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Wed, 12 Aug 2020 15:26:43 +0000 From: Song Liu To: Jiri Olsa CC: Alexei Starovoitov , Daniel Borkmann , "netdev@vger.kernel.org" , "bpf@vger.kernel.org" , Martin Lau , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh Subject: Re: [RFC PATCH bpf-next] bpf: Iterate through all PT_NOTE sections when looking for build id Thread-Topic: [RFC PATCH bpf-next] bpf: Iterate through all PT_NOTE sections when looking for build id Thread-Index: AQHWcKR6wbf6sGirtEeRTemTlUmcHak0mKwA Date: Wed, 12 Aug 2020 15:26:43 +0000 Message-ID: <5238E896-6A88-4857-B8D4-3C2E8C4E9F2C@fb.com> References: <20200812123102.20032-1-jolsa@kernel.org> In-Reply-To: <20200812123102.20032-1-jolsa@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.80.23.2.2) authentication-results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=fb.com; x-originating-ip: [2620:10d:c090:400::5:8f7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 99835a5f-aca8-48b2-a8c7-08d83ed41e46 x-ms-traffictypediagnostic: BYAPR15MB2646: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:5797; 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charset="us-ascii" Content-ID: <9B764552574D7344BE012B98C9CCD7B6@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB2999.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 99835a5f-aca8-48b2-a8c7-08d83ed41e46 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Aug 2020 15:26:43.3512 (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: t8xHvQoJK2QeI5p47ASwgIE5Gbc7MPfYsAAwhqrW2kqtRnIpTedzkxGLCPw4hnAlqcnRORfVj3428pacR87S5A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2646 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-08-12_09:2020-08-11,2020-08-12 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 impostorscore=0 adultscore=0 mlxscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 mlxlogscore=999 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008120107 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > On Aug 12, 2020, at 5:31 AM, Jiri Olsa wrote: >=20 > Currently when we look for build id within bpf_get_stackid helper > call, we check the first NOTE section and we fail if build id is > not there. >=20 > However on some system (Fedora) there can be multiple NOTE sections > in binaries and build id data is not always the first one, like: >=20 > $ readelf -a /usr/bin/ls > ... > [ 2] .note.gnu.propert NOTE 0000000000000338 00000338 > 0000000000000020 0000000000000000 A 0 0 8358 > [ 3] .note.gnu.build-i NOTE 0000000000000358 00000358 > 0000000000000024 0000000000000000 A 0 0 437c > [ 4] .note.ABI-tag NOTE 000000000000037c 0000037c > ... >=20 > So the stack_map_get_build_id function will fail on build id retrieval > and fallback to BPF_STACK_BUILD_ID_IP. >=20 > This patch is changing the stack_map_get_build_id code to iterate > through all the NOTE sections and try to get build id data from > each of them. >=20 > When tracing on sched_switch tracepoint that does bpf_get_stackid > helper call kernel build, I can see about 60% increase of successful > build id retrieval. The rest seems fails on -EFAULT. >=20 > Signed-off-by: Jiri Olsa LGTM. Thanks for the fix! Acked-by: Song Liu