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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Wed, 11 Oct 2023 19:44:23 +0200
Message-ID: <CANiq72=wAOryvUW3whsGRvribm2eYT+Z-KsJKCkZ0g8b3P+jQg@mail.gmail.com>
Subject: Re: [PATCH] x86: Enable IBT in Rust if enabled in C
To:     Matthew Maurer <mmaurer@google.com>
Cc:     peterz@infradead.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alice Ryhl <aliceryhl@google.com>,
        linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
        Josh Poimboeuf <jpoimboe@kernel.org>
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On Tue, Oct 10, 2023 at 12:43=E2=80=AFAM Matthew Maurer <mmaurer@google.com=
> wrote:
>
> These flags are not made conditional on compiler support because at the
> moment exactly one version of rustc supported, and that one supports
> these flags.
>
> Building without these additional flags will manifest as objtool
> printing a large number of errors about missing ENDBR and if CFI is
> enabled (not currently possible) will result in incorrectly structured
> function prefixes.
>
> Signed-off-by: Matthew Maurer <mmaurer@google.com>
> ---
>
> Split out the IBT additions as per
> https://lkml.kernel.org/linux-fsdevel/CANiq72kK6ppBE7j=3Dz7uua1cJMKaLoR5U=
3NUAZXT5MrNEs9ZhfQ@mail.gmail.com/

Thanks a lot Matthew for this! It is great to see those warnings
finally go away.

I have added the `objtool` pass to the intermediate Rust object files
and, with that + this patch applied + IBT enabled (but not
rethunk/retpoline), the only thing I see is:

    samples/rust/rust_print.o: warning: objtool: init_module(): not an
indirect call target
    samples/rust/rust_print.o: warning: objtool: cleanup_module(): not
an indirect call target

But we can fix those independently of this (ideally we want to reuse
the C macros, rather than putting more complexity in `module!`), so:

Acked-by: Miguel Ojeda <ojeda@kernel.org>

I will send the patch for adding `objtool`.

Cheers,
Miguel