On Fri, May 6, 2022 at 4:27 PM Yifei Ma <yifeima@xxxxxxxxxxxxx> wrote: > > Hi all, > > I hit an issue when a function symbol can't be found in bpf object file when generating skeleton. if anyone can kindly give me some suggestions on it, that would be a big help. > Here is what I am doing: > - I am playing with the patch from Roman "bpf: sched: basic infrastructure for scheduler bpf" > - It adds three hooks in CFS scheduler, and three BPF helper functions. > - I patched his work on the kerenl and libbpf and bpftool (v5.16) > - When I compiled this example BPF code (https://github.com/rgushchin/atc), BPF skeleton generator can't find the BTF for the helper function. > ----------------------------------------------- > More information about my environment: > - on linux 5.16 with the patch > - enabled "CONFIG_DEBUG_INFO_BTF=y CONFIG_PAHOLE_HAS_SPLIT_BTF=y CONFIG_DEBUG_INFO_BTF_MODULES=y" > - rebuilt lib/bpf and bpftool > - generated vmlinux.h using the bpftool > - grep bpf_sched_entity_belongs_to_cgrp vmlinux.h ==> Found it > - clang -g -O2 -target bpf -D__TARGET_ARCH_x86 -I$LINUX/tools/include/uapi -I$LINUX/tools/lib/ -I$LINUX/tools/bpf/bpftool/ -I. -o atc.bpf.o -c atc.bpf.c > - clang --version ==> Ubuntu clang version 12.0.0-3ubuntu1~20.04.5 > - llvm-strip -g atc.bpf.o > - bpftool gen skeleton atc.bpf.o > atc.skel.h > - "libbpf: failed to find BTF for extern 'bpf_sched_entity_belongs_to_cgrp': -2" > - backtrace where 'bpf_sched_entity_belongs_to_cgrp' can't be found in BTF > #0 find_extern_btf_id (ext_name= "bpf_sched_entity_belongs_to_cgrp",) at libbpf.c:3589 > #1 bpf_object__collect_externs at libbpf.c:3589 > #2 __bpf_object__open () at libbpf.c:6808 > #3 __bpf_object__open () at libbpf.c:6750 > #4 bpf_object__open_mem () at libbpf.c:6872 > #5 bpf_object__open_mem () at libbpf.c:6866 > #6 in do_skeleton () at libbpf.c:728 > #7 main () at libbpf.c:728 > ------------------------------------ > > > Do you have any idea or suggestion on it? Thank you I think you have to either re-generate bpf_helper_defs.h ([0]) or just add your own definitions for those new helpers. See [0] for how libbpf does it for current helpers and just do the same (but with correct helper ID, of course). [0] https://github.com/libbpf/libbpf/blob/master/src/bpf_helper_defs.h#L287 > > Yifei >
