linux-kernel - [PATCH v2 2/7] rust: io: always inline functions using build

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Message-Id: <20251128-io-build-assert-v2-2-a9ea9ce7d45d@nvidia.com>
Date: Fri, 28 Nov 2025 11:11:38 +0900
From: Alexandre Courbot <acourbot@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Daniel Almeida <daniel.almeida@...labora.com>, 
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Trevor Gross <tmgross@...ch.edu>, "Rafael J. Wysocki" <rafael@...nel.org>, 
 Viresh Kumar <viresh.kumar@...aro.org>, Will Deacon <will@...nel.org>, 
 Peter Zijlstra <peterz@...radead.org>, Mark Rutland <mark.rutland@....com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-pm@...r.kernel.org, Alexandre Courbot <acourbot@...dia.com>
Subject: [PATCH v2 2/7] rust: io: always inline functions using
 build_assert with arguments

`build_assert` relies on the compiler to optimize out its error path.
Functions using it with its arguments must thus always be inlined,
otherwise the error path of `build_assert` might not be optimized out,
triggering a build error.

Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
 rust/kernel/io.rs          | 9 ++++++---
 rust/kernel/io/resource.rs | 2 ++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index ee182b0b5452..ccdd394099cb 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -120,7 +120,8 @@ macro_rules! define_read {
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
-        #[inline]
+        // Always inline to optimize out error path of `io_addr_assert`.
+        #[inline(always)]
         pub fn $name(&self, offset: usize) -> $type_name {
             let addr = self.io_addr_assert::<$type_name>(offset);

@@ -149,7 +150,8 @@ macro_rules! define_write {
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
-        #[inline]
+        // Always inline to optimize out error path of `io_addr_assert`.
+        #[inline(always)]
         pub fn $name(&self, value: $type_name, offset: usize) {
             let addr = self.io_addr_assert::<$type_name>(offset);

@@ -217,7 +219,8 @@ fn io_addr<U>(&self, offset: usize) -> Result<usize> {
         self.addr().checked_add(offset).ok_or(EINVAL)
     }

-    #[inline]
+    // Always inline to optimize out error path of `build_assert`.
+    #[inline(always)]
     fn io_addr_assert<U>(&self, offset: usize) -> usize {
         build_assert!(Self::offset_valid::<U>(offset, SIZE));

diff --git a/rust/kernel/io/resource.rs b/rust/kernel/io/resource.rs
index bea3ee0ed87b..d9851923562c 100644
--- a/rust/kernel/io/resource.rs
+++ b/rust/kernel/io/resource.rs
@@ -223,6 +223,8 @@ impl Flags {
     /// Resource represents a memory region that must be ioremaped using `ioremap_np`.
     pub const IORESOURCE_MEM_NONPOSTED: Flags = Flags::new(bindings::IORESOURCE_MEM_NONPOSTED);

+    // Always inline to optimize out error path of `build_assert`.
+    #[inline(always)]
     const fn new(value: u32) -> Self {
         crate::build_assert!(value as u64 <= c_ulong::MAX as u64);
         Flags(value as c_ulong)

-- 
2.52.0