3 files changed, 71 insertions, 1 deletions

diff --git a/rust/macros/export.rs b/rust/macros/export.rs
new file mode 100644
index 000000000000..a08f6337d5c8
--- /dev/null
+++ b/rust/macros/export.rs
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use crate::helpers::function_name;
+use proc_macro::TokenStream;
+
+/// Please see [`crate::export`] for documentation.
+pub(crate) fn export(_attr: TokenStream, ts: TokenStream) -> TokenStream {
+    let Some(name) = function_name(ts.clone()) else {
+        return "::core::compile_error!(\"The #[export] attribute must be used on a function.\");"
+            .parse::<TokenStream>()
+            .unwrap();
+    };
+
+    // This verifies that the function has the same signature as the declaration generated by
+    // bindgen. It makes use of the fact that all branches of an if/else must have the same type.
+    let signature_check = quote!(
+        const _: () = {
+            if true {
+                ::kernel::bindings::#name
+            } else {
+                #name
+            };
+        };
+    );
+
+    let no_mangle = quote!(#[no_mangle]);
+
+    TokenStream::from_iter([signature_check, no_mangle, ts])
+}
diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index 563dcd2b7ace..3e04f8ecfc74 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro::{token_stream, Group, TokenStream, TokenTree};
+use proc_macro::{token_stream, Group, Ident, TokenStream, TokenTree};
 
 pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
     if let Some(TokenTree::Ident(ident)) = it.next() {
@@ -215,3 +215,20 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
         rest,
     )
 }
+
+/// Given a function declaration, finds the name of the function.
+pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
+    let mut input = input.into_iter();
+    while let Some(token) = input.next() {
+        match token {
+            TokenTree::Ident(i) if i.to_string() == "fn" => {
+                if let Some(TokenTree::Ident(i)) = input.next() {
+                    return Some(i);
+                }
+                return None;
+            }
+            _ => continue,
+        }
+    }
+    None
+}
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index d61bc6a56425..a52443a3dbb9 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -9,6 +9,7 @@
 #[macro_use]
 mod quote;
 mod concat_idents;
+mod export;
 mod helpers;
 mod module;
 mod paste;
@@ -174,6 +175,29 @@ pub fn vtable(attr: TokenStream, ts: TokenStream) -> TokenStream {
     vtable::vtable(attr, ts)
 }
 
+/// Export a function so that C code can call it via a header file.
+///
+/// Functions exported using this macro can be called from C code using the declaration in the
+/// appropriate header file. It should only be used in cases where C calls the function through a
+/// header file; cases where C calls into Rust via a function pointer in a vtable (such as
+/// `file_operations`) should not use this macro.
+///
+/// This macro has the following effect:
+///
+/// * Disables name mangling for this function.
+/// * Verifies at compile-time that the function signature matches the declaration in the header
+///   file.
+///
+/// You must declare the signature of the Rust function in a header file that is included by
+/// `rust/bindings/bindings_helper.h`.
+///
+/// This macro is *not* the same as the C macros `EXPORT_SYMBOL_*`. All Rust symbols are currently
+/// automatically exported with `EXPORT_SYMBOL_GPL`.
+#[proc_macro_attribute]
+pub fn export(attr: TokenStream, ts: TokenStream) -> TokenStream {
+    export::export(attr, ts)
+}
+
 /// Concatenate two identifiers.
 ///
 /// This is useful in macros that need to declare or reference items with names