1 //! Implementation of various bits and pieces of the `panic!` macro and 2 //! associated runtime pieces. 3 //! 4 //! Specifically, this module contains the implementation of: 5 //! 6 //! * Panic hooks 7 //! * Executing a panic up to doing the actual implementation 8 //! * Shims around "try" 9 10 #![deny(unsafe_op_in_unsafe_fn)] 11 12 use crate::std::panic::BacktraceStyle; 13 use core::panic::{BoxMeUp, Location, PanicInfo}; 14 15 use crate::std::any::Any; 16 use crate::std::fmt; 17 use crate::std::intrinsics; 18 use crate::std::mem::{self, ManuallyDrop}; 19 use crate::std::process; 20 use crate::std::sync::atomic::{AtomicBool, Ordering}; 21 use crate::std::sync::{PoisonError, RwLock}; 22 use crate::std::sys::stdio::panic_output; 23 use crate::std::sys_common::backtrace; 24 use crate::std::sys_common::thread_info; 25 use crate::std::thread; 26 27 #[cfg(not(test))] 28 use crate::std::io::set_output_capture; 29 // make sure to use the stderr output configured 30 // by libtest in the real copy of std 31 #[cfg(test)] 32 use realstd::io::set_output_capture; 33 34 // Binary interface to the panic runtime that the standard library depends on. 35 // 36 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in 37 // RFC 1513) to indicate that it requires some other crate tagged with 38 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to 39 // implement these symbols (with the same signatures) so we can get matched up 40 // to them. 41 // 42 // One day this may look a little less ad-hoc with the compiler helping out to 43 // hook up these functions, but it is not this day! 44 #[allow(improper_ctypes)] 45 extern "C" { 46 fn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static); 47 } 48 49 extern "Rust" { 50 /// `BoxMeUp` lazily performs allocation only when needed (this avoids 51 /// allocations when using the "abort" panic runtime). 52 fn __rust_start_panic(payload: &mut dyn BoxMeUp) -> u32; 53 } 54 55 /// This function is called by the panic runtime if FFI code catches a Rust 56 /// panic but doesn't rethrow it. We don't support this case since it messes 57 /// with our panic count. 58 #[cfg(not(test))] 59 #[rustc_std_internal_symbol] 60 extern "C" fn __rust_drop_panic() -> ! { 61 rtabort!("Rust panics must be rethrown"); 62 } 63 64 /// This function is called by the panic runtime if it catches an exception 65 /// object which does not correspond to a Rust panic. 66 #[cfg(not(test))] 67 #[rustc_std_internal_symbol] 68 extern "C" fn __rust_foreign_exception() -> ! { 69 rtabort!("Rust cannot catch foreign exceptions"); 70 } 71 72 enum Hook { 73 Default, 74 Custom(Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>), 75 } 76 77 impl Hook { 78 #[inline] 79 fn into_box(self) -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> { 80 match self { 81 Hook::Default => Box::new(default_hook), 82 Hook::Custom(hook) => hook, 83 } 84 } 85 } 86 87 impl Default for Hook { 88 #[inline] 89 fn default() -> Hook { 90 Hook::Default 91 } 92 } 93 94 static HOOK: RwLock<Hook> = RwLock::new(Hook::Default); 95 96 /// Registers a custom panic hook, replacing the previously registered hook. 97 /// 98 /// The panic hook is invoked when a thread panics, but before the panic runtime 99 /// is invoked. As such, the hook will run with both the aborting and unwinding 100 /// runtimes. 101 /// 102 /// The default hook, which is registered at startup, prints a message to standard error and 103 /// generates a backtrace if requested. This behavior can be customized using the `set_hook` function. 104 /// The current hook can be retrieved while reinstating the default hook with the [`take_hook`] 105 /// function. 106 /// 107 /// [`take_hook`]: ./fn.take_hook.html 108 /// 109 /// The hook is provided with a `PanicInfo` struct which contains information 110 /// about the origin of the panic, including the payload passed to `panic!` and 111 /// the source code location from which the panic originated. 112 /// 113 /// The panic hook is a global resource. 