Date:   Mon, 13 Feb 2023 16:01:05 +0100
From:   Andrea Righi <andrea.righi@canonical.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc:     Eric Curtin <ecurtin@redhat.com>, Daniel Xu <dxu@dxuuu.xyz>,
        Martin Reboredo <yakoyoku@gmail.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        bjorn3_gh@protonmail.com, rust-for-linux@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rust: fix regexp in scripts/is_rust_module.sh
Message-ID: <Y+pQsfNiLkspVIK2@righiandr-XPS-13-7390>
References: <20230210152622.92912-1-andrea.righi@canonical.com>
 <CANiq72=FZtNmYvbb-YPHmQ=bm8rH8VO3M9nemT4i03g9A2PD2Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CANiq72=FZtNmYvbb-YPHmQ=bm8rH8VO3M9nemT4i03g9A2PD2Q@mail.gmail.com>
Precedence: bulk

On Mon, Feb 13, 2023 at 02:19:38PM +0100, Miguel Ojeda wrote:
> On Fri, Feb 10, 2023 at 4:26 PM Andrea Righi <andrea.righi@canonical.com> wrote:
> >
> > nm can use "R" or "r" to show read-only data sections, but
> > scripts/is_rust_module.sh can only recognize "r", so with some versions
> > of binutils it can fail to detect if a module is a Rust module or not.
> 
> Do you know which versions? If so, it would be nice to document it here.
> 
> > Moreover, with this patch applied I can also relax the constraint of
> > "RUST depends on !DEBUG_INFO_BTF" and build a kernel with Rust and BTF
> > enabled at the same time (of course BTF generation is still skipped for
> > Rust modules).
> 
> Even if that build succeeds, can you load the modules? i.e. the
> constraint was there due to
> https://github.com/Rust-for-Linux/linux/issues/735.

This patch simply fixes scripts/is_rust_module.sh to recognize Rust
modules from "regular" C modules with certain versions of binutils, so
that BTF generation is properly skipped for Rust modules.

In this way both C and Rust modules can be loaded correctly (at least in
my tests I'm able load both with CONFIG_DEBUG_INFO_BTF enabled).

I haven't dropped the "RUST depends on !DEBUG_INFO_BTF" yet, but I think
with this fix is applied we can relax this constraint.

-Andrea

> 
> Also Cc'ing Daniel, Eric and Martin since they are the ones working on this.
> 
> Cheers,
> Miguel