1 files changed, 74 insertions, 0 deletions
diff --git a/rust/kernel/jump_label.rs b/rust/kernel/jump_label.rs
new file mode 100644
index 000000000000..4e974c768dbd
--- /dev/null
+++ b/rust/kernel/jump_label.rs
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Logic for static keys.
+//!
+//! C header: [`include/linux/jump_label.h`](srctree/include/linux/jump_label.h).
+
+/// Branch based on a static key.
+///
+/// Takes three arguments:
+///
+/// * `key` - the path to the static variable containing the `static_key`.
+/// * `keytyp` - the type of `key`.
+/// * `field` - the name of the field of `key` that contains the `static_key`.
+///
+/// # Safety
+///
+/// The macro must be used with a real static key defined by C.
+#[macro_export]
+macro_rules! static_branch_unlikely {
+    ($key:path, $keytyp:ty, $field:ident) => {{
+        let _key: *const $keytyp = ::core::ptr::addr_of!($key);
+        let _key: *const $crate::bindings::static_key_false = ::core::ptr::addr_of!((*_key).$field);
+        let _key: *const $crate::bindings::static_key = _key.cast();
+
+        #[cfg(not(CONFIG_JUMP_LABEL))]
+        {
+            $crate::bindings::static_key_count(_key.cast_mut()) > 0
+        }
+
+        #[cfg(CONFIG_JUMP_LABEL)]
+        $crate::jump_label::arch_static_branch! { $key, $keytyp, $field, false }
+    }};
+}
+pub use static_branch_unlikely;
+
+/// Assert that the assembly block evaluates to a string literal.
+#[cfg(CONFIG_JUMP_LABEL)]
+const _: &str = include!(concat!(
+    env!("OBJTREE"),
+    "/rust/kernel/generated_arch_static_branch_asm.rs"
+));
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(CONFIG_JUMP_LABEL)]
+macro_rules! arch_static_branch {
+    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
+        $crate::asm!(
+            include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_static_branch_asm.rs"));
+            l_yes = label {
+                break 'my_label true;
+            },
+            symb = sym $key,
+            off = const ::core::mem::offset_of!($keytyp, $field),
+            branch = const $crate::jump_label::bool_to_int($branch),
+        );
+
+        break 'my_label false;
+    }};
+}
+
+#[cfg(CONFIG_JUMP_LABEL)]
+pub use arch_static_branch;
+
+/// A helper used by inline assembly to pass a boolean to as a `const` parameter.
+///
+/// Using this function instead of a cast lets you assert that the input is a boolean, and not some
+/// other type that can also be cast to an integer.
+#[doc(hidden)]
+pub const fn bool_to_int(b: bool) -> i32 {
+    b as i32
+}