Linux kernel mirror (for testing)
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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, $field, false }
34 }};
35}
36pub use static_branch_unlikely;
37
38/// Assert that the assembly block evaluates to a string literal.
39#[cfg(CONFIG_JUMP_LABEL)]
40const _: &str = include!(concat!(
41 env!("OBJTREE"),
42 "/rust/kernel/generated_arch_static_branch_asm.rs"
43));
44
45#[macro_export]
46#[doc(hidden)]
47#[cfg(CONFIG_JUMP_LABEL)]
48macro_rules! arch_static_branch {
49 ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
50 $crate::asm!(
51 include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_static_branch_asm.rs"));
52 l_yes = label {
53 break 'my_label true;
54 },
55 symb = sym $key,
56 off = const ::core::mem::offset_of!($keytyp, $field),
57 branch = const $crate::jump_label::bool_to_int($branch),
58 );
59
60 break 'my_label false;
61 }};
62}
63
64#[cfg(CONFIG_JUMP_LABEL)]
65pub use arch_static_branch;
66
67/// A helper used by inline assembly to pass a boolean to as a `const` parameter.
68///
69/// Using this function instead of a cast lets you assert that the input is a boolean, and not some
70/// other type that can also be cast to an integer.
71#[doc(hidden)]
72pub const fn bool_to_int(b: bool) -> i32 {
73 b as i32
74}