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"
29 use sys::stdio::Stderr;
30 use sys_common::rwlock::RWLock;
31 use sys_common::thread_info;
36 pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
41 // Binary interface to the panic runtime that the standard library depends on.
43 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in
44 // RFC 1513) to indicate that it requires some other crate tagged with
45 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
46 // implement these symbols (with the same signatures) so we can get matched up
49 // One day this may look a little less ad-hoc with the compiler helping out to
50 // hook up these functions, but it is not this day!
51 #[allow(improper_ctypes)]
53 fn __rust_maybe_catch_panic(f: fn(*mut u8),
56 vtable_ptr: *mut usize) -> u32;
58 fn __rust_start_panic(data: usize, vtable: usize) -> u32;
61 #[derive(Copy, Clone)]
64 Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
67 static HOOK_LOCK: RWLock = RWLock::new();
68 static mut HOOK: Hook = Hook::Default;
70 /// Registers a custom panic hook, replacing any that was previously registered.
72 /// The panic hook is invoked when a thread panics, but before the panic runtime
73 /// is invoked. As such, the hook will run with both the aborting and unwinding
74 /// runtimes. The default hook prints a message to standard error and generates
75 /// a backtrace if requested, but this behavior can be customized with the
76 /// `set_hook` and `take_hook` functions.
78 /// The hook is provided with a `PanicInfo` struct which contains information
79 /// about the origin of the panic, including the payload passed to `panic!` and
80 /// the source code location from which the panic originated.
82 /// The panic hook is a global resource.
86 /// Panics if called from a panicking thread.
90 /// The following will print "Custom panic hook":
95 /// panic::set_hook(Box::new(|_| {
96 /// println!("Custom panic hook");
99 /// panic!("Normal panic");
101 #[stable(feature = "panic_hooks", since = "1.10.0")]
102 pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
103 if thread::panicking() {
104 panic!("cannot modify the panic hook from a panicking thread");
110 HOOK = Hook::Custom(Box::into_raw(hook));
111 HOOK_LOCK.write_unlock();
113 if let Hook::Custom(ptr) = old_hook {
119 /// Unregisters the current panic hook, returning it.
121 /// If no custom hook is registered, the default hook will be returned.
125 /// Panics if called from a panicking thread.
129 /// The following will print "Normal panic":
134 /// panic::set_hook(Box::new(|_| {
135 /// println!("Custom panic hook");
138 /// let _ = panic::take_hook();
140 /// panic!("Normal panic");
142 #[stable(feature = "panic_hooks", since = "1.10.0")]
143 pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
144 if thread::panicking() {
145 panic!("cannot modify the panic hook from a panicking thread");
151 HOOK = Hook::Default;
152 HOOK_LOCK.write_unlock();
155 Hook::Default => Box::new(default_hook),
156 Hook::Custom(ptr) => Box::from_raw(ptr),
161 /// A struct providing information about a panic.
163 /// `PanicInfo` structure is passed to a panic hook set by the [`set_hook()`]
166 /// [`set_hook()`]: ../../std/panic/fn.set_hook.html
173 /// panic::set_hook(Box::new(|panic_info| {
174 /// println!("panic occured: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
177 /// panic!("Normal panic");
179 #[stable(feature = "panic_hooks", since = "1.10.0")]
181 pub struct PanicInfo<'a> {
182 payload: &'a (Any + Send),
183 location: Location<'a>,
186 impl<'a> PanicInfo<'a> {
187 /// Returns the payload associated with the panic.
189 /// This will commonly, but not always, be a `&'static str` or [`String`].
191 /// [`String`]: ../../std/string/struct.String.html
198 /// panic::set_hook(Box::new(|panic_info| {
199 /// println!("panic occured: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
202 /// panic!("Normal panic");
204 #[stable(feature = "panic_hooks", since = "1.10.0")]
205 pub fn payload(&self) -> &(Any + Send) {
209 /// Returns information about the location from which the panic originated,
212 /// This method will currently always return [`Some`], but this may change
213 /// in future versions.
215 /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
222 /// panic::set_hook(Box::new(|panic_info| {
223 /// if let Some(location) = panic_info.location() {
224 /// println!("panic occured in file '{}' at line {}", location.file(), location.line());
226 /// println!("panic occured but can't get location information...");
230 /// panic!("Normal panic");
232 #[stable(feature = "panic_hooks", since = "1.10.0")]
233 pub fn location(&self) -> Option<&Location> {
238 /// A struct containing information about the location of a panic.
