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Message-ID: <20250611202952.1670168-3-andrewjballance@gmail.com>
Date: Wed, 11 Jun 2025 15:29:51 -0500
From: Andrew Ballance <andrewjballance@...il.com>
To: jbaron@...mai.com,
jim.cromie@...il.com,
daniel.almeida@...labora.com,
acourbot@...dia.com,
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rafael@...nel.org,
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Cc: viresh.kumar@...aro.org,
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Subject: [RFC PATCH 2/3] rust: device add support for dynamic debug to pr_debug!
adds support for dynamic debug for the pr_debug macro.
Signed-off-by: Andrew Ballance <andrewjballance@...il.com>
---
rust/bindings/bindings_helper.h | 1 +
rust/kernel/print.rs | 167 +++++++++++++++++++++++++++++++-
2 files changed, 164 insertions(+), 4 deletions(-)
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index bc494745f67b..e05e9ce5d887 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -46,6 +46,7 @@
#include <linux/cred.h>
#include <linux/device/faux.h>
#include <linux/dma-mapping.h>
+#include <linux/dynamic_debug.h>
#include <linux/errname.h>
#include <linux/ethtool.h>
#include <linux/file.h>
diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
index 9783d960a97a..4f0d79804d23 100644
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -371,13 +371,15 @@ macro_rules! pr_info (
///
/// Use this level for debug messages.
///
-/// Equivalent to the kernel's [`pr_debug`] macro, except that it doesn't support dynamic debug
-/// yet.
+/// Equivalent to the kernel's [`pr_debug`] macro.
+///
+/// This has support for [`dynamic debug`].
///
/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
/// [`std::format!`] for information about the formatting syntax.
///
/// [`pr_debug`]: https://docs.kernel.org/core-api/printk-basics.html#c.pr_debug
+/// [`dynamic debug`]: https://docs.kernel.org/admin-guide/dynamic-debug-howto.html
/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
/// [`std::format!`]: https://doc.rust-lang.org/std/macro.format.html
///
@@ -390,8 +392,18 @@ macro_rules! pr_info (
#[doc(alias = "print")]
macro_rules! pr_debug (
($($arg:tt)*) => (
- if cfg!(debug_assertions) {
- $crate::print_macro!($crate::print::format_strings::DEBUG, false, $($arg)*)
+ #[cfg(any(DYNAMIC_DEBUG_MODULE, CONFIG_DYNAMIC_DEBUG))]
+ {
+ if cfg!(debug_assertions) {
+ $crate::dynamic_pr_debug_unlikely!($($arg)*);
+ }
+ }
+
+ #[cfg(not(any(DYNAMIC_DEBUG_MODULE, CONFIG_DYNAMIC_DEBUG)))]
+ {
+ if cfg!(debug_assertions) {
+ $crate::print_macro!($crate::print::format_strings::DEBUG, false, $($arg)*)
+ }
}
)
);
@@ -423,3 +435,150 @@ macro_rules! pr_cont (
$crate::print_macro!($crate::print::format_strings::CONT, true, $($arg)*)
)
);
+
+/// all of the code that is used for dynamic debug for pr_debug!
+/// this is public but hidden. This code should only be called
+/// by the `pr_debug!` or `dev_dbg!` macros.
+#[cfg(CONFIG_DYNAMIC_DEBUG_CORE)]
+#[doc(hidden)]
+pub mod dynamic_debug {
+
+ pub use bindings::_ddebug;
+
+ use crate::c_str;
+ use core::fmt;
+ use kernel::str::CStr;
+
+ /// a wrapper around the C `struct _ddebug`.
+ /// this is public but hidden.
+ ///
+ /// # Invariants
+ /// - this is always static mut.
+ /// - this is always located in the "__dyndbg" section.
+ /// - this has the same layout as `_ddebug`.
