make the reachability requirement more **prominent**

since we can't statically check that it holds

Author: japaric

cortex-m-rt/macros/src/lib.rs

@@ -15,8 +15,9 @@ use proc_macro::TokenStream;
 
 /// Attribute to declare the entry point of the program
 ///
-/// **NOTE** This macro must be invoked once and must be invoked from an accessible module, ideally
-/// from the root of the crate.
+/// **IMPORTANT**: This attribute must be used once in the dependency graph and must be used on a
+/// reachable item (i.e. there must be no private modules between the item and the root of the
+/// crate). If the item is in the root of the crate you'll be fine.
 ///
 /// The specified function will be called by the reset handler *after* RAM has been initialized. In
 /// the case of the `thumbv7em-none-eabihf` target the FPU will also be enabled before the function
@@ -136,8 +137,9 @@ pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
 
 /// Attribute to declare an exception handler
 ///
-/// **NOTE** This macro must be invoked from an accessible module, ideally from the root of the
-/// crate.
+/// **IMPORTANT**: This attribute must be used on reachable items (i.e. there must be no private
+/// modules between the item and the root of the crate). If the item is in the root of the crate
+/// you'll be fine.
 ///
 /// # Syntax
 ///
@@ -429,6 +431,10 @@ pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
 
 /// Attribute to mark which function will be called at the beginning of the reset handler.
 ///
+/// **IMPORTANT**: This attribute must be used once in the dependency graph and must be used on a
+/// reachable item (i.e. there must be no private modules between the item and the root of the
+/// crate). If the item is in the root of the crate you'll be fine.
+///
 /// The function must have the signature of `unsafe fn()`.
 ///
 /// The function passed will be called before static variables are initialized. Any access of static