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rust: bug: prevent dead_code warning from warn_on!'s flags constant

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Fix the following dead_code warning on some configurations in an
atomic development branch:

warning: constant `WARN_ON_FLAGS` is never used
   --> linux/rust/kernel/bug.rs:126:19
    |
126 |               const WARN_ON_FLAGS: u32 = $crate:🐛:bugflag_taint($crate::bindings::TAINT_WARN);
    |                     ^^^^^^^^^^^^^
    |
   ::: linux/rust/kernel/sync/srcu.rs:106:12
    |
106 |           if crate::warn_on!(
    |  ____________-
107 | |             // SAFETY: By the type invariants, `self` contains a valid and pinned `struct srcu_struct`
108 | |             // and `srcu_readers_active()` only checks the active reader count.
109 | |             unsafe { bindings::srcu_readers_active(ptr) }
110 | |         ) {
    | |_________- in this macro invocation
    |
    = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default
    = note: this warning originates in the macro `crate::warn_on` (in Nightly builds, run with -Z macro-backtrace for more info)

The warn_on! macro always defines a WARN_ON_FLAGS constant and hands it
to warn_flags!. On configurations where warn_flags! does not reference
its flags argument (the LOONGARCH/ARM variant, which only calls
WARN_ON(), and the !CONFIG_BUG no-op variant), the constant is left
unused and triggers a dead_code warning.

warn_flags! is the macro that accepts (and here discards) the flags
argument, so make it responsible for the argument it drops.

Also rename `_COND_STR` to `COND_STR` and consume `$file` for consistency.

Fixes: dff64b0727 ("rust: Add warn_on macro")
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260801024841.786664-1-tomo@flapping.org
[ Added newlines. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
FUJITA Tomonori 2026-08-01 11:48:41 +09:00 committed by Miguel Ojeda
parent 359af52575
commit e66cfc29e0
1 changed files with 22 additions and 4 deletions
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26
rust/kernel/bug.rs
View File

@ -53,6 +53,10 @@ macro_rules! warn_flags {
($file:expr, $flags:expr) => {
const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
if false {
_ = $file;
}
// SAFETY:
// - `flags` and `size` are all compile-time constants, preventing
// any invalid memory access.
@ -76,6 +80,10 @@ macro_rules! warn_flags {
#[cfg(all(CONFIG_BUG, CONFIG_UML))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {
if false {
_ = $file;
}
// SAFETY: It is always safe to call `warn_slowpath_fmt()`
// with a valid null-terminated string.
unsafe {
@ -94,6 +102,11 @@ macro_rules! warn_flags {
#[cfg(all(CONFIG_BUG, any(CONFIG_LOONGARCH, CONFIG_ARM)))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {
if false {
_ = $file;
_ = $flags;
}
// SAFETY: It is always safe to call `WARN_ON()`.
unsafe { $crate::bindings::WARN_ON(true) }
};
@ -103,7 +116,12 @@ macro_rules! warn_flags {
#[doc(hidden)]
#[cfg(not(CONFIG_BUG))]
macro_rules! warn_flags {
($file:expr, $flags:expr) => {};
($file:expr, $flags:expr) => {
if false {
_ = $file;
_ = $flags;
}
};
}
#[doc(hidden)]
@ -118,14 +136,14 @@ macro_rules! warn_on {
let cond = $cond;
#[cfg(CONFIG_DEBUG_BUGVERBOSE_DETAILED)]
const _COND_STR: &str = concat!("[", stringify!($cond), "] ", file!());
const COND_STR: &str = concat!("[", stringify!($cond), "] ", file!());
#[cfg(not(CONFIG_DEBUG_BUGVERBOSE_DETAILED))]
const _COND_STR: &str = file!();
const COND_STR: &str = file!();
if cond {
const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
$crate::warn_flags!(_COND_STR, WARN_ON_FLAGS);
$crate::warn_flags!(COND_STR, WARN_ON_FLAGS);
}
cond
}};