diff mbox series

[v6,5/5] rust: add arch_static_branch

Message ID 20240808-tracepoint-v6-5-a23f800f1189@google.com (mailing list archive)
State Superseded
Headers show
Series Tracepoints and static branch in Rust | expand

Commit Message

Alice Ryhl Aug. 8, 2024, 5:23 p.m. UTC
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 <peterz@infradead.org>
Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 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                      | 30 ++++++++++++++++
 scripts/Makefile.build                  |  9 ++++-
 6 files changed, 115 insertions(+), 3 deletions(-)

Comments

Peter Zijlstra Aug. 10, 2024, 9:03 p.m. UTC | #1
On Thu, Aug 08, 2024 at 05:23:41PM +0000, Alice Ryhl wrote:

> +/// Wrapper around `asm!` that uses at&t syntax on x86.
> +// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`
> +// syntax.
> +#[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!` that uses at&t syntax on x86.

^ the above line seems out of place given the 'not' below.

> +// 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)* )
> +    };
> +}
Alice Ryhl Aug. 10, 2024, 9:44 p.m. UTC | #2
On Sat, Aug 10, 2024 at 11:04 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Aug 08, 2024 at 05:23:41PM +0000, Alice Ryhl wrote:
>
> > +/// Wrapper around `asm!` that uses at&t syntax on x86.
> > +// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`
> > +// syntax.
> > +#[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!` that uses at&t syntax on x86.
>
> ^ the above line seems out of place given the 'not' below.

Comments with three slashes are what gets rendered in the html version
of the docs [1]. This way, the rendered docs will say that the `asm!`
macro is a wrapper around the built-in `asm!` that uses at&t syntax on
x86 regardless of which platform you build the docs on.

[1]: https://rust.docs.kernel.org/kernel/

> > +// 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)* )
> > +    };
> > +}
Peter Zijlstra Aug. 10, 2024, 9:57 p.m. UTC | #3
On Sat, Aug 10, 2024 at 11:44:13PM +0200, Alice Ryhl wrote:
> On Sat, Aug 10, 2024 at 11:04 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Thu, Aug 08, 2024 at 05:23:41PM +0000, Alice Ryhl wrote:
> >
> > > +/// Wrapper around `asm!` that uses at&t syntax on x86.
> > > +// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`
> > > +// syntax.
> > > +#[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!` that uses at&t syntax on x86.
> >
> > ^ the above line seems out of place given the 'not' below.
> 
> Comments with three slashes are what gets rendered in the html version
> of the docs [1]. This way, the rendered docs will say that the `asm!`
> macro is a wrapper around the built-in `asm!` that uses at&t syntax on
> x86 regardless of which platform you build the docs on.
> 

Urgh, that's not half-way confusing. Also, whoever wants to read HTML
when you already have the code open in your text-editor?
diff mbox series

Patch

diff --git a/rust/Makefile b/rust/Makefile
index 199e0db67962..277fcef656b8 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -14,6 +14,8 @@  CFLAGS_REMOVE_helpers.o = -Wmissing-prototypes -Wmissing-declarations
 always-$(CONFIG_RUST) += libmacros.so
 no-clean-files += libmacros.so
 
+always-$(subst y,$(CONFIG_RUST),$(CONFIG_JUMP_LABEL)) += kernel/arch_static_branch_asm.rs
+
 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
 obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
@@ -409,7 +411,8 @@  $(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..9e373d4f7567
--- /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 011e1fc1d19a..7757e4f8e85e 100644
--- a/rust/kernel/jump_label.rs
+++ b/rust/kernel/jump_label.rs
@@ -23,7 +23,69 @@  macro_rules! static_key_false {
         let _key: *const $keytyp = ::core::ptr::addr_of!($key);
         let _key: *const $crate::bindings::static_key = ::core::ptr::addr_of!((*_key).$field);
 
-        $crate::bindings::static_key_count(_key.cast_mut()) > 0
+        #[cfg(not(CONFIG_JUMP_LABEL))]
+        {
+            $crate::bindings::static_key_count(_key.cast_mut()) > 0
+        }
+
+        #[cfg(CONFIG_JUMP_LABEL)]
+        $crate::jump_label::arch_static_branch! { $key, $keytyp, $field, false }
     }};
 }
 pub use static_key_false;
+
+/// Assert that the assembly block evaluates to a string literal.
+#[cfg(CONFIG_JUMP_LABEL)]
+const _: &str = include!("arch_static_branch_asm.rs");
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(CONFIG_JUMP_LABEL)]
+#[cfg(not(CONFIG_HAVE_JUMP_LABEL_HACK))]
+macro_rules! arch_static_branch {
+    ($key:path, $keytyp:ty, $field:ident, $branch:expr) => {'my_label: {
+        $crate::asm!(
+            include!(concat!(env!("SRCTREE"), "/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!("SRCTREE"), "/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 d00a44b000b6..9e9b95ab6966 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -145,3 +145,33 @@  macro_rules! container_of {
         ptr.sub(offset) as *const $type
     }}
 }
+
+/// Helper for `.rs.S` files.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! concat_literals {
+    ($( $asm:literal )* ) => {
+        ::core::concat!($($asm),*)
+    };
+}
+
+/// Wrapper around `asm!` that uses at&t syntax on x86.
+// Uses a semicolon to avoid parsing ambiguities, even though this does not match native `asm!`
+// syntax.
+#[cfg(target_arch = "x86_64")]
+#[macro_export]
+macro_rules! asm {
+    ($($asm:expr),* ; $($rest:tt)*) => {
+        ::core::arch::asm!( $($asm)*, options(att_syntax), $($rest)* )
+    };
+}
+
+/// Wrapper around `asm!` that uses at&t syntax on x86.
+// 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 72b1232b1f7d..59fe83fba647 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -263,12 +263,13 @@  $(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 = \
+	SRCTREE=$(abspath $(srctree)) \
 	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
 	-Zallow-features=$(rust_allowed_features) \
 	-Zcrate-attr=no_std \
@@ -318,6 +319,12 @@  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)
 # ---------------------------------------------------------------------------