Commit 169484ab authored by Alice Ryhl's avatar Alice Ryhl Committed by Steven Rostedt (Google)
Browse files

rust: add arch_static_branch 

To allow the Rust implementation of static_key_false to use runtime code
patching instead of the generic implementation, pull in the relevant
inline assembly from the jump_label.h header by running the C
preprocessor on a .rs.S file. Build rules are added for .rs.S files.

Since the relevant inline asm has been adjusted to export the inline asm
via the ARCH_STATIC_BRANCH_ASM macro in a consistent way, the Rust side
does not need architecture specific code to pull in the asm.

It is not possible to use the existing C implementation of
arch_static_branch via a Rust helper because it passes the argument
`key` to inline assembly as an 'i' parameter. 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.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " <bjorn3_gh@protonmail.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: Andreas Hindborg <a.hindborg@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Anup Patel <apatel@ventanamicro.com>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Conor Dooley <conor.dooley@microchip.com>
Cc: Samuel Holland <samuel.holland@sifive.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Bibo Mao <maobibo@loongson.cn>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tianrui Zhao <zhaotianrui@loongson.cn>
Link: https://lore.kernel.org/20241030-tracepoint-v12-5-eec7f0f8ad22@google.com


Suggested-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Reviewed-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent aecaf181

rust/Makefile

+6 −0
Original line number Diff line number Diff line
@@ -36,6 +36,8 @@ always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c 
obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.o

obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.o



always-$(subst y,$(CONFIG_RUST),$(CONFIG_JUMP_LABEL)) += kernel/arch_static_branch_asm.rs



# Avoids running `$(RUSTC)` for the sysroot when it may not be available.

ifdef CONFIG_RUST
@@ -424,4 +426,8 @@ $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \ 
    $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE

	+$(call if_changed_rule,rustc_library)



ifdef CONFIG_JUMP_LABEL

$(obj)/kernel.o: $(obj)/kernel/arch_static_branch_asm.rs

endif



endif # CONFIG_RUST

rust/kernel/.gitignore

0 → 100644
+3 −0
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0



/arch_static_branch_asm.rs

rust/kernel/arch_static_branch_asm.rs.S

0 → 100644
+7 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */



#include <linux/jump_label.h>



// Cut here.



::kernel::concat_literals!(ARCH_STATIC_BRANCH_ASM("{symb} + {off} + {branch}", "{l_yes}"))

rust/kernel/jump_label.rs

+45 −1
Original line number Diff line number Diff line
@@ -24,7 +24,51 @@ macro_rules! static_branch_unlikely { 
        let _key: *const $crate::bindings::static_key_false = ::core::ptr::addr_of!((*_key).$field);

        let _key: *const $crate::bindings::static_key = _key.cast();



        $crate::bindings::static_key_count(_key.cast_mut()) > 0

        #[cfg(not(CONFIG_JUMP_LABEL))]

        {

            $crate::bindings::static_key_count(_key) > 0

        }



        #[cfg(CONFIG_JUMP_LABEL)]

        $crate::jump_label::arch_static_branch! { $key, $keytyp, $field, false }

    }};

}

pub use static_branch_unlikely;



/// Assert that the assembly block evaluates to a string literal.

#[cfg(CONFIG_JUMP_LABEL)]

const _: &str = include!(concat!(

    env!("OBJTREE"),

    "/rust/kernel/arch_static_branch_asm.rs"

));



#[macro_export]

#[doc(hidden)]

#[cfg(CONFIG_JUMP_LABEL)]

macro_rules! arch_static_branch {

    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {

        $crate::asm!(

            include!(concat!(env!("OBJTREE"), "/rust/kernel/arch_static_branch_asm.rs"));

            l_yes = label {

                break 'my_label true;

            },

            symb = sym $key,

            off = const ::core::mem::offset_of!($keytyp, $field),

            branch = const $crate::jump_label::bool_to_int($branch),

        );



        break 'my_label false;

    }};

}



#[cfg(CONFIG_JUMP_LABEL)]

pub use arch_static_branch;



/// 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, and not some

/// other type that can also be cast to an integer.

#[doc(hidden)]

pub const fn bool_to_int(b: bool) -> i32 {

    b as i32

}

rust/kernel/lib.rs

+35 −0
Original line number Diff line number Diff line
@@ -148,3 +148,38 @@ macro_rules! container_of { 
        ptr.sub(offset) as *const $type

    }}

}



/// Helper for `.rs.S` files.

#[doc(hidden)]

#[macro_export]

macro_rules! concat_literals {

    ($( $asm:literal )* ) => {

        ::core::concat!($($asm),*)

    };

}



/// Wrapper around `asm!` configured for use in the kernel.

///

/// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`

/// syntax.

// For x86, `asm!` uses intel syntax by default, but we want to use at&t syntax in the kernel.

#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]

#[macro_export]

macro_rules! asm {

    ($($asm:expr),* ; $($rest:tt)*) => {

        ::core::arch::asm!( $($asm)*, options(att_syntax), $($rest)* )

    };

}



/// Wrapper around `asm!` configured for use in the kernel.

///

/// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`

/// syntax.

// For non-x86 arches we just pass through to `asm!`.

#[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]

#[macro_export]

macro_rules! asm {

    ($($asm:expr),* ; $($rest:tt)*) => {

        ::core::arch::asm!( $($asm)*, $($rest)* )

    };

}