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BLAPR10MB5267.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Jan 2023 23:15:16.2792 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: jmvtXOsmi3Yffqii+Qq/Fws9Q+VKqAMdpEFrhJxeQGPnIM66p/wT6Xs0t0lXiA0NwFX5O7u1sRfhP8u1L6/erQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR10MB4281 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-01-24_17,2023-01-24_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 spamscore=0 phishscore=0 suspectscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2301240214 X-Proofpoint-GUID: E2kiWOPmxrtojft0Jv6vMNd9dKnNgZCk X-Proofpoint-ORIG-GUID: E2kiWOPmxrtojft0Jv6vMNd9dKnNgZCk Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 24/01/2023 18:26, Kui-Feng Lee wrote: > On 1/23/23 16:21, Jason Ling wrote: >> Some context: >> >> The devices I am interested in have a small kernel partition (~16MB). >> Building the kernel with CONFIG_DEBUG_INFO_BTF=y increases the kernel >> size by about ~1.7M. Would it help in this environment if vmlinux BTF was in a module? I've been exploring supporting CONFIG_DEBUG_INFO_BTF=m which would involve having a vmlinux_btf module that could be loaded on demand. Alan >> So I've tried to use an external BTF (generating my own vmlinux BTF >> and placing it on a more spacious partition) but it seems like my >> eBPFs that attach to fexit hooks now fail loading. According to some >> comments in libbpf this seems to be expected. >> >> e.g an eBPF program that looks like this >> >> SEC("fexit/ksys_unshare") >> int BPF_PROG(handle_exit, unsigned long unshare_flags, int rv) { >> } >> >> fails the loading process. >> >> >> My guess is that there is additional debug/BTF information beyond what >> is available in vmlinux BTF that gets linked into vmlinuz and without >> this information the attaching to certain hooks fail. > > IIRC, the verifier running in the kernel also needs BTF to verify the code. > > That means you need a way to load BTF to kernel manually as well. > > >> >> So my question is: >> >> is there a way to achieve my goal of using a kernel that has been >> built with CONFIG_DEBUG_INFO_BTF=n and still be able to use >> fentry/fexit type hooks?