Re: [PATCH] rust: sync: optimize rust symbol generation for CondVar

From: Kunwu Chan
Date: Mon Mar 24 2025 - 02:03:27 EST


On 2025/3/24 12:23, Boqun Feng wrote:
On Mon, Mar 24, 2025 at 10:08:29AM +0800, Kunwu Chan wrote:
On 2025/3/24 01:59, Boqun Feng wrote:
On Mon, Mar 17, 2025 at 04:13:50PM +0800, Kunwu Chan wrote:
From: Kunwu Chan <kunwu.chan@xxxxxxxxxxx>

When build the kernel using the llvm-18.1.3-rust-1.85.0-x86_64
with ARCH=arm64, the following symbols are generated:

$nm vmlinux | grep ' _R'.*CondVar | rustfilt
... T <kernel::sync::condvar::CondVar>::notify_all
... T <kernel::sync::condvar::CondVar>::notify_one
... T <kernel::sync::condvar::CondVar>::notify_sync
... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::poll::PollCondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::poll::PollCondVar as core::ops::drop::Drop>::drop

These notify* symbols are trivial wrappers around the C functions
__wake_up and __wake_up_sync.
It doesn't make sense to go through a trivial wrapper for these
functions, so mark them inline.

Link: https://github.com/Rust-for-Linux/linux/issues/1145
Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Co-developed-by: Grace Deng <Grace.Deng006@xxxxxxxxx>
Signed-off-by: Grace Deng <Grace.Deng006@xxxxxxxxx>
Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxxxx>
---
rust/kernel/sync/condvar.rs | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 7df565038d7d..a826896ba3f0 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -181,6 +181,7 @@ pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
}
/// Calls the kernel function to notify the appropriate number of threads.
+ #[inline]
fn notify(&self, count: c_int) {
Hmm.. I think CondVar::notify() gets inlined even without this
`#[inline]` attribute, do we need this actually?
Actualy, after add '#[inline]', the build result is (compilecmd is 'make
ARCH=arm64 LLVM=1-j8' ):

$nm vmlinux | grep ' _R'.*CondVar | rustfilt
ffff800080019e90 T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_ex
plicit
ffff800080019e90 T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_ex
plicit
ffff800080019e90 T <kernel::sync::poll::PollCondVar>::new::{closure#0}::{closure#0}::panic_cold_e
xplicit
ffff8000805b8c7c T <kernel::sync::poll::PollCondVar as
core::ops::drop::Drop>::drop


And before add '#[inline]',the 'nm vmlinux | grep ' _R'.*CondVar | rustfilt'
appear 'notify' function,

Seems like the LLVM didn't make it inline.

Your commit log said:

... the following symbols are generated:

$nm vmlinux | grep ' _R'.*CondVar | rustfilt
... T <kernel::sync::condvar::CondVar>::notify_all
... T <kernel::sync::condvar::CondVar>::notify_one
... T <kernel::sync::condvar::CondVar>::notify_sync
... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::condvar::CondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::poll::PollCondVar>::new::{closure#0}::{closure#0}::panic_cold_explicit
... T <kernel::sync::poll::PollCondVar as core::ops::drop::Drop>::drop

so no *notify* symbol even before the patch, right? I also checked with

My bad,I mistakenly thought it was some other 'notify_*' functions,

it should be LLVM automatically inline 'notify', I will remove it in the next version.

my local build, without your patch, there is still no symbol for
notify().

Regards,
Boqun

--
Thanks,
Kunwu.Chan(Tao.Chan)