1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Implementation of various bits and pieces of the `panic!` macro and
12 //! associated runtime pieces.
14 //! Specifically, this module contains the implementation of:
17 //! * Executing a panic up to doing the actual implementation
18 //! * Shims around "try"
20 use core::panic::BoxMeUp;
26 use core::panic::{PanicInfo, Location};
32 use sys::stdio::panic_output;
33 use sys_common::rwlock::RWLock;
34 use sys_common::thread_info;
39 pub static LOCAL_STDERR: RefCell<Option<Box<dyn Write + Send>>> = {
44 // Binary interface to the panic runtime that the standard library depends on.
46 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in
47 // RFC 1513) to indicate that it requires some other crate tagged with
48 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
49 // implement these symbols (with the same signatures) so we can get matched up
52 // One day this may look a little less ad-hoc with the compiler helping out to
53 // hook up these functions, but it is not this day!
54 #[allow(improper_ctypes)]
56 fn __rust_maybe_catch_panic(f: fn(*mut u8),
59 vtable_ptr: *mut usize) -> u32;
61 fn __rust_start_panic(payload: usize) -> u32;
64 #[derive(Copy, Clone)]
67 Custom(*mut (dyn Fn(&PanicInfo) + 'static + Sync + Send)),
70 static HOOK_LOCK: RWLock = RWLock::new();
71 static mut HOOK: Hook = Hook::Default;
73 /// Registers a custom panic hook, replacing any that was previously registered.
75 /// The panic hook is invoked when a thread panics, but before the panic runtime
76 /// is invoked. As such, the hook will run with both the aborting and unwinding
77 /// runtimes. The default hook prints a message to standard error and generates
78 /// a backtrace if requested, but this behavior can be customized with the
79 /// `set_hook` and [`take_hook`] functions.
81 /// [`take_hook`]: ./fn.take_hook.html
83 /// The hook is provided with a `PanicInfo` struct which contains information
84 /// about the origin of the panic, including the payload passed to `panic!` and
85 /// the source code location from which the panic originated.
87 /// The panic hook is a global resource.
91 /// Panics if called from a panicking thread.
95 /// The following will print "Custom panic hook":
100 /// panic::set_hook(Box::new(|_| {
101 /// println!("Custom panic hook");
104 /// panic!("Normal panic");
106 #[stable(feature = "panic_hooks", since = "1.10.0")]
107 pub fn set_hook(hook: Box<dyn Fn(&PanicInfo) + 'static + Sync + Send>) {
108 if thread::panicking() {
109 panic!("cannot modify the panic hook from a panicking thread");
115 HOOK = Hook::Custom(Box::into_raw(hook));
116 HOOK_LOCK.write_unlock();
118 if let Hook::Custom(ptr) = old_hook {
124 /// Unregisters the current panic hook, returning it.
126 /// *See also the function [`set_hook`].*
128 /// [`set_hook`]: ./fn.set_hook.html
130 /// If no custom hook is registered, the default hook will be returned.
134 /// Panics if called from a panicking thread.
138 /// The following will print "Normal panic":
143 /// panic::set_hook(Box::new(|_| {
144 /// println!("Custom panic hook");
147 /// let _ = panic::take_hook();
149 /// panic!("Normal panic");
151 #[stable(feature = "panic_hooks", since = "1.10.0")]
152 pub fn take_hook() -> Box<dyn Fn(&PanicInfo) + 'static + Sync + Send> {
153 if thread::panicking() {
154 panic!("cannot modify the panic hook from a panicking thread");
160 HOOK = Hook::Default;
161 HOOK_LOCK.write_unlock();
164 Hook::Default => Box::new(default_hook),
165 Hook::Custom(ptr) => Box::from_raw(ptr),
170 fn default_hook(info: &PanicInfo) {
171 #[cfg(feature = "backtrace")]
172 use sys_common::backtrace;
174 // If this is a double panic, make sure that we print a backtrace
175 // for this panic. Otherwise only print it if logging is enabled.
