linux-kernel - Re: [PATCH v2] rust: alloc: satisfy `aligned

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Message-ID: <d00561e2-145f-42e0-8fb2-5ca3556afac8@cs.ucla.edu>
Date: Sat, 8 Feb 2025 12:09:40 -0800
From: Paul Eggert <eggert@...ucla.edu>
To: Alejandro Colomar <alx@...nel.org>
Cc: DJ Delorie <dj@...hat.com>, Eric Blake <eblake@...hat.com>,
 Will Newton <will.newton@...aro.org>, linux-man@...r.kernel.org,
 Danilo Krummrich <dakr@...nel.org>, Tamir Duberstein <tamird@...il.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.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@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Subject: Re: [PATCH v2] rust: alloc: satisfy `aligned_alloc` requirements

On 2025-02-08 11:19, Alejandro Colomar wrote:
> I wonder why glibc silently overaligns aligned_alloc() without reporting
> an error for an alignment of 2, while it reports an error for an
> alignment of 3.  It doesn't make much sense at first glance.

Why doesn't it make sense?

If the underlying memory management system supports only some 
power-of-two alignments including one alignment greater than 2, it is 
easy to support alignment of 2 by overaligning, but it is not possible 
to support an alignment of 3.