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.
87 #[stable(feature = "panic_hooks", since = "1.10.0")]
88 pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
89 if thread::panicking() {
90 panic!("cannot modify the panic hook from a panicking thread");
96 HOOK = Hook::Custom(Box::into_raw(hook));
97 HOOK_LOCK.write_unlock();
99 if let Hook::Custom(ptr) = old_hook {
105 /// Unregisters the current panic hook, returning it.
107 /// If no custom hook is registered, the default hook will be returned.
111 /// Panics if called from a panicking thread.
112 #[stable(feature = "panic_hooks", since = "1.10.0")]
113 pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
114 if thread::panicking() {
115 panic!("cannot modify the panic hook from a panicking thread");
121 HOOK = Hook::Default;
122 HOOK_LOCK.write_unlock();
125 Hook::Default => Box::new(default_hook),
126 Hook::Custom(ptr) => {Box::from_raw(ptr)} // FIXME #30530
131 /// A struct providing information about a panic.
132 #[stable(feature = "panic_hooks", since = "1.10.0")]
133 pub struct PanicInfo<'a> {
134 payload: &'a (Any + Send),
135 location: Location<'a>,
138 impl<'a> PanicInfo<'a> {
139 /// Returns the payload associated with the panic.
141 /// This will commonly, but not always, be a `&'static str` or `String`.
142 #[stable(feature = "panic_hooks", since = "1.10.0")]
143 pub fn payload(&self) -> &(Any + Send) {
147 /// Returns information about the location from which the panic originated,
150 /// This method will currently always return `Some`, but this may change
151 /// in future versions.
152 #[stable(feature = "panic_hooks", since = "1.10.0")]
153 pub fn location(&self) -> Option<&Location> {
158 /// A struct containing information about the location of a panic.
159 #[stable(feature = "panic_hooks", since = "1.10.0")]
160 pub struct Location<'a> {
165 impl<'a> Location<'a> {
166 /// Returns the name of the source file from which the panic originated.
167 #[stable(feature = "panic_hooks", since = "1.10.0")]
168 pub fn file(&self) -> &str {
172 /// Returns the line number from which the panic originated.
173 #[stable(feature = "panic_hooks", since = "1.10.0")]
174 pub fn line(&self) -> u32 {
179 fn default_hook(info: &PanicInfo) {
180 #[cfg(any(not(cargobuild), feature = "backtrace"))]
181 use sys_common::backtrace;
183 // If this is a double panic, make sure that we print a backtrace
184 // for this panic. Otherwise only print it if logging is enabled.
185 #[cfg(any(not(cargobuild), feature = "backtrace"))]
186 let log_backtrace = {
187 let panics = update_panic_count(0);
189 panics >= 2 || backtrace::log_enabled()
192 let file = info.location.file;
193 let line = info.location.line;
195 let msg = match info.payload.downcast_ref::<&'static str>() {
197 None => match info.payload.downcast_ref::<String>() {
202 let mut err = Stderr::new().ok();
203 let thread = thread_info::current_thread();
204 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
206 let write = |err: &mut ::io::Write| {
207 let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}",
208 name, msg, file, line);
210 #[cfg(any(not(cargobuild), feature = "backtrace"))]
212 use sync::atomic::{AtomicBool, Ordering};
214 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
217 let _ = backtrace::write(err);
218 } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
219 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
224 let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
225 match (prev, err.as_mut()) {
226 (Some(mut stderr), _) => {
228 let mut s = Some(stderr);
229 LOCAL_STDERR.with(|slot| {
230 *slot.borrow_mut() = s.take();
233 (None, Some(ref mut err)) => { write(err) }
241 #[unstable(feature = "update_panic_count", issue = "0")]
242 pub fn update_panic_count(amt: isize) -> usize {
244 thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
246 PANIC_COUNT.with(|c| {
247 let next = (c.get() as isize + amt) as usize;
254 pub use realstd::rt::update_panic_count;
256 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
257 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
263 // We do some sketchy operations with ownership here for the sake of
264 // performance. The `Data` structure is never actually fully valid, but
265 // instead it always contains at least one uninitialized field. We can only
266 // pass pointers down to `__rust_maybe_catch_panic` (can't pass objects by
267 // value), so we do all the ownership tracking here manully.
269 // Note that this is all invalid if any of these functions unwind, but the
270 // whole point of this function is to prevent that! As a result we go
271 // through a transition where:
273 // * First, only the closure we're going to call is initialized. The return
274 // value is uninitialized.
275 // * When we make the function call, the `do_call` function below, we take
276 // ownership of the function pointer, replacing it with uninitialized
277 // data. At this point the `Data` structure is entirely uninitialized, but
278 // it won't drop due to an unwind because it's owned on the other side of
280 // * If the closure successfully returns, we write the return value into the
281 // data's return slot. Note that `ptr::write` is used as it's overwriting
282 // uninitialized data.
