| // Copyright (C) 2017-2018 Baidu, Inc. All Rights Reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions |
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| // |
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| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above copyright |
| // notice, this list of conditions and the following disclaimer in |
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| // distribution. |
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| // from this software without specific prior written permission. |
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| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| //! Panic support in the standard library |
| |
| use panicking; |
| use core::any::Any; |
| use core::cell::UnsafeCell; |
| use core::fmt; |
| use core::ops::{Deref, DerefMut, Fn}; |
| use core::ptr::{Unique, NonNull}; |
| use core::sync::atomic; |
| use alloc::boxed::Box; |
| use alloc::rc::Rc; |
| use alloc::sync::Arc; |
| |
| pub use panicking::set_panic_handler; |
| pub use core::panic::{PanicInfo, Location}; |
| /// A marker trait which represents "panic safe" types in Rust. |
| /// |
| /// This trait is implemented by default for many types and behaves similarly in |
| /// terms of inference of implementation to the `Send` and `Sync` traits. The |
| /// purpose of this trait is to encode what types are safe to cross a `catch_unwind` |
| /// boundary with no fear of unwind safety. |
| /// |
| /// ## What is unwind safety? |
| /// |
| /// In Rust a function can "return" early if it either panics or calls a |
| /// function which transitively panics. This sort of control flow is not always |
| /// anticipated, and has the possibility of causing subtle bugs through a |
| /// combination of two cricial components: |
| /// |
| /// 1. A data structure is in a temporarily invalid state when the thread |
| /// panics. |
| /// 2. This broken invariant is then later observed. |
| /// |
| /// Typically in Rust, it is difficult to perform step (2) because catching a |
| /// panic involves either spawning a thread (which in turns makes it difficult |
| /// to later witness broken invariants) or using the `catch_unwind` function in this |
| /// module. Additionally, even if an invariant is witnessed, it typically isn't a |
| /// problem in Rust because there are no uninitialized values (like in C or C++). |
| /// |
| /// It is possible, however, for **logical** invariants to be broken in Rust, |
| /// which can end up causing behavioral bugs. Another key aspect of unwind safety |
| /// in Rust is that, in the absence of `unsafe` code, a panic cannot lead to |
| /// memory unsafety. |
| /// |
| /// That was a bit of a whirlwind tour of unwind safety, but for more information |
| /// about unwind safety and how it applies to Rust, see an [associated RFC][rfc]. |
| /// |
| /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md |
| /// |
| /// ## What is `UnwindSafe`? |
| /// |
| /// Now that we've got an idea of what unwind safety is in Rust, it's also |
| /// important to understand what this trait represents. As mentioned above, one |
| /// way to witness broken invariants is through the `catch_unwind` function in this |
| /// module as it allows catching a panic and then re-using the environment of |
| /// the closure. |
| /// |
| /// Simply put, a type `T` implements `UnwindSafe` if it cannot easily allow |
| /// witnessing a broken invariant through the use of `catch_unwind` (catching a |
| /// panic). This trait is a marker trait, so it is automatically implemented for |
| /// many types, and it is also structurally composed (e.g. a struct is unwind |
| /// safe if all of its components are unwind safe). |
| /// |
| /// Note, however, that this is not an unsafe trait, so there is not a succinct |
| /// contract that this trait is providing. Instead it is intended as more of a |
| /// "speed bump" to alert users of `catch_unwind` that broken invariants may be |
| /// witnessed and may need to be accounted for. |
| /// |
| /// ## Who implements `UnwindSafe`? |
