 // * First, we set the data to be the closure that we're going to call.
245 // * When we make the function call, the `do_call` function below, we take
246 // ownership of the function pointer. At this point the `Data` union is
247 // entirely uninitialized.
248 // * If the closure successfully returns, we write the return value into the
249 // data's return slot. Note that `ptr::write` is used as it's overwriting
250 // uninitialized data.
251 // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
252 // in one of two states:
254 // 1. The closure didn't panic, in which case the return value was
255 // filled in. We move it out of `data` and return it.
256 // 2. The closure panicked, in which case the return value wasn't
257 // filled in. In this case the entire `data` union is invalid, so
258 // there is no need to drop anything.
260 // Once we stack all that together we should have the "most efficient'
261 // method of calling a catch panic whilst juggling ownership.
262 let mut any_data = 0;
263 let mut any_vtable = 0;
264 let mut data = Data {
265 f: ManuallyDrop::new(f)
268 let r = __rust_maybe_catch_panic(do_call::<F, R>,
269 &mut data as *mut _ as *mut u8,
274 debug_assert!(update_panic_count(0) == 0);
275 Ok(ManuallyDrop::into_inner(data.r))
277 update_panic_count(-1);
278 debug_assert!(update_panic_count(0) == 0);
279 Err(mem::transmute(raw::TraitObject {
280 data: any_data as *mut _,
281 vtable: any_vtable as *mut _,
285 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
287 let data = data as *mut Data<F, R>;
288 let data = &mut (*data);
289 let f = ManuallyDrop::take(&mut data.f);
290 data.r = ManuallyDrop::new(f());
295 /// Determines whether the current thread is unwinding because of panic.
296 pub fn panicking() -> bool {
297 update_panic_count(0) != 0
300 /// The entry point for panicking with a formatted message.
302 /// This is designed to reduce the amount of code required at the call
303 /// site as much as possible (so that `panic!()` has as low an impact
304 /// on (e.g.) the inlining of other functions as possible), by moving
305 /// the actual formatting into this shared place.
306 #[unstable(feature = "libstd_sys_internals",
307 reason = "used by the panic! macro",
310 // If panic_immediate_abort, inline the abort call,
311 // otherwise avoid inlining because of it is cold path.
312 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
313 #[cfg_attr( feature="panic_immediate_abort" ,inline)]
314 pub fn begin_panic_fmt(msg: &fmt::Arguments<'_>,
315 file_line_col: &(&'static str, u32, u32)) -> ! {
316 if cfg!(feature = "panic_immediate_abort") {
317 unsafe { intrinsics::abort() }
320 // Just package everything into a `PanicInfo` and continue like libcore panics.
321 let (file, line, col) = *file_line_col;
322 let location = Location::internal_constructor(file, line, col);
323 let info = PanicInfo::internal_constructor(Some(msg), &location);
324 begin_panic_handler(&info)
327 /// Entry point of panics from the libcore crate (`panic_impl` lang item).
328 #[cfg_attr(not(test), panic_handler)]
330 pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
331 struct PanicPayload<'a> {
332 inner: &'a fmt::Arguments<'a>,
333 string: Option<String>,
336 impl<'a> PanicPayload<'a> {
337 fn new(inner: &'a fmt::Arguments<'a>) -> PanicPayload<'a> {
338 PanicPayload { inner, string: None }
341 fn fill(&mut self) -> &mut String {
342 use crate::fmt::Write;
344 let inner = self.inner;
345 // Lazily, the first time this gets called, run the actual string formatting.
346 self.string.get_or_insert_with(|| {
347 let mut s = String::new();
348 drop(s.write_fmt(*inner));
354 unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
355 fn take_box(&mut self) -> *mut (dyn Any + Send) {
356 let contents = mem::take(self.fill());
357 Box::into_raw(Box::new(contents))
360 fn get(&mut self) -> &(dyn Any + Send) {
365 // We do two allocations here, unfortunately. But (a) they're
366 // required with the current scheme, and (b) we don't handle
367 // panic + OOM properly anyway (see comment in begin_panic
370 let loc = info.location().unwrap(); // The current implementation always returns Some
371 let msg = info.message().unwrap(); // The current implementation always returns Some
372 let file_line_col = (loc.file(), loc.line(), loc.column());
373 rust_panic_with_hook(
374 &mut PanicPayload::new(msg),
379 /// This is the entry point of panicking for the non-format-string variants of
380 /// panic!() and assert!(). In particular, this is the only entry point that supports
381 /// arbitrary payloads, not just format strings.
