| Message ID | 20240610-tracepoint-v2-1-faebad81b355@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Tracepoints and static branch in Rust | expand |
On Mon, Jun 10, 2024 at 02:01:04PM +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> > +#[cfg(target_arch = "x86_64")] > +#[cfg(target_arch = "aarch64")] This patch breaks the build on riscv (and I assume loongarch): error[E0432]: unresolved import `_static_key_false` --> /stuff/linux/rust/kernel/static_key.rs:87:10 | 87 | pub use {_static_key_false, static_key_false}; | ^^^^^^^^^^^^^^^^^ no external crate `_static_key_false` Cheers, Conor.
On Wed, Jun 12, 2024 at 5:03 PM Conor Dooley <conor@kernel.org> wrote: > > On Mon, Jun 10, 2024 at 02:01:04PM +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> > > > +#[cfg(target_arch = "x86_64")] > > > +#[cfg(target_arch = "aarch64")] > > This patch breaks the build on riscv (and I assume loongarch): > > error[E0432]: unresolved import `_static_key_false` > --> /stuff/linux/rust/kernel/static_key.rs:87:10 > | > 87 | pub use {_static_key_false, static_key_false}; > | ^^^^^^^^^^^^^^^^^ no external crate `_static_key_false` > > Cheers, > Conor. Thank you. Fixed in v3. https://lore.kernel.org/all/20240621-tracepoint-v3-0-9e44eeea2b85@google.com/ Alice
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..6c3dbe14c98a --- /dev/null +++ b/rust/kernel/static_key.rs @@ -0,0 +1,87 @@ +// 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, $field), + ); + + break 'my_label false; + }}; +} + +/// Branch based on a static key. +/// +/// Takes three arguments: +/// +/// * `key` - the path to the static variable containing the `static_key`. +/// * `keytyp` - the type of `key`. +/// * `field` - the name of the field of `key` that contains the `static_key`. +#[macro_export] +macro_rules! static_key_false { + // Forward to the real implementation. Separated like this so that we don't have to duplicate + // the documentation. + ($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}; 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
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/lib.rs | 1 + rust/kernel/static_key.rs | 87 +++++++++++++++++++++++++++++++++++++++++++++++ scripts/Makefile.build | 2 +- 3 files changed, 89 insertions(+), 1 deletion(-)