| /// |
| /// Types such as `&mut T` and `&RefCell<T>` are examples which are **not** |
| /// unwind safe. The general idea is that any mutable state which can be shared |
| /// across `catch_unwind` is not unwind safe by default. This is because it is very |
| /// easy to witness a broken invariant outside of `catch_unwind` as the data is |
| /// simply accessed as usual. |
| /// |
| /// Types like `&SgxMutex<T>`, however, are unwind safe because they implement |
| /// poisoning by default. They still allow witnessing a broken invariant, but |
| /// they already provide their own "speed bumps" to do so. |
| /// |
| /// ## When should `UnwindSafe` be used? |
| /// |
| /// Is not intended that most types or functions need to worry about this trait. |
| /// It is only used as a bound on the `catch_unwind` function and as mentioned above, |
| /// the lack of `unsafe` means it is mostly an advisory. The `AssertUnwindSafe` |
| /// wrapper struct in this module can be used to force this trait to be |
| /// implemented for any closed over variables passed to the `catch_unwind` function |
| /// (more on this below). |
| pub auto trait UnwindSafe {} |
| |
| /// A marker trait representing types where a shared reference is considered |
| /// unwind safe. |
| /// |
| /// This trait is namely not implemented by `UnsafeCell`, the root of all |
| /// interior mutability. |
| /// |
| /// This is a "helper marker trait" used to provide impl blocks for the |
| /// `UnwindSafe` trait, for more information see that documentation. |
| pub auto trait RefUnwindSafe {} |
| |
| /// A simple wrapper around a type to assert that it is unwind safe. |
| /// |
| /// When using `catch_unwind` it may be the case that some of the closed over |
| /// variables are not unwind safe. For example if `&mut T` is captured the |
| /// compiler will generate a warning indicating that it is not unwind safe. It |
| /// may not be the case, however, that this is actually a problem due to the |
| /// specific usage of `catch_unwind` if unwind safety is specifically taken into |
| /// account. This wrapper struct is useful for a quick and lightweight |
| /// annotation that a variable is indeed unwind safe. |
| /// |
| pub struct AssertUnwindSafe<T>( |
| pub T |
| ); |
| |
| // Implementations of the `UnwindSafe` trait: |
| // |
| // * By default everything is unwind safe |
| // * pointers T contains mutability of some form are not unwind safe |
| // * Unique, an owning pointer, lifts an implementation |
| // * Types like Mutex/RwLock which are explicilty poisoned are unwind safe |
| // * Our custom AssertUnwindSafe wrapper is indeed unwind safe |
| |
| impl<'a, T: ?Sized> !UnwindSafe for &'a mut T {} |
| impl<'a, T: RefUnwindSafe + ?Sized> UnwindSafe for &'a T {} |
| impl<T: RefUnwindSafe + ?Sized> UnwindSafe for *const T {} |
| impl<T: RefUnwindSafe + ?Sized> UnwindSafe for *mut T {} |
| impl<T: UnwindSafe + ?Sized> UnwindSafe for Unique<T> {} |
| impl<T: RefUnwindSafe + ?Sized> UnwindSafe for NonNull<T> {} |
| impl<T> UnwindSafe for AssertUnwindSafe<T> {} |
| |
| // not covered via the Shared impl above b/c the inner contents use |
| // Cell/AtomicUsize, but the usage here is unwind safe so we can lift the |
| // impl up one level to Arc/Rc itself |
| impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Rc<T> {} |
| impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Arc<T> {} |
| |
| // Pretty simple implementations for the `RefUnwindSafe` marker trait, |
| // basically just saying that `UnsafeCell` is the |
| // only thing which doesn't implement it (which then transitively applies to |
| // everything else). |
| |
| impl<T: ?Sized> !RefUnwindSafe for UnsafeCell<T> {} |
| impl<T> RefUnwindSafe for AssertUnwindSafe<T> {} |
| |
| impl RefUnwindSafe for Fn() {} |
| |
| #[cfg(target_has_atomic = "ptr")] |
| impl RefUnwindSafe for atomic::AtomicIsize {} |
| #[cfg(target_has_atomic = "8")] |
| impl RefUnwindSafe for atomic::AtomicI8 {} |
| #[cfg(target_has_atomic = "16")] |
| impl RefUnwindSafe for atomic::AtomicI16 {} |
