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Message-ID: <20250227-export-macro-v1-2-948775fc37aa@google.com>
Date: Thu, 27 Feb 2025 17:02:00 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Miguel Ojeda <ojeda@...nel.org>
Cc: Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>, Sergey Senozhatsky <senozhatsky@...omium.org>,
Andrew Morton <akpm@...ux-foundation.org>, Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
dri-devel@...ts.freedesktop.org, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH 2/4] rust: add #[export] macro
This macro behaves like #[no_mangle], but also performs an assertion
that the Rust function has the same signature as what is declared in the
C header.
If the signatures don't match, you will get errors that look like this:
error[E0308]: `if` and `else` have incompatible types
--> <linux>/rust/kernel/print.rs:22:22
|
21 | #[export]
| --------- expected because of this
22 | unsafe extern "C" fn rust_fmt_argument(
| ^^^^^^^^^^^^^^^^^ expected `u8`, found `i8`
|
= note: expected fn item `unsafe extern "C" fn(*mut u8, *mut u8, *mut c_void) -> *mut u8 {bindings::rust_fmt_argument}`
found fn item `unsafe extern "C" fn(*mut i8, *mut i8, *const c_void) -> *mut i8 {print::rust_fmt_argument}`
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
rust/kernel/prelude.rs | 2 +-
rust/macros/export.rs | 25 +++++++++++++++++++++++++
rust/macros/helpers.rs | 19 ++++++++++++++++++-
rust/macros/lib.rs | 18 ++++++++++++++++++
rust/macros/quote.rs | 21 +++++++++++++++++++--
5 files changed, 81 insertions(+), 4 deletions(-)
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index dde2e0649790..889102f5a81e 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -17,7 +17,7 @@
pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec, Vec};
#[doc(no_inline)]
-pub use macros::{module, pin_data, pinned_drop, vtable, Zeroable};
+pub use macros::{export, module, pin_data, pinned_drop, vtable, Zeroable};
pub use super::{build_assert, build_error};
diff --git a/rust/macros/export.rs b/rust/macros/export.rs
new file mode 100644
index 000000000000..3398e1655124
--- /dev/null
+++ b/rust/macros/export.rs
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use crate::helpers::function_name;
+use proc_macro::TokenStream;
+
+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();
+ };
+
+ let signature_check = quote!(
+ const _: () = {
+ if true {
+ ::kernel::bindings::#name
+ } else {
+ #name
+ };
+ };
+ );
+
+ let no_mangle = "#[no_mangle]".parse::<TokenStream>().unwrap();
+ 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..3cbf7705c4c1 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 +175,23 @@ pub fn vtable(attr: TokenStream, ts: TokenStream) -> TokenStream {
vtable::vtable(attr, ts)
}
+/// Export a function so that C code can call it.
+///
+/// This macro has the following effect:
+///
+/// * Disables name mangling for this function.
+/// * Verifies at compile-time that the function signature matches what's in the header file.
+///
+/// This macro requires that the function is mentioned in a C header file, and that the header file
+/// is included in `rust/bindings/bindings_helper.h`.
+///
+/// This macro is *not* the same as the C macro `EXPORT_SYMBOL*`, since 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
diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs
index 33a199e4f176..c18960a91082 100644
--- a/rust/macros/quote.rs
+++ b/rust/macros/quote.rs
@@ -20,6 +20,12 @@ fn to_tokens(&self, tokens: &mut TokenStream) {
}
}
+impl ToTokens for proc_macro::Ident {
+ fn to_tokens(&self, tokens: &mut TokenStream) {
+ tokens.extend([TokenTree::from(self.clone())]);
+ }
+}
+
impl ToTokens for TokenTree {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.extend([self.clone()]);
@@ -40,7 +46,7 @@ fn to_tokens(&self, tokens: &mut TokenStream) {
/// `quote` crate but provides only just enough functionality needed by the current `macros` crate.
macro_rules! quote_spanned {
($span:expr => $($tt:tt)*) => {{
- let mut tokens;
+ let mut tokens: ::std::vec::Vec<::proc_macro::TokenTree>;
#[allow(clippy::vec_init_then_push)]
{
tokens = ::std::vec::Vec::new();
@@ -65,7 +71,8 @@ macro_rules! quote_spanned {
quote_spanned!(@proc $v $span $($tt)*);
};
(@proc $v:ident $span:ident ( $($inner:tt)* ) $($tt:tt)*) => {
- let mut tokens = ::std::vec::Vec::new();
+ #[allow(unused_mut)]
+ let mut tokens = ::std::vec::Vec::<::proc_macro::TokenTree>::new();
quote_spanned!(@proc tokens $span $($inner)*);
$v.push(::proc_macro::TokenTree::Group(::proc_macro::Group::new(
::proc_macro::Delimiter::Parenthesis,
@@ -136,6 +143,16 @@ macro_rules! quote_spanned {
));
quote_spanned!(@proc $v $span $($tt)*);
};
+ (@proc $v:ident $span:ident = $($tt:tt)*) => {
+ $v.push(::proc_macro::TokenTree::Punct(
+ ::proc_macro::Punct::new('=', ::proc_macro::Spacing::Alone)
+ ));
+ quote_spanned!(@proc $v $span $($tt)*);
+ };
+ (@proc $v:ident $span:ident _ $($tt:tt)*) => {
+ $v.push(::proc_macro::TokenTree::Ident(::proc_macro::Ident::new("_", $span)));
+ quote_spanned!(@proc $v $span $($tt)*);
+ };
(@proc $v:ident $span:ident $id:ident $($tt:tt)*) => {
$v.push(::proc_macro::TokenTree::Ident(::proc_macro::Ident::new(stringify!($id), $span)));
quote_spanned!(@proc $v $span $($tt)*);
--
2.48.1.658.g4767266eb4-goog
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