From nobody Mon Oct 6 11:49:34 2025 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 480272877E8 for ; Tue, 22 Jul 2025 21:58:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753221487; cv=none; b=aai2is4/+YGE5jZVRr5vlyQdX/I/I+kH+irduqGkY9CwJLK628wpDIo1+fDJgcqHOKPDavAvi3ky8zArOhq7b0XxBToM9gBZ0EzVwxh8EEJUZSmwka7CNLWJayVNhatzYWNMX3DM4C7CehWDB5gvoR4Yl/h0t0JLBmeKz4U+/5s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753221487; c=relaxed/simple; bh=dPokapA0VT0ZnXYTCDP2a7rcIZaZMOL43bSgz1bdtMI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=qD1QVta71htDQQjtvNW46rSQ+i0ddnrMRzbA6U/iRuB2jAwx6QVpd0oQwN1j8t0MwvIkikBfrApGbh/JsgadXr1pv/72aojGxCLfZ0qPrqv/D9rkVSO4T6kMlEpPXkRGaXMF3mDwRrM1yDar6qWvtouerD+4JedaqKqJQZlrUZ4= 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=1fV7J+vD; arc=none smtp.client-ip=209.85.216.74 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="1fV7J+vD" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-31202bbaafaso5122815a91.1 for ; Tue, 22 Jul 2025 14:58:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753221485; x=1753826285; 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=/ex2r39vcgr2S7UXWSrh8npW0q87ZA58tBDtcoAjsEk=; b=1fV7J+vDHTqUNZTUd+8ChLp8JZ3q4Wg9F9b7Y1jd1sJQCOjm8nwILHy3cHKeO2Bc7t y3A/ZaUm/D/cEoz9kYenKGYUW5iDBTc0ydcUr5DG+wyQ1n1hYOhymBwOyfKf5n80hX7n oRt4ZMMYLZumHGKqmA23Qbn3yYu+kU5tMDL8qzBVFxcxUAC7fFTp+2xPhZp9vOVtSjKK me695lBOfsvLhc616pbYLOeDvAWipS1hjPkQyXLQchTptBT9EMH1q2sNoHd+F6qodxxr NktkGCWwedFH3jw8yiAkJxd7Y+2/LjYUnfhtk0rdibTCkIZNBrXaRzwQZ4Wlm4D7tTCC D4sg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753221485; x=1753826285; 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=/ex2r39vcgr2S7UXWSrh8npW0q87ZA58tBDtcoAjsEk=; b=HrXeB5NuX7n3xL6fAic6wx46VCssWxtp8UVUi2ZYD6tvmbKwa9Tew+gPdVh2ANMEdL rNd6oCqETKAgZ81ihfCJrIidl0b818V8ytYPQL8JrByNGfKznM3cCT8kMx3IipJ2YG4B SCUfFTQuJOaMRfYluvTmEloVg86GOhZcvRIT2+vyT4t7TBv2ulfQm+ow6TmaUIa3OMu2 14BMYUscCdizUCUyf3tK3Ra06mMRQoUGXHbSRU4CTuGtkqF7NyPgMTpkxR8RrOKeARag 69NuuNlpCmsFqe3AznUbjM/IO7GK1sT517ibg5qMrtw20i0oNOdJxglu2FR3LdxdWkWj BMQw== X-Forwarded-Encrypted: i=1; AJvYcCUhb8YW2ZOZRn4XOVG3Z+eCOQ/D0I6H4FGAfeaEy4tS5xN4UhQKEnn5RVf6r4luMlV/8YPmaNOVl9BnJUM=@vger.kernel.org X-Gm-Message-State: AOJu0Yy3xywHRsM4+OoezMYsofu22JQKQiObHlpEhhc7T8GfyI/jbWvX /nZ1DzurBSrVTn23vS70G/kqOMvzVvEr0Wl7KPsUuJ1W8F646/251V4qswPFYrAtxhjaF/C/iix CfhlGyeI0+g== X-Google-Smtp-Source: AGHT+IFHjCyshWMiMylV9kR4oGPMWesB02y/L8dbpSt1huhYstubrB/LU+NNIVLFr/jyTqh/1k1ekykqex5b X-Received: from pjp6.prod.google.com ([2002:a17:90b:55c6:b0:30e:5bd5:880d]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4fc3:b0:311:9c1f:8524 with SMTP id 98e67ed59e1d1-31e507cdde8mr1232496a91.15.1753221485505; Tue, 22 Jul 2025 14:58:05 -0700 (PDT) Date: Tue, 22 Jul 2025 14:57:52 -0700 In-Reply-To: <20250722215754.672330-1-irogers@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250722215754.672330-1-irogers@google.com> X-Mailer: git-send-email 2.50.0.727.gbf7dc18ff4-goog Message-ID: <20250722215754.672330-2-irogers@google.com> Subject: [PATCH v4 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 | 41 ++++++++++++++++++++++++++++++++++------ 1 file changed, 35 insertions(+), 6 deletions(-) diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h index ff0c06b6513e..9076483c9fbb 100644 --- a/include/vdso/unaligned.h +++ b/include/vdso/unaligned.h @@ -2,14 +2,43 @@ #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 + * __get_unaligned_ctrl_type gives __unqual_scalar_typeof its required + * expression rather than type, a pointer is used to avoid warnings about = mixing + * the use of 0 and NULL. The void* cast silences ubsan warnings. + */ +#define __get_unaligned_t(type, ptr) ({ \ + type *__get_unaligned_ctrl_type __always_unused =3D NULL; \ + __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