+ #[repr(transparent)]
+ pub struct _Ddebug {
+ pub inner: bindings::_ddebug,
+ }
+
+ impl _Ddebug {
+ pub const fn new_unlikely(
+ modname: &'static CStr,
+ function: &'static CStr,
+ filename: &'static CStr,
+ format: &'static CStr,
+ line_num: u32,
+ ) -> Self {
+ // rust does not have support for c like bit fields. so
+ // do some bit fiddling to set the line, class and flags varibles
+ let class: u32 = bindings::_DPRINTK_CLASS_DFLT << 18;
+ let flags: u32 = bindings::_DPRINTK_FLAGS_NONE << 24;
+ let bit_fields: u32 = line_num | class | flags;
+
+ let arr: [u8; 4] = bit_fields.to_ne_bytes();
+ let bits = bindings::__BindgenBitfieldUnit::new(arr);
+
+ #[cfg(CONFIG_JUMP_LABEL)]
+ {
+ Self {
+ inner: bindings::_ddebug {
+ modname: modname.as_char_ptr(),
+ function: function.as_char_ptr(),
+ filename: filename.as_char_ptr(),
+ format: format.as_char_ptr(),
+ _bitfield_align_1: [],
+ _bitfield_1: bits,
+ // SAFETY: STATIC_KEY_INIT_FALSE is initialized as zero
+ key: unsafe { core::mem::zeroed() },
+ },
+ }
+ }
+
+ #[cfg(not(CONFIG_JUMP_LABEL))]
+ {
+ Self {
+ inner: bindings::_ddebug {
+ modname: modname.as_char_ptr(),
+ function: function.as_char_ptr(),
+ filename: filename.as_char_ptr(),
+ format: format.as_char_ptr(),
+ _bitfield_align_1: [],
+ _bitfield_1: bits,
+ __bindgen_padding_0: 0,
+ },
+ }
+ }
+ }
+ }
+
+ /// a wrapper function around the c function `__dynamic_pr_debug`.
+ /// # Safety
+ /// - descriptor must be a valid reference to a `static mut` _Ddebug
+ pub unsafe fn dynamic_pr_debug(descriptor: &mut _Ddebug, args: fmt::Arguments<'_>) {
+ // SAFETY:
+ // - "%pA" is null terminated and is the format for rust printing
+ // - descriptor.inner is a valid _ddebug
+ unsafe {
+ bindings::__dynamic_pr_debug(
+ &raw mut descriptor.inner,
+ c_str!("%pA").as_char_ptr(),
+ (&raw const args).cast::<ffi::c_void>(),
+ );
+ }
+ }
+
+ /// macro for dynamic debug equilant to the C `pr_debug` macro
+ #[doc(hidden)]
+ #[macro_export]
+ macro_rules! dynamic_pr_debug_unlikely {
+ ($($f:tt)*) => {{
+ use $crate::c_str;
+ use $crate::str::CStr;
+ use $crate::print::dynamic_debug::{_ddebug, _Ddebug};
+
+ const MOD_NAME: &CStr = c_str!(module_path!());
+ // right now rust does not have a function! macro. so, hard code this to be
+ // the name of the macro that is printing
+ // TODO:
+ // replace this once either a function! macro exists
+ // or core::any::type_name becomes const
+ const FN_NAME: &CStr = c_str!("pr_debug!");
+ const FILE_NAME: &CStr = c_str!(file!());
+ const MESSAGE: &CStr = c_str!(stringify!($($f)*));
+ const LINE: u32 = line!();
+
+ #[link_section = "__dyndbg"]
+ static mut DEBUG_INFO: _Ddebug =
+ _Ddebug::new_unlikely(MOD_NAME, FN_NAME, FILE_NAME, MESSAGE, LINE);
+
+ // SAFETY:
+ // - this is reading from a `static mut` variable
+ // - key.dd_key_false is a valid static key
+ let should_print: bool = unsafe {
+ #[cfg(CONFIG_JUMP_LABEL)]
+ {
+ $crate::jump_label::static_branch_unlikely!(
+ DEBUG_INFO,
+ _Ddebug,
+ inner.key.dd_key_false
+ )
+ }
+ #[cfg(not(CONFIG_JUMP_LABEL))]
+ {
+ // gets the _DPRINTK_FLAGS_PRINT bit
+ DEBUG_INFO.inner.flags() & 1 != 0
+ }
+ };
+
+ if should_print {
+ // SAFETY: `&mut DEBUG_INFO` is a valid reference to a static mut _Ddebug
+ unsafe {
+ $crate::print::dynamic_debug::dynamic_pr_debug(
+ &mut DEBUG_INFO,
+ format_args!($($f)*)
+ );
+ }
+ }
+ }};
+ }
+}
--
2.49.0
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