diff options
| -rw-r--r-- | library/core/src/lib.rs | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs index b97cb652076..c3edd3a9d7d 100644 --- a/library/core/src/lib.rs +++ b/library/core/src/lib.rs @@ -20,11 +20,19 @@ // FIXME: Fill me in with more detail when the interface settles //! This library is built on the assumption of a few existing symbols: //! -//! * `memcpy`, `memcmp`, `memset`, `strlen` - These are core memory routines which are -//! often generated by LLVM. Additionally, this library can make explicit -//! calls to these functions. Their signatures are the same as found in C. -//! These functions are often provided by the system libc, but can also be -//! provided by the [compiler-builtins crate](https://crates.io/crates/compiler_builtins). +//! * `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. Furthermore, for `memcpy`, if +//! source and target pointer are equal, the function is assumed to not be UB. +//! (Note that these are [standard assumptions](https://reviews.llvm.org/D86993) among compilers.) +//! These functions are often provided by the system libc, but can also be provided by the +//! [compiler-builtins crate](https://crates.io/crates/compiler_builtins). +//! 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`). //! //! * `rust_begin_panic` - This function takes four arguments, a //! `fmt::Arguments`, a `&'static str`, and two `u32`'s. These four arguments |