283 // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
284 // in one of two states:
286 // 1. The closure didn't panic, in which case the return value was
287 // filled in. We have to be careful to `forget` the closure,
288 // however, as ownership was passed to the `do_call` function.
289 // 2. The closure panicked, in which case the return value wasn't
290 // filled in. In this case the entire `data` structure is invalid,
291 // so we forget the entire thing.
293 // Once we stack all that together we should have the "most efficient'
294 // method of calling a catch panic whilst juggling ownership.
295 let mut any_data = 0;
296 let mut any_vtable = 0;
297 let mut data = Data {
299 r: mem::uninitialized(),
302 let r = __rust_maybe_catch_panic(do_call::<F, R>,
303 &mut data as *mut _ as *mut u8,
308 let Data { f, r } = data;
310 debug_assert!(update_panic_count(0) == 0);
314 update_panic_count(-1);
315 debug_assert!(update_panic_count(0) == 0);
316 Err(mem::transmute(raw::TraitObject {
317 data: any_data as *mut _,
318 vtable: any_vtable as *mut _,
322 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
324 let data = data as *mut Data<F, R>;
325 let f = ptr::read(&mut (*data).f);
326 ptr::write(&mut (*data).r, f());
331 /// Determines whether the current thread is unwinding because of panic.
332 pub fn panicking() -> bool {
333 update_panic_count(0) != 0
336 /// Entry point of panic from the libcore crate.
338 #[lang = "panic_fmt"]
340 pub extern fn rust_begin_panic(msg: fmt::Arguments,
343 begin_panic_fmt(&msg, &(file, line))
346 /// The entry point for panicking with a formatted message.
348 /// This is designed to reduce the amount of code required at the call
349 /// site as much as possible (so that `panic!()` has as low an impact
350 /// on (e.g.) the inlining of other functions as possible), by moving
351 /// the actual formatting into this shared place.
352 #[unstable(feature = "libstd_sys_internals",
353 reason = "used by the panic! macro",
355 #[inline(never)] #[cold]
356 pub fn begin_panic_fmt(msg: &fmt::Arguments,
357 file_line: &(&'static str, u32)) -> ! {
360 // We do two allocations here, unfortunately. But (a) they're
361 // required with the current scheme, and (b) we don't handle
362 // panic + OOM properly anyway (see comment in begin_panic
365 let mut s = String::new();
366 let _ = s.write_fmt(*msg);
367 begin_panic(s, file_line)
370 /// This is the entry point of panicking for panic!() and assert!().
371 #[unstable(feature = "libstd_sys_internals",
372 reason = "used by the panic! macro",
374 #[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
375 pub fn begin_panic<M: Any + Send>(msg: M, file_line: &(&'static str, u32)) -> ! {
376 // Note that this should be the only allocation performed in this code path.
377 // Currently this means that panic!() on OOM will invoke this code path,
378 // but then again we're not really ready for panic on OOM anyway. If
379 // we do start doing this, then we should propagate this allocation to
380 // be performed in the parent of this thread instead of the thread that's
383 rust_panic_with_hook(Box::new(msg), file_line)
386 /// Executes the primary logic for a panic, including checking for recursive
387 /// panics and panic hooks.
389 /// This is the entry point or panics from libcore, formatted panics, and
390 /// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
391 /// run panic hooks, and then delegate to the actual implementation of panics.
394 fn rust_panic_with_hook(msg: Box<Any + Send>,
395 file_line: &(&'static str, u32)) -> ! {
396 let (file, line) = *file_line;
398 let panics = update_panic_count(1);
400 // If this is the third nested call (e.g. panics == 2, this is 0-indexed),
401 // the panic hook probably triggered the last panic, otherwise the
402 // double-panic check would have aborted the process. In this case abort the
403 // process real quickly as we don't want to try calling it again as it'll
404 // probably just panic again.
406 util::dumb_print(format_args!("thread panicked while processing \
407 panic. aborting.\n"));
408 unsafe { intrinsics::abort() }
412 let info = PanicInfo {
421 Hook::Default => default_hook(&info),
422 Hook::Custom(ptr) => (*ptr)(&info),
424 HOOK_LOCK.read_unlock();
428 // If a thread panics while it's already unwinding then we
429 // have limited options. Currently our preference is to
430 // just abort. In the future we may consider resuming
431 // unwinding or otherwise exiting the thread cleanly.
432 util::dumb_print(format_args!("thread panicked while panicking. \
434 unsafe { intrinsics::abort() }
440 /// Shim around rust_panic. Called by resume_unwind.
441 pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
442 update_panic_count(1);
446 /// A private no-mangle function on which to slap yer breakpoints.
448 #[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
449 pub fn rust_panic(msg: Box<Any + Send>) -> ! {
451 let obj = mem::transmute::<_, raw::TraitObject>(msg);
452 __rust_start_panic(obj.data as usize, obj.vtable as usize)
454 rtabort!("failed to initiate panic, error {}", code)