From nobody Wed Oct 8 17:34:04 2025 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 692D11991DD for ; Thu, 26 Jun 2025 05:48:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750916915; cv=none; b=BltFHkjzL2r2hSNkCxc4EFXt6d8WYy1nUuVpotg2DvbwU8fzsZDEC9p82x7gYs2uL7il1/EzCgwTDPnpMjlQ/Otaj7P3opLMRp5iWhIjzNMvz3a1K4siUobTVFVzJSzYMzZk3LO3QUCZ0eihABcNLUHU0+rx2B5sE7yeurbUZjA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750916915; c=relaxed/simple; bh=NUQiHaB/oRFvduMBrU+FyUVv6t6Xgm9DuO0q9cjaySQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=MCUYEI91t2ucCZA2LCHCz5EG7D73X+2f9Gar5omPW6HJNQCYzNMZjq123SPcQR6jTS25Wk23+7zMOs5/zqWLoTV03fWSLAm+stn9mF1f4oPzjJb2ltp+eH5er0t1+Ud3+wdfl8z2kUtz3xxsYs+S9WL7dOMUyLTD2Y30sZCd3IA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=sD7pKzYr; arc=none smtp.client-ip=209.85.216.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="sD7pKzYr" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-3132e7266d3so579520a91.2 for ; Wed, 25 Jun 2025 22:48:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1750916914; x=1751521714; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=R1vSzONkvWVxKMWdZPze+udgL8T24sLZ921TIUfWjXQ=; b=sD7pKzYr4gCmmQyqLYn4JkEluNyEz5B0TZTFFjysiO/UZaeRR9UrsR0NiF+xUAkSKM jY9CAKRCOBQ5k7ysSvEmcbO8LYHZPDEnIlS4GjdZA8xonlb3ryOg2EoD3ib6sF5Ff0I6 oPKG0UXIKUSyOI9Aqz1vvaP4Rtz5SbXeouzC3SJpP2yE9tMOLtynHK77R8/RgZCJW3/Z 4rFerA7y7gwr/IMzNgouQxUFgVxKJXNf2DtW0JcLPW6vZI01DOQ9vYpfL4oA6S/8VtVV OUAKSqkuCBSfXoCEA54RcWVid4UEu3cuWi+MItb3Ejzi7OmQ2AuzU/psO3Be985iTUS3 +HoA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750916914; x=1751521714; 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=R1vSzONkvWVxKMWdZPze+udgL8T24sLZ921TIUfWjXQ=; b=b3+tWLbgllGmPKdblM9HVTGZwP/l/C8umIvo+mM/p5xtVFyV+fbMXL6agE2ZfO+JeZ Wv5/0YemVLFS4yRKfw4bb4sRiZqPXEd3xJ4eLUWn3X6Yz/Fpm8yD9V68FIdm7YJBQvZp itHHvS2dX2wZOYBE+QuMm+/hk5EVBtmo2B6qf7jTMTxOrD+4eb8+5In4VZ7Ob2UhB4VA wFmv8bXLZv8QFPpO4ZLCKQFRFRyC2J8hm5vDP65du5bhZFdLz//tQpZwINzrTG72lT6P 4jVwv4NLUKnfefXxe3t9AxDUPwfyI5QUnudhkEPaRgSXJR4FlwZIAP+j9gKFaJZf+WIw u7eQ== X-Forwarded-Encrypted: i=1; AJvYcCWF+VK4uCsxsVArx48zg6JNTEKrdMMhhMw5k3pqgqW2Qjqaa99HqAJcF/nE465pJcRDEDGOUTg9ANIPIT0=@vger.kernel.org X-Gm-Message-State: AOJu0Yzq3TclY3Ji7C7MLjhrlDiFivaaxg5CYLZQAxCXAABqnD2zO9eS 4snf6WX3uSIE9+J2ZIaV3egeSgeh4JuANqRNPb1VENIOUsOUlvKiLuu+iQzGh+z2rs+SzkB8qp1 6hUaIzMW3yQ== X-Google-Smtp-Source: AGHT+IEs8IO1q36YQk0nSSiSi5GU+GN5WZXfosdQGqxbw2barm/yUUYBYTVH1YWmhz9R0wChcSGLtxRfAZXS X-Received: from pjbsv14.prod.google.com ([2002:a17:90b:538e:b0:312:fb53:41c0]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2f0c:b0:312:26d9:d5b4 with SMTP id 98e67ed59e1d1-315f2674a05mr9030490a91.17.1750916913698; Wed, 25 Jun 2025 22:48:33 -0700 (PDT) Date: Wed, 25 Jun 2025 22:48:24 -0700 In-Reply-To: <20250626054826.433453-1-irogers@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250626054826.433453-1-irogers@google.com> X-Mailer: