Re: Problem with endianess of pahole BTF output for vmlinux

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Mon, Sep 28, 2020 at 11:48 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
>
> On Mon, 28 Sep 2020 at 21:15, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >
> > On Mon, Sep 28, 2020 at 8:41 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
> > >
> [...]
> > > 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!
> >
> Sounds good. However, malta is actually a MIPS platform. I've been using it

I don't care about ARM vs MIPS specifically. Needed 32-bit and
big-endian, just to test different variations. MIPS works just fine, I
think.

> a long time because it makes things particularly easy to switch configuration
> between different word-sizes and endianness.
>
> I had some malta mips images ready to go, but if you need ARM I'll need
> to look into building images for big-endian ARM. Big-endian isn't so common
> in the wild, and I'll need to see if OpenWRT supports these, and how to
> configure with QEMU's 'armvirt' target if possible...
>
> > >
> > > 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.
> >
> Meantime, I can package up what I have and send you the details. That
> would include images for mips32/64 big-endian and arm32/64 little-endian,
> plus usage examples. Is that still helpful for you?

Yeah, tremendously! After fighting my local qemu setup I managed to
run malta-be image successfully. Thanks a lot, that saves me lots of
gray hair. I'll get to testing this hopefully today-tomorrow, will let
you know if I had any more problems.

>
> Thanks,
> Tony