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rust: Add warn_on macro
Add warn_on macro, uses the BUG/WARN feature (lib/bug.c) via assembly for x86_64/arm64/riscv. The current Rust code simply wraps BUG() macro but doesn't provide the proper debug information. The BUG/WARN feature can only be used from assembly. This uses the assembly code exported by the C side via ARCH_WARN_ASM macro. To avoid duplicating the assembly code, this approach follows the same strategy as the static branch code: it generates the assembly code for Rust using the C preprocessor at compile time. Similarly, ARCH_WARN_REACHABLE is also used at compile time to generate the assembly code; objtool's reachable annotation code. It's used for only architectures that use objtool. For now, Loongarch and arm just use a wrapper for WARN macro. UML doesn't use the assembly BUG/WARN feature; just wrapping generic BUG/WARN functions implemented in C works. Signed-off-by: FUJITA Tomonori <[email protected]> Reviewed-by: Alice Ryhl <[email protected]> Link: https://lore.kernel.org/r/[email protected] [ Avoid evaluating the condition twice (a good idea in general, but it also matches the C side). Simplify with `as_char_ptr()` to avoid a cast. Cast to `ffi` integer types for `warn_slowpath_fmt`. Avoid cast for `null()`. - Miguel ] Signed-off-by: Miguel Ojeda <[email protected]>
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‎rust/Makefile

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@@ -34,6 +34,9 @@ obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.o
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obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.o
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always-$(subst y,$(CONFIG_RUST),$(CONFIG_JUMP_LABEL)) += kernel/generated_arch_static_branch_asm.rs
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ifndef CONFIG_UML
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always-$(subst y,$(CONFIG_RUST),$(CONFIG_BUG)) += kernel/generated_arch_warn_asm.rs kernel/generated_arch_reachable_asm.rs
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endif
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# Avoids running `$(RUSTC)` when it may not be available.
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ifdef CONFIG_RUST
@@ -540,5 +543,10 @@ $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o $(obj)/pin_init.o \
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ifdef CONFIG_JUMP_LABEL
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$(obj)/kernel.o: $(obj)/kernel/generated_arch_static_branch_asm.rs
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endif
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ifndef CONFIG_UML
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ifdef CONFIG_BUG
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$(obj)/kernel.o: $(obj)/kernel/generated_arch_warn_asm.rs $(obj)/kernel/generated_arch_reachable_asm.rs
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endif
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endif
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endif # CONFIG_RUST

‎rust/helpers/bug.c

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

‎rust/kernel/.gitignore

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

‎rust/kernel/bug.rs

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@@ -0,0 +1,126 @@
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// SPDX-License-Identifier: GPL-2.0
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// Copyright (C) 2024, 2025 FUJITA Tomonori <[email protected]>
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//! Support for BUG and WARN functionality.
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//!
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//! C header: [`include/asm-generic/bug.h`](srctree/include/asm-generic/bug.h)
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#[macro_export]
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#[doc(hidden)]
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#[cfg(all(CONFIG_BUG, not(CONFIG_UML), not(CONFIG_LOONGARCH), not(CONFIG_ARM)))]
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#[cfg(CONFIG_DEBUG_BUGVERBOSE)]
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macro_rules! warn_flags {
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($flags:expr) => {
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const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
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const _FILE: &[u8] = file!().as_bytes();
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// Plus one for null-terminator.
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static FILE: [u8; _FILE.len() + 1] = {
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let mut bytes = [0; _FILE.len() + 1];
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let mut i = 0;
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while i < _FILE.len() {
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bytes[i] = _FILE[i];
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i += 1;
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}
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bytes
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};
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// SAFETY:
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// - `file`, `line`, `flags`, and `size` are all compile-time constants or
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// symbols, preventing any invalid memory access.
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// - The asm block has no side effects and does not modify any registers
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// or memory. It is purely for embedding metadata into the ELF section.
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unsafe {
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$crate::asm!(
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concat!(
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"/* {size} */",
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include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_warn_asm.rs")),
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include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_reachable_asm.rs")));
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file = sym FILE,
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line = const line!(),
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flags = const FLAGS,
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size = const ::core::mem::size_of::<$crate::bindings::bug_entry>(),
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);
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}
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}
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}
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#[macro_export]
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#[doc(hidden)]
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#[cfg(all(CONFIG_BUG, not(CONFIG_UML), not(CONFIG_LOONGARCH), not(CONFIG_ARM)))]
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#[cfg(not(CONFIG_DEBUG_BUGVERBOSE))]
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macro_rules! warn_flags {
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($flags:expr) => {
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const FLAGS: u32 = $crate::bindings::BUGFLAG_WARNING | $flags;
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// SAFETY:
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// - `flags` and `size` are all compile-time constants, preventing
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// any invalid memory access.
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// - The asm block has no side effects and does not modify any registers
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// or memory. It is purely for embedding metadata into the ELF section.
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unsafe {
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$crate::asm!(
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concat!(
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"/* {size} */",
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include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_warn_asm.rs")),
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include!(concat!(env!("OBJTREE"), "/rust/kernel/generated_arch_reachable_asm.rs")));
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flags = const FLAGS,
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size = const ::core::mem::size_of::<$crate::bindings::bug_entry>(),
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);
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}
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}
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}
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#[macro_export]
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#[doc(hidden)]
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#[cfg(all(CONFIG_BUG, CONFIG_UML))]
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macro_rules! warn_flags {
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($flags:expr) => {
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// SAFETY: It is always safe to call `warn_slowpath_fmt()`
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// with a valid null-terminated string.
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unsafe {
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$crate::bindings::warn_slowpath_fmt(
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$crate::c_str!(::core::file!()).as_char_ptr(),
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line!() as $crate::ffi::c_int,
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$flags as $crate::ffi::c_uint,
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::core::ptr::null(),
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);
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}
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};
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}
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#[macro_export]
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#[doc(hidden)]
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#[cfg(all(CONFIG_BUG, any(CONFIG_LOONGARCH, CONFIG_ARM)))]
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macro_rules! warn_flags {
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($flags:expr) => {
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// SAFETY: It is always safe to call `WARN_ON()`.
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unsafe { $crate::bindings::WARN_ON(true) }
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};
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}
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#[macro_export]
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#[doc(hidden)]
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#[cfg(not(CONFIG_BUG))]
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macro_rules! warn_flags {
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($flags:expr) => {};
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}
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#[doc(hidden)]
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pub const fn bugflag_taint(value: u32) -> u32 {
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value << 8
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}
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/// Report a warning if `cond` is true and return the condition's evaluation result.
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#[macro_export]
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macro_rules! warn_on {
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($cond:expr) => {{
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let cond = $cond;
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if cond {
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const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
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$crate::warn_flags!(WARN_ON_FLAGS);
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}
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cond
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}};
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}

‎rust/kernel/generated_arch_reachable_asm.rs.S

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

‎rust/kernel/generated_arch_warn_asm.rs.S

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

‎rust/kernel/lib.rs

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@@ -57,6 +57,7 @@ pub mod auxiliary;
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pub mod bits;
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#[cfg(CONFIG_BLOCK)]
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pub mod block;
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pub mod bug;
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#[doc(hidden)]
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pub mod build_assert;
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pub mod clk;

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