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 <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Jason Baron <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Alex Gaynor <[email protected]>
Cc: Wedson Almeida Filho <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " <[email protected]>
Cc: Benno Lossin <[email protected]>
Cc: Andreas Hindborg <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Uros Bizjak <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Oliver Upton <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Fuad Tabba <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Anup Patel <[email protected]>
Cc: Andrew Jones <[email protected]>
Cc: Alexandre Ghiti <[email protected]>
Cc: Conor Dooley <[email protected]>
Cc: Samuel Holland <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: WANG Xuerui <[email protected]>
Cc: Bibo Mao <[email protected]>
Cc: Tiezhu Yang <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Tianrui Zhao <[email protected]>
Link: https://lore.kernel.org/[email protected]
Suggested-by: Peter Zijlstra (Intel) <[email protected]>
Co-developed-by: Miguel Ojeda <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

1 files changed, 7 insertions, 0 deletions

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}"))