rust/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]
  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, $field, false }
  34     }};
  35 }
  36 pub use static_branch_unlikely;
  37
  38 /// Assert that the assembly block evaluates to a string literal.
  39 #[cfg(CONFIG_JUMP_LABEL)]
  40 const _: &str = include!(concat!(
  41     env!("OBJTREE"),
  42     "/rust/kernel/generated_arch_static_branch_asm.rs"
  43 ));
  44
  45 #[macro_export]
  46 #[doc(hidden)]
  47 #[cfg(CONFIG_JUMP_LABEL)]
  48 macro_rules! arch_static_branch {
  49     ($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)]
  65 pub 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)]
  72 pub const fn bool_to_int(b: bool) -> i32 {
  73     b as i32
  74 }