176 #[cfg(feature = "backtrace")]
177 let log_backtrace = {
178 let panics = update_panic_count(0);
181 Some(backtrace::PrintFormat::Full)
183 backtrace::log_enabled()
187 let location = info.location().unwrap(); // The current implementation always returns Some
189 let msg = match info.payload().downcast_ref::<&'static str>() {
191 None => match info.payload().downcast_ref::<String>() {
196 let thread = thread_info::current_thread();
197 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
199 let write = |err: &mut dyn (::io::Write)| {
200 let _ = writeln!(err, "thread '{}' panicked at '{}', {}",
201 name, msg, location);
203 #[cfg(feature = "backtrace")]
205 use sync::atomic::{AtomicBool, Ordering};
207 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
209 if let Some(format) = log_backtrace {
210 let _ = backtrace::print(err, format);
211 } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
212 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` \
213 environment variable to display a backtrace.");
218 if let Some(mut local) = LOCAL_STDERR.with(|s| s.borrow_mut().take()) {
220 let mut s = Some(local);
221 LOCAL_STDERR.with(|slot| {
222 *slot.borrow_mut() = s.take();
224 } else if let Some(mut out) = panic_output() {
232 #[unstable(feature = "update_panic_count", issue = "0")]
233 pub fn update_panic_count(amt: isize) -> usize {
235 thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
237 PANIC_COUNT.with(|c| {
238 let next = (c.get() as isize + amt) as usize;
245 pub use realstd::rt::update_panic_count;
247 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
248 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
249 #[allow(unions_with_drop_fields)]
255 // We do some sketchy operations with ownership here for the sake of
256 // performance. We can only pass pointers down to
257 // `__rust_maybe_catch_panic` (can't pass objects by value), so we do all
258 // the ownership tracking here manually using a union.
260 // We go through a transition where:
262 // * First, we set the data to be the closure that we're going to call.
263 // * When we make the function call, the `do_call` function below, we take
264 // ownership of the function pointer. At this point the `Data` union is
265 // entirely uninitialized.
266 // * If the closure successfully returns, we write the return value into the
267 // data's return slot. Note that `ptr::write` is used as it's overwriting
268 // uninitialized data.
269 // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
270 // in one of two states:
272 // 1. The closure didn't panic, in which case the return value was
273 // filled in. We move it out of `data` and return it.
274 // 2. The closure panicked, in which case the return value wasn't
275 // filled in. In this case the entire `data` union is invalid, so
276 // there is no need to drop anything.
278 // Once we stack all that together we should have the "most efficient'
279 // method of calling a catch panic whilst juggling ownership.
280 let mut any_data = 0;
281 let mut any_vtable = 0;
282 let mut data = Data {
286 let r = __rust_maybe_catch_panic(do_call::<F, R>,
287 &mut data as *mut _ as *mut u8,
292 debug_assert!(update_panic_count(0) == 0);
295 update_panic_count(-1);
296 debug_assert!(update_panic_count(0) == 0);
297 Err(mem::transmute(raw::TraitObject {
298 data: any_data as *mut _,
299 vtable: any_vtable as *mut _,
303 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
305 let data = data as *mut Data<F, R>;
306 let f = ptr::read(&mut (*data).f);
307 ptr::write(&mut (*data).r, f());
312 /// Determines whether the current thread is unwinding because of panic.
313 pub fn panicking() -> bool {
314 update_panic_count(0) != 0
317 /// Entry point of panic from the libcore crate.
321 pub fn rust_begin_panic(info: &PanicInfo) -> ! {
322 continue_panic_fmt(&info)
325 /// The entry point for panicking with a formatted message.
327 /// This is designed to reduce the amount of code required at the call
328 /// site as much as possible (so that `panic!()` has as low an impact
329 /// on (e.g.) the inlining of other functions as possible), by moving
330 /// the actual formatting into this shared place.
331 #[unstable(feature = "libstd_sys_internals",
332 reason = "used by the panic! macro",
335 // If panic_immediate_abort, inline the abort call,
336 // otherwise avoid inlining because of it is cold path.
337 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
338 #[cfg_attr( feature="panic_immediate_abort" ,inline)]
339 pub fn begin_panic_fmt(msg: &fmt::Arguments,
340 file_line_col: &(&'static str, u32, u32)) -> ! {
341 if cfg!(feature = "panic_immediate_abort") {
342 unsafe { intrinsics::abort() }
345 let (file, line, col) = *file_line_col;
346 let info = PanicInfo::internal_constructor(
348 Location::internal_constructor(file, line, col),
350 continue_panic_fmt(&info)
353 fn continue_panic_fmt(info: &PanicInfo) -> ! {
354 struct PanicPayload<'a> {
355 inner: &'a fmt::Arguments<'a>,
356 string: Option<String>,
359 impl<'a> PanicPayload<'a> {
360 fn new(inner: &'a fmt::Arguments<'a>) -> PanicPayload<'a> {
361 PanicPayload { inner, string: None }
364 fn fill(&mut self) -> &mut String {
367 let inner = self.inner;
368 self.string.get_or_insert_with(|| {
369 let mut s = String::new();
370 drop(s.write_fmt(*inner));
376 unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
377 fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
378 let contents = mem::replace(self.fill(), String::new());
379 Box::into_raw(Box::new(contents))
382 fn get(&mut self) -> &(dyn Any + Send) {
387 // We do two allocations here, unfortunately. But (a) they're
388 // required with the current scheme, and (b) we don't handle
389 // panic + OOM properly anyway (see comment in begin_panic
392 let loc = info.location().unwrap(); // The current implementation always returns Some
393 let msg = info.message().unwrap(); // The current implementation always returns Some
394 let file_line_col = (loc.file(), loc.line(), loc.column());
395 rust_panic_with_hook(
396 &mut PanicPayload::new(msg),
401 /// This is the entry point of panicking for panic!() and assert!().
