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Thu, 20 Aug 2020 17:54:35 +0000 Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong alignment To: Mark Wielaard , =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= , Jiri Olsa CC: Nick Desaulniers , Alexei Starovoitov , Daniel Borkmann , Nick Clifton , Jesper Dangaard Brouer , Network Development , bpf , Martin KaFai Lau , Song Liu , Andrii Nakryiko , John Fastabend , KP Singh , clang-built-linux References: <20200819092342.259004-1-jolsa@kernel.org> <254246ed-1b76-c435-a7bd-0783a29094d9@fb.com> <20200819173618.GH177896@krava> <2e35cf9e-d815-5cd7-9106-7947e5b9fe3f@fb.com> <5ef90a283aa2f68018763258999fa66cd34cb3bb.camel@klomp.org> <7029ff8f-77d3-584b-2e7e-388c001cd648@fb.com> From: Yonghong Song Message-ID: <35b05eda-f76a-a071-d69e-9ba8c6f48382@fb.com> Date: Thu, 20 Aug 2020 10:54:29 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MN2PR16CA0032.namprd16.prod.outlook.com (2603:10b6:208:134::45) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from 255.255.255.255 (255.255.255.255) by MN2PR16CA0032.namprd16.prod.outlook.com (2603:10b6:208:134::45) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3305.24 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 1244b5aa-96c1-4bc2-f481-08d84532198d X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Aug 2020 17:54:35.4898 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ojzU6FNsC5rLeQi63O+QOllswYClNza7AVrCFbHeuXvv/bJFOXoQjrZ8t1uTN6Su X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2198 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-08-20_03:2020-08-19,2020-08-20 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 spamscore=0 impostorscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 mlxscore=0 clxscore=1015 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008200145 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 8/20/20 10:36 AM, Mark Wielaard wrote: > Hi > > On Thu, 2020-08-20 at 08:51 -0700, Yonghong Song wrote: >>>> Do you think we could skip these .debug_* sections somehow in elf >>>> parsing in resolve_btfids? resolve_btfids does not need to read >>>> these sections. This way, no need to change their alignment >>>> either. >>> >>> The issue is that elfutils libelf will not allow writing out the >>> section when it notices the sh_addralign field is setup wrongly. >> >> Maybe resolve_btfids can temporarily change sh_addralign to 4/8 >> before elf manipulation (elf_write) to make libelf happy. >> After all elf_write is done, change back to whatever the >> original value (1). Does this work? > > Unfortunately no, because there is no elf_write, elf_update is how you > write out the ELF image to disc. > > Since the code is using ELF_F_LAYOUT this will not change the actual > layout of the ELF image if that is what you are worried about. > > And the workaround to set sh_addralign correctly before calling > elf_update is precisely what the fix in elfutils libelf will do itself > in the next release. Also binutils ld has been fixed to setup > sh_addralign to 4/8 as appropriate now (in git). Sounds good then. Thanks for fixing the issue in upstream, both libelf and binutils! > > Cheers, > > Mark >