114 /// 115 /// # Panics 116 /// 117 /// Panics if called from a panicking thread. 118 /// 119 /// # Examples 120 /// 121 /// The following will print "Custom panic hook": 122 /// 123 /// ```should_panic 124 /// use std::panic; 125 /// 126 /// panic::set_hook(Box::new(|_| { 127 /// println!("Custom panic hook"); 128 /// })); 129 /// 130 /// panic!("Normal panic"); 131 /// ``` 132 pub fn set_hook(hook: Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>) { 133 if thread::panicking() { 134 panic!("cannot modify the panic hook from a panicking thread"); 135 } 136 137 let new = Hook::Custom(hook); 138 let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner); 139 let old = mem::replace(&mut *hook, new); 140 drop(hook); 141 // Only drop the old hook after releasing the lock to avoid deadlocking 142 // if its destructor panics. 143 drop(old); 144 } 145 146 /// Unregisters the current panic hook and returns it, registering the default hook 147 /// in its place. 148 /// 149 /// *See also the function [`set_hook`].* 150 /// 151 /// [`set_hook`]: ./fn.set_hook.html 152 /// 153 /// If the default hook is registered it will be returned, but remain registered. 154 /// 155 /// # Panics 156 /// 157 /// Panics if called from a panicking thread. 158 /// 159 /// # Examples 160 /// 161 /// The following will print "Normal panic": 162 /// 163 /// ```should_panic 164 /// use std::panic; 165 /// 166 /// panic::set_hook(Box::new(|_| { 167 /// println!("Custom panic hook"); 168 /// })); 169 /// 170 /// let _ = panic::take_hook(); 171 /// 172 /// panic!("Normal panic"); 173 /// ``` 174 #[must_use] 175 pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> { 176 if thread::panicking() { 177 panic!("cannot modify the panic hook from a panicking thread"); 178 } 179 180 let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner); 181 let old_hook = mem::take(&mut *hook); 182 drop(hook); 183 184 old_hook.into_box() 185 } 186 187 /// Atomic combination of [`take_hook`] and [`set_hook`]. Use this to replace the panic handler with 188 /// a new panic handler that does something and then executes the old handler. 189 /// 190 /// [`take_hook`]: ./fn.take_hook.html 191 /// [`set_hook`]: ./fn.set_hook.html 192 /// 193 /// # Panics 194 /// 195 /// Panics if called from a panicking thread. 196 /// 197 /// # Examples 198 /// 199 /// The following will print the custom message, and then the normal output of panic. 200 /// 201 /// ```should_panic 202 /// #![feature(panic_update_hook)] 203 /// use std::panic; 204 /// 205 /// // Equivalent to 206 /// // let prev = panic::take_hook(); 207 /// // panic::set_hook(move |info| { 208 /// // println!("..."); 209 /// // prev(info); 210 /// // ); 211 /// panic::update_hook(move |prev, info| { 212 /// println!("Print custom message and execute panic handler as usual"); 213 /// prev(info); 214 /// }); 215 /// 216 /// panic!("Custom and then normal"); 217 /// ``` 218 pub fn update_hook<F>(hook_fn: F) 219 where 220 F: Fn(&(dyn Fn(&PanicInfo<'_>) + Send + Sync + 'static), &PanicInfo<'_>) 221 + Sync 222 + Send 223 + 'static, 224 { 225 if thread::panicking() { 226 panic!("cannot modify the panic hook from a panicking thread"); 227 } 228 229 let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner); 230 let prev = mem::take(&mut *hook).into_box(); 231 *hook = Hook::Custom(Box::new(move |info| hook_fn(&prev, info))); 232 } 233 234 /// The default panic handler. 235 fn default_hook(info: &PanicInfo<'_>) { 236 panic_hook_with_disk_dump(info, None) 237 } 238 239 /// The implementation of the default panic handler. 240 /// 241 /// It can also write the backtrace to a given `path`. This functionality is used only by `rustc`. 242 pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::std::path::Path>) { 243 // If this is a double panic, make sure that we print a backtrace 244 // for this panic. Otherwise only print it if logging is enabled. 245 // let backtrace = if info.force_no_backtrace() { 246 // None 247 // } else if panic_count::get_count() >= 2 { 248 // BacktraceStyle::full() 249 // } else { 250 // crate::std::panic::get_backtrace_style() 251 // }; 252 253 // // The current implementation always returns `Some`. 