Re: Problem with endianess of pahole BTF output for vmlinux

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Tony Ambardar <tony.ambardar@gmail.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Ilya Leoshkevich <iii@linux.ibm.com>, bpf <bpf@vger.kernel.org>,
	dwarves@vger.kernel.org,
	David Marcinkovic <david.marcinkovic@sartura.hr>,
	Luka Perkov <luka.perkov@sartura.hr>,
	Borna Cafuk <borna.cafuk@sartura.hr>,
	Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>
Subject: Re: Problem with endianess of pahole BTF output for vmlinux
Date: Mon, 28 Sep 2020 21:15:07 -0700	[thread overview]
Message-ID: <CAEf4Bza2D2MQ_F7+vNg7x05JachvJ5bLM3Uyjv+oEx=xna_u4g@mail.gmail.com> (raw)
In-Reply-To: <CAPGftE9iVH=eG_FRxSFJC0B3FX8LVdKStfvLbs0gRt8kvMoqJw@mail.gmail.com>

On Mon, Sep 28, 2020 at 8:41 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
>
> Hello Andrii!
>
> On Mon, 28 Sep 2020 at 13:19, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >
> > On Mon, Sep 21, 2020 at 11:19 AM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > I have a bunch of code changes locally. I'll clean that up, partition
> > > libbpf and pahole patches, and post them for review this week. To
> > > address endianness support, those are the prerequisites. Once those
> > > changes land, I'll be able to solve endianness issues you are having.
> > > So just a bit longer till all that is done, sorry for the wait!
> > >
> >
> > Question to folks that are working with 32-bit and/or big-endian
> > architectures. Do you guys have an VM image that you'd be able to
> > share with me, such that I can use it with qemu to test patches like
> > this. My normal setup is all 64-bit/little-endian, so testing changes
> > like this (and a few more I'm planning to do to address mixed 32-bit
> > on the host vs 64-bit in BPF cases) is a bit problematic. And it's
> > hard to get superpumped about spending lots of time setting up a new
> > Linux image (never goes easy or fast for me).
> >
> > So, if you do have something like this, please share. Thank you!
> >
>
> I can provide 32-bit and 64-bit big-endian system images for running
> on QEMU's malta target. These are built using OpenWRT's build system
> and include a recent stable bpftool (v5.8.x) and v5.4.x kernel. Is
> that sufficient? It would work if manually creating raw or elf-based
> BTF files on a build host, then copying into the QEMU target to test
> parsing with bpftool (linked with the standard libbpf).

That would be great! I intend to run them under qemu-system-arm and
supply latest kernel through -kernel option, so kernel itself is not
that critical. Same for bpftool, pahole, etc, I'll just supply them
from my host environment. So please let me know how I can get ahold of
those. Sample qemu invocation command line would be highly appreciated
as well. Thank you!

>
> For changes to the Linux build system itself (e.g. pahole endian
> options and target endian awareness), you would need to set up a

I think that shouldn't be a problem and should be handled
transparently, even in a cross-compilation case, but let's see.

> standard OpenWRT build environment. I can help with that, or simply
> integrate your patches myself for testing. As you say, nothing to be
> super pumped about...
>
> Let me know what's easiest and how best to get images to you.

Any way you like and can. Dropbox, Google drive, what have you.

>
> Many thanks,
> Tony