402 #[unstable(feature = "libstd_sys_internals",
403 reason = "used by the panic! macro",
405 #[cfg_attr(not(test), lang = "begin_panic")]
406 // never inline unless panic_immediate_abort to avoid code
407 // bloat at the call sites as much as possible
408 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
410 pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
411 if cfg!(feature = "panic_immediate_abort") {
412 unsafe { intrinsics::abort() }
415 // Note that this should be the only allocation performed in this code path.
416 // Currently this means that panic!() on OOM will invoke this code path,
417 // but then again we're not really ready for panic on OOM anyway. If
418 // we do start doing this, then we should propagate this allocation to
419 // be performed in the parent of this thread instead of the thread that's
422 rust_panic_with_hook(&mut PanicPayload::new(msg), None, file_line_col);
424 struct PanicPayload<A> {
428 impl<A: Send + 'static> PanicPayload<A> {
429 fn new(inner: A) -> PanicPayload<A> {
430 PanicPayload { inner: Some(inner) }
434 unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
435 fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
436 let data = match self.inner.take() {
437 Some(a) => Box::new(a) as Box<dyn Any + Send>,
438 None => Box::new(()),
443 fn get(&mut self) -> &(dyn Any + Send) {
452 /// Central point for dispatching panics.
454 /// Executes the primary logic for a panic, including checking for recursive
455 /// panics, panic hooks, and finally dispatching to the panic runtime to either
457 fn rust_panic_with_hook(payload: &mut dyn BoxMeUp,
458 message: Option<&fmt::Arguments>,
459 file_line_col: &(&str, u32, u32)) -> ! {
460 let (file, line, col) = *file_line_col;
462 let panics = update_panic_count(1);
464 // If this is the third nested call (e.g., panics == 2, this is 0-indexed),
465 // the panic hook probably triggered the last panic, otherwise the
466 // double-panic check would have aborted the process. In this case abort the
467 // process real quickly as we don't want to try calling it again as it'll
468 // probably just panic again.
470 util::dumb_print(format_args!("thread panicked while processing \
471 panic. aborting.\n"));
472 unsafe { intrinsics::abort() }
476 let mut info = PanicInfo::internal_constructor(
478 Location::internal_constructor(file, line, col),
482 // Some platforms know that printing to stderr won't ever actually
483 // print anything, and if that's the case we can skip the default
485 Hook::Default if panic_output().is_none() => {}
487 info.set_payload(payload.get());
490 Hook::Custom(ptr) => {
491 info.set_payload(payload.get());
495 HOOK_LOCK.read_unlock();
499 // If a thread panics while it's already unwinding then we
500 // have limited options. Currently our preference is to
501 // just abort. In the future we may consider resuming
502 // unwinding or otherwise exiting the thread cleanly.
503 util::dumb_print(format_args!("thread panicked while panicking. \
505 unsafe { intrinsics::abort() }
511 /// Shim around rust_panic. Called by resume_unwind.
512 pub fn update_count_then_panic(msg: Box<dyn Any + Send>) -> ! {
513 update_panic_count(1);
515 struct RewrapBox(Box<dyn Any + Send>);
517 unsafe impl BoxMeUp for RewrapBox {
518 fn box_me_up(&mut self) -> *mut (dyn Any + Send) {
519 Box::into_raw(mem::replace(&mut self.0, Box::new(())))
522 fn get(&mut self) -> &(dyn Any + Send) {
527 rust_panic(&mut RewrapBox(msg))
530 /// An unmangled function (through `rustc_std_internal_symbol`) on which to slap
533 #[cfg_attr(not(test), rustc_std_internal_symbol)]
534 fn rust_panic(mut msg: &mut dyn BoxMeUp) -> ! {
536 let obj = &mut msg as *mut &mut dyn BoxMeUp;
537 __rust_start_panic(obj as usize)
539 rtabort!("failed to initiate panic, error {}", code)