Re: Problem with endianess of pahole BTF output for vmlinux

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On Mon, 28 Sep 2020 at 21:15, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Mon, Sep 28, 2020 at 8:41 PM Tony Ambardar <tony.ambardar@xxxxxxxxx> 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
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?

Thanks,
Tony



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