87 lines
3.4 KiB
Rust
87 lines
3.4 KiB
Rust
//! Panic support for libcore
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//!
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//! The core library cannot define panicking, but it does *declare* panicking. This
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//! means that the functions inside of libcore are allowed to panic, but to be
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//! useful an upstream crate must define panicking for libcore to use. The current
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//! interface for panicking is:
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//!
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//! ```
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//! fn panic_impl(pi: &core::panic::PanicInfo<'_>) -> !
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//! # { loop {} }
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//! ```
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//!
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//! This definition allows for panicking with any general message, but it does not
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//! allow for failing with a `Box<Any>` value. (`PanicInfo` just contains a `&(dyn Any + Send)`,
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//! for which we fill in a dummy value in `PanicInfo::internal_constructor`.)
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//! The reason for this is that libcore is not allowed to allocate.
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//!
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//! This module contains a few other panicking functions, but these are just the
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//! necessary lang items for the compiler. All panics are funneled through this
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//! one function. The actual symbol is declared through the `#[panic_handler]` attribute.
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#![allow(dead_code, missing_docs)]
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#![unstable(
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feature = "core_panic",
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reason = "internal details of the implementation of the `panic!` and related macros",
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issue = "none"
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)]
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use crate::fmt;
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use crate::panic::{Location, PanicInfo};
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/// The underlying implementation of libcore's `panic!` macro when no formatting is used.
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#[cold]
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// never inline unless panic_immediate_abort to avoid code
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// bloat at the call sites as much as possible
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#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
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#[track_caller]
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#[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
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pub fn panic(expr: &'static str) -> ! {
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if cfg!(feature = "panic_immediate_abort") {
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super::intrinsics::abort()
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}
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// Use Arguments::new_v1 instead of format_args!("{}", expr) to potentially
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// reduce size overhead. The format_args! macro uses str's Display trait to
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// write expr, which calls Formatter::pad, which must accommodate string
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// truncation and padding (even though none is used here). Using
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// Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
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// output binary, saving up to a few kilobytes.
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panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
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}
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#[cold]
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#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
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#[track_caller]
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#[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
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fn panic_bounds_check(index: usize, len: usize) -> ! {
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if cfg!(feature = "panic_immediate_abort") {
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super::intrinsics::abort()
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}
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panic!("index out of bounds: the len is {} but the index is {}", len, index)
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}
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/// The underlying implementation of libcore's `panic!` macro when formatting is used.
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#[cold]
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#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
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#[cfg_attr(feature = "panic_immediate_abort", inline)]
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#[track_caller]
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pub fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
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if cfg!(feature = "panic_immediate_abort") {
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super::intrinsics::abort()
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}
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// NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
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// that gets resolved to the `#[panic_handler]` function.
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extern "Rust" {
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#[lang = "panic_impl"]
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fn panic_impl(pi: &PanicInfo<'_>) -> !;
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}
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let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller());
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// SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
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unsafe { panic_impl(&pi) }
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}
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