Crate core

The Rust Core Library

The Rust Core Library is the dependency-free¹ foundation of The Rust Standard Library. It is the portable glue between the language and its libraries, defining the intrinsic and primitive building blocks of all Rust code. It links to no upstream libraries, no system libraries, and no libc.

The core library is minimal: it isn’t even aware of heap allocation, nor does it provide concurrency or I/O. These things require platform integration, and this library is platform-agnostic.

How to use the core library

Please note that all of these details are currently not considered stable.

This library is built on the assumption of a few existing symbols:

• memcpy, memmove, memset, memcmp, bcmp, strlen - These are core memory routines which are generated by Rust codegen backends. Additionally, this library can make explicit calls to strlen. Their signatures are the same as found in C, but there are extra assumptions about their semantics: For memcpy, memmove, memset, memcmp, and bcmp, if the n parameter is 0, the function is assumed to not be UB, even if the pointers are NULL or dangling. (Note that making extra assumptions about these functions is common among compilers: clang and GCC do the same.) These functions are often provided by the system libc, but can also be provided by the compiler-builtins crate. Note that the library does not guarantee that it will always make these assumptions, so Rust user code directly calling the C functions should follow the C specification! The advice for Rust user code is to call the functions provided by this library instead (such as ptr::copy).

• Panic handler - This function takes one argument, a &panic::PanicInfo. It is up to consumers of this core library to define this panic function; it is only required to never return. You should mark your implementation using #[panic_handler].

• rust_eh_personality - is used by the failure mechanisms of the compiler. This is often mapped to GCC’s personality function, but crates which do not trigger a panic can be assured that this function is never called. The lang attribute is called eh_personality.

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1. Strictly speaking, there are some symbols which are needed but they aren’t always necessary. ↩

Modules

• alloc
  Memory allocation APIs
• any
  Utilities for dynamic typing or type reflection.
• arch
  SIMD and vendor intrinsics module.
• array
  Utilities for the array primitive type.
• ascii
  Operations on ASCII strings and characters.
• borrow