1 //! Panic support for libcore
3 //! The core library cannot define panicking, but it does *declare* panicking. This
4 //! means that the functions inside of libcore are allowed to panic, but to be
5 //! useful an upstream crate must define panicking for libcore to use. The current
6 //! interface for panicking is:
9 //! fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !
13 //! This definition allows for panicking with any general message, but it does not
14 //! allow for failing with a `Box<Any>` value. (`PanicInfo` just contains a `&(dyn Any + Send)`,
15 //! for which we fill in a dummy value in `PanicInfo::internal_constructor`.)
16 //! The reason for this is that libcore is not allowed to allocate.
18 //! This module contains a few other panicking functions, but these are just the
19 //! necessary lang items for the compiler. All panics are funneled through this
20 //! one function. The actual symbol is declared through the `#[panic_handler]` attribute.
22 #![allow(dead_code, missing_docs)]
24 feature = "core_panic",
25 reason = "internal details of the implementation of the `panic!` and related macros",
30 use crate::panic::{Location, PanicInfo};
32 /// The underlying implementation of libcore's `panic!` macro when no formatting is used.
34 // never inline unless panic_immediate_abort to avoid code
35 // bloat at the call sites as much as possible
36 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
38 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
39 pub fn panic(expr: &str) -> ! {
40 if cfg!(feature = "panic_immediate_abort") {
41 super::intrinsics::abort()
44 // Use Arguments::new_v1 instead of format_args!("{}", expr) to potentially
45 // reduce size overhead. The format_args! macro uses str's Display trait to
46 // write expr, which calls Formatter::pad, which must accommodate string
47 // truncation and padding (even though none is used here). Using
48 // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
49 // output binary, saving up to a few kilobytes.
50 panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
54 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
56 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
57 fn panic_bounds_check(index: usize, len: usize) -> ! {
58 if cfg!(feature = "panic_immediate_abort") {
59 super::intrinsics::abort()
62 panic!("index out of bounds: the len is {} but the index is {}", len, index)
65 /// The underlying implementation of libcore's `panic!` macro when formatting is used.
67 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
68 #[cfg_attr(feature = "panic_immediate_abort", inline)]
70 pub fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
71 if cfg!(feature = "panic_immediate_abort") {
72 super::intrinsics::abort()
75 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
76 // that gets resolved to the `#[panic_handler]` function.
78 #[lang = "panic_impl"]
79 fn panic_impl(pi: &PanicInfo<'_>) -> !;
82 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller());
84 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
85 unsafe { panic_impl(&pi) }