[PATCH v10 5/5] rust: add arch_static_branch
From: Alice Ryhl
Date: Fri Oct 11 2024 - 06:15:54 EST
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.
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Co-developed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
---
rust/Makefile | 5 ++-
rust/kernel/.gitignore | 3 ++
rust/kernel/arch_static_branch_asm.rs.S | 7 ++++
rust/kernel/jump_label.rs | 64 ++++++++++++++++++++++++++++++++-
rust/kernel/lib.rs | 35 ++++++++++++++++++
scripts/Makefile.build | 9 ++++-
6 files changed, 120 insertions(+), 3 deletions(-)
diff --git a/rust/Makefile b/rust/Makefile
index b5e0a73b78f3..09ea07cc4001 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -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
@@ -421,7 +423,8 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
$(obj)/kernel.o: private rustc_target_flags = --extern alloc \
--extern build_error --extern macros --extern bindings --extern uapi
$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
- $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
+ $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o \
+ $(obj)/kernel/arch_static_branch_asm.rs FORCE
+$(call if_changed_rule,rustc_library)
endif # CONFIG_RUST
diff --git a/rust/kernel/.gitignore b/rust/kernel/.gitignore
new file mode 100644
index 000000000000..d082731007c6
--- /dev/null
+++ b/rust/kernel/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+/arch_static_branch_asm.rs
diff --git a/rust/kernel/arch_static_branch_asm.rs.S b/rust/kernel/arch_static_branch_asm.rs.S
new file mode 100644
index 000000000000..2afb638708db
--- /dev/null
+++ b/rust/kernel/arch_static_branch_asm.rs.S
@@ -0,0 +1,7 @@
+/* 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}"))
diff --git a/rust/kernel/jump_label.rs b/rust/kernel/jump_label.rs
index 4b7655b2a022..cbd0ec00f0c5 100644
--- a/rust/kernel/jump_label.rs
+++ b/rust/kernel/jump_label.rs
@@ -24,7 +24,69 @@ 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, $field, false }
}};
}
pub use static_branch_unlikely;
+
+/// Assert that the assembly block evaluates to a string literal.
+#[cfg(CONFIG_JUMP_LABEL)]
+const _: &str = include!(concat!(env!("OBJTREE"), "/rust/kernel/arch_static_branch_asm.rs"));
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(CONFIG_JUMP_LABEL)]
+#[cfg(not(CONFIG_HAVE_JUMP_LABEL_HACK))]
+macro_rules! arch_static_branch {
+ ($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;
+ }};
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(CONFIG_JUMP_LABEL)]
+#[cfg(CONFIG_HAVE_JUMP_LABEL_HACK)]
+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 2 | $crate::jump_label::bool_to_int($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
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 55f81f49024e..c0ae9ddd9468 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -148,3 +148,38 @@ macro_rules! container_of {
ptr.sub(offset) as *const $type
}}
}
+
+/// Helper for `.rs.S` files.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! concat_literals {
+ ($( $asm:literal )* ) => {
+ ::core::concat!($($asm),*)
+ };
+}
+
+/// Wrapper around `asm!` configured for use in the kernel.
+///
+/// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`
+/// syntax.
+// For x86, `asm!` uses intel syntax by default, but we want to use at&t syntax in the kernel.
+#[cfg(target_arch = "x86_64")]
+#[macro_export]
+macro_rules! asm {
+ ($($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(target_arch = "x86_64"))]
+#[macro_export]
+macro_rules! asm {
+ ($($asm:expr),* ; $($rest:tt)*) => {
+ ::core::arch::asm!( $($asm)*, $($rest)* )
+ };
+}
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 8f423a1faf50..03ee558fcd4d 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -248,12 +248,13 @@ $(obj)/%.lst: $(obj)/%.c FORCE
# Compile Rust sources (.rs)
# ---------------------------------------------------------------------------
-rust_allowed_features := new_uninit
+rust_allowed_features := asm_const,asm_goto,new_uninit
# `--out-dir` is required to avoid temporaries being created by `rustc` in the
# current working directory, which may be not accessible in the out-of-tree
# modules case.
rust_common_cmd = \
+ OBJTREE=$(abspath $(objtree)) \
RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
-Zallow-features=$(rust_allowed_features) \
-Zcrate-attr=no_std \
@@ -303,6 +304,12 @@ quiet_cmd_rustc_ll_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
$(obj)/%.ll: $(obj)/%.rs FORCE
+$(call if_changed_dep,rustc_ll_rs)
+quiet_cmd_rustc_rs_rs_S = RSCPP $(quiet_modtag) $@
+ cmd_rustc_rs_rs_S = $(CPP) $(c_flags) -xc -C -P $< | sed '1,/^\/\/ Cut here.$$/d' >$@
+
+$(obj)/%.rs: $(obj)/%.rs.S FORCE
+ +$(call if_changed_dep,rustc_rs_rs_S)
+
# Compile assembler sources (.S)
# ---------------------------------------------------------------------------
--
2.47.0.rc1.288.g06298d1525-goog