1//! Panic support for core
2//!
3//! In core, panicking is always done with a message, resulting in a `core::panic::PanicInfo`
4//! containing a `fmt::Arguments`. In std, however, panicking can be done with panic_any, which
5//! throws a `Box<dyn Any>` containing any type of value. Because of this,
6//! `std::panic::PanicHookInfo` is a different type, which contains a `&dyn Any` instead of a
7//! `fmt::Arguments`. std's panic handler will convert the `fmt::Arguments` to a `&dyn Any`
8//! containing either a `&'static str` or `String` containing the formatted message.
9//!
10//! The core library cannot define any panic handler, but it can invoke it.
11//! This means that the functions inside of core are allowed to panic, but to be
12//! useful an upstream crate must define panicking for core to use. The current
13//! interface for panicking is:
14//!
15//! ```
16//! fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !
17//! # { loop {} }
18//! ```
19//!
20//! This module contains a few other panicking functions, but these are just the
21//! necessary lang items for the compiler. All panics are funneled through this
22//! one function. The actual symbol is declared through the `#[panic_handler]` attribute.
23
24#![allow(dead_code, missing_docs)]
25#![unstable(
26 feature = "panic_internals",
27 reason = "internal details of the implementation of the `panic!` and related macros",
28 issue = "none"
29)]
30
31use crate::fmt;
32use crate::intrinsics::const_eval_select;
33use crate::panic::{Location, PanicInfo};
34
35#[cfg(feature = "panic_immediate_abort")]
36const _: () = assert!(cfg!(panic = "abort"), "panic_immediate_abort requires -C panic=abort");
37
38// First we define the two main entry points that all panics go through.
39// In the end both are just convenience wrappers around `panic_impl`.
40
41/// The entry point for panicking with a formatted message.
42///
43/// This is designed to reduce the amount of code required at the call
44/// site as much as possible (so that `panic!()` has as low an impact
45/// on (e.g.) the inlining of other functions as possible), by moving
46/// the actual formatting into this shared place.
47// If panic_immediate_abort, inline the abort call,
48// otherwise avoid inlining because of it is cold path.
49#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
50#[cfg_attr(feature = "panic_immediate_abort", inline)]
51#[track_caller]
52#[lang = "panic_fmt"] // needed for const-evaluated panics
53#[rustc_do_not_const_check] // hooked by const-eval
54#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
55pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
56 if cfg!(feature = "panic_immediate_abort") {
57 super::intrinsics::abort()
58 }
59
60 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
61 // that gets resolved to the `#[panic_handler]` function.
62 unsafe extern "Rust" {
63 #[lang = "panic_impl"]
64 unsafefn panic_impl(pi: &PanicInfo<'_>) -> !;
65 }
66
67 let pi: PanicInfo<'_> = PanicInfo::new(
68 &fmt,
69 Location::caller(),
70 /* can_unwind */ can_unwind:true,
71 /* force_no_backtrace */ force_no_backtrace:false,
72 );
73
74 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
75 unsafe { panic_impl(&pi) }
76}
77
78/// Like `panic_fmt`, but for non-unwinding panics.
79///
80/// Has to be a separate function so that it can carry the `rustc_nounwind` attribute.
81#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
82#[cfg_attr(feature = "panic_immediate_abort", inline)]
83#[track_caller]
84// This attribute has the key side-effect that if the panic handler ignores `can_unwind`
85// and unwinds anyway, we will hit the "unwinding out of nounwind function" guard,
86// which causes a "panic in a function that cannot unwind".
87#[rustc_nounwind]
88#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
89#[rustc_allow_const_fn_unstable(const_eval_select)]
90pub const fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
91 const_eval_select!(
92 @capture { fmt: fmt::Arguments<'_>, force_no_backtrace: bool } -> !:
93 if const #[track_caller] {
94 // We don't unwind anyway at compile-time so we can call the regular `panic_fmt`.
95 panic_fmt(fmt)
96 } else #[track_caller] {
97 if cfg!(feature = "panic_immediate_abort") {
98 super::intrinsics::abort()
99 }
100
101 // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
102 // that gets resolved to the `#[panic_handler]` function.
103 unsafe extern "Rust" {
104 #[lang = "panic_impl"]
105 fn panic_impl(pi: &PanicInfo<'_>) -> !;
106 }
107
108 // PanicInfo with the `can_unwind` flag set to false forces an abort.
