Re: [PATCH v4 1/2] rust: add static_key_false

[hev <r@hev.cc>]

Hi Alice

On Fri, Jun 28, 2024 at 9:24 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> 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.
>
> It is not possible to use the existing C implementation of
> arch_static_branch because it passes the argument `key` to inline
> assembly as an 'i' parameter, so any attempt to add a C helper for this
> function will fail to compile because the value of `key` must be known
> at compile-time.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/arch/arm64/jump_label.rs     | 34 ++++++++++++++++++++++++++++
>  rust/kernel/arch/loongarch/jump_label.rs | 35 +++++++++++++++++++++++++++++
>  rust/kernel/arch/mod.rs                  | 24 ++++++++++++++++++++
>  rust/kernel/arch/riscv/jump_label.rs     | 38 ++++++++++++++++++++++++++++++++
>  rust/kernel/arch/x86/jump_label.rs       | 35 +++++++++++++++++++++++++++++
>  rust/kernel/lib.rs                       |  2 ++
>  rust/kernel/static_key.rs                | 32 +++++++++++++++++++++++++++
>  scripts/Makefile.build                   |  2 +-
>  8 files changed, 201 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/arch/arm64/jump_label.rs b/rust/kernel/arch/arm64/jump_label.rs
> new file mode 100644
> index 000000000000..5eede2245718
> --- /dev/null
> +++ b/rust/kernel/arch/arm64/jump_label.rs
> @@ -0,0 +1,34 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Arm64 Rust implementation of jump_label.h
> +
> +/// arm64 implementation of arch_static_branch
> +#[macro_export]
> +#[cfg(target_arch = "aarch64")]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        core::arch::asm!(
> +            r#"
> +            1: nop
> +
> +            .pushsection __jump_table,  "aw"
> +            .align 3
> +            .long 1b - ., {0} - .
> +            .quad {1} + {2} + {3} - .
> +            .popsection
> +            "#,
> +            label {
> +                break 'my_label true;
> +            },
> +            sym $key,
> +            const ::core::mem::offset_of!($keytyp, $field),
> +            const $crate::arch::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}
> +
> +pub use arch_static_branch;
> diff --git a/rust/kernel/arch/loongarch/jump_label.rs b/rust/kernel/arch/loongarch/jump_label.rs
> new file mode 100644
> index 000000000000..8d31318aeb11
> --- /dev/null
> +++ b/rust/kernel/arch/loongarch/jump_label.rs
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Loongarch Rust implementation of jump_label.h
> +
> +/// loongarch implementation of arch_static_branch
> +#[doc(hidden)]
> +#[macro_export]
> +#[cfg(target_arch = "loongarch64")]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        core::arch::asm!(
> +            r#"
> +            1: nop
> +
> +            .pushsection __jump_table,  "aw"
> +            .align 3
> +            .long 1b - ., {0} - .
> +            .quad {1} + {2} + {3} - .
> +            .popsection
> +            "#,
> +            label {
> +                break 'my_label true;
> +            },
> +            sym $key,
> +            const ::core::mem::offset_of!($keytyp, $field),
> +            const $crate::arch::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}

I have tested these patches on LoongArch and it works as expected.

Tested-by: WANG Rui <wangrui@loongson.cn>

Thanks,
-Rui

> +
> +pub use arch_static_branch;
> diff --git a/rust/kernel/arch/mod.rs b/rust/kernel/arch/mod.rs
> new file mode 100644
> index 000000000000..14271d2530e9
> --- /dev/null
> +++ b/rust/kernel/arch/mod.rs
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Architecture specific code.
> +
> +#[cfg_attr(target_arch = "aarch64", path = "arm64")]
> +#[cfg_attr(target_arch = "x86_64", path = "x86")]
> +#[cfg_attr(target_arch = "loongarch64", path = "loongarch")]
> +#[cfg_attr(target_arch = "riscv64", path = "riscv")]
> +mod inner {
> +    pub mod jump_label;
> +}
> +
> +pub use self::inner::*;
> +
> +/// A helper used by inline assembly to pass a boolean to as a `const` parameter.
> +///
> +/// Using this function instead of a cast lets you assert that the input is a boolean, rather than
> +/// some other type that can be cast to an integer.
> +#[doc(hidden)]
> +pub const fn bool_to_int(b: bool) -> i32 {
> +    b as i32
> +}
> diff --git a/rust/kernel/arch/riscv/jump_label.rs b/rust/kernel/arch/riscv/jump_label.rs
> new file mode 100644
> index 000000000000..2672e0c6f033
> --- /dev/null
> +++ b/rust/kernel/arch/riscv/jump_label.rs
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! RiscV Rust implementation of jump_label.h
> +
> +/// riscv implementation of arch_static_branch
> +#[macro_export]
> +#[cfg(target_arch = "riscv64")]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
> +        core::arch::asm!(
> +            r#"
> +            .align  2
> +            .option push
> +            .option norelax
> +            .option norvc
> +            1: nop
> +            .option pop
> +            .pushsection __jump_table,  "aw"
> +            .align 3
> +            .long 1b - ., {0} - .
> +            .dword {1} + {2} + {3} - .
> +            .popsection
> +            "#,
> +            label {
> +                break 'my_label true;
> +            },
> +            sym $key,
> +            const ::core::mem::offset_of!($keytyp, $field),
> +            const $crate::arch::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}
> +
> +pub use arch_static_branch;
> diff --git a/rust/kernel/arch/x86/jump_label.rs b/rust/kernel/arch/x86/jump_label.rs
> new file mode 100644
> index 000000000000..383bed273c50
> --- /dev/null
> +++ b/rust/kernel/arch/x86/jump_label.rs
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! X86 Rust implementation of jump_label.h
> +
> +/// x86 implementation of arch_static_branch
> +#[macro_export]
> +#[cfg(target_arch = "x86_64")]
> +macro_rules! arch_static_branch {
> +    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'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} + {3} - .
> +            .popsection
> +            "#,
> +            label {
> +                break 'my_label true;
> +            },
> +            sym $key,
> +            const ::core::mem::offset_of!($keytyp, $field),
> +            const $crate::arch::bool_to_int($branch),
> +        );
> +
> +        break 'my_label false;
> +    }};
> +}
> +
> +pub use arch_static_branch;
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index fbd91a48ff8b..fffd4e1dd1c1 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -27,6 +27,7 @@
>  extern crate self as kernel;
>
>  pub mod alloc;
> +pub mod arch;
>  mod build_assert;
>  pub mod error;
>  pub mod init;
> @@ -38,6 +39,7 @@
>  pub mod prelude;
>  pub mod print;
>  mod static_assert;
> +pub mod static_key;
>  #[doc(hidden)]
>  pub mod std_vendor;
>  pub mod str;
> diff --git a/rust/kernel/static_key.rs b/rust/kernel/static_key.rs
> new file mode 100644
> index 000000000000..32cf027ef091
> --- /dev/null
> +++ b/rust/kernel/static_key.rs
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Logic for static keys.
> +
> +use crate::bindings::*;
> +
> +/// 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 {
> +    ($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::arch::jump_label::arch_static_branch! { $key, $keytyp, $field, false }
> +    }};
> +}
> +
> +pub use static_key_false;
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index efacca63c897..60197c1c063f 100644
> --- a/scripts/Makefile.build
> +++ b/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
>
> --
> 2.45.2.803.g4e1b14247a-goog
>
>