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 $crate::bindings::static_key_false = ::core::ptr::addr_of!((*_key).$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, $field, false } 34 }}; 35 } 36 pub use static_branch_unlikely; 37 38 /// Assert that the assembly block evaluates to a string literal. 39 #[cfg(CONFIG_JUMP_LABEL)] 40 const _: &str = include!(concat!( 41 env!("OBJTREE"), 42 "/rust/kernel/generated_arch_static_branch_asm.rs" 43 )); 44 45 #[macro_export] 46 #[doc(hidden)] 47 #[cfg(not(testlib))] 48 #[cfg(CONFIG_JUMP_LABEL)] 49 macro_rules! arch_static_branch { 50 ($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)] 69 macro_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)] 77 pub 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)] 84 pub const fn bool_to_int(b: bool) -> i32 { 85 b as i32 86 } 87