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Tue, 26 Jan 2021 21:00:08 +0000 Subject: Re: [PATCH bpf-next 2/3] bpf: Add size arg to build_id_parse function To: Jiri Olsa , Alexei Starovoitov CC: Jiri Olsa , Arnaldo Carvalho de Melo , Alexei Starovoitov , Song Liu , lkml , bpf , Peter Zijlstra , Ingo Molnar , Mark Rutland , Namhyung Kim , Alexander Shishkin , Michael Petlan , Ian Rogers , Stephane Eranian , Alexei Budankov , Andi Kleen , Adrian Hunter References: <20210114134044.1418404-1-jolsa@kernel.org> <20210114134044.1418404-3-jolsa@kernel.org> <19f16729-96d6-cc8e-5bd5-c3f5940365d4@fb.com> <20210114200120.GF1416940@krava> <20210114220234.GA1456269@krava> <5043cef5-eda7-4373-dcb5-546f6192e1a9@fb.com> <20210126205236.GD120879@krava> From: Yonghong Song Message-ID: <9490aa32-ad01-4a55-c2a0-e688226ecc71@fb.com> Date: Tue, 26 Jan 2021 13:00:06 -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: <20210126205236.GD120879@krava> Content-Type: text/plain; charset=utf-8; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?QW51YmZhY1JhdWhXNEdKUDBhcHVlN0N6ak5BeUcyRGNtNU51ODRUL2JNSlFl?= =?utf-8?B?OVBFRUJKRi96dEJieVdiMzFabjBkQUVPdU92MTZZeHRrRzczeGNYc3QrdGQ1?= =?utf-8?B?dnBqNXdlaFA2Y2xqdGRxRGJ4WHQ1eHRtMmkzSmJheS9FQ3lYaEFnVjBIVlBV?= =?utf-8?B?bWdneldrTlNzUkN5YTBoSm9KV0pnUWo4UWtnTzRKcUFzNnZrZ3Zja21UcWN3?= =?utf-8?B?K2V0bFpBa0lXLzJmVkFVaFNHNFd3WkRMc1NsL1NFS2U1SWkxTVNabkxycVhl?= =?utf-8?B?YjFxdnJ5WWZsZlZqb3BzanZSQitiOVdJRDVULzVtQmJYWkZMRHFoWVRuRHo0?= =?utf-8?B?aVc5ekwvOVBjTjBiYXByNmlNcldaUjlEN1pwMjVldXF2TVFtTFk0eTlGc1lo?= =?utf-8?B?NVVBZytwRkZGN0w2Qk0xQUNpZ1BnUXpZbFpOZkg5QlIwamNYbDBFR1BkNVE3?= =?utf-8?B?VGFEZ3JFT2xpcHBZTExlK0M3eU1EbmNMNEhHSUE4VS83ZUVHSTcveTBLNmNr?= =?utf-8?B?QmJZSWEzdURHTG50ZVZUUzh5RmJJYlg4N21zWGRBVWpNYzNtNG80QmJhNDFx?= =?utf-8?B?NnB3SFRpRE0zOFhaREswd2dPK2NOZVR4TzJjcUQvMW5zdEZpVFZOcmtkbHlP?= =?utf-8?B?QjFNU0loa0xndGZPL1N2M2R5NDBGTllZMXM0OFBTRmJHUmZrSGkwNHVsYnJY?= =?utf-8?B?QnI0bmdMUTRmZ0FqQ3VVNngvODBSNjVKenVTVkZBbzlCeSs5Z3FmVjRHTUNm?= =?utf-8?B?NnB6dWNRU25lVm1PVVRJUWZiTlFqa0ltQVJTT1FQQ2NWQTVkT0RjM1BzdmtD?= =?utf-8?B?VythMTNIUW5mblpTdkg5ZGJacW9kZGFMYThmc2svZ1dHdDA0eUdGb05MQ3dq?= =?utf-8?B?eFlsbzErYWN0MFpHMG5rNENYVEZ3Yk5qTWlMdm53Y0prSTV4RVZzRXJWbkox?= =?utf-8?B?V2VtMUh2NEdpL1htaTJvbVo3dnA2blJmdXF0YzFld3A4eEVrTmFQOTN2UUs1?= =?utf-8?B?SThFd2JHWTVuOG1kNW1zTUlSSTRCRmh3b3BSQUVRak56NERnRWdUWWNwRjJU?= =?utf-8?B?Mk1tanYvbHZjRlJXdTdmYTRjRHAxbGRrOTRWS2NXUGVGMjRUM0Ivd2V3VHA4?= =?utf-8?B?ODlLbWZTZnozMXNQS2h2cCt4TkViRkJwaGhLZ3lCU2V0N1lZQm1Ia3ZlQkhW?= =?utf-8?B?bzFaZkxWamVvQXorYmt1S3RxTVRzNFVYTmZBWFpzZDZmbVkzd2JHMWJPZjV2?= =?utf-8?B?aVRnRHBUbzVJUW5CdGFhcmVmNStWaHpOS1BKMU1OcVVsRVY2UERoem5CWHdk?= =?utf-8?B?ZnJsV2ZsTldzNnA2Z04wOVFPcktYb1FQSDhGTW14Z2hBNS9HbHp6bnFpM2sz?= =?utf-8?B?VGRPQVhvcm1yY0xwcXRiaGczVW0rbHJ6ZVFPVjVVdk45WUN2L0pzVkdyUHVJ?= =?utf-8?B?azNtcE5tYVNIaWtVd1BadUQ2SVhQdnFaZEdBVWRDMXZkUGRlbFhHUGZGN1lO?