254 // let location = info.location().unwrap(); 255 256 // let msg = match info.payload().downcast_ref::<&'static str>() { 257 // Some(s) => *s, 258 // None => match info.payload().downcast_ref::<String>() { 259 // Some(s) => &s[..], 260 // None => "Box<dyn Any>", 261 // }, 262 // }; 263 // let thread = thread_info::current_thread(); 264 // let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>"); 265 266 // let write = |err: &mut dyn crate::std::io::Write, backtrace: Option<BacktraceStyle>| { 267 // let _ = writeln!(err, "thread '{name}' panicked at {location}:\n{msg}"); 268 269 // static FIRST_PANIC: AtomicBool = AtomicBool::new(true); 270 271 // // match backtrace { 272 // // Some(BacktraceStyle::Short) => { 273 // // drop(backtrace::print(err, crate::std::backtrace_rs::PrintFmt::Short)) 274 // // } 275 // // Some(BacktraceStyle::Full) => { 276 // // drop(backtrace::print(err, crate::std::backtrace_rs::PrintFmt::Full)) 277 // // } 278 // // Some(BacktraceStyle::Off) => { 279 // // if FIRST_PANIC.swap(false, Ordering::SeqCst) { 280 // // if let Some(path) = path { 281 // // let _ = writeln!( 282 // // err, 283 // // "note: a backtrace for this error was stored at `{}`", 284 // // path.display(), 285 // // ); 286 // // } else { 287 // // let _ = writeln!( 288 // // err, 289 // // "note: run with `RUST_BACKTRACE=1` environment variable to display a \ 290 // // backtrace" 291 // // ); 292 // // } 293 // // } 294 // // } 295 // // If backtraces aren't supported or are forced-off, do nothing. 296 // // None => {} 297 // // } 298 // }; 299 300 // if let Some(path) = path 301 // && let Ok(mut out) = crate::std::fs::File::options().create(true).append(true).open(&path) 302 // { 303 // write(&mut out, BacktraceStyle::full()); 304 // } 305 306 // if let Some(local) = set_output_capture(None) { 307 // write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()), backtrace); 308 // set_output_capture(Some(local)); 309 // } else if let Some(mut out) = panic_output() { 310 // write(&mut out, backtrace); 311 // } 312 () 313 } 314 315 #[cfg(not(test))] 316 #[doc(hidden)] 317 pub mod panic_count { 318 use crate::std::cell::Cell; 319 use crate::std::sync::atomic::{AtomicUsize, Ordering}; 320 321 pub const ALWAYS_ABORT_FLAG: usize = 1 << (usize::BITS - 1); 322 323 /// A reason for forcing an immediate abort on panic. 324 #[derive(Debug)] 325 pub enum MustAbort { 326 AlwaysAbort, 327 PanicInHook, 328 } 329 330 // Panic count for the current thread and whether a panic hook is currently 331 // being executed.. 332 thread_local! { 333 static LOCAL_PANIC_COUNT: Cell<(usize, bool)> = const { Cell::new((0, false)) } 334 } 335 336 // Sum of panic counts from all threads. The purpose of this is to have 337 // a fast path in `count_is_zero` (which is used by `panicking`). In any particular 338 // thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero, 339 // then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before 340 // and after increase and decrease, but not necessarily during their execution. 341 // 342 // Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG) 343 // records whether panic::always_abort() has been called. This can only be 344 // set, never cleared. 345 // panic::always_abort() is usually called to prevent memory allocations done by 346 // the panic handling in the child created by `dlibc::fork`. 347 // Memory allocations performed in a child created with `dlibc::fork` are undefined 348 // behavior in most operating systems. 349 // Accessing LOCAL_PANIC_COUNT in a child created by `dlibc::fork` would lead to a memory 350 // allocation. Only GLOBAL_PANIC_COUNT can be accessed in this situation. This is 351 // sufficient because a child process will always have exactly one thread only. 352 // See also #85261 for details. 