From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
To: Thomas Bertschinger <tahbertschinger@gmail.com>
Cc: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com,
rust-for-linux@vger.kernel.org,
Martin Rodriguez Reboredo <yakoyoku@gmail.com>,
Alice Ryhl <aliceryhl@google.com>
Subject: Re: [PATCH v3] rust: place generated init_module() function in .init.text
Date: Sun, 25 Feb 2024 21:28:38 +0100 [thread overview]
Message-ID: <CANiq72=eh3a-s06EAzKZnU-_3ciYtygx4dkRf0pH10TTy4ga4Q@mail.gmail.com> (raw)
In-Reply-To: <20240206153806.567055-1-tahbertschinger@gmail.com>
On Tue, Feb 6, 2024 at 4:39 PM Thomas Bertschinger
<tahbertschinger@gmail.com> wrote:
>
> Currently Rust kernel modules have their init code placed in the `.text`
> section of the .ko file. I don't think this causes any real problems
> for Rust modules as long as all code called during initialization lives
> in `.text`.
>
> However, if a Rust `init_module()` function (that lives in `.text`)
> calls a function marked with `__init` (in C) or
> `#[link_section = ".init.text"]` (in Rust), then a warning is
> generated by modpost because that function lives in `.init.text`.
> For example:
>
> WARNING: modpost: fs/bcachefs/bcachefs: section mismatch in reference: init_module+0x6 (section: .text) -> _RNvXCsj7d3tFpT5JS_15bcachefs_moduleNtB2_8BcachefsNtCsjDtqRIL3JAG_6kernel6Module4init (section: .init.text)
>
> I ran into this while experimenting with converting the bcachefs kernel
> module from C to Rust. The module's `init()`, written in Rust, calls C
> functions like `bch2_vfs_init()` which are placed in `.init.text`.
>
> This patch places the macro-generated `init_module()` Rust function in
> the `.init.text` section. It also marks `init_module()` as unsafe--now
> it may not be called after module initialization completes because it
> may be freed already.
>
> Note that this is not enough on its own to actually get all the module
> initialization code in that section. The module author must still add
> the `#[link_section = ".init.text"]` attribute to the Rust `init()` in
> the `impl kernel::Module` block in order to then call `__init`
> functions. However, this patch enables module authors do so, when
> previously it would not be possible (without warnings).
>
> Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Applied to `rust-next` -- thanks everyone!
[ Reworded title to add prefix. ]
Cheers,
Miguel
prev parent reply other threads:[~2024-02-25 20:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-06 15:38 [PATCH v3] rust: place generated init_module() function in .init.text Thomas Bertschinger
2024-02-25 20:28 ` Miguel Ojeda [this message]
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