kernel/
jump_label.rs

1// SPDX-License-Identifier: GPL-2.0
2
3// Copyright (C) 2024 Google LLC.
4
5//! Logic for static keys.
6//!
7//! C header: [`include/linux/jump_label.h`](srctree/include/linux/jump_label.h).
8
9/// Branch based on a static key.
10///
11/// Takes three arguments:
12///
13/// * `key` - the path to the static variable containing the `static_key`.
14/// * `keytyp` - the type of `key`.
15/// * `field` - the name of the field of `key` that contains the `static_key`.
16///
17/// # Safety
18///
19/// The macro must be used with a real static key defined by C.
20#[macro_export]
21macro_rules! static_branch_unlikely {
22    ($key:path, $keytyp:ty, $field:ident) => {{
23        let _key: *const $keytyp = ::core::ptr::addr_of!($key);
24        let _key: *const $crate::bindings::static_key_false = ::core::ptr::addr_of!((*_key).$field);
25        let _key: *const $crate::bindings::static_key = _key.cast();
26
27        #[cfg(not(CONFIG_JUMP_LABEL))]
28        {
29            $crate::bindings::static_key_count(_key.cast_mut()) > 0
30        }
31
32        #[cfg(CONFIG_JUMP_LABEL)]
33        $crate::jump_label::arch_static_branch! { $key, $keytyp, $field, false }
34    }};
35}
36pub use static_branch_unlikely;
37
38/// Assert that the assembly block evaluates to a string literal.
39#[cfg(CONFIG_JUMP_LABEL)]
40const _: &str = include!(concat!(
41    env!("OBJTREE"),
42    "/rust/kernel/generated_arch_static_branch_asm.rs"
43));
44
45#[macro_export]
46#[doc(hidden)]
47#[cfg(not(testlib))]
48#[cfg(CONFIG_JUMP_LABEL)]
49macro_rules! arch_static_branch {
50    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
51        $crate::asm!(
52            include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_static_branch_asm.rs"));
53            l_yes = label {
54                break 'my_label true;
55            },
56            symb = sym $key,
57            off = const ::core::mem::offset_of!($keytyp, $field),
58            branch = const $crate::jump_label::bool_to_int($branch),
59        );
60
61        break 'my_label false;
62    }};
63}
64
65#[macro_export]
66#[doc(hidden)]
67#[cfg(testlib)]
68#[cfg(CONFIG_JUMP_LABEL)]
69macro_rules! arch_static_branch {
70    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {
71        // The asm falls through until patched, which never happens on the host.
72        false
73    };
74}
75
76#[cfg(CONFIG_JUMP_LABEL)]
77pub use arch_static_branch;
78
79/// A helper used by inline assembly to pass a boolean to as a `const` parameter.
80///
81/// Using this function instead of a cast lets you assert that the input is a boolean, and not some
82/// other type that can also be cast to an integer.
83#[doc(hidden)]
84pub const fn bool_to_int(b: bool) -> i32 {
85    b as i32
86}
kernel/jump_label.rs

kernel/
jump_label.rs
