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X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?41GVSzO+FgPntlzx6wlDD7FDImo+XIoAsxzKAGIUX2IV0S4iplELSd5fQySE?= =?us-ascii?Q?5Shnnmu6lWBJmA4MFlrFMmTOXjTVcdZdfvdWs1jael2Oy/hQyWafd3IIYJGT?= =?us-ascii?Q?eNcT6gT0WLP+Sjcct4koeqBmCKU9UGVLXHanJkp01pFjJUjKsO0tm+Y35mYB?= =?us-ascii?Q?IHGVt/iThlLRc5pZttrP+IQnLMl6/23eeSwZt8F0H/WShsZpeMf/kg8RslxD?= =?us-ascii?Q?XoHUdHY1Nh4Mmt0lbJ9S39xtvXZGOgm3/d8UkgoePrBg7NV67nTHuO77mAx+?= =?us-ascii?Q?Ndje3fA1NUbDp08HjX5JohnQfDVN4OL9UfO33jZck1izDhXGe17SYo+BQ/Rs?= =?us-ascii?Q?ZuomRGMnySVaFVqkdhEBh19c27nMLQE4xV0tswzdCByOopwOkcjHP5q2uggy?= =?us-ascii?Q?bEOlM+PaknHkE4pRCqL+QdFe0eMtsYGu41mJAfRe0xFRZ8SnrgLqJYtsoNHN?= =?us-ascii?Q?INXw0OTVgyLP+FE8eQ5aoWIU49gsRtsB5+BLAx+vVk6lUC7nJRl4SG1me2wg?= =?us-ascii?Q?wkWu9W/SeqqoKgyy1ZBSWI4wXSAwo7sXl1w+yfInR8wAfaBeuxgREzv7Qebv?= =?us-ascii?Q?glL+bu0obG1cB/8EMHbhkc14fnqeX12VU3IEJM7jsiIokWd8OWBHfinH2HVa?= =?us-ascii?Q?fw5S8LR91Qf6FtmJZKo4AQRXhW8d3vj/Hks9JFOyksIcsuU3Nzhd8M/SvsyW?= =?us-ascii?Q?sdVejjmbWhnw5TEAnAXNTS0CmSnJ/JtNM5fVSmA8aTMY3yQXzh1bH+Ob2h5L?= =?us-ascii?Q?OSSND47NeTLnwxUS2NQbKuE2GbA6MgUtKc4W0WKbmAwcHqiY/vrBejk6+apG?= =?us-ascii?Q?dFRR+gJcjTFkpnU3yZzSpMHm7lYpaBcRxqTMtE8rJdScqID+A66WCQr7BZCt?= =?us-ascii?Q?zUPDgN9hOj/MG4aNg/BR9IqAY8SbFyL7aAkJkZfv9zEnme0ID3ZORZPe6vSm?= =?us-ascii?Q?a5ugHiznXeUUfz2SUg2tBsLfFwIN78iE2LAiLHTTGv9CW+W0N/RnaJESbgkO?= =?us-ascii?Q?Hz6EVsBnnZu7yAxapjtBplo+whLr8eqZVnef94V3iCybqGqxallLypQwz8sD?= =?us-ascii?Q?D2vkB6lwsKMrtHVM6LyeDbz4CbOxQ2bfunwGORnmVZFi5YBkShDXnDgPDYdQ?= =?us-ascii?Q?nBxXWwczAgINP28fxV6uOaffqQbu9VhPlEg7vkYsEsDNXlikuUv/NMBmKRBG?= =?us-ascii?Q?T2WQpV6rd17KLHkWfKusophFVPXIz/SiBOsRlbs13ioUqgKg5LfYkTmpsaWk?= =?us-ascii?Q?qe62a4A1lYeC85gY021bVokWtj6nydi9mARTNinGS7fD7TapPenG2h+ybCNx?= =?us-ascii?Q?yGQOiWG3s4+G/gY8mGDGxh4A4wcNTTOtJNJrk6+tiHDmug=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 67db12cf-4148-4249-09fe-08d8edb7d79a X-MS-Exchange-CrossTenant-AuthSource: BY5PR15MB3571.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Mar 2021 04:55:12.6808 (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: iYbqP/BA6V6wyQqcTRvN7fA+EzZKe1IlDOl1vBOQSob9LHdFeaOfBDrkS+w3Wf3c X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2951 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-03-23_01:2021-03-22,2021-03-23 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 phishscore=0 priorityscore=1501 clxscore=1015 mlxlogscore=999 suspectscore=0 adultscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2103230032 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sat, Mar 20, 2021 at 10:18:36AM -0700, Andrii Nakryiko wrote: > > From test_ksyms.c: > > [22] DATASEC '.ksyms' size=0 vlen=5 > > type_id=12 offset=0 size=1 > > type_id=13 offset=0 size=1 > > > > For extern, does it make sense for the libbpf to assign 0 to > > both var offset and size since it does not matter? > > That's how it is generated and yes, I think that's how it should be > kept once kernel supports EXTERN VAR. libbpf is adjusting offsets and > sizes in addition to marking VAR itself as GLOBAL_ALLOCATED. If kernel > supports EXTERN VAR natively, none of that needs to happen (on newer > kernels only, of course). > > > In the kernel, it can ensure a datasec only has all extern or no extern. > > array_map_check_btf() will ensure the datasec has no extern. > > It certainly makes it less surprising from handling BTF, but it feels > like an arbitrary policy, rather than technical restriction. You can > mark allocated variables and externs with the same section name and > Clang will probably happily generate a single DATASEC with a mix of > externs and non-externs. Is that inherently a bad thing? I'm not sure. > Basically, I don't know if the kernel should care and enforce or not. I have thought a bit more on this. The offset=0 of extern var can be used in the verification but I think it will still have some open ended questions like arraymap. I will use your suggestion in libbpf and do something similar as the extern VAR: replace the FUNC in datasec with INT (btf__add_var() if needed). > > > > > > But of course to support older kernels libbpf will still have to > > > do this. EXTERN vars won't reduce the amount of libbpf logic.