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

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

Hi Mark,

On Mon, Jun 03, 2024 at 09:18:33PM +0200, Mark Wielaard wrote:
> On Mon, Jun 03, 2024 at 02:40:45PM -0300, Arnaldo Carvalho de Melo wrote:
> > Couldn't find a way to ask eu-readelf for more verbose output, where we
> > could perhaps get some clue as to why it produces nothing while binutils
> > readelf manages to grok it, Mark, do you know some other way to ask
> > eu-readelf to produce more debug output?
> > 
> > I'm unsure if the netdevsim.ko file was left in a semi encoded BTF state
> > that then made eu-readelf to not be able to process it while pahole,
> > that uses eltuils' libraries, was able to process the first two CUs for
> > a kernel module and all the CUs for the vmlinux file :-\
> > 
> > Mark, the whole thread is available at:
> > 
> > https://lore.kernel.org/all/Zl3Zp5r9m6X_i_J4@x1/T/#u
> 
> I haven't looked at the vmlinux file. But for the .ko file the issue
> is that the elfutils MIPS backend isn't complete. Specifically MIPS
> relocations aren't recognized (and so cannot be applied). There are
> some pending patches which try to fix that:
> 
> https://patchwork.sourceware.org/project/elfutils/list/?series=31601

Earlier in the thread, Hengqi Chen pointed out the latest elfutils backend
work for MIPS, and I locally rebuilt elfutils and then pahole from their
respective next/main branches. For elfutils, main (935ee131cf7c) includes

  e259f126 Support Mips architecture
  f2acb069 stack: Fix stack unwind failure on mips
  db33cb0c backends: Add register_info, return_value_location, core_note mips

which partially applies the patchwork series but leaves out the support for
readelf, strip, and elflint.

I believe this means the vmlinux and .ko files I shared are OK, or is there
more backend work needed for MIPS?

The bits missing in eu-readelf would explain the blank output both Arnaldo
and I see from "$ eu-readelf -winfo vmlinux". I tried rebuilding with the
patchwork readelf patch locally but ran into merge conflicts.

CCing Ying Huang for any more insight.

Thanks,
Tony