On 2/3/24 19:45, Manu Bretelle wrote: > On Sat, Feb 03, 2024 at 03:40:24PM +0100, Jiri Olsa wrote: >> On Fri, Feb 02, 2024 at 03:09:05PM -0800, Manu Bretelle wrote: >>> On Sun, Jan 28, 2024 at 06:24:05PM -0700, Daniel Xu wrote: >>>> === Description === >>>> >>>> This is a bpf-treewide change that annotates all kfuncs as such inside >>>> .BTF_ids. This annotation eventually allows us to automatically generate >>>> kfunc prototypes from bpftool. >>>> >>>> We store this metadata inside a yet-unused flags field inside struct >>>> btf_id_set8 (thanks Kumar!). pahole will be taught where to look. >>>> >>>> More details about the full chain of events are available in commit 3's >>>> description. >>>> >>>> The accompanying pahole and bpftool changes can be viewed >>>> here on these "frozen" branches [0][1]. >>>> >>>> [0]: https://github.com/danobi/pahole/tree/kfunc_btf-v3-mailed >>>> [1]: https://github.com/danobi/linux/tree/kfunc_bpftool-mailed >>> >>> >>> I hit a similar issue to [0] on master >>> 943b043aeecc ("selftests/bpf: Fix bench runner SIGSEGV") >>> when cross-compiling on x86_64 (LE) to s390x (BE). >>> I do have CONFIG_DEBUG_INFO_BTF enable and the issue would not trigger if >>> I disabled CONFIG_DEBUG_INFO_BTF (and with the fix mentioned in [0]). >>> >>> What seems to happen is that `tools/resolve_btfids` is ran in the context of the >>> host endianess and if I printk before the WARN_ON: >>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c >>> index ef380e546952..a9ed7a1a4936 100644 >>> --- a/kernel/bpf/btf.c >>> +++ b/kernel/bpf/btf.c >>> @@ -8128,6 +8128,7 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type, >>> * WARN() for initcall registrations that do not check errors. >>> */ >>> if (!(kset->set->flags & BTF_SET8_KFUNCS)) { >>> + printk("Flag 0x%08X, expected 0x%08X\n", kset->set->flags, BTF_SET8_KFUNCS); >>> WARN_ON(!kset->owner); >>> return -EINVAL; >>> } >>> >>> the boot logs would show: >>> Flag 0x01000000, expected 0x00000001 >>> >>> The issue did not happen prior to >>> 6f3189f38a3e ("bpf: treewide: Annotate BPF kfuncs in BTF") >>> has only 0 was written before. >>> >>> It seems [1] will be addressing cross-compilation, but it did not fix it as is >>> by just applying on top of master, so probably some of the changes will also need >>> to be ported to `tools/include/linux/btf_ids.h`? >> >> the fix in [1] is fixing flags in set8's pairs, but not the global flags >> >> it looks like Viktor's fix should now also swap that as well? like in the >> change below on top of Viktor's changes (untested) >> >> jirka >> >> >> --- >> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c >> index d01603ef6283..c44d57fec390 100644 >> --- a/tools/bpf/resolve_btfids/main.c >> +++ b/tools/bpf/resolve_btfids/main.c >> @@ -706,6 +706,8 @@ static int sets_patch(struct object *obj) >> * correctly translate everything. >> */ >> if (need_bswap) { >> + set8->flags = bswap_32(set8->flags); >> + >> for (i = 0; i < cnt; i++) { >> set8->pairs[i].flags = >> bswap_32(set8->pairs[i].flags); >> > > That should work. Here are a few tests I ran: > > $ md5sum /tmp/kbuild-s390x/vmlinux.* > eb658e51e089f3c5b2c8909a29dc9997 /tmp/kbuild-s390x/vmlinux.a > # plain vmlinux before running resolv_btfids (all 0s) > ea907cd46a1a73b8276b5f2a82af00ca /tmp/kbuild-s390x/vmlinux.before_resolv > # x86_64 resolv_btfids on master without Viktor's patch > 980a40c3a3ff563d1c2d1ebdd5071a23 /tmp/kbuild-s390x/vmlinux.resolv_native > # x86_64 resolv_btfids on master with Viktor's patch > b986d19e242719ebea41c578235da662 /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor > # x86_64 resolv_btfids on master with Viktor's patch and your suggested patch > 4edd8752ff01129945bd442689b1927b /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor_patched > # s390x resolv_btfids run with qemu-s390x-static > 4edd8752ff01129945bd442689b1927b /tmp/kbuild-s390x/vmlinux.resolv_s390x > > > and some hexdiff of those binaries: > > > # difference between master's native build and s390x build.... has byte swapping for set8 and others > diff -ruN <(xxd /tmp/kbuild-s390x/vmlinux.resolv_s390x) <(xxd /tmp/kbuild-s390x/vmlinux.resolv_native) > diff_s390x_native.diff > https://gist.github.com/chantra/c3d58637a08a6f7340953dc155bb18cc > > # difference betwee Viktor's version and s390x build.... squinting my eyes I only see the global set8 is missing > diff -ruN <(xxd /tmp/kbuild-s390x/vmlinux.resolv_s390x) <(xxd /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor) > diff_s390x_native_viktor.diff > https://gist.github.com/chantra/61cfff02b456ae72d3c0161ce1897097 Thanks for the testing Manu! Jiri's suggested fix is now a part of [1]. Viktor [1] https://lore.kernel.org/bpf/cover.1707157553.git.vmalik@xxxxxxxxxx/ > > Have a good weekend all! > > Manu >