382 #[unstable(feature = "libstd_sys_internals",
383 reason = "used by the panic! macro",
385 #[cfg_attr(not(test), lang = "begin_panic")] // lang item for CTFE panic support
386 // never inline unless panic_immediate_abort to avoid code
387 // bloat at the call sites as much as possible
388 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
390 pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
391 if cfg!(feature = "panic_immediate_abort") {
392 unsafe { intrinsics::abort() }
395 // Note that this should be the only allocation performed in this code path.
396 // Currently this means that panic!() on OOM will invoke this code path,
397 // but then again we're not really ready for panic on OOM anyway. If
398 // we do start doing this, then we should propagate this allocation to
399 // be performed in the parent of this thread instead of the thread that's
402 rust_panic_with_hook(&mut PanicPayload::new(msg), None, file_line_col);
404 struct PanicPayload<A> {
408 impl<A: Send + 'static> PanicPayload<A> {
409 fn new(inner: A) -> PanicPayload<A> {
410 PanicPayload { inner: Some(inner) }
414 unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
415 fn take_box(&mut self) -> *mut (dyn Any + Send) {
416 let data = match self.inner.take() {
417 Some(a) => Box::new(a) as Box<dyn Any + Send>,
418 None => process::abort(),
423 fn get(&mut self) -> &(dyn Any + Send) {
426 None => process::abort(),
432 /// Central point for dispatching panics.
434 /// Executes the primary logic for a panic, including checking for recursive
435 /// panics, panic hooks, and finally dispatching to the panic runtime to either
437 fn rust_panic_with_hook(payload: &mut dyn BoxMeUp,
438 message: Option<&fmt::Arguments<'_>>,
439 file_line_col: &(&str, u32, u32)) -> ! {
440 let (file, line, col) = *file_line_col;
442 let panics = update_panic_count(1);
444 // If this is the third nested call (e.g., panics == 2, this is 0-indexed),
445 // the panic hook probably triggered the last panic, otherwise the
446 // double-panic check would have aborted the process. In this case abort the
447 // process real quickly as we don't want to try calling it again as it'll
448 // probably just panic again.
450 util::dumb_print(format_args!("thread panicked while processing \
451 panic. aborting.\n"));
452 unsafe { intrinsics::abort() }
456 let location = Location::internal_constructor(file, line, col);
457 let mut info = PanicInfo::internal_constructor(message, &location);
460 // Some platforms (like wasm) know that printing to stderr won't ever actually
461 // print anything, and if that's the case we can skip the default
462 // hook. Since string formatting happens lazily when calling `payload`
463 // methods, this means we avoid formatting the string at all!
464 // (The panic runtime might still call `payload.take_box()` though and trigger
466 Hook::Default if panic_output().is_none() => {}
468 info.set_payload(payload.get());
471 Hook::Custom(ptr) => {
472 info.set_payload(payload.get());
476 HOOK_LOCK.read_unlock();
480 // If a thread panics while it's already unwinding then we
481 // have limited options. Currently our preference is to
482 // just abort. In the future we may consider resuming
483 // unwinding or otherwise exiting the thread cleanly.
484 util::dumb_print(format_args!("thread panicked while panicking. \
486 unsafe { intrinsics::abort() }
492 /// Shim around rust_panic. Called by resume_unwind.
493 pub fn update_count_then_panic(msg: Box<dyn Any + Send>) -> ! {
494 update_panic_count(1);
496 struct RewrapBox(Box<dyn Any + Send>);
498 unsafe impl BoxMeUp for RewrapBox {
499 fn take_box(&mut self) -> *mut (dyn Any + Send) {
500 Box::into_raw(mem::replace(&mut self.0, Box::new(())))
503 fn get(&mut self) -> &(dyn Any + Send) {
508 rust_panic(&mut RewrapBox(msg))
511 /// An unmangled function (through `rustc_std_internal_symbol`) on which to slap
514 #[cfg_attr(not(test), rustc_std_internal_symbol)]
515 fn rust_panic(mut msg: &mut dyn BoxMeUp) -> ! {
517 let obj = &mut msg as *mut &mut dyn BoxMeUp;
518 __rust_start_panic(obj as usize)
520 rtabort!("failed to initiate panic, error {}", code)