linux-kernel - Re: [PATCH] btf, scripts: rust: drop is_rust

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Date:   Tue, 11 Jul 2023 11:22:17 -0600
From:   Daniel Xu <dxu@...uu.xyz>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Andrea Righi <andrea.righi@...onical.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH] btf, scripts: rust: drop is_rust_module.sh

Hi Miguel, Andrea,

On Tue, Jul 11, 2023 at 04:39:27PM +0200, Miguel Ojeda wrote:
> On Tue, Jul 4, 2023 at 7:21 AM Andrea Righi <andrea.righi@...onical.com> wrote:
> >
> > With commit c1177979af9c ("btf, scripts: Exclude Rust CUs with pahole")
> > we are now able to use pahole directly to identify Rust compilation
> > units (CUs) and exclude them from generating BTF debugging information
> > (when DEBUG_INFO_BTF is enabled).
> >
> > And if pahole doesn't support the --lang-exclude flag, we can't enable
> > both RUST and DEBUG_INFO_BTF at the same time.
> >
> > So, in any case, the script is_rust_module.sh is just redundant and we
> > can drop it.
> >
> > NOTE: we may also be able to drop the "Rust loadable module" mark
> > inside Rust modules, but it seems safer to keep it for now to make sure
> > we are not breaking any external tool that may potentially rely on it.
> 
> Just to recall the history of these changes:
> 
>   - The script got added in order to skip the BTF generation in the
> `BTF [M]` step (under `DEBUG_INFO_BTF_MODULES`, which depends on
> `DEBUG_INFO_BTF`).
> 
>   - A few months later, it was noticed that C modules couldn't be
> loaded if Rust was enabled, due to the base BTF info in `vmlinux`.
> That triggered the eventual addition of `--lang_exclude=` to `pahole`,
> but meanwhile, we made `DEBUG_INFO_BTF` and `RUST` exclusive.
> 
>   - Now, this patch removes the script because having a newer `pahole`
> also correctly skips the Rust CUs in the `BTF [M]` steps (i.e. and not
> just the `vmlinux` one), since we pass `--lang_exclude=` to both cases
> (`link-vmlinux.sh` and `Makefile.modfinal`), if I understand correctly
> (the script could, in principle, have been removed even before
> `pahole` got the new feature, given the exclusivity of the options).
> 
> If this is all correct, then the patch looks good to me. I am Cc'ing
> Arnaldo, Martin and the BPF list.

I believe I authored the original script. This all sounds right to me.

Acked-by: Daniel Xu <dxu@...uu.xyz>

Thanks,
Daniel