From patchwork Mon Mar 27 17:41:38 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Moon X-Patchwork-Id: 13189750 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 BB119C76195 for ; Mon, 27 Mar 2023 17:42:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229631AbjC0RmZ (ORCPT ); Mon, 27 Mar 2023 13:42:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229452AbjC0RmY (ORCPT ); Mon, 27 Mar 2023 13:42:24 -0400 Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6159B10EA; Mon, 27 Mar 2023 10:42:23 -0700 (PDT) Received: from pps.filterd (m0279873.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 32RALBNT011118; Mon, 27 Mar 2023 17:41:56 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h=from : to : cc : subject : date : message-id : mime-version : content-type; s=qcppdkim1; bh=gd41agZAFBrdyQ2rYAAIcve8FqL8Ny9Ztm92PCMYCcc=; b=A4maCPUU3qlFoV9QJps+26IR6R0KD4LANM2F+gsNUa/MxYYvM9MpvzBnXOLx+CV25mDK GWkKe2LCRHwNNRmBLNeIyp6iLl6T6UVyydtADfPWJMpAaMcxJIEvGnD/7X1p7tSmrMA/ 67YTr8SeR95hWJjtzFk5+P8cE5ptaNaZtSJp7nDWIvv+9u4E2eenBOjMVRqchrg0NE/h 7iLtgibGczsVZPKATf39luFXknaTFRoyF33u3jcwO9JHxCyUP4z2BM5RE/MLXqu+Asnx NByjUpxmsHgaTF/uVA3uKc2Sf8tZGI5sYdliKqz6vL5q+Zn8JlJWOsgWlHEJ1ESt5C80 pg== Received: from nalasppmta05.qualcomm.com (Global_NAT1.qualcomm.com [129.46.96.20]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3pk53yhr43-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 27 Mar 2023 17:41:56 +0000 Received: from nalasex01c.na.qualcomm.com (nalasex01c.na.qualcomm.com [10.47.97.35]) by NALASPPMTA05.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 32RHftJN032624 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 27 Mar 2023 17:41:55 GMT Received: from hu-johmoo-lv.qualcomm.com (10.49.16.6) by nalasex01c.na.qualcomm.com (10.47.97.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.41; Mon, 27 Mar 2023 10:41:54 -0700 From: John Moon To: Masahiro Yamada , Nathan Chancellor , Nick Desaulniers , "Nicolas Schier" CC: John Moon , , , , , Greg Kroah-Hartman , Randy Dunlap , "Arnd Bergmann" , Bjorn Andersson , Todd Kjos , Matthias Maennich , Giuliano Procida , , , Jordan Crouse , Trilok Soni , Satya Durga Srinivasu Prabhala , Elliot Berman , "Guru Das Srinagesh" Subject: [PATCH v4 0/2] Validating UAPI backwards compatibility Date: Mon, 27 Mar 2023 10:41:38 -0700 Message-ID: <20230327174140.8169-1-quic_johmoo@quicinc.com> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01b.na.qualcomm.com (10.47.209.197) To nalasex01c.na.qualcomm.com (10.47.97.35) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: hXteiBBLw_53QzlszTJKScp2GjLA9o9y X-Proofpoint-ORIG-GUID: hXteiBBLw_53QzlszTJKScp2GjLA9o9y X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-24_11,2023-03-27_02,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 mlxlogscore=999 spamscore=0 clxscore=1015 impostorscore=0 phishscore=0 malwarescore=0 adultscore=0 bulkscore=0 suspectscore=0 priorityscore=1501 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2303270144 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org The kernel community has rigorously enforced a policy of backwards compatibility in its UAPI headers for a long time. This has allowed user applications to enjoy stability across kernel upgrades without recompiling. Our goal is to add tooling and documentation to help kernel developers maintain this stability. We see in the kernel documentation: "Kernel headers are backwards compatible, but not forwards compatible. This means that a program built against a C library using older kernel headers should run on a newer kernel (although it may not have access to new features), but a program built against newer kernel headers may not work on an older kernel."[1] How does the kernel community enforce this guarantee? As we understand it, it's enforced with thorough code review and testing. Is there any tooling outside of this being used to help the process? Also, could documentation on UAPI maintenance (from a developer's point of view) be expanded? Internally, we have a set of guidelines for our kernel developers regarding UAPI compatibility techniques. If there's interest in supplying a document on this topic with the kernel, we'd be happy to submit a draft detailing what we have so far as a jumping off point. In terms of tooling, I've attached a shell script we've been using internally to validate backwards compatibility of our UAPI headers. The script uses libabigail's[2] tool abidiff[3] to compare a modified header's ABI before and after a patch is applied. If an existing UAPI is modified, the script exits non-zero. We use this script in our continuous integration system to block changes that fail the check. It generates output like this when a backwards-incompatible change is made to a UAPI header: !!! ABI differences detected in include/uapi/linux/bpf.h from HEAD~1 -> HEAD !!! [C] 'struct bpf_insn' changed: type size hasn't changed 1 data member change: type of '__s32 imm' changed: typedef name changed from __s32 to __u32 at int-ll64.h:27:1 underlying type 'int' changed: type name changed from 'int' to 'unsigned int' type size hasn't changed We wanted to share this script with the community and hopefully also receive general feedback when it comes to tooling/policy surrounding this issue. Our hope is that the script will help kernel UAPI authors maintain good discipline and avoid breaking userspace. In v4, we've updated the script to operate exclusively on the trees generated by "make headers_install" at the two git references. This catches several classes of false negatives brought up in earlier revisions. Thanks for the helpful reviews of previous revs! We're looking forward to any additional feedback you may have on v4. [1] Documentation/kbuild/headers_install.rst [2] https://sourceware.org/libabigail/manual/libabigail-overview.html [3] https://sourceware.org/libabigail/manual/abidiff.html P.S. While at Qualcomm, Jordan Crouse authored the original version of the UAPI checker script. Thanks Jordan! John Moon (2): check-uapi: Introduce check-uapi.sh docs: dev-tools: Add UAPI checker documentation Documentation/dev-tools/checkuapi.rst | 479 +++++++++++++++++++++++++ Documentation/dev-tools/index.rst | 1 + scripts/check-uapi.sh | 490 ++++++++++++++++++++++++++ 3 files changed, 970 insertions(+) create mode 100644 Documentation/dev-tools/checkuapi.rst create mode 100755 scripts/check-uapi.sh base-commit: e76db6e50c85cce9e68c47076f8eab06189fe4db --- 2.17.1