109 let pi = PanicInfo::new(
110 &fmt,
111 Location::caller(),
112 /* can_unwind */ false,
113 force_no_backtrace,
114 );
115
116 // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
117 unsafe { panic_impl(&pi) }
118 }
119 )
120}
121
122// Next we define a bunch of higher-level wrappers that all bottom out in the two core functions
123// above.
124
125/// The underlying implementation of core's `panic!` macro when no formatting is used.
126// Never inline unless panic_immediate_abort to avoid code
127// bloat at the call sites as much as possible.
128#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
129#[cfg_attr(feature = "panic_immediate_abort", inline)]
130#[track_caller]
131#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
132#[lang = "panic"] // used by lints and miri for panics
133pub const fn panic(expr: &'static str) -> ! {
134 // Use Arguments::new_const instead of format_args!("{expr}") to potentially
135 // reduce size overhead. The format_args! macro uses str's Display trait to
136 // write expr, which calls Formatter::pad, which must accommodate string
137 // truncation and padding (even though none is used here). Using
138 // Arguments::new_const may allow the compiler to omit Formatter::pad from the
139 // output binary, saving up to a few kilobytes.
140 // However, this optimization only works for `'static` strings: `new_const` also makes this
141 // message return `Some` from `Arguments::as_str`, which means it can become part of the panic
142 // payload without any allocation or copying. Shorter-lived strings would become invalid as
143 // stack frames get popped during unwinding, and couldn't be directly referenced from the
144 // payload.
145 panic_fmt(fmt::Arguments::new_const(&[expr]));
146}
147
148// We generate functions for usage by compiler-generated assertions.
149//
150// Placing these functions in libcore means that all Rust programs can generate a jump into this
151// code rather than expanding to panic("...") above, which adds extra bloat to call sites (for the
152// constant string argument's pointer and length).
153//
154// This is especially important when this code is called often (e.g., with -Coverflow-checks) for
155// reducing binary size impact.
156macro_rules! panic_const {
157 ($($lang:ident = $message:expr,)+) => {
158 pub mod panic_const {
159 use super::*;
160
161 $(
162 /// This is a panic called with a message that's a result of a MIR-produced Assert.
163 //
164 // never inline unless panic_immediate_abort to avoid code
165 // bloat at the call sites as much as possible
166 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
167 #[cfg_attr(feature = "panic_immediate_abort", inline)]
168 #[track_caller]
169 #[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
170 #[lang = stringify!($lang)]
171 pub const fn $lang() -> ! {
172 // Use Arguments::new_const instead of format_args!("{expr}") to potentially
173 // reduce size overhead. The format_args! macro uses str's Display trait to
174 // write expr, which calls Formatter::pad, which must accommodate string
175 // truncation and padding (even though none is used here). Using
176 // Arguments::new_const may allow the compiler to omit Formatter::pad from the
177 // output binary, saving up to a few kilobytes.
178 panic_fmt(fmt::Arguments::new_const(&[$message]));
179 }
180 )+
181 }
182 }
183}
184
185// Unfortunately this set of strings is replicated here and in a few places in the compiler in
186// slightly different forms. It's not clear if there's a good way to deduplicate without adding
187// special cases to the compiler (e.g., a const generic function wouldn't have a single definition
188// shared across crates, which is exactly what we want here).
189panic_const! {
190 panic_const_add_overflow = "attempt to add with overflow",
191 panic_const_sub_overflow = "attempt to subtract with overflow",
192 panic_const_mul_overflow = "attempt to multiply with overflow",
193 panic_const_div_overflow = "attempt to divide with overflow",
194 panic_const_rem_overflow = "attempt to calculate the remainder with overflow",
195 panic_const_neg_overflow = "attempt to negate with overflow",
196 panic_const_shr_overflow = "attempt to shift right with overflow",
197 panic_const_shl_overflow = "attempt to shift left with overflow",
198 panic_const_div_by_zero = "attempt to divide by zero",
199 panic_const_rem_by_zero = "attempt to calculate the remainder with a divisor of zero",
200 panic_const_coroutine_resumed = "coroutine resumed after completion",
201 panic_const_async_fn_resumed = "`async fn` resumed after completion",
202 panic_const_async_gen_fn_resumed = "`async gen fn` resumed after completion",
203 panic_const_gen_fn_none = "`gen fn` should just keep returning `None` after completion",
204 panic_const_coroutine_resumed_panic = "coroutine resumed after panicking",
205 panic_const_async_fn_resumed_panic = "`async fn` resumed after panicking",
206 panic_const_async_gen_fn_resumed_panic = "`async gen fn` resumed after panicking",
207 panic_const_gen_fn_none_panic = "`gen fn` should just keep returning `None` after panicking",
208}
209
210/// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize on the caller.
