Commit 5e3b8356 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
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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] a6ca88b2 ("trace_uprobe: support reference counter in fd-based uprobe")

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-16-andrii@kernel.org
parent 0a80cf67

tools/lib/bpf/libbpf.c

+13 −4
Original line number Diff line number Diff line
@@ -9152,13 +9152,19 @@ static int determine_uprobe_retprobe_bit(void) 
	return parse_uint_from_file(file, "config:%d\n");

}



#define PERF_UPROBE_REF_CTR_OFFSET_BITS 32

#define PERF_UPROBE_REF_CTR_OFFSET_SHIFT 32



static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,

				 uint64_t offset, int pid)

				 uint64_t offset, int pid, size_t ref_ctr_off)

{

	struct perf_event_attr attr = {};

	char errmsg[STRERR_BUFSIZE];

	int type, pfd, err;



	if (ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))

		return -EINVAL;



	type = uprobe ? determine_uprobe_perf_type()

		      : determine_kprobe_perf_type();

	if (type < 0) {
@@ -9181,6 +9187,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name, 
	}

	attr.size = sizeof(attr);

	attr.type = type;

	attr.config |= (__u64)ref_ctr_off << PERF_UPROBE_REF_CTR_OFFSET_SHIFT;

	attr.config1 = ptr_to_u64(name); /* kprobe_func or uprobe_path */

	attr.config2 = offset;		 /* kprobe_addr or probe_offset */
@@ -9219,7 +9226,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog, 
	pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);



	pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,

				    offset, -1 /* pid */);

				    offset, -1 /* pid */, 0 /* ref_ctr_off */);

	if (pfd < 0) {

		pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",

			prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
@@ -9289,6 +9296,7 @@ bpf_program__attach_uprobe_opts(struct bpf_program *prog, pid_t pid, 
	DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);

	char errmsg[STRERR_BUFSIZE];

	struct bpf_link *link;

	size_t ref_ctr_off;

	int pfd, err;

	bool retprobe;
@@ -9296,10 +9304,11 @@ bpf_program__attach_uprobe_opts(struct bpf_program *prog, pid_t pid, 
		return libbpf_err_ptr(-EINVAL);



	retprobe = OPTS_GET(opts, retprobe, false);

	ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);

	pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);



	pfd = perf_event_open_probe(true /* uprobe */, retprobe,

				    binary_path, func_offset, pid);

	pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,

				    func_offset, pid, ref_ctr_off);

	if (pfd < 0) {

		pr_warn("prog '%s': failed to create %s '%s:0x%zx' perf event: %s\n",

			prog->name, retprobe ? "uretprobe" : "uprobe",

tools/lib/bpf/libbpf.h

+4 −0
Original line number Diff line number Diff line
@@ -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 */