linux-kernel - Re: [PATCH v2] uaccess: decouple INLINE_COPY_FROM_USER and CONFIG

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Message-ID: <aRzZgzPmoTSacCv_@google.com>
Date: Tue, 18 Nov 2025 20:39:31 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Danilo Krummrich <dakr@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	John Hubbard <jhubbard@...dia.com>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Philip Li <philip.li@...el.com>, Yujie Liu <yujie.liu@...el.com>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2] uaccess: decouple INLINE_COPY_FROM_USER and CONFIG_RUST

On Tue, Nov 18, 2025 at 02:51:52PM -0500, Yury Norov wrote:
> + Philip, Yujie
> 
> On Tue, Nov 18, 2025 at 09:18:18AM -0800, Andrew Morton wrote:
> > On Tue, 18 Nov 2025 10:39:56 +0000 Alice Ryhl <aliceryhl@...gle.com> wrote:
> > 
> > > On Fri, Oct 24, 2025 at 11:47:53AM -0400, Yury Norov (NVIDIA) wrote:
> > > > Commit 1f9a8286bc0c ("uaccess: always export _copy_[from|to]_user with
> > > > CONFIG_RUST") exports _copy_{from,to}_user() unconditionally, if RUST
> > > > is enabled. This pollutes exported symbols namespace, and spreads RUST
> > > > ifdefery in core files.
> > > > 
> > > > It's better to declare a corresponding helper under the rust/helpers,
> > > > similarly to how non-underscored copy_{from,to}_user() is handled.
> > > > 
> > > > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > Tested-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
> > > 
> > > It looks like this is not quite correct. The header file still has this
> > > declaration unconditionally:
> > > 
> > > extern __must_check unsigned long
> > > _copy_from_user(void *, const void __user *, unsigned long);
> > > 
> > > extern __must_check unsigned long
> > > _copy_to_user(void __user *, const void *, unsigned long);
> > > 
> > > this causes:
> > > 
> > > ERROR: modpost: "_copy_from_user" [samples/rust/rust_misc_device.ko] undefined!
> > > ERROR: modpost: "_copy_to_user" [samples/rust/rust_misc_device.ko] undefined!
> > 
> > I wonder why this wasn't caught in linux-next testing.
> > 
> > Please check the rust Kconfig defaults, see if there's something we can
> > do to get more compilation test coverage?
> 
> I'm second to that.
> 
> Philip added my git repo under his testing a while ago, and also enabled
> Rust config. I received a 'build success' email from his robot before
> submitting this.
> 
> Alice, can you please share your config? Philip, can you add Alice's
> config in the testing grid so that we don't slip through such things
> in future?

If I were to guess the reason, then I would say the architecture. Are
you only testing it on x86? I found it on arm64 with the Nov 18th
linux-next.

Alice

View attachment ".config" of type "text/plain" (194304 bytes)