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: > > > 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. That sounds really good to me, thanks!
