From patchwork Fri Apr 7 20:34:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Moon X-Patchwork-Id: 55670 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id E59E83857713 for ; Fri, 7 Apr 2023 20:35:45 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E59E83857713 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1680899745; bh=RnM21H93KsCfKYDZySXqH9aFxlviESAjiVNz4+3cpTA=; h=To:CC:Subject:Date:List-Id:List-Unsubscribe:List-Archive: List-Help:List-Subscribe:From:Reply-To:From; b=Wo6P/8rKXFRsEzcPr3W5S4+ZYKaxmlcNhnZ9VvIXc99bRmSQfdtIyVNaRhgF9BCuj u7ouNaTEK8nKRYuONg7N9MDdTzZ7if6Hvm7aaJxf51lUP/OKC6UYD35vEVM0OlqOFV 5bDC+61MMKtmYlID4/K5P50b4vPvHix1h/TiWbAY= X-Original-To: libabigail@sourceware.org Delivered-To: libabigail@sourceware.org Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) by sourceware.org (Postfix) with ESMTPS id 2C3B73858D35 for ; Fri, 7 Apr 2023 20:35:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 2C3B73858D35 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 337KZJv0010775; Fri, 7 Apr 2023 20:35:19 GMT Received: from nalasppmta05.qualcomm.com (Global_NAT1.qualcomm.com [129.46.96.20]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3psv4dm47x-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 07 Apr 2023 20:35:19 +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 337KZI46014700 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 7 Apr 2023 20:35:18 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 15.2.986.42; Fri, 7 Apr 2023 13:35:17 -0700 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 v5 0/2] Validating UAPI backwards compatibility Date: Fri, 7 Apr 2023 13:34:54 -0700 Message-ID: <20230407203456.27141-1-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: nmIcOJr4FzDw2GJLhfO-FOoFk4ib5q4w X-Proofpoint-ORIG-GUID: nmIcOJr4FzDw2GJLhfO-FOoFk4ib5q4w 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=2023-04-07_13,2023-04-06_03,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 impostorscore=0 mlxscore=0 lowpriorityscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 spamscore=0 mlxlogscore=954 phishscore=0 bulkscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304070184 X-Spam-Status: No, score=-5.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libabigail@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Mailing list of the Libabigail project List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-Patchwork-Original-From: John Moon via Libabigail From: John Moon Reply-To: John Moon Errors-To: libabigail-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libabigail" 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 v5, we've made a few code quality improvements based on review feedback. Thanks! [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 | 480 +++++++++++++++++++++++++ Documentation/dev-tools/index.rst | 1 + scripts/check-uapi.sh | 489 ++++++++++++++++++++++++++ 3 files changed, 970 insertions(+) create mode 100644 Documentation/dev-tools/checkuapi.rst create mode 100755 scripts/check-uapi.sh base-commit: f2afccfefe7be1f7346564fe619277110d341f9b --- 2.17.1