* [PATCH v1] rust: add mark_used macro
@ 2026-08-10 7:51 FUJITA Tomonori
2026-08-10 10:41 ` Gary Guo
0 siblings, 1 reply; 2+ messages in thread
From: FUJITA Tomonori @ 2026-08-10 7:51 UTC (permalink / raw)
To: aliceryhl, ojeda, rostedt
Cc: a.hindborg, acourbot, bjorn3_gh, boqun, dakr, daniel.almeida,
gary, lossin, mathieu.desnoyers, mhiramat, tamird, tmgross, work,
linux-trace-kernel, rust-for-linux, FUJITA Tomonori
From: FUJITA Tomonori <fujita.tomonori@gmail.com>
Macros whose expansion depends on the kernel configuration end up
ignoring some of their arguments, resulting in unused warnings.
Add a macro for the `if false { _ = ...; }` idiom used to avoid them,
and convert the existing open-coded users in `warn_flags!` and
`declare_trace!`.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
rust/kernel/bug.rs | 18 ++++--------------
rust/kernel/lib.rs | 12 ++++++++++++
rust/kernel/tracepoint.rs | 5 ++---
3 files changed, 18 insertions(+), 17 deletions(-)
diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
index 3566f0234ca4..c1e4eb7d4a70 100644
--- a/rust/kernel/bug.rs
+++ b/rust/kernel/bug.rs
@@ -55,9 +55,7 @@ macro_rules! warn_flags {
($file:expr, $flags:expr) => {
const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
- if false {
- _ = $file;
- }
+ $crate::mark_used!($file);
// SAFETY:
// - `flags` and `size` are all compile-time constants, preventing
@@ -83,9 +81,7 @@ macro_rules! warn_flags {
#[cfg(all(CONFIG_BUG, CONFIG_UML))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {
- if false {
- _ = $file;
- }
+ $crate::mark_used!($file);
// SAFETY: It is always safe to call `warn_slowpath_fmt()`
// with a valid null-terminated string.
@@ -106,10 +102,7 @@ macro_rules! warn_flags {
#[cfg(all(CONFIG_BUG, any(CONFIG_LOONGARCH, CONFIG_ARM)))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {
- if false {
- _ = $file;
- _ = $flags;
- }
+ $crate::mark_used!($file, $flags);
// SAFETY: It is always safe to call `WARN_ON()`.
unsafe { $crate::bindings::WARN_ON(true) }
@@ -121,10 +114,7 @@ macro_rules! warn_flags {
#[cfg(any(testlib, not(CONFIG_BUG)))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {
- if false {
- _ = $file;
- _ = $flags;
- }
+ $crate::mark_used!($file, $flags);
};
}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 9512af7156df..2f770d80bd8a 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -266,6 +266,18 @@ macro_rules! container_of {
#[doc(hidden)]
pub fn assert_same_type<T>(_: T, _: T) {}
+/// Marks the given expressions as used.
+///
+/// This avoids "unused" warnings in kernel configurations that do not otherwise use them.
+#[macro_export]
+macro_rules! mark_used {
+ ($($e:expr),* $(,)?) => {
+ if false {
+ $( _ = $e; )*
+ }
+ };
+}
+
/// Helper for `.rs.S` files.
#[doc(hidden)]
#[macro_export]
diff --git a/rust/kernel/tracepoint.rs b/rust/kernel/tracepoint.rs
index c6e80aa99e8e..cb06fec4c4d9 100644
--- a/rust/kernel/tracepoint.rs
+++ b/rust/kernel/tracepoint.rs
@@ -38,9 +38,8 @@ macro_rules! declare_trace {
#[cfg(not(CONFIG_TRACEPOINTS))]
{
- // If tracepoints are disabled, insert a trivial use of each argument
- // to avoid unused argument warnings.
- $( let _unused = $argname; )*
+ // If tracepoints are disabled, the arguments are unused.