240 /// This structure is created by the [`location()`] method of [`PanicInfo`].
242 /// [`location()`]: ../../std/panic/struct.PanicInfo.html#method.location
243 /// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
250 /// panic::set_hook(Box::new(|panic_info| {
251 /// if let Some(location) = panic_info.location() {
252 /// println!("panic occured in file '{}' at line {}", location.file(), location.line());
254 /// println!("panic occured but can't get location information...");
258 /// panic!("Normal panic");
261 #[stable(feature = "panic_hooks", since = "1.10.0")]
262 pub struct Location<'a> {
267 impl<'a> Location<'a> {
268 /// Returns the name of the source file from which the panic originated.
275 /// panic::set_hook(Box::new(|panic_info| {
276 /// if let Some(location) = panic_info.location() {
277 /// println!("panic occured in file '{}'", location.file());
279 /// println!("panic occured but can't get location information...");
283 /// panic!("Normal panic");
285 #[stable(feature = "panic_hooks", since = "1.10.0")]
286 pub fn file(&self) -> &str {
290 /// Returns the line number from which the panic originated.
297 /// panic::set_hook(Box::new(|panic_info| {
298 /// if let Some(location) = panic_info.location() {
299 /// println!("panic occured at line {}", location.line());
301 /// println!("panic occured but can't get location information...");
305 /// panic!("Normal panic");
307 #[stable(feature = "panic_hooks", since = "1.10.0")]
308 pub fn line(&self) -> u32 {
313 fn default_hook(info: &PanicInfo) {
314 #[cfg(feature = "backtrace")]
315 use sys_common::backtrace;
317 // If this is a double panic, make sure that we print a backtrace
318 // for this panic. Otherwise only print it if logging is enabled.
319 #[cfg(feature = "backtrace")]
320 let log_backtrace = {
321 let panics = update_panic_count(0);
323 panics >= 2 || backtrace::log_enabled()
326 let file = info.location.file;
327 let line = info.location.line;
329 let msg = match info.payload.downcast_ref::<&'static str>() {
331 None => match info.payload.downcast_ref::<String>() {
336 let mut err = Stderr::new().ok();
337 let thread = thread_info::current_thread();
338 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
340 let write = |err: &mut ::io::Write| {
341 let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}",
342 name, msg, file, line);
344 #[cfg(feature = "backtrace")]
346 use sync::atomic::{AtomicBool, Ordering};
348 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
351 let _ = backtrace::write(err);
352 } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
353 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
358 let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
359 match (prev, err.as_mut()) {
360 (Some(mut stderr), _) => {
362 let mut s = Some(stderr);
363 LOCAL_STDERR.with(|slot| {
364 *slot.borrow_mut() = s.take();
367 (None, Some(ref mut err)) => { write(err) }
375 #[unstable(feature = "update_panic_count", issue = "0")]
376 pub fn update_panic_count(amt: isize) -> usize {
378 thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
380 PANIC_COUNT.with(|c| {
381 let next = (c.get() as isize + amt) as usize;
388 pub use realstd::rt::update_panic_count;
390 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
391 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
397 // We do some sketchy operations with ownership here for the sake of
398 // performance. The `Data` structure is never actually fully valid, but
399 // instead it always contains at least one uninitialized field. We can only
400 // pass pointers down to `__rust_maybe_catch_panic` (can't pass objects by
401 // value), so we do all the ownership tracking here manully.
403 // Note that this is all invalid if any of these functions unwind, but the
404 // whole point of this function is to prevent that! As a result we go
405 // through a transition where:
407 // * First, only the closure we're going to call is initialized. The return
408 // value is uninitialized.
409 // * When we make the function call, the `do_call` function below, we take
410 // ownership of the function pointer, replacing it with uninitialized
411 // data. At this point the `Data` structure is entirely uninitialized, but
412 // it won't drop due to an unwind because it's owned on the other side of
414 // * If the closure successfully returns, we write the return value into the
415 // data's return slot. Note that `ptr::write` is used as it's overwriting
416 // uninitialized data.
417 // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
418 // in one of two states:
420 // 1. The closure didn't panic, in which case the return value was
421 // filled in. We have to be careful to `forget` the closure,
422 // however, as ownership was passed to the `do_call` function.
423 // 2. The closure panicked, in which case the return value wasn't
424 // filled in. In this case the entire `data` structure is invalid,
425 // so we forget the entire thing.
427 // Once we stack all that together we should have the "most efficient'
428 // method of calling a catch panic whilst juggling ownership.
