From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit dbdea9b36fb61da3b9a1be0dd63542e2bfd3e5d7 ]
When attach_prog_fd field was removed in libbpf 1.0 and replaced with `long: 0` placeholder, it actually shifted all the subsequent fields by 8 byte. This is due to `long: 0` promising to adjust next field's offset to long-aligned offset. But in this case we were already long-aligned as pin_root_path is a pointer. So `long: 0` had no effect, and thus didn't feel the gap created by removed attach_prog_fd.
Non-zero bitfield should have been used instead. I validated using pahole. Originally kconfig field was at offset 40. With `long: 0` it's at offset 32, which is wrong. With this change it's back at offset 40.
While technically libbpf 1.0 is allowed to break backwards compatibility and applications should have been recompiled against libbpf 1.0 headers, but given how trivial it is to preserve memory layout, let's fix this.
Reported-by: Grant Seltzer Richman grantseltzer@gmail.com Fixes: 146bf811f5ac ("libbpf: remove most other deprecated high-level APIs") Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/r/20220923230559.666608-1-andrii@kernel.org Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/libbpf.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 61493c4cddac..9f956e6058ed 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -118,7 +118,9 @@ struct bpf_object_open_opts { * auto-pinned to that path on load; defaults to "/sys/fs/bpf". */ const char *pin_root_path; - long :0; + + __u32 :32; /* stub out now removed attach_prog_fd */ + /* Additional kernel config content that augments and overrides * system Kconfig for CONFIG_xxx externs. */