btf_dump_type_data_check_zero() uses -ENODATA to indicate that a value is zero. The array path handles this sentinel correctly, but the struct and union path compares the return value against positive ENODATA.
As a result, the member loop returns after examining its first member. A nested struct or union whose first member is zero can therefore be treated as entirely zero even when a later member is non-zero. Compare against -ENODATA so zero members are skipped while looking for a non-zero member. Add a regression test with a nested struct whose first member is zero and second member is non-zero. Signed-off-by: Luis Vieira <[email protected]> --- tools/lib/bpf/btf_dump.c | 2 +- tools/testing/selftests/bpf/prog_tests/btf_dump.c | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index fa995c02a170..dbf9f17e4b37 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -2474,7 +2474,7 @@ static int btf_dump_type_data_check_zero(struct btf_dump *d, bit_sz = btf_member_bitfield_size(t, i); err = btf_dump_type_data_check_zero(d, mtype, m->type, data + moffset / 8, moffset % 8, bit_sz); - if (err != ENODATA) + if (err != -ENODATA) return err; } return -ENODATA; diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dump.c b/tools/testing/selftests/bpf/prog_tests/btf_dump.c index fe04a955d46c..dd1241fcdb01 100644 --- a/tools/testing/selftests/bpf/prog_tests/btf_dump.c +++ b/tools/testing/selftests/bpf/prog_tests/btf_dump.c @@ -886,6 +886,11 @@ static void test_btf_dump_struct_data(struct btf *btf, struct btf_dump *d, "(union bpf_iter_link_info){.map = (struct){.map_fd = (__u32)1,},.cgroup = (struct){.order = (enum bpf_cgroup_iter_order)BPF_CGROUP_ITER_SELF_ONLY,.cgroup_fd = (__u32)1,},.task = (struct){.tid = (__u32)1,.pid = (__u32)1,},}", { .cgroup = { .order = 1, .cgroup_fd = 1, }}); + /* nested structs with zero first member and non-zero second member */ + TEST_BTF_DUMP_DATA(btf, d, "union", str, union bpf_iter_link_info, BTF_F_COMPACT, + "(union bpf_iter_link_info){.cgroup = (struct){.cgroup_fd = (__u32)1,},.task = (struct){.pid = (__u32)1,},}", + { .cgroup = { .cgroup_fd = 1 }}); + /* struct skb with nested structs/unions; because type output is so * complex, we don't do a string comparison, just verify we return * the type size as the amount of data displayed. --- base-commit: ea9358e1270ab2c3ba6f36bd9bdda68617665516 change-id: 20260928-libbpf-btf-enodata-fix-ac6381645ab8 Best regards, -- Luis Vieira <[email protected]>
