From nobody Tue Feb 10 13:33:00 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98BBFC77B7E for ; Thu, 1 Jun 2023 13:51:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233287AbjFANvU (ORCPT ); Thu, 1 Jun 2023 09:51:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49162 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233267AbjFANvR (ORCPT ); Thu, 1 Jun 2023 09:51:17 -0400 Received: from mail-ed1-x549.google.com (mail-ed1-x549.google.com [IPv6:2a00:1450:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F7D21AD for ; Thu, 1 Jun 2023 06:51:11 -0700 (PDT) Received: by mail-ed1-x549.google.com with SMTP id 4fb4d7f45d1cf-514b05895f7so783241a12.0 for ; Thu, 01 Jun 2023 06:51:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1685627470; x=1688219470; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=CFWZiTMzRcsx84Z5SYXbngPTfzR7GjN80EhCOaRTPas=; b=6U1LmEILAkXt1ykhx/Ehu4FX/iB1ojm/m3YZhZZkMXOJ1AUeWEH2jlJbqb665k/3Zl UyRA+zunWEjQTWb6+7BglNY3ssL/IdWy8mC00gdGNfPYWvpX92UeVIpgmBeIVWJ7dWlg zA9q4amy/WFWI5coaOYgwbUHvE17fLTDf3pxodr/okPUFMqLBlKBIn36kKRjcDOmY/tm mTIKZ8119pOSw08AkUN26fS9yvv4y6RVrmd22szoQMDHDN5qguhwAG5ZeSbKzcNoZ8tk +dVRxL08TvQCZ+aWANc8BUah0e4E0MRnbTZid/0ie+ioPBhISLnEadvuBGWRLZhe/nWc CmDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685627470; x=1688219470; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=CFWZiTMzRcsx84Z5SYXbngPTfzR7GjN80EhCOaRTPas=; b=gdPdXHwz+76fK41CG0nVn3AchzuExG28B0YhjqZoOOI65m7/sYd/V+CHbuE/FaHfmv vVhhnNdTq1qzU5PNoFkcMYUQ2ewwOx5xkKHcDyUMg2/NPFXw3c1pTBwMz18fMkLOnL7y weehT+k0LBvYb8UaG88nUpqqzg227fi3ikT8P3agpSyLL6BQ6dbRu3/uW3iwSGbtwOsZ CbkOe3WibQk2vuyh3Q82x6yIKnHdNoif+wIHAhuimk9WhbcHJ7e7YR/wJKRhVo/C5pYG 8PxQnv1eANA/7DOi+z+5JLdvA3GDy/v2LI6TYeFP2c0e/rvVxqZVZuG23IQ23H3hJ/DB LruA== X-Gm-Message-State: AC+VfDyfCrX4MpK0CZNSwNC4L0SMhktyjY0XkHWpEdC70rBFIdbBAXBq OTVSFjXXGYkcileIEtzMwbzjsoA/UqfaHqs= X-Google-Smtp-Source: ACHHUZ7ST9mZi4kYui3d3gUljsAefg4w47aEs4JF/TBbtRVokn5rwijE56vtX4t1Q6J90rRBY+JFA2F75r1jcsw= X-Received: from aliceryhl.c.googlers.com ([fda3:e722:ac3:cc00:31:98fb:c0a8:6c8]) (user=aliceryhl job=sendgmr) by 2002:a17:906:9bc3:b0:947:f975:cc09 with SMTP id de3-20020a1709069bc300b00947f975cc09mr2209092ejc.1.1685627469897; Thu, 01 Jun 2023 06:51:09 -0700 (PDT) Date: Thu, 1 Jun 2023 13:49:40 +0000 In-Reply-To: <20230601134946.3887870-1-aliceryhl@google.com> Mime-Version: 1.0 References: <20230601134946.3887870-1-aliceryhl@google.com> X-Mailer: git-send-email 2.41.0.rc0.172.g3f132b7071-goog Message-ID: <20230601134946.3887870-3-aliceryhl@google.com> Subject: [PATCH v2 2/8] rust: add offset_of! macro From: Alice Ryhl To: rust-for-linux@vger.kernel.org Cc: Miguel Ojeda , Wedson Almeida Filho , Tejun Heo , Lai Jiangshan , Alex Gaynor , Boqun Feng , Gary Guo , "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" , Benno Lossin , Alice Ryhl , linux-kernel@vger.kernel.org, patches@lists.linux.dev, Wedson Almeida Filho , Martin Rodriguez Reboredo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Wedson Almeida Filho This macro is used to compute the offset of a field in a struct. This commit enables an unstable feature that is necessary for using the macro in a constant. However, this is not a problem as the macro will become available from the Rust standard library soon [1]. The unstable feature can be disabled again once that happens. The macro in this patch does not support sub-fields. That is, you cannot write `offset_of!