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: > > Hello, > > > > I'm using GCC 8.4.0, binutils 2.34 and pahole 1.17, compiling on an > > Ubuntu/x86_64 host and targeting both little- and big-endian mips > > running on malta/qemu. When cross-compiling Linux 5.4.x LTS and > > testing bpftool/BTF functionality on the target, I encounter errors > > on > > big-endian targets: > > > > > root@OpenWrt:/# bpftool btf dump file /sys/kernel/btf/vmlinux > > > libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux > > > Error: failed to load BTF from /sys/kernel/btf/vmlinux: No error > > > information > > > > After investigating, the problem appears to be that "pahole -J" > > running on the x86_64 little-endian host will always generate raw BTF > > of native endianness (based on BTF magic), which causes the error > > above on big-endian targets. > > > > 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? 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. > > > > Thanks for any feedback or suggestions, > > Tony > > We have the same problem on s390, and I'm not aware of any solution at > the moment. It would be great if we could figure out how to resolve > this. 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). Hope this plan works for you guys. > > Best regards, > Ilya >
