On Mon, Sep 21, 2020 at 11:19 AM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Sat, Sep 19, 2020 at 12:58 AM Tony Ambardar <tony.ambardar@xxxxxxxxx> wrote: > > > > On Wed, 9 Sep 2020 at 07:27, Arnaldo Carvalho de Melo > > <arnaldo.melo@xxxxxxxxx> wrote: > > > > > > Em Wed, Sep 09, 2020 at 11:02:24AM +0200, Ilya Leoshkevich escreveu: > > > > On Tue, 2020-09-08 at 13:18 -0700, Andrii Nakryiko wrote: > > > > > On Mon, Sep 7, 2020 at 9:02 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote: > > > > > > On Sat, 2020-09-05 at 21:16 -0700, Tony Ambardar wrote: > > > > > [...] > > > > > > > Is this expected? Is DEBUG_INFO_BTF supported in general when > > > > > > > cross-compiling? How does one generate BTF encoded for the > > > > > > > target endianness with pahole? > > > > > > The BTF loader has support for endianness, its just the encoder that > > > doesn't :-\ > > > > > > I.e. pahole can grok a big endian BTF payload on a little endian machine > > > and vice-versa, just can't cross-build BTF payloads ATM. > > > > > > > > Yes, it's expected, unfortunately. Right now cross-compiling to a > > > > > different endianness isn't supported. You can cross-compile only if > > > > > target endianness matches host endianness. > > > > > > I agree that having this in libbpf is better, it should be done as part > > > of producing the result of the deduplication phase. > > > > > Thanks for confirming this wasn't a case of operator error. My platforms for > > learning/experimenting with BPF have been small embedded ones, including > > cross-compiling to different archs, word-size and endianness, which have > > "helped" me run into multiple problems till now. This one is the first I > > couldn't work around however... > > > > [...] > > > > > I'm working on extending BTF APIs in libbpf at the moment. Switching > > > > > endianness would be rather easy once all that is done. With these new > > > > > APIs it will be possible to switch pahole to use libbpf APIs to > > > > > produce BTF output and support arbitrary endianness as well. Right > > > > > now, I'd rather avoid implementing this in pahole, libbpf is a much > > > > > better place for this (and will require ongoing updates if/when we > > > > > introduce new types and fields to BTF). > > > > > > Right, we could do it right after btf_dedup() and before > > > btf_elf__write(), doing the same process as in btf_loader.c, i.e. > > > checking if the ELF target arch is different in endianness and doing the > > > reverse of the loader. > > > > > > > > Hope this plan works for you guys. > > > > > > > > That sounds really good to me, thanks! > > > > > Andrii and Arnaldo, I really appreciate your working on a proper endianness fix. > > If you have a WIP or staging branch and could use some help please let me know. > > > > 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! > > Best regards, > > Tony
