adds support for dynamic debug for the pr_debug macro.
Signed-off-by: Andrew Ballance <andrewjballance@gmail.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 {
+ $crate::print::dynamic_debug::dynamic_pr_debug(
+ &mut DEBUG_INFO,
+ format_args!($($f)*)
+ );
+ }
+ }
+ }};
+ }
+}
--
2.49.0On Wed, Jun 11, 2025 at 10:30 PM Andrew Ballance
<andrewjballance@gmail.com> wrote:
>
> adds support for dynamic debug for the pr_debug macro.
>
> Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
> ---
> rust/bindings/bindings_helper.h | 1 +
> rust/kernel/print.rs | 167 +++++++++++++++++++++++++++++++-
> 2 files changed, 164 insertions(+), 4 deletions(-)
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index bc494745f67b..e05e9ce5d887 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -46,6 +46,7 @@
> #include <linux/cred.h>
> #include <linux/device/faux.h>
> #include <linux/dma-mapping.h>
> +#include <linux/dynamic_debug.h>
> #include <linux/errname.h>
> #include <linux/ethtool.h>
> #include <linux/file.h>
> diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
> index 9783d960a97a..4f0d79804d23 100644
> --- a/rust/kernel/print.rs
> +++ b/rust/kernel/print.rs
> @@ -371,13 +371,15 @@ macro_rules! pr_info (
> ///
> /// Use this level for debug messages.
> ///
> -/// Equivalent to the kernel's [`pr_debug`] macro, except that it doesn't support dynamic debug
> -/// yet.
> +/// Equivalent to the kernel's [`pr_debug`] macro.
> +///
> +/// This has support for [`dynamic debug`].
> ///
> /// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
> /// [`std::format!`] for information about the formatting syntax.
> ///
> /// [`pr_debug`]: https://docs.kernel.org/core-api/printk-basics.html#c.pr_debug
> +/// [`dynamic debug`]: https://docs.kernel.org/admin-guide/dynamic-debug-howto.html
> /// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
> /// [`std::format!`]: https://doc.rust-lang.org/std/macro.format.html
> ///
> @@ -390,8 +392,18 @@ macro_rules! pr_info (
> #[doc(alias = "print")]
> macro_rules! pr_debug (
> ($($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() },
Please define a STATIC_KEY_INIT_FALSE constant in
rust/kernel/jump_label.rs and refer to it. You can use mem::zeroed()
in the definition of the constant.
> + },
> + }
> + }
> +
> + #[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
typo
> + #[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
No, we can't use mutable references like this. In Rust, the real
meaning of &mut is exclusive, not mutable. (And the real meaning of &
is shared.) We don't have exclusive access to the DEBUG_INFO static
here - the access is shared, so we must use &_ references instead of
&mut _ references here.
Note that by using Opaque, it's possible to mutate the value even if
it's behind a &_ reference.
#[repr(transparent)]
pub struct _Ddebug {
pub inner: Opaque<bindings::_ddebug>,
}
and then you can do DEBUG_INFO.inner.get() to obtain a mutable raw
pointer to the contents.
> + unsafe {
> + $crate::print::dynamic_debug::dynamic_pr_debug(
> + &mut DEBUG_INFO,
> + format_args!($($f)*)
> + );
> + }
> + }
> + }};
> + }
> +}
> --
> 2.49.0
>
On 6/11/25 4:38 PM, Alice Ryhl wrote:
> Please define a STATIC_KEY_INIT_FALSE constant in
> rust/kernel/jump_label.rs and refer to it. You can use mem::zeroed()
> in the definition of the constant.
Will do for the v2.
> No, we can't use mutable references like this. In Rust, the real
> meaning of &mut is exclusive, not mutable. (And the real meaning of &
> is shared.) We don't have exclusive access to the DEBUG_INFO static
> here - the access is shared, so we must use &_ references instead of
> &mut _ references here.
>
> Note that by using Opaque, it's possible to mutate the value even if
> it's behind a &_ reference.
> #[repr(transparent)]
> pub struct _Ddebug {
> pub inner: Opaque<bindings::_ddebug>,
> }
> and then you can do DEBUG_INFO.inner.get() to obtain a mutable raw
> pointer to the contents.
>
Unfortunately, static_branch_unlikely does not work with keys contained
within a Opaque, because it uses offset_of and sym. I can create a macro
specifically for dealing with Opaque::<type_that_contains_a_static_key>
because I imagine that many uses of static branch will end up wrapped
in an Opaque.
Best regards,
Andrew Ballance
On Thu, Jun 12, 2025 at 6:02 AM Andrew Ballance
<andrewjballance@gmail.com> wrote:
>
> On 6/11/25 4:38 PM, Alice Ryhl wrote:
> > Please define a STATIC_KEY_INIT_FALSE constant in
> > rust/kernel/jump_label.rs and refer to it. You can use mem::zeroed()
> > in the definition of the constant.
>
> Will do for the v2.
>
> > No, we can't use mutable references like this. In Rust, the real
> > meaning of &mut is exclusive, not mutable. (And the real meaning of &
> > is shared.) We don't have exclusive access to the DEBUG_INFO static
> > here - the access is shared, so we must use &_ references instead of
> > &mut _ references here.
> >
> > Note that by using Opaque, it's possible to mutate the value even if
> > it's behind a &_ reference.
> > #[repr(transparent)]
> > pub struct _Ddebug {
> > pub inner: Opaque<bindings::_ddebug>,
> > }
> > and then you can do DEBUG_INFO.inner.get() to obtain a mutable raw
> > pointer to the contents.
> >
>
> Unfortunately, static_branch_unlikely does not work with keys contained
> within a Opaque, because it uses offset_of and sym. I can create a macro
> specifically for dealing with Opaque::<type_that_contains_a_static_key>
> because I imagine that many uses of static branch will end up wrapped
> in an Opaque.
Ah, fair enough. In that case, you can also do this:
$crate::print::dynamic_debug::dynamic_pr_debug(
&raw mut DEBUG_INFO,
format_args!($($f)*)
);
using &raw mut creates a raw pointer directly without creating a
reference, so that also solves my concern.
Alice
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