Re: [PATCH v3 1/2] rust: add static_key_false
From: Boqun Feng <hidden>
Date: 2024-06-25 16:18:41
Also in:
linux-arch, linux-riscv, lkml, loongarch, rust-for-linux
Hi Alice, On Fri, Jun 21, 2024 at 10:35:26AM +0000, Alice Ryhl 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>
[Add linux-arch, and related arch maintainers Cced] Since inline asms are touched here, please consider copying linux-arch and arch maintainers next time ;-)
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--- rust/kernel/lib.rs | 1 + rust/kernel/static_key.rs | 143 ++++++++++++++++++++++++++++++++++++++++++++++ scripts/Makefile.build | 2 +- 3 files changed, 145 insertions(+), 1 deletion(-)diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index fbd91a48ff8b..a0be9544996d 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs@@ -38,6 +38,7 @@ 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..9c844fe3e3a3 --- /dev/null +++ b/rust/kernel/static_key.rs@@ -0,0 +1,143 @@ +// 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")] +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, $field), + ); + + break 'my_label false; + }}; +} + +#[doc(hidden)] +#[macro_export] +#[cfg(target_arch = "aarch64")] +macro_rules! _static_key_false { + ($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, $field), + ); + + break 'my_label false; + }}; +} +
For x86_64 and arm64 bits: Acked-by: Boqun Feng <redacted> One thing though, we should split the arch-specific impls into different files, for example: rust/kernel/arch/arm64.rs or rust/arch/arm64.rs. That'll be easier for arch maintainers to watch the Rust changes related to a particular architecture. Another thought is that, could you implement an arch_static_branch!() (instead of _static_key_false!()) and use it for static_key_false!() similar to what we have in C? The benefit is that at least for myself it'll be easier to compare the implementation between C and Rust. Regards, Boqun
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+#[doc(hidden)] +#[macro_export] +#[cfg(target_arch = "loongarch64")] +macro_rules! _static_key_false { + ($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, $field), + ); + + break 'my_label false; + }}; +} + +#[doc(hidden)] +#[macro_export] +#[cfg(target_arch = "riscv64")] +macro_rules! _static_key_false { + ($key:path, $keytyp:ty, $field:ident) => {'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} - . + .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_false! { $key, $keytyp, $field } + }}; +} + +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-- 2.45.2.741.gdbec12cfda-goog