linux-kernel - Re: [PATCH] x86: rust: Disable entry padding with Rust

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Date: Tue, 30 Jan 2024 15:46:00 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
 Matthew Maurer <mmaurer@...gle.com>
Cc: 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
Subject: Re: [PATCH] x86: rust: Disable entry padding with Rust

On 1/28/24 09:48, Miguel Ojeda wrote:
> On Fri, Dec 15, 2023 at 8:48 PM Matthew Maurer <mmaurer@...gle.com> wrote:
>> rustc-1.73.0 used by Linux does not support entry padding. Mark entry
>> padding support as explicitly incompatible with Rust.
> We are now at 1.74.1 and moving to 1.75.0 for the next cycle, which
> does not support it yet, in case whoever applies the patch wants to
> update it in the description.
> 
>> Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> x86: are you picking this one up through your tree? Thanks!

Do we need a 'rust-option' equivalent of 'cc-option', like:

config CC_HAS_ENTRY_PADDING
        def_bool $(cc-option,-fpatchable-function-entry=16,16)

That way this doesn't become a temporary option at all.  We just do:

config RUST_HAS_ENTRY_PADDING
        def_bool $(rust-option,-fpatchable-function-entry) # or whatever

and:

config HAVE_ENTRY_PADDING
	def_bool CC_HAS_ENTRY_PADDING
	depends on !RUST || RUST_HAS_ENTRY_PADDING

and never have to touch this again.