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]
21 macro_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 $crate::bindings::static_key = ::core::ptr::addr_of!((*_key).$field);
25
26 #[cfg(not(CONFIG_JUMP_LABEL))]
27 {
28 $crate::bindings::static_key_count(_key.cast_mut()) > 0
29 }
30
31 #[cfg(CONFIG_JUMP_LABEL)]
32 $crate::jump_label::arch_static_branch! { $key, $keytyp, $field, false }
33 }};
34 }
35 pub use static_branch_unlikely;
36
37 /// Assert that the assembly block evaluates to a string literal.
38 #[cfg(CONFIG_JUMP_LABEL)]
39 const _: &str = include!(concat!(
40 env!("OBJTREE"),
41 "/rust/kernel/generated_arch_static_branch_asm.rs"
42 ));
43
44 #[macro_export]
45 #[doc(hidden)]
46 #[cfg(CONFIG_JUMP_LABEL)]
47 macro_rules! arch_static_branch {
48 ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
49 $crate::asm!(
50 include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_static_branch_asm.rs"));
51 l_yes = label {
52 break 'my_label true;
53 },
54 symb = sym $key,
55 off = const ::core::mem::offset_of!($keytyp, $field),
56 branch = const $crate::jump_label::bool_to_int($branch),
57 );
58
59 break 'my_label false;
60 }};
61 }
62
63 #[cfg(CONFIG_JUMP_LABEL)]
64 pub use arch_static_branch;
65
66 /// A helper used by inline assembly to pass a boolean to as a `const` parameter.
67 ///
68 /// Using this function instead of a cast lets you assert that the input is a boolean, and not some
69 /// other type that can also be cast to an integer.
70 #[doc(hidden)]
bool_to_int(b: bool) -> i3271 pub const fn bool_to_int(b: bool) -> i32 {
72 b as i32
73 }
74