353 // 354 // This could be viewed as a struct containing a single bit and an n-1-bit 355 // value, but if we wrote it like that it would be more than a single word, 356 // and even a newtype around usize would be clumsy because we need atomics. 357 // But we use such a tuple for the return type of increase(). 358 // 359 // Stealing a bit is fine because it just amounts to assuming that each 360 // panicking thread consumes at least 2 bytes of address space. 361 static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0); 362 363 // Increases the global and local panic count, and returns whether an 364 // immediate abort is required. 365 // 366 // This also updates thread-local state to keep track of whether a panic 367 // hook is currently executing. 368 pub fn increase(run_panic_hook: bool) -> Option<MustAbort> { 369 let global_count = GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed); 370 if global_count & ALWAYS_ABORT_FLAG != 0 { 371 return Some(MustAbort::AlwaysAbort); 372 } 373 374 LOCAL_PANIC_COUNT.with(|c| { 375 let (count, in_panic_hook) = c.get(); 376 if in_panic_hook { 377 return Some(MustAbort::PanicInHook); 378 } 379 c.set((count + 1, run_panic_hook)); 380 None 381 }) 382 } 383 384 pub fn finished_panic_hook() { 385 LOCAL_PANIC_COUNT.with(|c| { 386 let (count, _) = c.get(); 387 c.set((count, false)); 388 }); 389 } 390 391 pub fn decrease() { 392 GLOBAL_PANIC_COUNT.fetch_sub(1, Ordering::Relaxed); 393 LOCAL_PANIC_COUNT.with(|c| { 394 let (count, _) = c.get(); 395 c.set((count - 1, false)); 396 }); 397 } 398 399 pub fn set_always_abort() { 400 GLOBAL_PANIC_COUNT.fetch_or(ALWAYS_ABORT_FLAG, Ordering::Relaxed); 401 } 402 403 // Disregards ALWAYS_ABORT_FLAG 404 #[must_use] 405 pub fn get_count() -> usize { 406 LOCAL_PANIC_COUNT.with(|c| c.get().0) 407 } 408 409 // Disregards ALWAYS_ABORT_FLAG 410 #[must_use] 411 #[inline] 412 pub fn count_is_zero() -> bool { 413 if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) & !ALWAYS_ABORT_FLAG == 0 { 414 // Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads 415 // (including the current one) will have `LOCAL_PANIC_COUNT` 416 // equal to zero, so TLS access can be avoided. 417 // 418 // In terms of performance, a relaxed atomic load is similar to a normal 419 // aligned memory read (e.g., a mov instruction in x86), but with some 420 // compiler optimization restrictions. On the other hand, a TLS access 421 // might require calling a non-inlinable function (such as `__tls_get_addr` 422 // when using the GD TLS model). 423 true 424 } else { 425 is_zero_slow_path() 426 } 427 } 428 429 // Slow path is in a separate function to reduce the amount of code 430 // inlined from `count_is_zero`. 431 #[inline(never)] 432 #[cold] 433 fn is_zero_slow_path() -> bool { 434 LOCAL_PANIC_COUNT.with(|c| c.get().0 == 0) 435 } 436 } 437 438 #[cfg(test)] 439 pub use realstd::rt::panic_count; 440 441 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs. 442 pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> { 443 union Data<F, R> { 444 f: ManuallyDrop<F>, 445 r: ManuallyDrop<R>, 446 p: ManuallyDrop<Box<dyn Any + Send>>, 447 } 448 449 // We do some sketchy operations with ownership here for the sake of 450 // performance. We can only pass pointers down to `do_call` (can't pass 451 // objects by value), so we do all the ownership tracking here manually 452 // using a union. 453 // 454 // We go through a transition where: 455 // 456 // * First, we set the data field `f` to be the argumentless closure that we're going to call. 457 // * When we make the function call, the `do_call` function below, we take 458 // ownership of the function pointer. At this point the `data` union is 459 // entirely uninitialized. 460 // * If the closure successfully returns, we write the return value into the 461 // data's return slot (field `r`). 462 // * If the closure panics (`do_catch` below), we write the panic payload into field `p`. 