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Date:   Mon, 9 Oct 2023 19:37:00 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc:     Matthew Maurer <mmaurer@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Peter Zijlstra <peterz@infradead.org>, rcvalle@google.com,
        Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, patches@lists.linux.dev,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        David Gow <davidgow@google.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        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,
        "H. Peter Anvin" <hpa@zytor.com>, linux-doc@vger.kernel.org
Subject: Re: [PATCH v10 25/27] x86: enable initial Rust support
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On Mon, Oct 09, 2023 at 06:31:13PM +0200, Miguel Ojeda wrote:
> On Mon, Oct 9, 2023 at 6:01 PM Matthew Maurer <mmaurer@google.com> wrote:
> >
> > If the IBT part would be helpful by itself immediately, I can split
> > that out - it's only the KCFI portion that won't currently work.
> 
> Thanks Matthew. I don't think we are in a rush, but if it is not too
> much work to split it, that would be great, instead of adding the
> restriction.
> 
> For retthunk, by the way, I forgot to mention to Greg above that (in
> the original discussion with PeterZ) that I did a quick test back then
> to hack the equivalent of `-mfunction-return=thunk-extern` into
> `rustc` to show that the compiler could use it via LLVM (by passing
> the attribute in the IR). At least at a basic level it seemed to work:
> I got a userspace program to count the times that it went through the
> return thunk. I didn't try to do anything on the kernel side, but at
> least for the compiler side, it seemed OK. So it may be way easier (on
> the compiler side) than the CFI work?

It should hopefully be much easier than CFI, it was a much simpler
change to gcc and clang when it landed.

thanks,

greg k-h