211/// If you want `#[track_caller]` for nicer errors, call `panic_nounwind_fmt` directly.
212#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
213#[cfg_attr(feature = "panic_immediate_abort", inline)]
214#[lang = "panic_nounwind"] // needed by codegen for non-unwinding panics
215#[rustc_nounwind]
216#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
217pub const fn panic_nounwind(expr: &'static str) -> ! {
218 panic_nounwind_fmt(fmt:fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ force_no_backtrace:false);
219}
220
221/// Like `panic_nounwind`, but also inhibits showing a backtrace.
222#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
223#[cfg_attr(feature = "panic_immediate_abort", inline)]
224#[rustc_nounwind]
225pub fn panic_nounwind_nobacktrace(expr: &'static str) -> ! {
226 panic_nounwind_fmt(fmt:fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ force_no_backtrace:true);
227}
228
229#[track_caller]
230#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
231#[cfg_attr(feature = "panic_immediate_abort", inline)]
232#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
233pub const fn panic_explicit() -> ! {
234 panic_display(&"explicit panic");
235}
236
237#[inline]
238#[track_caller]
239#[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
240pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
241 panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
242}
243
244/// This exists solely for the 2015 edition `panic!` macro to trigger
245/// a lint on `panic!(my_str_variable);`.
246#[inline]
247#[track_caller]
248#[rustc_diagnostic_item = "panic_str_2015"]
249#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
250pub const fn panic_str_2015(expr: &str) -> ! {
251 panic_display(&expr);
252}
253
254#[inline]
255#[track_caller]
256#[rustc_do_not_const_check] // hooked by const-eval
257// enforce a &&str argument in const-check and hook this by const-eval
258#[rustc_const_panic_str]
259#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
260pub const fn panic_display<T: fmt::Display>(x: &T) -> ! {
261 panic_fmt(format_args!("{}", *x));
262}
263
264#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
265#[cfg_attr(feature = "panic_immediate_abort", inline)]
266#[track_caller]
267#[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
268fn panic_bounds_check(index: usize, len: usize) -> ! {
269 if cfg!(feature = "panic_immediate_abort") {
270 super::intrinsics::abort()
271 }
272
273 panic!("index out of bounds: the len is {len} but the index is {index}")
274}
275
276#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
277#[cfg_attr(feature = "panic_immediate_abort", inline)]
278#[track_caller]
279#[lang = "panic_misaligned_pointer_dereference"] // needed by codegen for panic on misaligned pointer deref
280#[rustc_nounwind] // `CheckAlignment` MIR pass requires this function to never unwind
281fn panic_misaligned_pointer_dereference(required: usize, found: usize) -> ! {
282 if cfg!(feature = "panic_immediate_abort") {
283 super::intrinsics::abort()
284 }
285
286 panic_nounwind_fmt(
287 fmt:format_args!(
288 "misaligned pointer dereference: address must be a multiple of {required:#x} but is {found:#x}"
289 ),
290 /* force_no_backtrace */ force_no_backtrace:false,
291 )
292}
293
294#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
295#[cfg_attr(feature = "panic_immediate_abort", inline)]
296#[track_caller]
297#[lang = "panic_null_pointer_dereference"] // needed by codegen for panic on null pointer deref
298#[rustc_nounwind] // `CheckNull` MIR pass requires this function to never unwind
299fn panic_null_pointer_dereference() -> ! {
300 if cfg!(feature = "panic_immediate_abort") {
301 super::intrinsics::abort()
302 }
303
304 panic_nounwind_fmt(
305 fmt:format_args!("null pointer dereference occurred"),
306 /* force_no_backtrace */ force_no_backtrace:false,
307 )
308}
309
310/// Panics because we cannot unwind out of a function.
311///
312/// This is a separate function to avoid the codesize impact of each crate containing the string to
313/// pass to `panic_nounwind`.
