diff options
| -rw-r--r-- | cortex-m-rt/src/lib.rs | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/cortex-m-rt/src/lib.rs b/cortex-m-rt/src/lib.rs index 40b10dc..3522476 100644 --- a/cortex-m-rt/src/lib.rs +++ b/cortex-m-rt/src/lib.rs @@ -658,9 +658,18 @@ pub use macros::exception; /// /// The function must have the signature of `unsafe fn()`. /// -/// The function passed will be called before static variables are initialized. Any access of static +/// # Safety +/// +/// The function will be called before static variables are initialized. Any access of static /// variables will result in undefined behavior. /// +/// **Warning**: Due to [rvalue static promotion][rfc1414] static variables may be accessed whenever +/// taking a reference to a constant. This means that even trivial expressions such as `&1` in the +/// `#[pre_init]` function *or any code called by it* will cause **immediate undefined behavior**. +/// +/// Users are advised to only use the `#[pre_init]` feature when absolutely necessary as these +/// constraints make safe usage difficult. +/// /// # Examples /// /// ``` @@ -672,6 +681,8 @@ pub use macros::exception; /// /// # fn main() {} /// ``` +/// +/// [rfc1414]: https://github.com/rust-lang/rfcs/blob/master/text/1414-rvalue_static_promotion.md pub use macros::pre_init; #[export_name = "error: cortex-m-rt appears more than once in the dependency graph"] |