@@ -34,6 +34,9 @@ obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.o
 obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.o
 
 always-$(subst y,$(CONFIG_RUST),$(CONFIG_JUMP_LABEL)) += kernel/generated_arch_static_branch_asm.rs
+ifndef CONFIG_UML
+always-$(subst y,$(CONFIG_RUST),$(CONFIG_BUG)) += kernel/generated_arch_warn_asm.rs kernel/generated_arch_reachable_asm.rs
+endif
 
 # Avoids running `$(RUSTC)` when it may not be available.
 ifdef CONFIG_RUST

@@ -481,5 +484,10 @@ $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o \
 ifdef CONFIG_JUMP_LABEL
 $(obj)/kernel.o: $(obj)/kernel/generated_arch_static_branch_asm.rs
 endif
+ifndef CONFIG_UML
+ifdef CONFIG_BUG
+$(obj)/kernel.o: $(obj)/kernel/generated_arch_warn_asm.rs $(obj)/kernel/generated_arch_reachable_asm.rs
+endif
+endif
 
 endif # CONFIG_RUST

@@ -6,3 +6,8 @@ __noreturn void rust_helper_BUG(void)
 {
 	BUG();
 }
+
+bool rust_helper_WARN_ON(bool cond)
+{
+	return WARN_ON(cond);
+}

@@ -1,3 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 
 /generated_arch_static_branch_asm.rs
+/generated_arch_warn_asm.rs
+/generated_arch_reachable_asm.rs

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024, 2025 FUJITA Tomonori <fujita.tomonori@gmail.com>
+
+//! Support for BUG and WARN functionality.
+//!
+//! C header: [`include/asm-generic/bug.h`](srctree/include/asm-generic/bug.h)
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(all(CONFIG_BUG, not(CONFIG_UML), not(CONFIG_LOONGARCH)))]
+#[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+macro_rules! warn_flags {
+    ($flags:expr) => {
+        const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
+        const _FILE: &[u8] = file!().as_bytes();
+        // Plus one for null-terminator.
+        static FILE: [u8; _FILE.len() + 1] = {
+            let mut bytes = [0; _FILE.len() + 1];
+            let mut i = 0;
+            while i < _FILE.len() {
+                bytes[i] = _FILE[i];
+                i += 1;
+            }
+            bytes
+        };
+        // SAFETY: Just an FFI call.
+        unsafe {
+            $crate::asm!(concat!(
+                "/* {size} */",
+                include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_warn_asm.rs")),
+                include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_reachable_asm.rs")));
+            file = sym FILE,
+            line = const line!(),
+            flags = const FLAGS,
+            size = const ::core::mem::size_of::<$crate::bindings::bug_entry>(),
+            );
+        }
+    }
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(all(CONFIG_BUG, not(CONFIG_UML), not(CONFIG_LOONGARCH)))]
+#[cfg(not(CONFIG_DEBUG_BUGVERBOSE))]
+macro_rules! warn_flags {
+    ($flags:expr) => {
+        const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
+        // SAFETY: Just an FFI call.
+        unsafe {
+            $crate::asm!(
+            concat!(
+                "/* {size} */",
+                include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_warn_asm.rs")),
+                include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_reachable_asm.rs")));
+            flags = const FLAGS,
+            size = const ::core::mem::size_of::<$crate::bindings::bug_entry>(),
+            );
+        }
+    }
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(all(CONFIG_BUG, CONFIG_UML))]
+macro_rules! warn_flags {
+    ($flags:expr) => {
+        // SAFETY: Just an FFI call.
+        unsafe {
+            $crate::bindings::warn_slowpath_fmt(
+                $crate::c_str!(::core::file!()).as_ptr() as *const ::core::ffi::c_uchar,
+                line!() as i32,
+                $flags as u32,
+                ::core::ptr::null() as *const ::core::ffi::c_uchar,
+            );
+        }
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(all(CONFIG_BUG, CONFIG_LOONGARCH))]
+macro_rules! warn_flags {
+    ($flags:expr) => {
+        // SAFETY: Just an FFI call.
+        unsafe { $crate::bindings::WARN_ON(true) }
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[cfg(not(CONFIG_BUG))]
+macro_rules! warn_flags {
+    ($flags:expr) => {};
+}
+
+#[doc(hidden)]
+pub const fn bugflag_taint(value: u32) -> u32 {
+    value << 8
+}
+
+/// Report a warning if `cond` is true and return the condition's evaluation result.
+#[macro_export]
+macro_rules! warn_on {
+    ($cond:expr) => {{
+        if $cond {
+            const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
+
+            $crate::warn_flags!(WARN_ON_FLAGS);
+        }
+        $cond
+    }};
+}

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/bug.h>
+
+// Cut here.
+
+::kernel::concat_literals!(ARCH_WARN_REACHABLE)

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/bug.h>
+
+// Cut here.
+
+::kernel::concat_literals!(ARCH_WARN_ASM("{file}", "{line}",  "{flags}", "{size}"))

@@ -38,6 +38,7 @@
 pub mod alloc;
 #[cfg(CONFIG_BLOCK)]
 pub mod block;
+pub mod bug;
 #[doc(hidden)]
 pub mod build_assert;
 pub mod cred;