463 // * Finally, when we come back out of the `try` intrinsic we're 464 // in one of two states: 465 // 466 // 1. The closure didn't panic, in which case the return value was 467 // filled in. We move it out of `data.r` and return it. 468 // 2. The closure panicked, in which case the panic payload was 469 // filled in. We move it out of `data.p` and return it. 470 // 471 // Once we stack all that together we should have the "most efficient' 472 // method of calling a catch panic whilst juggling ownership. 473 let mut data = Data { 474 f: ManuallyDrop::new(f), 475 }; 476 477 let data_ptr = &mut data as *mut _ as *mut u8; 478 // SAFETY: 479 // 480 // Access to the union's fields: this is `std` and we know that the `r#try` 481 // intrinsic fills in the `r` or `p` union field based on its return value. 482 // 483 // The call to `intrinsics::r#try` is made safe by: 484 // - `do_call`, the first argument, can be called with the initial `data_ptr`. 485 // - `do_catch`, the second argument, can be called with the `data_ptr` as well. 486 // See their safety preconditions for more information 487 unsafe { 488 return if intrinsics::r#try(do_call::<F, R>, data_ptr, do_catch::<F, R>) == 0 { 489 Ok(ManuallyDrop::into_inner(data.r)) 490 } else { 491 Err(ManuallyDrop::into_inner(data.p)) 492 }; 493 } 494 495 // We consider unwinding to be rare, so mark this function as cold. However, 496 // do not mark it no-inline -- that decision is best to leave to the 497 // optimizer (in most cases this function is not inlined even as a normal, 498 // non-cold function, though, as of the writing of this comment). 499 #[cold] 500 unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send + 'static> { 501 // SAFETY: The whole unsafe block hinges on a correct implementation of 502 // the panic handler `__rust_panic_cleanup`. As such we can only 503 // assume it returns the correct thing for `Box::from_raw` to work 504 // without undefined behavior. 505 let obj = unsafe { Box::from_raw(__rust_panic_cleanup(payload)) }; 506 panic_count::decrease(); 507 obj 508 } 509 510 // SAFETY: 511 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>` 512 // Its must contains a valid `f` (type: F) value that can be use to fill 513 // `data.r`. 514 // 515 // This function cannot be marked as `unsafe` because `intrinsics::r#try` 516 // expects normal function pointers. 517 #[inline] 518 fn do_call<F: FnOnce() -> R, R>(data: *mut u8) { 519 // SAFETY: this is the responsibility of the caller, see above. 520 unsafe { 521 let data = data as *mut Data<F, R>; 522 let data = &mut (*data); 523 let f = ManuallyDrop::take(&mut data.f); 524 data.r = ManuallyDrop::new(f()); 525 } 526 } 527 528 // We *do* want this part of the catch to be inlined: this allows the 529 // compiler to properly track accesses to the Data union and optimize it 530 // away most of the time. 531 // 532 // SAFETY: 533 // data must be non-NUL, correctly aligned, and a pointer to a `Data<F, R>` 534 // Since this uses `cleanup` it also hinges on a correct implementation of 535 // `__rustc_panic_cleanup`. 536 // 537 // This function cannot be marked as `unsafe` because `intrinsics::r#try` 538 // expects normal function pointers. 539 #[inline] 540 #[rustc_nounwind] // `intrinsic::r#try` requires catch fn to be nounwind 541 fn do_catch<F: FnOnce() -> R, R>(data: *mut u8, payload: *mut u8) { 542 // SAFETY: this is the responsibility of the caller, see above. 543 // 544 // When `__rustc_panic_cleaner` is correctly implemented we can rely 545 // on `obj` being the correct thing to pass to `data.p` (after wrapping 546 // in `ManuallyDrop`). 547 unsafe { 548 let data = data as *mut Data<F, R>; 549 let data = &mut (*data); 550 let obj = cleanup(payload); 551 data.p = ManuallyDrop::new(obj); 552 } 553 } 554 } 555 556 /// Determines whether the current thread is unwinding because of panic. 557 #[inline] 558 pub fn panicking() -> bool { 559 !panic_count::count_is_zero() 560 } 561 562 /// Entry point of panics from the core crate (`panic_impl` lang item). 