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

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On Mon, Jul 11, 2022 at 1:34 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> 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

$ pahole --version
v1.22

>   - clang/gcc? versions
>   - V=1 compile log
>   - command line options

I will need some more time to gather the logs. Hopefully the pahole
and kernel branch will give some initial clue.

>   - tree/branch you're on

This is from Yocto and they use 5.15 -
https://git.yoctoproject.org/linux-yocto/tree/?h=v5.15/standard/base&id=ebfb1822e9f9726d8c587fc0f60cfed43fa0873e

>   - 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



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