git-send-email 2.50.0.727.gbf7dc18ff4-goog Message-ID: <20250626054826.433453-2-irogers@google.com> Subject: [PATCH v3 1/3] vdso: Switch get/put unaligned from packed struct to memcpy From: Ian Rogers To: Eric Biggers , Yuzhuo Jing , Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , Arnaldo Carvalho de Melo , Al Viro , Christophe Leroy , "Jason A. Donenfeld" , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Cc: Ian Rogers Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Type punning is necessary for get/put unaligned but the use of a packed struct violates strict aliasing rules, requiring -fno-strict-aliasing to be passed to the C compiler. Switch to using memcpy so that -fno-strict-aliasing isn't necessary. Signed-off-by: Ian Rogers --- include/vdso/unaligned.h | 39 +++++++++++++++++++++++++++++++++------ 1 file changed, 33 insertions(+), 6 deletions(-) diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h index ff0c06b6513e..0ccbcc9aa493 100644 --- a/include/vdso/unaligned.h +++ b/include/vdso/unaligned.h @@ -2,14 +2,41 @@ #ifndef __VDSO_UNALIGNED_H #define __VDSO_UNALIGNED_H =20 -#define __get_unaligned_t(type, ptr) ({ \ - const struct { type x; } __packed * __get_pptr =3D (typeof(__get_pptr))(p= tr); \ - __get_pptr->x; \ +#include + +/** + * __get_unaligned_t - read an unaligned value from memory. + * @type: the type to load from the pointer. + * @ptr: the pointer to load from. + * + * Use memcpy to affect an unaligned type sized load avoiding undefined be= havior + * from approaches like type punning that require -fno-strict-aliasing in = order + * to be correct. As type may be const, use __unqual_scalar_typeof to map = to a + * non-const type - you can't memcpy into a const type. The void* cast sil= ences + * ubsan warnings. + */ +#define __get_unaligned_t(type, ptr) ({ \ + type __get_unaligned_ctrl_type __always_unused; \ + __unqual_scalar_typeof(__get_unaligned_ctrl_type) __get_unaligned_val; \ + __builtin_memcpy(&__get_unaligned_val, (void *)(ptr), \ + sizeof(__get_unaligned_val)); \ + __get_unaligned_val; \ }) =20 -#define __put_unaligned_t(type, val, ptr) do { \ - struct { type x; } __packed * __put_pptr =3D (typeof(__put_pptr))(ptr); \ - __put_pptr->x =3D (val); \ +/** + * __put_unaligned_t - write an unaligned value to memory. + * @type: the type of the value to store. + * @val: the value to store. + * @ptr: the pointer to store to. + * + * Use memcpy to affect an unaligned type sized store avoiding undefined + * behavior from approaches like type punning that require -fno-strict-ali= asing + * in order to be correct. The void* cast silences ubsan warnings. + */ +#define __put_unaligned_t(type, val, ptr) do { \ + type __put_unaligned_val =3D (val); \ + __builtin_memcpy((void *)(ptr), &__put_unaligned_val, \ + sizeof(__put_unaligned_val)); \ } while (0) =20 #endif /* __VDSO_UNALIGNED_H */ --=20 2.50.0.727.gbf7dc18ff4-goog