563 // #[cfg(not(test))] 564 // #[panic_handler] 565 // pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! { 566 // struct PanicPayload<'a> { 567 // inner: &'a fmt::Arguments<'a>, 568 // string: Option<String>, 569 // } 570 571 // impl<'a> PanicPayload<'a> { 572 // fn new(inner: &'a fmt::Arguments<'a>) -> PanicPayload<'a> { 573 // PanicPayload { inner, string: None } 574 // } 575 576 // fn fill(&mut self) -> &mut String { 577 // use crate::std::fmt::Write; 578 579 // let inner = self.inner; 580 // // Lazily, the first time this gets called, run the actual string formatting. 581 // self.string.get_or_insert_with(|| { 582 // let mut s = String::new(); 583 // let _err = s.write_fmt(*inner); 584 // s 585 // }) 586 // } 587 // } 588 589 // unsafe impl<'a> BoxMeUp for PanicPayload<'a> { 590 // fn take_box(&mut self) -> *mut (dyn Any + Send) { 591 // // We do two allocations here, unfortunately. But (a) they're required with the current 592 // // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in 593 // // begin_panic below). 594 // let contents = mem::take(self.fill()); 595 // Box::into_raw(Box::new(contents)) 596 // } 597 598 // fn get(&mut self) -> &(dyn Any + Send) { 599 // self.fill() 600 // } 601 // } 602 603 // struct StrPanicPayload(&'static str); 604 605 // unsafe impl BoxMeUp for StrPanicPayload { 606 // fn take_box(&mut self) -> *mut (dyn Any + Send) { 607 // Box::into_raw(Box::new(self.0)) 608 // } 609 610 // fn get(&mut self) -> &(dyn Any + Send) { 611 // &self.0 612 // } 613 // } 614 615 // let loc = info.location().unwrap(); // The current implementation always returns Some 616 // let msg = info.message().unwrap(); // The current implementation always returns Some 617 // crate::std::sys_common::backtrace::__rust_end_short_backtrace(move || { 618 // // FIXME: can we just pass `info` along rather than taking it apart here, only to have 619 // // `rust_panic_with_hook` construct a new `PanicInfo`? 620 // if let Some(msg) = msg.as_str() { 621 // rust_panic_with_hook( 622 // &mut StrPanicPayload(msg), 623 // info.message(), 624 // loc, 625 // info.can_unwind(), 626 // info.force_no_backtrace(), 627 // ); 628 // } else { 629 // rust_panic_with_hook( 630 // &mut PanicPayload::new(msg), 631 // info.message(), 632 // loc, 633 // info.can_unwind(), 634 // info.force_no_backtrace(), 635 // ); 636 // } 637 // }) 638 // } 639 640 /// This is the entry point of panicking for the non-format-string variants of 641 /// panic!() and assert!(). In particular, this is the only entry point that supports 642 /// arbitrary payloads, not just format strings. 643 #[cfg_attr(not(test), lang = "begin_panic")] 644 // lang item for CTFE panic support 645 // never inline unless panic_immediate_abort to avoid code 646 // bloat at the call sites as much as possible 647 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)] 648 #[cfg_attr(feature = "panic_immediate_abort", inline)] 649 #[track_caller] 650 #[rustc_do_not_const_check] // hooked by const-eval 651 pub const fn begin_panic<M: Any + Send>(msg: M) -> ! { 652 if cfg!(feature = "panic_immediate_abort") { 653 intrinsics::abort() 654 } 655 656 let loc = Location::caller(); 657 return crate::std::sys_common::backtrace::__rust_end_short_backtrace(move || { 658 rust_panic_with_hook( 659 &mut PanicPayload::new(msg), 660 None, 661 loc, 662 /* can_unwind */ true, 663 /* force_no_backtrace */ false, 664 ) 665 }); 666 667 struct PanicPayload<A> { 668 inner: Option<A>, 669 } 670 671 impl<A: Send + 'static> PanicPayload<A> { 672 fn new(inner: A) -> PanicPayload<A> { 673 PanicPayload { inner: Some(inner) } 674 } 675 } 676 677 unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> { 678 fn take_box(&mut self) -> *mut (dyn Any + Send) { 679 // Note that this should be the only allocation performed in this code path. Currently 680 // this means that panic!() on OOM will invoke this code path, but then again we're not 681 // really ready for panic on OOM anyway. If we do start doing this, then we should 682 // propagate this allocation to be performed in the parent of this thread instead of the 683 // thread that's panicking. 