[PATCH] rust_binder: replace is_aligned helper with is_multiple_of
From: KaiserGranatapfel via B4 Relay
Date: Mon Mar 02 2026 - 14:37:43 EST
From: KaiserGranatapfel <christopher.erleigh@xxxxxxxxx>
Remove the local `is_aligned` helper from the binder thread module and
replace all call sites with `usize::is_multiple_of`, which is the
idiomatic Rust API for checking divisibility.
Since `is_multiple_of` was only stabilized in Rust 1.87.0 and the
kernel MSRV is currently 1.78.0, introduce a `UsizeExt` extension
trait in `rust/kernel/usize_ext.rs` as a polyfill. The trait is
conditionally compiled behind `CONFIG_RUSTC_HAS_USIZE_IS_MULTIPLE_OF`
(set when rustc >= 1.87.0) and re-exported via the kernel prelude,
following the same pattern used for `AsFlattened` / `slice_flatten`.
The `offset % type_size == 0` expression in `rust/kernel/io.rs` is
intentionally left unchanged as it lives inside a `const fn` where
trait method calls are not permitted.
Link: https://github.com/Rust-for-Linux/linux/issues/1220
Signed-off-by: Christopher Erleigh (KaiserGranatapfel) <christopher.erleigh@xxxxxxxxx>
---
The recently landed patch "rust_binder: add additional alignment checks"
introduced a local `is_aligned` helper as a workaround for
`usize::is_multiple_of` not being available prior to Rust 1.87.0.
This patch replaces that helper with a `UsizeExt` extension trait that
provides `is_multiple_of` as a polyfill, following the same pattern used
for `AsFlattened` / `slice_flatten`. The trait is gated behind
`CONFIG_RUSTC_HAS_USIZE_IS_MULTIPLE_OF` and will become a no-op once
the kernel MSRV reaches 1.87.0.
Note: the From: header uses my GitHub username "KaiserGranatapfel", as
this is tied to my Git and GitHub identity. My real name is Christopher
Erleigh, as reflected in the Signed-off-by trailer.
---
drivers/android/binder/thread.rs | 14 +++++---------
init/Kconfig | 3 +++
rust/kernel/lib.rs | 1 +
rust/kernel/prelude.rs | 3 +++
rust/kernel/usize_ext.rs | 30 ++++++++++++++++++++++++++++++
5 files changed, 42 insertions(+), 9 deletions(-)
diff --git a/drivers/android/binder/thread.rs b/drivers/android/binder/thread.rs
index 0b62d24b2..25d499d05 100644
--- a/drivers/android/binder/thread.rs
+++ b/drivers/android/binder/thread.rs
@@ -36,10 +36,6 @@
use core::mem::size_of;
-fn is_aligned(value: usize, to: usize) -> bool {
- value % to == 0
-}
-
/// Stores the layout of the scatter-gather entries. This is used during the `translate_objects`
/// call and is discarded when it returns.
struct ScatterGatherState {
@@ -796,7 +792,7 @@ fn translate_object(
let num_fds = usize::try_from(obj.num_fds).map_err(|_| EINVAL)?;
let fds_len = num_fds.checked_mul(size_of::<u32>()).ok_or(EINVAL)?;
- if !is_aligned(parent_offset, size_of::<u32>()) {
+ if !parent_offset.is_multiple_of(size_of::<u32>()) {
return Err(EINVAL.into());
}
@@ -814,7 +810,7 @@ fn translate_object(
}
};
- if !is_aligned(parent_entry.sender_uaddr, size_of::<u32>()) {
+ if !parent_entry.sender_uaddr.is_multiple_of(size_of::<u32>()) {
return Err(EINVAL.into());
}
@@ -975,10 +971,10 @@ pub(crate) fn copy_transaction_data(
None => 0,
};
- if !is_aligned(offsets_size, size_of::<u64>()) {
+ if !offsets_size.is_multiple_of(size_of::<u64>()) {
return Err(EINVAL.into());
}
- if !is_aligned(buffers_size, size_of::<u64>()) {
+ if !buffers_size.is_multiple_of(size_of::<u64>()) {
return Err(EINVAL.into());
}
@@ -1047,7 +1043,7 @@ pub(crate) fn copy_transaction_data(
.try_into()
.map_err(|_| EINVAL)?;
- if offset < end_of_previous_object || !is_aligned(offset, size_of::<u32>()) {
+ if offset < end_of_previous_object || !offset.is_multiple_of(size_of::<u32>()) {
pr_warn!("Got transaction with invalid offset.");
return Err(EINVAL.into());
}
diff --git a/init/Kconfig b/init/Kconfig
index b55deae92..bd7493480 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -166,6 +166,9 @@ config LD_CAN_USE_KEEP_IN_OVERLAY
config RUSTC_HAS_SLICE_AS_FLATTENED
def_bool RUSTC_VERSION >= 108000
+config RUSTC_HAS_USIZE_IS_MULTIPLE_OF
+ def_bool RUSTC_VERSION >= 108700
+
config RUSTC_HAS_COERCE_POINTEE
def_bool RUSTC_VERSION >= 108400
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 3da92f18f..59216912a 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -157,6 +157,7 @@
pub mod uaccess;
#[cfg(CONFIG_USB = "y")]
pub mod usb;
+pub mod usize_ext;
pub mod workqueue;
pub mod xarray;
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 2877e3f7b..7e778a666 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -53,3 +53,6 @@
#[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
pub use super::slice::AsFlattened;
+
+#[cfg(not(CONFIG_RUSTC_HAS_USIZE_IS_MULTIPLE_OF))]
+pub use super::usize_ext::UsizeExt as _;
diff --git a/rust/kernel/usize_ext.rs b/rust/kernel/usize_ext.rs
new file mode 100644
index 000000000..690265bc0
--- /dev/null
+++ b/rust/kernel/usize_ext.rs
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Additional (and temporary) `usize` helpers.
+
+/// Extension trait providing a portable version of [`usize::is_multiple_of`].
+///
+/// `usize::is_multiple_of` was stabilized in Rust 1.87.0. This extension trait
+/// provides the same functionality for kernels built with older toolchains.
+///
+/// This trait can be removed once the MSRV passes 1.87.
+///
+/// [`usize::is_multiple_of`]: https://doc.rust-lang.org/std/primitive.usize.html#method.is_multiple_of
+#[cfg(not(CONFIG_RUSTC_HAS_USIZE_IS_MULTIPLE_OF))]
+pub trait UsizeExt {
+ /// Returns `true` if `self` is a multiple of `rhs`.
+ ///
+ /// This is a portable layer on top of [`usize::is_multiple_of`]; see its documentation for
+ /// details.
+ ///
+ /// [`usize::is_multiple_of`]: https://doc.rust-lang.org/std/primitive.usize.html#method.is_multiple_of
+ fn is_multiple_of(self, rhs: usize) -> bool;
+}
+
+#[cfg(not(CONFIG_RUSTC_HAS_USIZE_IS_MULTIPLE_OF))]
+impl UsizeExt for usize {
+ #[inline]
+ fn is_multiple_of(self, rhs: usize) -> bool {
+ self % rhs == 0
+ }
+}
---
base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
change-id: 20260302-rust-binder-is-multiple-of-2d757cf0a70f
Best regards,
--
KaiserGranatapfel <christopher.erleigh@xxxxxxxxx>