+ $crate::mark_used!($($argname),*);
}
}
)*}
base-commit: d8973c47544371613313ecb9a8c3e7b244aa9bbf
--
2.43.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v1] rust: add mark_used macro
2026-08-10 7:51 [PATCH v1] rust: add mark_used macro FUJITA Tomonori
@ 2026-08-10 10:41 ` Gary Guo
0 siblings, 0 replies; 2+ messages in thread
From: Gary Guo @ 2026-08-10 10:41 UTC (permalink / raw)
To: FUJITA Tomonori, aliceryhl, ojeda, rostedt
Cc: a.hindborg, acourbot, bjorn3_gh, boqun, dakr, daniel.almeida,
gary, lossin, mathieu.desnoyers, mhiramat, tamird, tmgross, work,
linux-trace-kernel, rust-for-linux, FUJITA Tomonori
On Mon Aug 10, 2026 at 8:51 AM BST, FUJITA Tomonori wrote:
> From: FUJITA Tomonori <fujita.tomonori@gmail.com>
>
> Macros whose expansion depends on the kernel configuration end up
> ignoring some of their arguments, resulting in unused warnings.
>
> Add a macro for the `if false { _ = ...; }` idiom used to avoid them,
> and convert the existing open-coded users in `warn_flags!` and
> `declare_trace!`.
>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
> ---
> rust/kernel/bug.rs | 18 ++++--------------
> rust/kernel/lib.rs | 12 ++++++++++++
> rust/kernel/tracepoint.rs | 5 ++---
> 3 files changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
> index 3566f0234ca4..c1e4eb7d4a70 100644
> --- a/rust/kernel/bug.rs
> +++ b/rust/kernel/bug.rs
> @@ -55,9 +55,7 @@ macro_rules! warn_flags {
> ($file:expr, $flags:expr) => {
> const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
>
> - if false {
> - _ = $file;
> - }
> + $crate::mark_used!($file);
>
> // SAFETY:
> // - `flags` and `size` are all compile-time constants, preventing
> @@ -83,9 +81,7 @@ macro_rules! warn_flags {
> #[cfg(all(CONFIG_BUG, CONFIG_UML))]
> macro_rules! warn_flags {
> ($file:expr, $flags:expr) => {
> - if false {
> - _ = $file;
> - }
> + $crate::mark_used!($file);
>
> // SAFETY: It is always safe to call `warn_slowpath_fmt()`
> // with a valid null-terminated string.
> @@ -106,10 +102,7 @@ macro_rules! warn_flags {
> #[cfg(all(CONFIG_BUG, any(CONFIG_LOONGARCH, CONFIG_ARM)))]
> macro_rules! warn_flags {
> ($file:expr, $flags:expr) => {
> - if false {
> - _ = $file;
> - _ = $flags;
> - }
> + $crate::mark_used!($file, $flags);
>
> // SAFETY: It is always safe to call `WARN_ON()`.
> unsafe { $crate::bindings::WARN_ON(true) }
> @@ -121,10 +114,7 @@ macro_rules! warn_flags {
> #[cfg(any(testlib, not(CONFIG_BUG)))]
> macro_rules! warn_flags {
> ($file:expr, $flags:expr) => {
> - if false {
> - _ = $file;
> - _ = $flags;
> - }
> + $crate::mark_used!($file, $flags);
> };
> }
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 9512af7156df..2f770d80bd8a 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -266,6 +266,18 @@ macro_rules! container_of {
> #[doc(hidden)]
> pub fn assert_same_type<T>(_: T, _: T) {}
>
> +/// Marks the given expressions as used.
> +///
> +/// This avoids "unused" warnings in kernel configurations that do not otherwise use them.
> +#[macro_export]
> +macro_rules! mark_used {
> + ($($e:expr),* $(,)?) => {
> + if false {
> + $( _ = $e; )*
> + }
> + };
> +}
> +
> /// Helper for `.rs.S` files.
> #[doc(hidden)]
> #[macro_export]
> diff --git a/rust/kernel/tracepoint.rs b/rust/kernel/tracepoint.rs
> index c6e80aa99e8e..cb06fec4c4d9 100644
> --- a/rust/kernel/tracepoint.rs
> +++ b/rust/kernel/tracepoint.rs
> @@ -38,9 +38,8 @@ macro_rules! declare_trace {
>
> #[cfg(not(CONFIG_TRACEPOINTS))]
> {
> - // If tracepoints are disabled, insert a trivial use of each argument
> - // to avoid unused argument warnings.
> - $( let _unused = $argname; )*
> + // If tracepoints are disabled, the arguments are unused.
nit: the comment seems redundant now that the macro name is self-documenting.
Best,
Gary
> + $crate::mark_used!($($argname),*);
> }
> }
> )*}
>
> base-commit: d8973c47544371613313ecb9a8c3e7b244aa9bbf
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