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"
30 use sys::stdio::Stderr;
31 use sys_common::rwlock::RWLock;
32 use sys_common::thread_info;
37 pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
42 // Binary interface to the panic runtime that the standard library depends on.
44 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in
45 // RFC 1513) to indicate that it requires some other crate tagged with
46 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
47 // implement these symbols (with the same signatures) so we can get matched up
50 // One day this may look a little less ad-hoc with the compiler helping out to
51 // hook up these functions, but it is not this day!
52 #[allow(improper_ctypes)]
54 fn __rust_maybe_catch_panic(f: fn(*mut u8),
57 vtable_ptr: *mut usize) -> u32;
59 fn __rust_start_panic(data: usize, vtable: usize) -> u32;
62 #[derive(Copy, Clone)]
65 Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
68 static HOOK_LOCK: RWLock = RWLock::new();
69 static mut HOOK: Hook = Hook::Default;
71 /// Registers a custom panic hook, replacing any that was previously registered.
73 /// The panic hook is invoked when a thread panics, but before the panic runtime
74 /// is invoked. As such, the hook will run with both the aborting and unwinding
75 /// runtimes. The default hook prints a message to standard error and generates
76 /// a backtrace if requested, but this behavior can be customized with the
77 /// `set_hook` and `take_hook` functions.
79 /// The hook is provided with a `PanicInfo` struct which contains information
80 /// about the origin of the panic, including the payload passed to `panic!` and
81 /// the source code location from which the panic originated.
83 /// The panic hook is a global resource.
87 /// Panics if called from a panicking thread.
88 #[stable(feature = "panic_hooks", since = "1.10.0")]
89 pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
90 if thread::panicking() {
91 panic!("cannot modify the panic hook from a panicking thread");
97 HOOK = Hook::Custom(Box::into_raw(hook));
98 HOOK_LOCK.write_unlock();
100 if let Hook::Custom(ptr) = old_hook {
106 /// Unregisters the current panic hook, returning it.
108 /// If no custom hook is registered, the default hook will be returned.
112 /// Panics if called from a panicking thread.
113 #[stable(feature = "panic_hooks", since = "1.10.0")]
114 pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
115 if thread::panicking() {
116 panic!("cannot modify the panic hook from a panicking thread");
122 HOOK = Hook::Default;
123 HOOK_LOCK.write_unlock();
126 Hook::Default => Box::new(default_hook),
127 Hook::Custom(ptr) => {Box::from_raw(ptr)} // FIXME #30530
132 /// A struct providing information about a panic.
133 #[stable(feature = "panic_hooks", since = "1.10.0")]
134 pub struct PanicInfo<'a> {
135 payload: &'a (Any + Send),
136 location: Location<'a>,
139 impl<'a> PanicInfo<'a> {
140 /// Returns the payload associated with the panic.
142 /// This will commonly, but not always, be a `&'static str` or `String`.
143 #[stable(feature = "panic_hooks", since = "1.10.0")]
144 pub fn payload(&self) -> &(Any + Send) {
148 /// Returns information about the location from which the panic originated,
151 /// This method will currently always return `Some`, but this may change
152 /// in future versions.
153 #[stable(feature = "panic_hooks", since = "1.10.0")]
154 pub fn location(&self) -> Option<&Location> {
159 /// A struct containing information about the location of a panic.
160 #[stable(feature = "panic_hooks", since = "1.10.0")]
161 pub struct Location<'a> {
166 impl<'a> Location<'a> {
167 /// Returns the name of the source file from which the panic originated.
168 #[stable(feature = "panic_hooks", since = "1.10.0")]
169 pub fn file(&self) -> &str {
173 /// Returns the line number from which the panic originated.
174 #[stable(feature = "panic_hooks", since = "1.10.0")]
175 pub fn line(&self) -> u32 {
180 fn default_hook(info: &PanicInfo) {
181 #[cfg(any(not(cargobuild), feature = "backtrace"))]
182 use sys_common::backtrace;
184 // If this is a double panic, make sure that we print a backtrace
185 // for this panic. Otherwise only print it if logging is enabled.
186 #[cfg(any(not(cargobuild), feature = "backtrace"))]
187 let log_backtrace = {
188 let panics = update_panic_count(0);
190 panics >= 2 || backtrace::log_enabled()
193 let file = info.location.file;
194 let line = info.location.line;
196 let msg = match info.payload.downcast_ref::<&'static str>() {
198 None => match info.payload.downcast_ref::<String>() {
203 let mut err = Stderr::new().ok();
204 let thread = thread_info::current_thread();
205 let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
207 let write = |err: &mut ::io::Write| {
208 let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}",
209 name, msg, file, line);
211 #[cfg(any(not(cargobuild), feature = "backtrace"))]
213 use sync::atomic::{AtomicBool, Ordering};
215 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
218 let _ = backtrace::write(err);
219 } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
220 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
225 let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
226 match (prev, err.as_mut()) {
227 (Some(mut stderr), _) => {
229 let mut s = Some(stderr);
230 LOCAL_STDERR.with(|slot| {
231 *slot.borrow_mut() = s.take();
234 (None, Some(ref mut err)) => { write(err) }
242 #[unstable(feature = "update_panic_count", issue = "0")]
243 pub fn update_panic_count(amt: isize) -> usize {
245 thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
247 PANIC_COUNT.with(|c| {
248 let next = (c.get() as isize + amt) as usize;
255 pub use realstd::rt::update_panic_count;
257 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
258 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
264 // We do some sketchy operations with ownership here for the sake of
265 // performance. The `Data` structure is never actually fully valid, but
266 // instead it always contains at least one uninitialized field. We can only
267 // pass pointers down to `__rust_maybe_catch_panic` (can't pass objects by
268 // value), so we do all the ownership tracking here manully.
