[PATCH bpf-next 1/2] libbpf: add support to set kprobe/uprobe attach mode

[menglong8.dong@gmail.com]

From: Menglong Dong <imagedong@tencent.com>

By default, libbpf will attach the kprobe/uprobe eBPF program in the
latest mode that supported by kernel. In this patch, we add the support
to let users manually attach kprobe/uprobe in legacy or perf mode.

There are 3 mode that supported by the kernel to attach kprobe/uprobe:

  LEGACY: create perf event in legacy way and don't use bpf_link
  PERF: create perf event with perf_event_open() and don't use bpf_link
  LINK: create perf event with perf_event_open() and use bpf_link

Users now can manually choose the mode with
bpf_program__attach_uprobe_opts()/bpf_program__attach_kprobe_opts().

Link: https://lore.kernel.org/bpf/20230113093427.1666466-1-imagedong@tencent.com/
Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
 tools/lib/bpf/libbpf.c | 26 +++++++++++++++++++++++++-
 tools/lib/bpf/libbpf.h | 19 ++++++++++++++++---
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index eed5cec6f510..0d20bf1ee301 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9784,7 +9784,7 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
 	link->link.dealloc = &bpf_link_perf_dealloc;
 	link->perf_event_fd = pfd;
 
-	if (kernel_supports(prog->obj, FEAT_PERF_LINK)) {
+	if (kernel_supports(prog->obj, FEAT_PERF_LINK) && !opts->no_link) {
 		DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts,
 			.perf_event.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0));
 
@@ -10148,16 +10148,28 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
 	struct bpf_link *link;
 	size_t offset;
 	bool retprobe, legacy;
+	enum probe_mode mode;
 	int pfd, err;
 
 	if (!OPTS_VALID(opts, bpf_kprobe_opts))
 		return libbpf_err_ptr(-EINVAL);
 
+	mode = OPTS_GET(opts, mode, PROBE_MODE_DEFAULT);
 	retprobe = OPTS_GET(opts, retprobe, false);
 	offset = OPTS_GET(opts, offset, 0);
 	pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
 
 	legacy = determine_kprobe_perf_type() < 0;
+	switch (mode) {
+	case PROBE_MODE_LEGACY:
+		legacy = true;
+	case PROBE_MODE_PERF:
+		pe_opts.no_link = true;
+		break;
+	default:
+		break;
+	}
+
 	if (!legacy) {
 		pfd = perf_event_open_probe(false /* uprobe */, retprobe,
 					    func_name, offset,
@@ -10817,10 +10829,12 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
 	int pfd, err;
 	bool retprobe, legacy;
 	const char *func_name;
+	enum probe_mode mode;
 
 	if (!OPTS_VALID(opts, bpf_uprobe_opts))
 		return libbpf_err_ptr(-EINVAL);
 
+	mode = OPTS_GET(opts, mode, PROBE_MODE_DEFAULT);
 	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);
@@ -10849,6 +10863,16 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
 	}
 
 	legacy = determine_uprobe_perf_type() < 0;
+	switch (mode) {
+	case PROBE_MODE_LEGACY:
+		legacy = true;
+	case PROBE_MODE_PERF:
+		pe_opts.no_link = true;
+		break;
+	default:
+		break;
+	}
+
 	if (!legacy) {
 		pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
 					    func_offset, pid, ref_ctr_off);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 8777ff21ea1d..7fb474e036a3 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -451,8 +451,10 @@ struct bpf_perf_event_opts {
 	size_t sz;
 	/* custom user-provided value fetchable through bpf_get_attach_cookie() */
 	__u64 bpf_cookie;
+	/* don't use bpf_link when attach eBPF pprogram */
+	bool no_link;
 };
-#define bpf_perf_event_opts__last_field bpf_cookie
+#define bpf_perf_event_opts__last_field no_link
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd);
@@ -461,6 +463,13 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event_opts(const struct bpf_program *prog, int pfd,
 				    const struct bpf_perf_event_opts *opts);
 
+enum probe_mode {
+	PROBE_MODE_DEFAULT = 0, /* latest supported by kernel */
+	PROBE_MODE_LEGACY,
+	PROBE_MODE_PERF,
+	PROBE_MODE_LINK,
+};
+
 struct bpf_kprobe_opts {
 	/* size of this struct, for forward/backward compatiblity */
 	size_t sz;
@@ -470,9 +479,11 @@ struct bpf_kprobe_opts {
 	size_t offset;
 	/* kprobe is return probe */
 	bool retprobe;
+	/* kprobe attach mode */
+	enum probe_mode mode;
 	size_t :0;
 };
-#define bpf_kprobe_opts__last_field retprobe
+#define bpf_kprobe_opts__last_field mode
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_kprobe(const struct bpf_program *prog, bool retprobe,
@@ -570,9 +581,11 @@ struct bpf_uprobe_opts {
 	 * binary_path.
 	 */
 	const char *func_name;
+	/* uprobe attach mode */
+	enum probe_mode mode;
 	size_t :0;
 };
-#define bpf_uprobe_opts__last_field func_name
+#define bpf_uprobe_opts__last_field mode
 
 /**
  * @brief **bpf_program__attach_uprobe()** attaches a BPF program
-- 
2.39.0