linux-kernel - Re: [PATCH 2/5] devres: export devres_node_init() and devres_node

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Message-ID: <CAH5fLggPi1zhQdUjt3WqDVUEWy1KVPK=iiQfbNSig697J7HS=g@mail.gmail.com>
Date: Fri, 6 Feb 2026 14:35:53 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org, ojeda@...nel.org, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	lossin@...nel.org, a.hindborg@...nel.org, tmgross@...ch.edu, 
	driver-core@...ts.linux.dev, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] devres: export devres_node_init() and devres_node_add()

On Fri, Feb 6, 2026 at 2:33 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On Fri Feb 6, 2026 at 2:25 PM CET, Greg KH wrote:
> > On Fri, Feb 06, 2026 at 02:20:06PM +0100, Alice Ryhl wrote:
> >> On Fri, Feb 6, 2026 at 2:16 PM Danilo Krummrich <dakr@...nel.org> wrote:
> >> >
> >> > On Fri Feb 6, 2026 at 1:34 PM CET, Greg KH wrote:
> >> > > That's fine, because the rust driver core code should also be built into
> >> > > the kernel, not as a module, right?
> >> >
> >> > Yes, but the Rust compiler may still choose to put some of the core code into
> >> > the module.
> >> >
> >> > Especially with generic types and functions the Rust compiler may move some the
> >> > generated code for a certain type instance into the module that instanciates the
> >> > type.
> >> >
> >> > For instance, even though rust/kernel/devres.rs is *always* built-in, we get the
> >> > following error when devres_node_init() is not exported when the users of this
> >> > built-in code are built as module.
> >> >
> >> >         ERROR: modpost: "devres_node_init" [drivers/pwm/pwm_th1520.ko] undefined!
> >> >         ERROR: modpost: "devres_node_init" [drivers/gpu/drm/tyr/tyr.ko] undefined!
> >> >         ERROR: modpost: "devres_node_init" [drivers/gpu/nova-core/nova_core.ko] undefined!
> >> >         ERROR: modpost: "devres_node_init" [samples/rust/rust_dma.ko] undefined!
> >> >         ERROR: modpost: "devres_node_init" [samples/rust/rust_driver_pci.ko] undefined!
> >> >         ERROR: modpost: "devres_node_init" [samples/rust/rust_driver_auxiliary.ko] undefined!
> >> >         make[2]: *** [scripts/Makefile.modpost:147: Module.symvers] Error 1
> >> >
> >> > However, sprinkling "raw" EXPORT_SYMBOL_GPL() due to that is not great at all.
> >> > Hence, we could do something like in [1] instead. I don't know if there are
> >> > other options that may be better though.
> >> >
> >> > [1] https://lore.kernel.org/all/DG7UR3WWZB4V.2MYMJJH1VDHH@kernel.org/
> >>
> >> You can use #[inline(never)] to prevent this.
> >
> > Ah, good!
>
> I tried this before, but it doesn't work. It might prevent inlining, but it does
> not prevent the compiler to move the function into the module binary.
>
> For instance, even with #[inline(never)] on Devres::new() I see this:
>
>         $ objdump -t drivers/pwm/pwm_th1520.o | grep " F " | grep Devres | grep new
>
>         0000000000000000 g     F .text  00000000000001d0 _RINvMNtCsgzhNYVB7wSz_6kernel6devresINtB3_6DevresINtNtNtB5_2io3mem5IoMemKjb0_EE3newNtNtB5_5error5ErrorINtNtCs4gKlGRWyJ5S_4core6result6ResultBK_B1i_EECsjBm7MKWXKwW_10pwm_th1520

Because it's generic, see my sibling reply.