= =?utf-8?Q?oA2U9Q=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: a3d39aa7-3002-48a9-fa40-08d8c23d5d10 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2021 21:00:08.5231 (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: 7vejVjcmaSj/KQqttAvSPlEYsckGcbupqTy0dAyQR+gGQyoGk39KD06a9T9ryFFo X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2456 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-26_11:2021-01-26,2021-01-26 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 priorityscore=1501 spamscore=0 clxscore=1015 bulkscore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101260109 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/26/21 12:52 PM, Jiri Olsa wrote: > On Thu, Jan 14, 2021 at 07:47:20PM -0800, Alexei Starovoitov wrote: >> On Thu, Jan 14, 2021 at 3:44 PM Yonghong Song wrote: >>> >>> >>> >>> On 1/14/21 2:02 PM, Jiri Olsa wrote: >>>> On Thu, Jan 14, 2021 at 01:05:33PM -0800, Yonghong Song wrote: >>>>> >>>>> >>>>> On 1/14/21 12:01 PM, Jiri Olsa wrote: >>>>>> On Thu, Jan 14, 2021 at 10:56:33AM -0800, Yonghong Song wrote: >>>>>>> >>>>>>> >>>>>>> On 1/14/21 5:40 AM, Jiri Olsa wrote: >>>>>>>> It's possible to have other build id types (other than default SHA1). >>>>>>>> Currently there's also ld support for MD5 build id. >>>>>>> >>>>>>> Currently, bpf build_id based stackmap does not returns the size of >>>>>>> the build_id. Did you see an issue here? I guess user space can check >>>>>>> the length of non-zero bits of the build id to decide what kind of >>>>>>> type it is, right? >>>>>> >>>>>> you can have zero bytes in the build id hash, so you need to get the size >>>>>> >>>>>> I never saw MD5 being used in practise just SHA1, but we added the >>>>>> size to be complete and make sure we'll fit with build id, because >>>>>> there's only limited space in mmap2 event >>>>> >>>>> I am asking to check whether we should extend uapi struct >>>>> bpf_stack_build_id to include build_id_size as well. I guess >>>>> we can delay this until a real use case. >>>> >>>> right, we can try make some MD5 build id binaries and check if it >>>> explodes with some bcc tools, but I don't expect that.. I'll try >>>> to find some time for that >>> >>> Thanks. We may have issues on bcc side. For build_id collected in >>> kernel, bcc always generates a length-20 string. But for user >>> binaries, the build_id string length is equal to actual size of >>> the build_id. They may not match (MD5 length is 16). >>> The fix is probably to append '0's (up to length 20) for user >>> binary build_id's. >>> >>> I guess MD5 is very seldom used. I will wait if you can reproduce >>> the issue and then we might fix it. >> >> Indeed. >> Jiri, please check whether md5 is really an issue. >> Sounds like we have to do something on the kernel side. >> Hopefully zero padding will be enough. >> I would prefer to avoid extending uapi struct to cover rare case. > > build_id_parse is already doing the zero padding, so we are ok > > I tried several bcc tools over perf bench with md5 buildid and > the results looked ok Great. Thanks for confirmation! > > jirka >