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

Boqun Feng
2025-03-24T04:23:50Z

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@hotmail.com>
> > >
> > > 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@google.com>
> > > Co-developed-by: Grace Deng <Grace.Deng006@Gmail.com>
> > > Signed-off-by: Grace Deng <Grace.Deng006@Gmail.com>
> > > Signed-off-by: Kunwu Chan <kunwu.chan@hotmail.com>
> > > ---
> > > 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 local build, without your patch, there is still no symbol for
notify().

Regards,
Boqun