From mboxrd@z Thu Jan 1 00:00:00 1970 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 6391DCCA485 for ; Mon, 13 Jun 2022 10:49:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346200AbiFMKsn (ORCPT ); Mon, 13 Jun 2022 06:48:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245056AbiFMKli (ORCPT ); Mon, 13 Jun 2022 06:41:38 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5601122BE0; Mon, 13 Jun 2022 03:23:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 14E26B80E90; Mon, 13 Jun 2022 10:23:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B646C34114; Mon, 13 Jun 2022 10:23:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655115833; bh=ZFNXhbHfbocFCUSfvXMVgWSinwDEA9oa7M4fSnZ4Qwg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eQ0XXlT9+Pinjq/Y/lCee3zJX3inHx9+AoLgIRqXt2sLbu+JtxVAlATjbTyBJ/23c Lqa4luLcvak4i3Re1kF0sSGzgkGCTq9qwRbJxIrRO6mhlbu2HTTIz9QcW94d9F+/xh e8NQRWAATBJ9gXFg2tREo0nvZHdE+ESF+IaLVaIs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sudip Mukherjee , Arnd Bergmann , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Linus Torvalds , Sasha Levin Subject: [PATCH 4.14 047/218] drm: fix EDID struct for old ARM OABI format Date: Mon, 13 Jun 2022 12:08:25 +0200 Message-Id: <20220613094919.530639897@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220613094908.257446132@linuxfoundation.org> References: <20220613094908.257446132@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds [ Upstream commit 47f15561b69e226bfc034e94ff6dbec51a4662af ] When building the kernel for arm with the "-mabi=apcs-gnu" option, gcc will force alignment of all structures and unions to a word boundary (see also STRUCTURE_SIZE_BOUNDARY and the "-mstructure-size-boundary=XX" option if you're a gcc person), even when the members of said structures do not want or need said alignment. This completely messes up the structure alignment of 'struct edid' on those targets, because even though all the embedded structures are marked with "__attribute__((packed))", the unions that contain them are not. This was exposed by commit f1e4c916f97f ("drm/edid: add EDID block count and size helpers"), but the bug is pre-existing. That commit just made the structure layout problem cause a build failure due to the addition of the BUILD_BUG_ON(sizeof(*edid) != EDID_LENGTH); sanity check in drivers/gpu/drm/drm_edid.c:edid_block_data(). This legacy union alignment should probably not be used in the first place, but we can fix the layout by adding the packed attribute to the union entries even when each member is already packed and it shouldn't matter in a sane build environment. You can see this issue with a trivial test program: union { struct { char c[5]; }; struct { char d; unsigned e; } __attribute__((packed)); } a = { "1234" }; where building this with a normal "gcc -S" will result in the expected 5-byte size of said union: .type a, @object .size a, 5 but with an ARM compiler and the old ABI: arm-linux-gnu-gcc -mabi=apcs-gnu -mfloat-abi=soft -S t.c you get .type a, %object .size a, 8 instead, because even though each member of the union is packed, the union itself still gets aligned. This was reported by Sudip for the spear3xx_defconfig target. Link: https://lore.kernel.org/lkml/YpCUzStDnSgQLNFN@debian/ Reported-by: Sudip Mukherjee Acked-by: Arnd Bergmann Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Daniel Vetter Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- include/drm/drm_edid.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h index 267e0426c479..0262e32ab59e 100644 --- a/include/drm/drm_edid.h +++ b/include/drm/drm_edid.h @@ -115,7 +115,7 @@ struct detailed_data_monitor_range { u8 supported_scalings; u8 preferred_refresh; } __attribute__((packed)) cvt; - } formula; + } __attribute__((packed)) formula; } __attribute__((packed)); struct detailed_data_wpindex { @@ -148,7 +148,7 @@ struct detailed_non_pixel { struct detailed_data_wpindex color; struct std_timing timings[6]; struct cvt_timing cvt[4]; - } data; + } __attribute__((packed)) data; } __attribute__((packed)); #define EDID_DETAIL_EST_TIMINGS 0xf7 @@ -166,7 +166,7 @@ struct detailed_timing { union { struct detailed_pixel_timing pixel_data; struct detailed_non_pixel other_data; - } data; + } __attribute__((packed)) data; } __attribute__((packed)); #define DRM_EDID_INPUT_SERRATION_VSYNC (1 << 0) -- 2.35.1