Re: [PATCH v9 1/5] rust: add generic static_key_false

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.

This patch only provides a generic implementation without code patching
(matching the one used when CONFIG_JUMP_LABEL is disabled). Later
patches add support for inline asm implementations that use runtime
patching.

When CONFIG_JUMP_LABEL is unset, `static_key_count` is a static inline
function, so a Rust helper is defined for `static_key_count` in this
case. If Rust is compiled with LTO, this call should get inlined. The
helper can be eliminated once we have the necessary inline asm to make
atomic operations from Rust.

Reviewed-by: Boqun Feng <redacted>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/bindings/bindings_helper.h |  1 +
 rust/helpers/helpers.c          |  1 +
 rust/helpers/jump_label.c       | 15 +++++++++++++++
 rust/kernel/jump_label.rs       | 29 +++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  1 +
 5 files changed, 47 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index ae82e9c941af..e0846e7e93e6 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h

@@ -14,6 +14,7 @@
 #include <linux/ethtool.h>
 #include <linux/firmware.h>
 #include <linux/jiffies.h>
+#include <linux/jump_label.h>
 #include <linux/mdio.h>
 #include <linux/phy.h>
 #include <linux/refcount.h>

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 30f40149f3a9..17e1b60d178f 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c

@@ -12,6 +12,7 @@
 #include "build_assert.c"
 #include "build_bug.c"
 #include "err.c"
+#include "jump_label.c"
 #include "kunit.c"
 #include "mutex.c"
 #include "page.c"

diff --git a/rust/helpers/jump_label.c b/rust/helpers/jump_label.c
new file mode 100644
index 000000000000..0e9ed15903f6
--- /dev/null
+++ b/rust/helpers/jump_label.c

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2024 Google LLC.
+ */
+
+#include <linux/jump_label.h>
+ 

+#ifndef CONFIG_JUMP_LABEL
+int rust_helper_static_key_count(struct static_key *key)
+{
+       return static_key_count(key);
+}
+EXPORT_SYMBOL_GPL(rust_helper_static_key_count);
+#endif

diff --git a/rust/kernel/jump_label.rs b/rust/kernel/jump_label.rs
new file mode 100644