429 let mut any_data = 0;
430 let mut any_vtable = 0;
431 let mut data = Data {
433 r: mem::uninitialized(),
436 let r = __rust_maybe_catch_panic(do_call::<F, R>,
437 &mut data as *mut _ as *mut u8,
442 let Data { f, r } = data;
444 debug_assert!(update_panic_count(0) == 0);
448 update_panic_count(-1);
449 debug_assert!(update_panic_count(0) == 0);
450 Err(mem::transmute(raw::TraitObject {
451 data: any_data as *mut _,
452 vtable: any_vtable as *mut _,
456 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
458 let data = data as *mut Data<F, R>;
459 let f = ptr::read(&mut (*data).f);
460 ptr::write(&mut (*data).r, f());
465 /// Determines whether the current thread is unwinding because of panic.
466 pub fn panicking() -> bool {
467 update_panic_count(0) != 0
470 /// Entry point of panic from the libcore crate.
472 #[lang = "panic_fmt"]
474 pub extern fn rust_begin_panic(msg: fmt::Arguments,
477 begin_panic_fmt(&msg, &(file, line))
480 /// The entry point for panicking with a formatted message.
482 /// This is designed to reduce the amount of code required at the call
483 /// site as much as possible (so that `panic!()` has as low an impact
484 /// on (e.g.) the inlining of other functions as possible), by moving
485 /// the actual formatting into this shared place.
486 #[unstable(feature = "libstd_sys_internals",
487 reason = "used by the panic! macro",
489 #[inline(never)] #[cold]
490 pub fn begin_panic_fmt(msg: &fmt::Arguments,
491 file_line: &(&'static str, u32)) -> ! {
494 // We do two allocations here, unfortunately. But (a) they're
495 // required with the current scheme, and (b) we don't handle
496 // panic + OOM properly anyway (see comment in begin_panic
499 let mut s = String::new();
500 let _ = s.write_fmt(*msg);
501 begin_panic(s, file_line)
504 /// This is the entry point of panicking for panic!() and assert!().
505 #[unstable(feature = "libstd_sys_internals",
506 reason = "used by the panic! macro",
508 #[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
509 pub fn begin_panic<M: Any + Send>(msg: M, file_line: &(&'static str, u32)) -> ! {
510 // Note that this should be the only allocation performed in this code path.
511 // Currently this means that panic!() on OOM will invoke this code path,
512 // but then again we're not really ready for panic on OOM anyway. If
513 // we do start doing this, then we should propagate this allocation to
514 // be performed in the parent of this thread instead of the thread that's
517 rust_panic_with_hook(Box::new(msg), file_line)
520 /// Executes the primary logic for a panic, including checking for recursive
521 /// panics and panic hooks.
523 /// This is the entry point or panics from libcore, formatted panics, and
524 /// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
525 /// run panic hooks, and then delegate to the actual implementation of panics.
528 fn rust_panic_with_hook(msg: Box<Any + Send>,
529 file_line: &(&'static str, u32)) -> ! {
530 let (file, line) = *file_line;
532 let panics = update_panic_count(1);
534 // If this is the third nested call (e.g. panics == 2, this is 0-indexed),
535 // the panic hook probably triggered the last panic, otherwise the
536 // double-panic check would have aborted the process. In this case abort the
537 // process real quickly as we don't want to try calling it again as it'll
538 // probably just panic again.
540 util::dumb_print(format_args!("thread panicked while processing \
541 panic. aborting.\n"));
542 unsafe { intrinsics::abort() }
546 let info = PanicInfo {
555 Hook::Default => default_hook(&info),
556 Hook::Custom(ptr) => (*ptr)(&info),
558 HOOK_LOCK.read_unlock();
562 // If a thread panics while it's already unwinding then we
563 // have limited options. Currently our preference is to
564 // just abort. In the future we may consider resuming
565 // unwinding or otherwise exiting the thread cleanly.
566 util::dumb_print(format_args!("thread panicked while panicking. \
568 unsafe { intrinsics::abort() }
574 /// Shim around rust_panic. Called by resume_unwind.
575 pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
576 update_panic_count(1);
580 /// A private no-mangle function on which to slap yer breakpoints.
582 #[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
583 pub fn rust_panic(msg: Box<Any + Send>) -> ! {
585 let obj = mem::transmute::<_, raw::TraitObject>(msg);
586 __rust_start_panic(obj.data as usize, obj.vtable as usize)
588 rtabort!("failed to initiate panic, error {}", code)