libbpf: Add uprobe ref counter offset support for USDT semaphores
When attaching to uprobes through perf subsystem, it's possible to specify
offset of a so-called USDT semaphore, which is just a reference counted u16,
used by kernel to keep track of how many tracers are attached to a given
location. Support for this feature was added in [0], so just wire this through
uprobe_opts. This is important to enable implementing USDT attachment and
tracing through libbpf's bpf_program__attach_uprobe_opts() API.
[0] a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-16-andrii@kernel.org
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 1f4a672..f177d89 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -284,6 +284,10 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
struct bpf_uprobe_opts {
/* size of this struct, for forward/backward compatiblity */
size_t sz;
+ /* offset of kernel reference counted USDT semaphore, added in
+ * a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
+ */
+ size_t ref_ctr_offset;
/* custom user-provided value fetchable through bpf_get_attach_cookie() */
__u64 bpf_cookie;
/* uprobe is return probe, invoked at function return time */