270 // Note that this is all invalid if any of these functions unwind, but the
271 // whole point of this function is to prevent that! As a result we go
272 // through a transition where:
274 // * First, only the closure we're going to call is initialized. The return
275 // value is uninitialized.
276 // * When we make the function call, the `do_call` function below, we take
277 // ownership of the function pointer, replacing it with uninitialized
278 // data. At this point the `Data` structure is entirely uninitialized, but
279 // it won't drop due to an unwind because it's owned on the other side of
281 // * If the closure successfully returns, we write the return value into the
282 // data's return slot. Note that `ptr::write` is used as it's overwriting
283 // uninitialized data.
284 // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
285 // in one of two states:
287 // 1. The closure didn't panic, in which case the return value was
288 // filled in. We have to be careful to `forget` the closure,
289 // however, as ownership was passed to the `do_call` function.
290 // 2. The closure panicked, in which case the return value wasn't
291 // filled in. In this case the entire `data` structure is invalid,
292 // so we forget the entire thing.
294 // Once we stack all that together we should have the "most efficient'
295 // method of calling a catch panic whilst juggling ownership.
296 let mut any_data = 0;
297 let mut any_vtable = 0;
298 let mut data = Data {
300 r: mem::uninitialized(),
303 let r = __rust_maybe_catch_panic(do_call::<F, R>,
304 &mut data as *mut _ as *mut u8,
309 let Data { f, r } = data;
311 debug_assert!(update_panic_count(0) == 0);
315 update_panic_count(-1);
316 debug_assert!(update_panic_count(0) == 0);
317 Err(mem::transmute(raw::TraitObject {
318 data: any_data as *mut _,
319 vtable: any_vtable as *mut _,
323 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
325 let data = data as *mut Data<F, R>;
326 let f = ptr::read(&mut (*data).f);
327 ptr::write(&mut (*data).r, f());
332 /// Determines whether the current thread is unwinding because of panic.
333 pub fn panicking() -> bool {
334 update_panic_count(0) != 0
337 /// Entry point of panic from the libcore crate.
339 #[lang = "panic_fmt"]
341 pub extern fn rust_begin_panic(msg: fmt::Arguments,
344 begin_panic_fmt(&msg, &(file, line))
347 /// The entry point for panicking with a formatted message.
349 /// This is designed to reduce the amount of code required at the call
350 /// site as much as possible (so that `panic!()` has as low an impact
351 /// on (e.g.) the inlining of other functions as possible), by moving
352 /// the actual formatting into this shared place.
353 #[unstable(feature = "libstd_sys_internals",
354 reason = "used by the panic! macro",
356 #[inline(never)] #[cold]
357 pub fn begin_panic_fmt(msg: &fmt::Arguments,
358 file_line: &(&'static str, u32)) -> ! {
361 // We do two allocations here, unfortunately. But (a) they're
362 // required with the current scheme, and (b) we don't handle
363 // panic + OOM properly anyway (see comment in begin_panic
366 let mut s = String::new();
367 let _ = s.write_fmt(*msg);
368 begin_panic(s, file_line)
371 /// This is the entry point of panicking for panic!() and assert!().
372 #[unstable(feature = "libstd_sys_internals",
373 reason = "used by the panic! macro",
375 #[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
376 pub fn begin_panic<M: Any + Send>(msg: M, file_line: &(&'static str, u32)) -> ! {
377 // Note that this should be the only allocation performed in this code path.
378 // Currently this means that panic!() on OOM will invoke this code path,
379 // but then again we're not really ready for panic on OOM anyway. If
380 // we do start doing this, then we should propagate this allocation to
381 // be performed in the parent of this thread instead of the thread that's
384 rust_panic_with_hook(Box::new(msg), file_line)
387 /// Executes the primary logic for a panic, including checking for recursive
388 /// panics and panic hooks.
390 /// This is the entry point or panics from libcore, formatted panics, and
391 /// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
392 /// run panic hooks, and then delegate to the actual implementation of panics.
395 fn rust_panic_with_hook(msg: Box<Any + Send>,
396 file_line: &(&'static str, u32)) -> ! {
397 let (file, line) = *file_line;
399 let panics = update_panic_count(1);
401 // If this is the third nested call (e.g. panics == 2, this is 0-indexed),
402 // the panic hook probably triggered the last panic, otherwise the
403 // double-panic check would have aborted the process. In this case abort the
404 // process real quickly as we don't want to try calling it again as it'll
405 // probably just panic again.
407 util::dumb_print(format_args!("thread panicked while processing \
408 panic. aborting.\n"));
409 unsafe { intrinsics::abort() }
413 let info = PanicInfo {
422 Hook::Default => default_hook(&info),
423 Hook::Custom(ptr) => (*ptr)(&info),
425 HOOK_LOCK.read_unlock();
429 // If a thread panics while it's already unwinding then we
430 // have limited options. Currently our preference is to
431 // just abort. In the future we may consider resuming
432 // unwinding or otherwise exiting the thread cleanly.
433 util::dumb_print(format_args!("thread panicked while panicking. \
435 unsafe { intrinsics::abort() }
441 /// Shim around rust_panic. Called by resume_unwind.
442 pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
443 update_panic_count(1);
447 /// A private no-mangle function on which to slap yer breakpoints.
449 #[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
450 pub fn rust_panic(msg: Box<Any + Send>) -> ! {
452 let obj = mem::transmute::<_, raw::TraitObject>(msg);
453 __rust_start_panic(obj.data as usize, obj.vtable as usize)
455 rtabort!("failed to initiate panic, error {}", code)