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

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Jul 11, 2022 at 09:19:45AM +0200, Jiri Olsa wrote:
> On Sun, Jul 10, 2022 at 10:57:01PM -0700, Donald Chan wrote:
> > 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

I compiled x86_64 bpf-next/master kernel with your config with no problems,
could you share more details? like:
  - version of dwarves/pahole
  - clang/gcc? versions
  - V=1 compile log
  - command line options
  - tree/branch you're on
  - anything else ;-)

thanks,
jirka

> > 
> > The issue exists on x86_64, I also have tried armv7 with the same
> > result so doesn't seem to be arch-specific.
> 
> hi,
> do you use any special command line options?
> what tree/branch are you on?
> 
> thanks,
> jirka
> 
> > 
> > Thanks
> > Donald