Missing .BTF section in vmlinux (x86_64) when building on Yocto

Donald Chan <hoiho.chan@xxxxxxxxx> · Sun, 10 Jul 2022 22:57:01 -0700

Hi,

I am trying to enable CONFIG_DEBUG_INFO_BTF when building a
Yocto-based Linux kernel....but it is failing with this error:

|   LD      .tmp_vmlinux.btf
|   BTF     .btf.vmlinux.bin.o
|   LD      .tmp_vmlinux.kallsyms1
|   KSYMS   .tmp_vmlinux.kallsyms1.S
|   AS      .tmp_vmlinux.kallsyms1.S
|   LD      .tmp_vmlinux.kallsyms2
|   KSYMS   .tmp_vmlinux.kallsyms2.S
|   AS      .tmp_vmlinux.kallsyms2.S
|   LD      vmlinux
|   BTFIDS  vmlinux
| FAILED: load BTF from vmlinux: No such file or directory

I dug deeper and it seems that the resolve_btfids utility is not able
to find any relevant .BTF section (at btf__parse from function
symbols_resolve).

Dumped the vmlinux and also confirmed there is only .BTF_ids section:

  [2993] .rela___ksymtab_g RELA             0000000000000000  17174de0
       0000000000000048  0000000000000018   I      22807   2992     8
  [2994] .BTF_ids          PROGBITS         0000000000000000  0105c504
       00000000000000fc  0000000000000000   A       0     0     1

What could be wrong? Sample config is available at
https://gist.github.com/hoiho-amzn/964eb0cf2b4459f6775d7af1da7b4056

The issue exists on x86_64, I also have tried armv7 with the same
result so doesn't seem to be arch-specific.

Thanks
Donald