Re: elfutils DWARF problem was: Re: Problem with BTF generation on mips64el

[Tony Ambardar <tony.ambardar@gmail.com>]

On Mon, Jun 10, 2024 at 11:36:54PM -0700, Tony Ambardar wrote:
> On Mon, Jun 03, 2024 at 08:47:24PM -0700, Tony Ambardar wrote:
> 
> [snip]
> 
> Arnaldo:
> 
> Your stepping through DWARF/reloc diagnostics earlier was helpful. Thanks!
> I reran your tests with the updated elfutils and latest pahole (pre-1.27),
> and then found:
> 
>   - everything that worked before, still works
>   - your observations from "btfdiff vmlinux" and 'struct dma_chan' persist
>   - we now see expected output from "eu-readelf -winfo netdevsim.ko"
> 
> Regarding pahole, DWARF parsing and BTF generation now works:
> (with no more die__process: error messages seen)
> 
>     kodidev:~/linux$ pahole -F dwarf netdevsim.ko |wc -l
>     14504
> 
> but strangely pahole still doesn't read its own generated BTF:
> 
>     kodidev:~/linux$ pahole -F btf netdevsim.ko
>     libbpf: Invalid BTF string section
>     pahole: file 'netdevsim.ko' has no btf type information.

After staring at this I realized that this is split BTF and we needed to
issue "pahole -F btf --btf_base vmlinux netdevsim.ko", which does work.
Unfortunately, the libbpf error message is a bit cryptic; perhaps a future
update could mention "--btf_base"?

>     
> [snip]
> 
> Many thanks everyone for your help,
> Tony
> 
> [1]: https://patchwork.sourceware.org/project/elfutils/list/?series=31601
> [2]: https://patchwork.sourceware.org/project/elfutils/list/?series=34310
> [3]:
> https://github.com/guidosarducci/elfutils/commits/main-fix-mips-support-reloc/