(MyStruct, field.sub_field)` to get the offset of `sub_field` with `field`'s type being a struct with a field called `sub_field`. This is because `field` might be a `Box`, which means that you would be trying to compute the offset to something in an entirely different allocation. There's no easy way to fix the current macro to support subfields, but the version being added to the standard library should support it, so the limitation is temporary and not a big deal. Link: https://github.com/rust-lang/rust/issues/106655 [1] Signed-off-by: Wedson Almeida Filho Co-developed-by: Alice Ryhl Signed-off-by: Alice Ryhl Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Benno Lossin Reviewed-by: Gary Guo --- rust/kernel/lib.rs | 35 +++++++++++++++++++++++++++++++++++ scripts/Makefile.build | 2 +- 2 files changed, 36 insertions(+), 1 deletion(-) diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index eaded02ffb01..7ea777b731e6 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -14,6 +14,7 @@ #![no_std] #![feature(allocator_api)] #![feature(coerce_unsized)] +#![feature(const_refs_to_cell)] #![feature(dispatch_from_dyn)] #![feature(new_uninit)] #![feature(receiver_trait)] @@ -98,3 +99,37 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! { // instead of `!`. See . loop {} } + +/// Calculates the offset of a field from the beginning of the struct it b= elongs to. +/// +/// # Examples +/// +/// ``` +/// #[repr(C)] +/// struct Test { +/// a: u64, +/// b: u32, +/// } +/// +/// assert_eq!(kernel::offset_of!(Test, b), 8); +/// ``` +#[macro_export] +macro_rules! offset_of { + ($type:path, $field:ident) =3D> {{ + let $type { $field: _, .. }; + let tmp =3D ::core::mem::MaybeUninit::<$type>::uninit(); + let outer =3D tmp.as_ptr(); + // To avoid warnings when nesting `unsafe` blocks. + #[allow(unused_unsafe)] + // SAFETY: The pointer is valid and aligned, just not initialised;= `addr_of` ensures that + // we don't actually read from `outer` (which would be UB) nor cre= ate an intermediate + // reference. + let inner =3D unsafe { ::core::ptr::addr_of!((*outer).$field) } as= *const u8; + // To avoid warnings when nesting `unsafe` blocks. + #[allow(unused_unsafe)] + // SAFETY: The two pointers are within the same allocation block. + unsafe { + inner.offset_from(outer as *const u8) as usize + } + }}; +} diff --git a/scripts/Makefile.build b/scripts/Makefile.build index 78175231c969..819510694769 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -277,7 +277,7 @@ $(obj)/%.lst: $(src)/%.c FORCE # Compile Rust sources (.rs) # ------------------------------------------------------------------------= --- =20 -rust_allowed_features :=3D new_uninit +rust_allowed_features :=3D const_refs_to_cell,new_uninit =20 rust_common_cmd =3D \ RUST_MODFILE=3D$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \ --=20 2.41.0.rc0.172.g3f132b7071-goog