| #[cfg(target_has_atomic = "32")] |
| impl RefUnwindSafe for atomic::AtomicI32 {} |
| #[cfg(target_has_atomic = "64")] |
| impl RefUnwindSafe for atomic::AtomicI64 {} |
| |
| #[cfg(target_has_atomic = "ptr")] |
| impl RefUnwindSafe for atomic::AtomicUsize {} |
| #[cfg(target_has_atomic = "8")] |
| impl RefUnwindSafe for atomic::AtomicU8 {} |
| #[cfg(target_has_atomic = "16")] |
| impl RefUnwindSafe for atomic::AtomicU16 {} |
| #[cfg(target_has_atomic = "32")] |
| impl RefUnwindSafe for atomic::AtomicU32 {} |
| #[cfg(target_has_atomic = "64")] |
| impl RefUnwindSafe for atomic::AtomicU64 {} |
| |
| #[cfg(target_has_atomic = "8")] |
| impl RefUnwindSafe for atomic::AtomicBool {} |
| |
| #[cfg(target_has_atomic = "ptr")] |
| impl<T> RefUnwindSafe for atomic::AtomicPtr<T> {} |
| |
| impl<T> Deref for AssertUnwindSafe<T> { |
| type Target = T; |
| |
| fn deref(&self) -> &T { |
| &self.0 |
| } |
| } |
| |
| impl<T> DerefMut for AssertUnwindSafe<T> { |
| fn deref_mut(&mut self) -> &mut T { |
| &mut self.0 |
| } |
| } |
| |
| impl<R, F: FnOnce() -> R> FnOnce<()> for AssertUnwindSafe<F> { |
| type Output = R; |
| |
| extern "rust-call" fn call_once(self, _args: ()) -> R { |
| (self.0)() |
| } |
| } |
| |
| impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| f.debug_tuple("AssertUnwindSafe") |
| .field(&self.0) |
| .finish() |
| } |
| } |
| |
| /// Invokes a closure, capturing the cause of an unwinding panic if one occurs. |
| /// |
| /// This function will return `Ok` with the closure's result if the closure |
| /// does not panic, and will return `Err(cause)` if the closure panics. The |
| /// `cause` returned is the object with which panic was originally invoked. |
| /// |
| /// It is currently undefined behavior to unwind from Rust code into foreign |
| /// code, so this function is particularly useful when Rust is called from |
| /// another language (normally C). This can run arbitrary Rust code, capturing a |
| /// panic and allowing a graceful handling of the error. |
| /// |
| /// It is **not** recommended to use this function for a general try/catch |
| /// mechanism. The `Result` type is more appropriate to use for functions that |
| /// can fail on a regular basis. Additionally, this function is not guaranteed |
| /// to catch all panics, see the "Notes" section below. |
| /// |
| /// The closure provided is required to adhere to the `UnwindSafe` trait to ensure |
| /// that all captured variables are safe to cross this boundary. The purpose of |
| /// this bound is to encode the concept of [exception safety][rfc] in the type |
| /// system. Most usage of this function should not need to worry about this |
| /// bound as programs are naturally unwind safe without `unsafe` code. If it |
| /// becomes a problem the associated `AssertUnwindSafe` wrapper type in this |
| /// module can be used to quickly assert that the usage here is indeed unwind |
| /// safe. |
| /// |
| /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md |
| /// |
| /// # Notes |
| /// |
| /// Note that this function **may not catch all panics** in Rust. A panic in |
| /// Rust is not always implemented via unwinding, but can be implemented by |
| /// aborting the process as well. This function *only* catches unwinding panics, |
| /// not those that abort the process. |
| /// |
| pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R, Box<Any + Send + 'static>> { |
| unsafe { |
| panicking::try(f) |
| } |
| } |
| |
| /// Triggers a panic without invoking the panic hook. |
| /// |
| /// This is designed to be used in conjunction with `catch_unwind` to, for |
| /// example, carry a panic across a layer of C code. |
| /// |
| /// # Notes |
| /// |
| /// Note that panics in Rust are not always implemented via unwinding, but they |
| /// may be implemented by aborting the process. If this function is called when |
| /// panics are implemented this way then this function will abort the process, |
| /// not trigger an unwind. |
| /// |
| pub fn resume_unwind(payload: Box<Any + Send>) -> ! { |
| panicking::update_count_then_panic(payload) |
| } |