314///
315/// This function is called directly by the codegen backend, and must not have
316/// any extra arguments (including those synthesized by track_caller).
317#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
318#[cfg_attr(feature = "panic_immediate_abort", inline)]
319#[lang = "panic_cannot_unwind"] // needed by codegen for panic in nounwind function
320#[rustc_nounwind]
321fn panic_cannot_unwind() -> ! {
322 // Keep the text in sync with `UnwindTerminateReason::as_str` in `rustc_middle`.
323 panic_nounwind(expr:"panic in a function that cannot unwind")
324}
325
326/// Panics because we are unwinding out of a destructor during cleanup.
327///
328/// This is a separate function to avoid the codesize impact of each crate containing the string to
329/// pass to `panic_nounwind`.
330///
331/// This function is called directly by the codegen backend, and must not have
332/// any extra arguments (including those synthesized by track_caller).
333#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
334#[cfg_attr(feature = "panic_immediate_abort", inline)]
335#[lang = "panic_in_cleanup"] // needed by codegen for panic in nounwind function
336#[rustc_nounwind]
337fn panic_in_cleanup() -> ! {
338 // Keep the text in sync with `UnwindTerminateReason::as_str` in `rustc_middle`.
339 panic_nounwind_nobacktrace(expr:"panic in a destructor during cleanup")
340}
341
342/// This function is used instead of panic_fmt in const eval.
343#[lang = "const_panic_fmt"] // needed by const-eval machine to replace calls to `panic_fmt` lang item
344#[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
345pub const fn const_panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
346 if let Some(msg: &'static str) = fmt.as_str() {
347 // The panic_display function is hooked by const eval.
348 panic_display(&msg);
349 } else {
350 // SAFETY: This is only evaluated at compile time, which reliably
351 // handles this UB (in case this branch turns out to be reachable
352 // somehow).
353 unsafe { crate::hint::unreachable_unchecked() };
354 }
355}
356
357#[derive(Debug)]
358#[doc(hidden)]
359pub enum AssertKind {
360 Eq,
361 Ne,
362 Match,
363}
364
365/// Internal function for `assert_eq!` and `assert_ne!` macros
366#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
367#[cfg_attr(feature = "panic_immediate_abort", inline)]
368#[track_caller]
369#[doc(hidden)]
370pub fn assert_failed<T, U>(
371 kind: AssertKind,
372 left: &T,
373 right: &U,
374 args: Option<fmt::Arguments<'_>>,
375) -> !
376where
377 T: fmt::Debug + ?Sized,
378 U: fmt::Debug + ?Sized,
379{
380 assert_failed_inner(kind, &left, &right, args)
381}
382
383/// Internal function for `assert_match!`
384#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
385#[cfg_attr(feature = "panic_immediate_abort", inline)]
386#[track_caller]
387#[doc(hidden)]
388pub fn assert_matches_failed<T: fmt::Debug + ?Sized>(
389 left: &T,
390 right: &str,
391 args: Option<fmt::Arguments<'_>>,
392) -> ! {
393 // The pattern is a string so it can be displayed directly.
394 struct Pattern<'a>(&'a str);
395 impl fmt::Debug for Pattern<'_> {
396 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
397 f.write_str(self.0)
398 }
399 }
400 assert_failed_inner(kind:AssertKind::Match, &left, &Pattern(right), args);
401}
402
403/// Non-generic version of the above functions, to avoid code bloat.
404#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold, optimize(size))]
405#[cfg_attr(feature = "panic_immediate_abort", inline)]
406#[track_caller]
407fn assert_failed_inner(
408 kind: AssertKind,
409 left: &dyn fmt::Debug,
410 right: &dyn fmt::Debug,
411 args: Option<fmt::Arguments<'_>>,
412) -> ! {
413 let op: &'static str = match kind {
414 AssertKind::Eq => "==",
415 AssertKind::Ne => "!=",
416 AssertKind::Match => "matches",
417 };
418
419 match args {
420 Some(args: Arguments<'_>) => panic!(
421 r#"assertion `left {op} right` failed: {args}
422 left: {left:?}
423 right: {right:?}"#
424 ),
425 None => panic!(
426 r#"assertion `left {op} right` failed
427 left: {left:?}
428 right: {right:?}"#
429 ),
430 }
431}
432

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