684 let data = match self.inner.take() { 685 Some(a) => Box::new(a) as Box<dyn Any + Send>, 686 None => process::abort(), 687 }; 688 Box::into_raw(data) 689 } 690 691 fn get(&mut self) -> &(dyn Any + Send) { 692 match self.inner { 693 Some(ref a) => a, 694 None => process::abort(), 695 } 696 } 697 } 698 } 699 700 /// Central point for dispatching panics. 701 /// 702 /// Executes the primary logic for a panic, including checking for recursive 703 /// panics, panic hooks, and finally dispatching to the panic runtime to either 704 /// abort or unwind. 705 fn rust_panic_with_hook( 706 payload: &mut dyn BoxMeUp, 707 message: Option<&fmt::Arguments<'_>>, 708 location: &Location<'_>, 709 can_unwind: bool, 710 force_no_backtrace: bool, 711 ) -> ! { 712 // let must_abort = panic_count::increase(true); 713 714 // // Check if we need to abort immediately. 715 // if let Some(must_abort) = must_abort { 716 // match must_abort { 717 // panic_count::MustAbort::PanicInHook => { 718 // // Don't try to print the message in this case 719 // // - perhaps that is causing the recursive panics. 720 // rtprintpanic!("thread panicked while processing panic. aborting.\n"); 721 // } 722 // panic_count::MustAbort::AlwaysAbort => { 723 // // Unfortunately, this does not print a backtrace, because creating 724 // // a `Backtrace` will allocate, which we must to avoid here. 725 // let panicinfo = PanicInfo::internal_constructor( 726 // message, 727 // location, 728 // can_unwind, 729 // force_no_backtrace, 730 // ); 731 // rtprintpanic!("{panicinfo}\npanicked after panic::always_abort(), aborting.\n"); 732 // } 733 // } 734 // crate::std::sys::abort_internal(); 735 // } 736 737 // let mut info = 738 // PanicInfo::internal_constructor(message, location, can_unwind, force_no_backtrace); 739 // let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner); 740 // match *hook { 741 // // Some platforms (like wasm) know that printing to stderr won't ever actually 742 // // print anything, and if that's the case we can skip the default 743 // // hook. Since string formatting happens lazily when calling `payload` 744 // // methods, this means we avoid formatting the string at all! 745 // // (The panic runtime might still call `payload.take_box()` though and trigger 746 // // formatting.) 747 // Hook::Default if panic_output().is_none() => {} 748 // Hook::Default => { 749 // info.set_payload(payload.get()); 750 // default_hook(&info); 751 // } 752 // Hook::Custom(ref hook) => { 753 // info.set_payload(payload.get()); 754 // hook(&info); 755 // } 756 // }; 757 // drop(hook); 758 759 // // Indicate that we have finished executing the panic hook. After this point 760 // // it is fine if there is a panic while executing destructors, as long as it 761 // // it contained within a `catch_unwind`. 762 // panic_count::finished_panic_hook(); 763 764 // if !can_unwind { 765 // // If a thread panics while running destructors or tries to unwind 766 // // through a nounwind function (e.g. extern "C") then we cannot continue 767 // // unwinding and have to abort immediately. 768 // rtprintpanic!("thread caused non-unwinding panic. aborting.\n"); 769 // crate::std::sys::abort_internal(); 770 // } 771 772 rust_panic(payload) 773 } 774 775 /// This is the entry point for `resume_unwind`. 776 /// It just forwards the payload to the panic runtime. 777 pub fn rust_panic_without_hook(payload: Box<dyn Any + Send>) -> ! { 778 panic_count::increase(false); 779 780 struct RewrapBox(Box<dyn Any + Send>); 781 782 unsafe impl BoxMeUp for RewrapBox { 783 fn take_box(&mut self) -> *mut (dyn Any + Send) { 784 Box::into_raw(mem::replace(&mut self.0, Box::new(()))) 785 } 786 787 fn get(&mut self) -> &(dyn Any + Send) { 788 &*self.0 789 } 790 } 791 792 rust_panic(&mut RewrapBox(payload)) 793 } 794 795 /// An unmangled function (through `rustc_std_internal_symbol`) on which to slap 796 /// yer breakpoints. 797 #[inline(never)] 798 #[cfg_attr(not(test), rustc_std_internal_symbol)] 799 fn rust_panic(msg: &mut dyn BoxMeUp) -> ! { 800 let code = unsafe { __rust_start_panic(msg) }; 801 rtabort!("failed to initiate panic, error {code}") 802 } 803