From: Alice Ryhl <alice@ryhl.io>
To: y86-dev@protonmail.com, "Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>
Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
patches@lists.linux.dev
Subject: Re: [PATCH v3 09/13] rust: init: add `Zeroable` trait and `init::zeroed` function
Date: Fri, 31 Mar 2023 00:40:34 +0200 [thread overview]
Message-ID: <19db6213-297b-a33d-7331-3c1a5b72fad9@ryhl.io> (raw)
In-Reply-To: <20230329223239.138757-10-y86-dev@protonmail.com>
On 3/30/23 00:33, y86-dev@protonmail.com wrote:
> From: Benno Lossin <y86-dev@protonmail.com>
>
> Add the `Zeroable` trait which marks types that can be initialized by
> writing `0x00` to every byte of the type. Also add the `init::zeroed`
> function that creates an initializer for a `Zeroable` type that writes
> `0x00` to every byte.
>
> Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
> ---
> +// SAFETY: `null` pointer is valid.
> +unsafe impl<T: ?Sized> Zeroable for *mut T {}
> +unsafe impl<T: ?Sized> Zeroable for *const T {}
Actually, I just realized that this is not ok for unsized types. When T
is unsized, the raw pointer is a fat pointer with a vtable, and the
vtable part is not necessarily zeroable.
However, it would be ok to do it for `*const [T]` since the fat part of
the pointer is just the length in this case, and a length of zero is fine.
See more here:
https://github.com/Lokathor/bytemuck/blob/8391afa876ba2e99dffb0c991cc7fa775287d106/src/zeroable.rs#L56-L65
next prev parent reply other threads:[~2023-03-30 22:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-29 22:33 [PATCH v3 09/13] rust: init: add `Zeroable` trait and `init::zeroed` function y86-dev
2023-03-30 11:06 ` Gary Guo
2023-03-30 22:36 ` Alice Ryhl
2023-03-30 22:40 ` Alice Ryhl [this message]
2023-03-31 0:20 ` Gary Guo
2023-03-31 7:09 ` Benno Lossin
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