linux-kernel - Re: C aggregate passing (Rust kernel policy)

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Message-ID: <75F703D5-5ECD-4DF5-97AA-0CBD5965F470@zytor.com>
Date: Thu, 27 Feb 2025 07:27:48 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Ventura Jack <venturajack85@...il.com>, Martin Uecker <uecker@...raz.at>
CC: Linus Torvalds <torvalds@...ux-foundation.org>, Ralf Jung <post@...fj.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Gary Guo <gary@...yguo.net>, airlied@...il.com, boqun.feng@...il.com,
        david.laight.linux@...il.com, ej@...i.de, gregkh@...uxfoundation.org,
        hch@...radead.org, ksummit@...ts.linux.dev,
        linux-kernel@...r.kernel.org, miguel.ojeda.sandonis@...il.com,
        rust-for-linux@...r.kernel.org
Subject: Re: C aggregate passing (Rust kernel policy)

On February 27, 2025 6:21:24 AM PST, Ventura Jack <venturajack85@...il.com> wrote:
>On Wed, Feb 26, 2025 at 1:00 PM Martin Uecker <uecker@...raz.at> wrote:
>>
>> I think C++ messed up a lot (including time-travel UB, uninitialized
>> variables, aliasing ules and much more), but I do not see
>> the problem here.
>
>C++26 actually changes the rules of reading uninitialized
>variables from being undefined behavior to being
>"erroneous behavior", for the purpose of decreasing instances
>that can cause UB. Though programmers can still opt-into
>the old behavior with UB, on a case by case basis, for the
>sake of performance.
>
>Best, VJ.
>
>

Of course, that is effectively what one gets if one treats the compiler warning as binding.