[PATCH bpf-next v2 1/2] libbpf: Fix struct and union zero detection in BTF dumper

[Luis Vieira <luisflavieira@gmail.com>]

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.

Signed-off-by: Luis Vieira <luisflavieira@gmail.com>
---
 tools/lib/bpf/btf_dump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 996e61b5f11f..ad43bbd3b442 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -2564,7 +2564,7 @@ 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;

-- 
2.43.0