rust: add static_key_false

Add just enough support for static key so that we can use it from
tracepoints. Tracepoints rely on `static_key_false` even though it is
deprecated, so we add the same functionality to Rust.

Signed-off-by: Alice Ryhl <[email protected]>

rust/kernel/lib.rs

@@ -39,6 +39,7 @@ pub mod prelude;
 pub mod print;
 mod static_assert;
 pub mod static_call;
+pub mod static_key;
 #[doc(hidden)]
 pub mod std_vendor;
 pub mod str;

rust/kernel/static_key.rs

@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Logic for static keys.
+
+use crate::bindings::*;
+
+#[doc(hidden)]
+#[macro_export]
+#[cfg(target_arch = "x86_64")]
+#[cfg(not(CONFIG_HAVE_RUST_ASM_GOTO))]
+macro_rules! _static_key_false {
+ ($key:path, $keytyp:ty, $field:ident) => {{
+ let mut output = 1u32;
+
+ core::arch::asm!(
+ r#"
+ 1: .byte 0x0f,0x1f,0x44,0x00,0x00
+
+ .pushsection __jump_table, "aw"
+ .balign 8
+ .long 1b - .
+ .long 3f - .
+ .quad {0} + {1} - .
+ .popsection
+
+ 2: mov {2:e}, 0
+ 3:
+ "#,
+ sym $key,
+ const ::core::mem::offset_of!($keytyp, $field),
+ inout(reg) output,
+ );
+
+ output != 0
+ }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+#[cfg(target_arch = "x86_64")]
+#[cfg(CONFIG_HAVE_RUST_ASM_GOTO)]
+macro_rules! _static_key_false {
+ ($key:path, $keytyp:ty, $field:ident) => {'my_label: {
+ core::arch::asm!(
+ r#"
+ 1: .byte 0x0f,0x1f,0x44,0x00,0x00
+
+ .pushsection __jump_table, "aw"
+ .balign 8
+ .long 1b - .
+ .long {0} - .
+ .quad {1} + {2} - .
+ .popsection
+ "#,
+ label {
+ break 'my_label true;
+ },
+ sym $key,
+ const ::core::mem::offset_of!($keytyp, $field),
+ );
+
+ break 'my_label false;
+ }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+#[cfg(target_arch = "aarch64")]
+#[cfg(not(CONFIG_HAVE_RUST_ASM_GOTO))]
+macro_rules! _static_key_false {
+ ($key:path, $keytyp:ty, $field:ident) => {{
+ let mut output = 1u32;
+
+ core::arch::asm!(
+ r#"
+ 1: nop
+
+ .pushsection __jump_table, "aw"
+ .align 3
+ .long 1b - ., 3f - .
+ .quad {0} + {1} - .
+ .popsection
+
+ 2: mov {2:w}, 0
+ 3:
+ "#,
+ sym $key,
+ const ::core::mem::offset_of!($keytyp, $field),
+ inout(reg) output
+ );
+
+ output != 0
+ }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+#[cfg(target_arch = "aarch64")]
+#[cfg(CONFIG_HAVE_RUST_ASM_GOTO)]
+macro_rules! _static_key_false {
+ ($key:path, $keytyp:ty, $field:ident) => {'my_label: {
+ core::arch::asm!(
+ r#"
+ 1: nop
+
+ .pushsection __jump_table, "aw"
+ .align 3
+ .long 1b - ., {0} - .
+ .quad {1} + {2} - .
+ .popsection
+ "#,
+ label {
+ break 'my_label true;
+ },
+ sym $key,
+ const ::core::mem::offset_of!($keytyp, $field),
+ );
+
+ break 'my_label false;
+ }};
+}
+
+/// Branch based on a static key.
+///
+/// Takes three arguments:
+///
+/// * `key` - the path to the static variable containing the `static_key`.
+/// * `keytyp` - the type of `key`.
+/// * `field` - the name of the field of `key` that contains the `static_key`.
+#[macro_export]
+macro_rules! static_key_false {
+ // Forward to the real implementation. Separated like this so that we don't have to duplicate
+ // the documentation.
+ ($key:path, $keytyp:ty, $field:ident) => {{
+ // Assert that `$key` has type `$keytyp` and that `$key.$field` has type `static_key`.
+ //
+ // SAFETY: We know that `$key` is a static because otherwise the inline assembly will not
+ // compile. The raw pointers created in this block are in-bounds of `$key`.
+ static _TY_ASSERT: () = unsafe {
+ let key: *const $keytyp = ::core::ptr::addr_of!($key);
+ let _: *const $crate::bindings::static_key = ::core::ptr::addr_of!((*key).$field);
+ };
+
+ $crate::static_key::_static_key_false! { $key, $keytyp, $field }
+ }};
+}
+
+pub use {_static_key_false, static_key_false};

scripts/Makefile.build

@@ -263,7 +263,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
 
-rust_allowed_features := new_uninit
+rust_allowed_features := asm_const,asm_goto,new_uninit
 
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree