> > On Fri, Jun 11, 2021 at 12:49 AM rainkin <rainkin1993@xxxxxxxxx> wrote: > > > > Hi, > > > > I try to run libbpf + CO-RE in old kernels (i.e., 4.19 here). > > I follow the discussion in this thread > > https://lore.kernel.org/bpf/CADmGQ+1euj7Uv9e8UyZMMXDiYAKqXe9=GSTBFNbbg1E0R-ejyg@xxxxxxxxxxxxxx/ > > and successfully run a binary which compiled in kernel v5.8 in old kernel 4.19. > > > > Basically, I just compile the linux kernel 4.19 source code and run > > pahole -J to generate a vmlinux containing .BTF sections. > > Then I copy this vmlinux file in kernel v4.19 /boot/vmlinux-xxx where > > libbpf will search vmlinux. > > You've probably also seen the discussion in that thread to make such > use case better supported through libbpf API directly without you > needing to put that vmlinux BTF in a special place. If you have such > use case, please consider contributing necessary fixes. Thanks! > > > Finally, I run the eBPF compiled binary and it works perfectly (I can > > get all the data I want). > > > > However, I find some error message shown by libbpf > > e.g., > > libbpf: Error loading BTF: Invalid argument(22) > > libbpf: magic: 0xeb9f > > ... > > [10] Invalid btf_info:840000ad > > libbpf: Error loading .BTF into kernel: -22. BTF is optional, ignoring. > > > > Although such errors do not prevent the binary running and the binary > > works well, I still wonder what such errors mean. > > Welcome any suggestions. > > > > The following is the complete logs: > > > > libbpf: loading object 'minimal_bpf' from buffer > > libbpf: elf: section(2) raw_tp/sched_process_exec, size 280, link 0, > > flags 6, type=1 > > libbpf: sec 'raw_tp/sched_process_exec': found program > > 'handle_sched_process_exec' at insn offset 0 (0 bytes), code size 35 > > insns (280 bytes) > > libbpf: elf: section(3) license, size 13, link 0, flags 3, type=1 > > libbpf: license of minimal_bpf is Dual BSD/GPL > > libbpf: elf: section(4) .rodata.str1.1, size 16, link 0, flags 32, type=1 > > libbpf: elf: skipping unrecognized data section(4) .rodata.str1.1 > > libbpf: elf: section(5) .BTF, size 23717, link 0, flags 0, type=1 > > libbpf: elf: section(6) .BTF.ext, size 364, link 0, flags 0, type=1 > > libbpf: elf: section(7) .symtab, size 96, link 11, flags 0, type=2 > > libbpf: looking for externs among 4 symbols... > > libbpf: collected 0 externs total > > libbpf: loading kernel BTF '/boot/vmlinux-4.19.0-041900-generic': 0 > > libbpf: Error loading BTF: Invalid argument(22) > > libbpf: magic: 0xeb9f > > version: 1 > > flags: 0x0 > > hdr_len: 24 > > type_off: 0 > > type_len: 14212 > > str_off: 14212 > > str_len: 9481 > > btf_total_size: 23717 > > [1] PTR (anon) type_id=2 > > [2] STRUCT bpf_raw_tracepoint_args size=0 vlen=1 > > args type_id=5 bits_offset=0 > > [3] TYPEDEF __u64 type_id=4 > > [4] INT long long unsigned int size=8 bits_offset=0 nr_bits=64 encoding=(none) > > [5] ARRAY (anon) type_id=3 index_type_id=6 nr_elems=0 > > [6] INT __ARRAY_SIZE_TYPE__ size=4 bits_offset=0 nr_bits=32 encoding=(none) > > [7] ENUM (anon) size=4 vlen=1 > > ctx val=1 > > [8] INT int size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > > [9] TYPEDEF handle_sched_process_exec type_id=7 > > [10] Invalid btf_info:840000ad > > libbpf: Error loading .BTF into kernel: -22. BTF is optional, ignoring. > > it's a STRUCT with kflag set to 1, which means that it has bitfields > with encoded bit offset and bit size in offset field. libbpf doesn't > detect and sanitize such cases. But this error is just a warning and > it doesn't influence correctness, so you can ignore that. But if you'd > like to avoid this, take a look at what would it take to sanitize such > cases. If it's not too gross and complicated, we can teach libbpf to > do it automatically. > > > [...] Thanks! I will take a look and fix it if possible. Rainkin
