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Sun, 17 Jan 2021 02:03:40 +0000 Subject: Re: [PATCH v2 bpf-next 1/2] trace: bpf: Allow bpf to attach to bare tracepoints To: Qais Yousef , , CC: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Steven Rostedt , "Peter Zijlstra (Intel)" , References: <20210116182133.2286884-1-qais.yousef@arm.com> <20210116182133.2286884-2-qais.yousef@arm.com> From: Yonghong Song Message-ID: <2e63b638-1500-c323-0fec-1aecfef5f033@fb.com> Date: Sat, 16 Jan 2021 18:03:37 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: <20210116182133.2286884-2-qais.yousef@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:a571] X-ClientProxiedBy: CO2PR04CA0135.namprd04.prod.outlook.com (2603:10b6:104::13) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21c8::1366] (2620:10d:c090:400::5:a571) by CO2PR04CA0135.namprd04.prod.outlook.com (2603:10b6:104::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3763.11 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?bTVNVzZMSHhmMndJeG5HMmJ1a2RnRzlDaXlWZXV0MURaekFwb1J1aUkxS3do?= =?utf-8?B?ZFdSVFlTcjB6M2RIekVOdDVrakV5dWFDS0xqZ3BiaE5nSU1nMW10cWhCSHRK?= =?utf-8?B?YzZvRFBGVjBleGVEL1RUc1Q5L1lhbW9PWkhONDFLaW54YmVCMitpNmNnS3Np?= =?utf-8?B?TFpCaExkMGR4M0xmRXhjSGRsajY2aUtIVnNoc0k1SWZIS1pQOU9pRXNwQVQz?= =?utf-8?B?eFB4SWdMUkpyMGxFZ1lnSnVoRlRWTzcrWTZJandGaGJkYVJ3d1dGb1JVdU1l?= =?utf-8?B?MEtrWmNGRFBiRDUxcENaTkJzUktlbVVTbHkwSlhYalBSNU51djNlaTBQSmdI?= =?utf-8?B?NHpzMHpJMFg0YmUySFhMQndGdGZNWWZ0RmpBUGVDRjIrcDBHcVdOV0krSHJM?= =?utf-8?B?SklsZHdSYmhwamNDYTlzem1hVDNoMFZ6VGh2ZTh2N3QydEtzUnlLNmpWY1Jv?= =?utf-8?B?RmozYjVTZXRCbmE3Mng0NEI4U2FENnlSYXRseUJZeiszZTJQUWxUZVJkMGx0?= =?utf-8?B?eW52UHBUYTg0TVl6cS9vd2tRck5yeTNHK0I3MUYxZmgxWWhkZENXMHZCMjdr?= =?utf-8?B?ZHI0a0wvV3FXeTY3YnFWUFozQithdHZvNDM0WE9KVkhreHNvVnBmaUVUY29s?= =?utf-8?B?K2t1N1VjMXpxdnliYVJoa0RSL0VnWGg2OGpvTkc1M0x1MUdQdGc1eGhVQ2Vu?= =?utf-8?B?WUQ4UVJjc2ZUb2JRSVJoMmpoVFVDRHZOZ3hUZzFtS1d6dlI5OGJobFFKWXpx?= =?utf-8?B?TFJ5L3NpUGRRVGlnQ2pqMlFDTVQvam9sVDZmQWNtN01hTFlVOEZLeVdXMFRq?= =?utf-8?B?R3FyS1JCNDZFaDBpZXYzR2FRdWZVYThIY0xOSnd4UmJSeVZiN1NEOU1kQ2ti?= =?utf-8?B?Ti8wakhPMnhzMWlIRU8yWks3SlpHeGRBUDdaOGhzNkJnZ3MxTWlwMUx2ZUE4?= =?utf-8?B?VHhvT0F0ZjlwWlN6emtURXBOTVZVZTBKd3hmdjBsSjd1SFc1RmdpMmxqbjV5?= =?utf-8?B?VlpjOUFMVUwxQmQ1KzBPeFBYSDFwYTQ2V2ZPcUxHZXd3WHlZWExXVHJxMkc3?= =?utf-8?B?SHNydTFnTjdEeUl0MWNJYzd6c1h4QXcvNW9IRERjL1hicXpGdGFtMTRWaHA3?= =?utf-8?B?VnRjRnRJR281UEZMSjg5UVB6Qi9rWCtmRmdKa1BGRUMydEljRWNZNzRMUURi?= =?utf-8?B?ODYzNFA1SGlscHZQT2lENDgzclFtSjNQdm9ITjJMdVZqRGRVSENuOFdLdUxK?= =?utf-8?B?WFhpVlZjcFV1Qmc3aUU4V3ZzSDZJVlJWOXlsR2djcXJVQ3ZuczJSakc1Tjhy?= =?utf-8?B?Tm1oUXhuemFtTStoaC9scXNpZjY4alhmb3QwYUZVQ204OXZiUXYvMHlFbEZF?= =?utf-8?B?TEYxS0Q0VXYyQXc9PQ==?= X-MS-Exchange-CrossTenant-Network-Message-Id: b5a6c00a-aa24-4f8c-418e-08d8ba8c1bd8 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jan 2021 02:03:40.1168 (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: 5aycdIf4YUsluPNTPXlvM19D9U6mJpCLNV6M5k4PHIrHKnYASFYyeKOvEDd+d8bu X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR15MB3714 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-16_16:2021-01-15,2021-01-16 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 malwarescore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=728 spamscore=0 suspectscore=0 phishscore=0 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101170011 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 1/16/21 10:21 AM, Qais Yousef wrote: > Some subsystems only have bare tracepoints (a tracepoint with no > associated trace event) to avoid the problem of trace events being an > ABI that can't be changed. > > From bpf presepective, bare tracepoints are what it calls > RAW_TRACEPOINT(). > > Since bpf assumed there's 1:1 mapping, it relied on hooking to > DEFINE_EVENT() macro to create bpf mapping of the tracepoints. Since > bare tracepoints use DECLARE_TRACE() to create the tracepoint, bpf had > no knowledge about their existence. > > By teaching bpf_probe.h to parse DECLARE_TRACE() in a similar fashion to > DEFINE_EVENT(), bpf can find and attach to the new raw tracepoints. > > Enabling that comes with the contract that changes to raw tracepoints > don't constitute a regression if they break existing bpf programs. > We need the ability to continue to morph and modify these raw > tracepoints without worrying about any ABI. > > Update Documentation/bpf/bpf_design_QA.rst to document this contract. > > Signed-off-by: Qais Yousef Acked-by: Yonghong Song