failed to open BPF object file: Operation not supported (Android Build via xmake)

[ghost]

From libbpf/bpftool#77

I have following map:

struct
{
  __uint(type, BPF_MAP_TYPE_RINGBUF);
  __uint(max_entries, MAX_ENTRIES);
} ring_map SEC(".maps");

under v7.0.0 it works, under v7.1.0 and v7.2.0 getting an error:
bpftool gen skeleton build/.gens/xxx/android/x86_64/release/rules/bpf/xxx.bpf.o -d -p

libbpf: map 'xxx': unsupported map linkage static.
{
    "error": "failed to open BPF object file: Operation not supported"
}

---

Reproduce error:

On the system there is bpftool v7.0.0 installed:

bpftool v7.0.0
using libbpf v1.0
features: libbpf_strict, skeletons

Get libbpf-bootstrap repo
git clone --recurse-submodules https://github.com/libbpf/libbpf-bootstrap

try to compile for Android via xmake according to the readme file:

$ git submodule update --init --recursive       # check out libbpf
$ cd examples/c
$ xmake f -p android
$ xmake

works.

---

Update the bpftool to v7.1.0
git clone --depth 1 --branch v7.1.0 ... && make install
bpftool version:

bpftool v7.1.0
using libbpf v1.1
features: llvm, skeletons

try again to compile via xmake:

[ 13%]: compiling.bpf uprobe.bpf.c
[ 13%]: compiling.bpf minimal.bpf.c
[ 13%]: compiling.bpf fentry.bpf.c
[ 13%]: compiling.bpf minimal_legacy.bpf.c
[ 17%]: cache compiling.release ../../libbpf/src/libbpf.c
[ 33%]: cache compiling.release ../../libbpf/src/netlink.c
[ 44%]: cache compiling.release ../../libbpf/src/bpf.c
[ 44%]: compiling.bpf bootstrap.bpf.c
libbpf: map 'my_pid_map': unsupported map linkage static.
Error: failed to open BPF object file: Operation not supported
error: execv(bpftool gen skeleton build/.gens/minimal_legacy/android/armeabi-v7a/release/rules/bpf/minimal_legacy.bpf.o) failed(161)

failed.

Seems like its for all .maps not only ringbuf.

---

Same for v.7.2.0

[anakryiko]

what's your Clang version you are using to build BPF code? Can you try upgrading it and check if that helps?

[qmonnet]

Copying my notes from the bpftool report, just in case it helps.

Bisecting between [libbf] 1.0.0 and 1.1.0 for bpftool (using bpftool 7.0.0), it looks like the issue was introduced in commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=4fcac46c7e107a93030d19c6ea7b90540fc80b1b (3cd45b6). I haven't looked at the details.

I note that there's a commit fixing that one (ce8d078) but that doesn't seem helpful here, it's in the version used by the master branch of bpftool, which fails to generate the skeleton as well.

[ghost]

Same for 7.3.0 (Github master branch)

bpftool v7.3.0
using libbpf v1.3
features: llvm, skeletons

[anakryiko]

I think this is due to old Clang that doesn't know how to produce global variables BTF information. Can you guys try to use newer Clang? Or at least please provide a dump of BTF for your BPF object file (bpftool btf dump file <.bpf.o>). Thanks.