Date:   Mon, 13 Feb 2023 16:48:05 +0100
From:   Andrea Righi <andrea.righi@canonical.com>
To:     Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Cc:     miguel.ojeda.sandonis@gmail.com, alex.gaynor@gmail.com,
        bjorn3_gh@protonmail.com, boqun.feng@gmail.com, dxu@dxuuu.xyz,
        ecurtin@redhat.com, gary@garyguo.net, linux-kernel@vger.kernel.org,
        ojeda@kernel.org, rust-for-linux@vger.kernel.org,
        wedsonaf@gmail.com
Subject: Re: [PATCH] rust: fix regexp in scripts/is_rust_module.sh
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 <20230213151339.661225-1-yakoyoku@gmail.com>
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On Mon, Feb 13, 2023 at 12:13:39PM -0300, Martin Rodriguez Reboredo wrote:
> On Mon, Feb 13, 2023 at 1:19 PM Miguel Ojeda <ojeda@kernel.org> 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.
> 
> Issue was that the kernel couldn't even load C modules, Rust CUs must be
> skipped in vmlinux for it to work, and because of that the constraint
> !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE [1] cannot be relaxed until
> version 1.24+ of Pahole is the minimum requirement by the kernel. I'm OK
> with this change but keep in mind that it won't remedy that condition.
> 
> Link: https://lore.kernel.org/bpf/20230111152050.559334-1-yakoyoku@gmail.com/ [1]

Oh yes, I'm using pahole 1.24, that's probably why it's all working for
me. So we can't just drop !DEBUG_INFO_BTF, but we can definitely relax
the constraint to "!DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE".

-Andrea