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libbpf: Add uprobe ref counter offset support for USDT semaphores

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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
This commit is contained in:
Andrii Nakryiko
2021-08-15 00:06:08 -07:00
committed by Andrii Nakryiko
parent 91259bc676
commit 6d67d53143
2 changed files with 17 additions and 4 deletions
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4
src/libbpf.h
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@@ -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 */