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 // First we define the two main entry points that all panics go through.
33 // In the end both are just convenience wrappers around `panic_impl`.
35 /// The entry point for panicking with a formatted message.
37 /// This is designed to reduce the amount of code required at the call
38 /// site as much as possible (so that `panic!()` has as low an impact
39 /// on (e.g.) the inlining of other functions as possible), by moving
40 /// the actual formatting into this shared place.
41 // If panic_immediate_abort, inline the abort call,
42 // otherwise avoid inlining because of it is cold path.
43 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
44 #[cfg_attr(feature = "panic_immediate_abort", inline)]
46 #[lang = "panic_fmt"] // needed for const-evaluated panics
47 #[rustc_do_not_const_check] // hooked by const-eval
48 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
49 pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
50 if cfg!(feature = "panic_immediate_abort") {
51 super::intrinsics::abort()
54 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
55 // that gets resolved to the `#[panic_handler]` function.
57 #[lang = "panic_impl"]
58 fn panic_impl(pi: &PanicInfo<'_>) -> !;
61 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
63 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
64 unsafe { panic_impl(&pi) }
67 /// Like panic_fmt, but without unwinding and track_caller to reduce the impact on codesize.
68 /// Also just works on `str`, as a `fmt::Arguments` needs more space to be passed.
69 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
70 #[cfg_attr(feature = "panic_immediate_abort", inline)]
72 pub fn panic_str_nounwind(msg: &'static str) -> ! {
73 if cfg!(feature = "panic_immediate_abort") {
74 super::intrinsics::abort()
77 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
78 // that gets resolved to the `#[panic_handler]` function.
80 #[lang = "panic_impl"]
81 fn panic_impl(pi: &PanicInfo<'_>) -> !;
84 // PanicInfo with the `can_unwind` flag set to false forces an abort.
86 let fmt = fmt::Arguments::new_v1(&pieces, &[]);
87 let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
89 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
90 unsafe { panic_impl(&pi) }
93 // Next we define a bunch of higher-level wrappers that all bottom out in the two core functions
96 /// The underlying implementation of libcore's `panic!` macro when no formatting is used.
97 // never inline unless panic_immediate_abort to avoid code
98 // bloat at the call sites as much as possible
99 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
100 #[cfg_attr(feature = "panic_immediate_abort", inline)]
102 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
103 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
104 pub const fn panic(expr: &'static str) -> ! {
105 // Use Arguments::new_v1 instead of format_args!("{expr}") to potentially
106 // reduce size overhead. The format_args! macro uses str's Display trait to
107 // write expr, which calls Formatter::pad, which must accommodate string
108 // truncation and padding (even though none is used here). Using
109 // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
110 // output binary, saving up to a few kilobytes.
111 panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
116 #[rustc_diagnostic_item = "panic_str"]
117 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
118 pub const fn panic_str(expr: &str) -> ! {
119 panic_display(&expr);
124 #[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
125 pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
126 panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
131 #[lang = "panic_display"] // needed for const-evaluated panics
132 #[rustc_do_not_const_check] // hooked by const-eval
133 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
134 pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
135 panic_fmt(format_args!("{}", *x));
138 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
139 #[cfg_attr(feature = "panic_immediate_abort", inline)]
141 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
142 fn panic_bounds_check(index: usize, len: usize) -> ! {
143 if cfg!(feature = "panic_immediate_abort") {
144 super::intrinsics::abort()
147 panic!("index out of bounds: the len is {len} but the index is {index}")
150 /// Panic because we cannot unwind out of a function.
152 /// This function is called directly by the codegen backend, and must not have
153 /// any extra arguments (including those synthesized by track_caller).
154 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
155 #[cfg_attr(feature = "panic_immediate_abort", inline)]
156 #[lang = "panic_no_unwind"] // needed by codegen for panic in nounwind function
158 fn panic_no_unwind() -> ! {
159 panic_str_nounwind("panic in a function that cannot unwind")
162 /// This function is used instead of panic_fmt in const eval.
163 #[lang = "const_panic_fmt"]
164 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
165 pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
166 if let Some(msg) = fmt.as_str() {
169 // SAFETY: This is only evaluated at compile time, which reliably
170 // handles this UB (in case this branch turns out to be reachable
172 unsafe { crate::hint::unreachable_unchecked() };
178 pub enum AssertKind {
184 /// Internal function for `assert_eq!` and `assert_ne!` macros
185 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
186 #[cfg_attr(feature = "panic_immediate_abort", inline)]
189 pub fn assert_failed<T, U>(
193 args: Option<fmt::Arguments<'_>>,
196 T: fmt::Debug + ?Sized,
197 U: fmt::Debug + ?Sized,
199 assert_failed_inner(kind, &left, &right, args)
202 /// Internal function for `assert_match!`
203 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
204 #[cfg_attr(feature = "panic_immediate_abort", inline)]
207 pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
210 args: Option<fmt::Arguments<'_>>,
212 // The pattern is a string so it can be displayed directly.
213 struct Pattern<'a>(&'a str);
214 impl fmt::Debug for Pattern<'_> {
215 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
219 assert_failed_inner(AssertKind::Match, &left, &Pattern(right), args);
222 /// Non-generic version of the above functions, to avoid code bloat.
223 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
224 #[cfg_attr(feature = "panic_immediate_abort", inline)]
226 fn assert_failed_inner(
228 left: &dyn fmt::Debug,
229 right: &dyn fmt::Debug,
230 args: Option<fmt::Arguments<'_>>,
232 let op = match kind {
233 AssertKind::Eq => "==",
234 AssertKind::Ne => "!=",
235 AssertKind::Match => "matches",
239 Some(args) => panic!(
240 r#"assertion failed: `(left {} right)`
243 op, left, right, args
246 r#"assertion failed: `(left {} right)`