linux-kernel - Re: [PATCH] x86: Enable IBT in Rust if enabled in C

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Date:   Thu, 12 Oct 2023 22:32:14 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Trevor Gross <tmgross@...ch.edu>
Cc:     Matthew Maurer <mmaurer@...gle.com>, peterz@...radead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        "H. Peter Anvin" <hpa@...or.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>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        Antoni Boucher <bouanto@...o.com>
Subject: Re: [PATCH] x86: Enable IBT in Rust if enabled in C

On Thu, Oct 12, 2023 at 10:13 PM Trevor Gross <tmgross@...ch.edu> wrote:
>
> I have not tested this, but is it possible to enable these options via
> `-Cllvm-args=...` instead of using the unstable flags?

We probably want to use the "real" flag eventually instead of
`-Cllvm-args`, right? So we would need to change it anyhow. And using
the `-Z` one means we test the "real" flag already.

Well, unless `-Cllvm-args` becomes the "official" way to enable this,
like you suggest in the Zulip, but should that really happen? e.g.
should not there be a generic flag for all backends for things like
these?

> If so, I think this would be preferred in case the exact flags change
> before they become stable. It sounds like they are likely to change,
> see [1].

That is fine, they will change anyway from `-Z` to `-C`, so having to
update those is expected.

> If not, no big deal since it would just need an update at a rust version bump.

Yeah, I don't think it is a big deal, and the version bump looks like
the best commit to put the change, in fact.

It is true, though, that these ones in particular are conditionally
enabled, so there is a slightly higher risk of forgetting about them.
But that is why we should get more `Tested-by`s! :)

Cheers,
Miguel