Subject: [PATCH v2 bpf-next 04/17] libbpf: Add support to attach to fentry/fexit tracing progs

From: Alexei Starovoitov <[email-masked]>
Date: Wed, 6 Nov 2019 21:46:31 -0800

Teach libbpf to recognize tracing programs types and attach them to
fentry/fexit.

Signed-off-by: Alexei Starovoitov <[email-masked]>
---
 tools/include/uapi/linux/bpf.h |  2 ++
 tools/lib/bpf/libbpf.c         | 61 +++++++++++++++++++++++++++++-----
 tools/lib/bpf/libbpf.h         |  5 +++
 tools/lib/bpf/libbpf.map       |  2 ++
 4 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index df6809a76404..69c200e6e696 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -201,6 +201,8 @@ enum bpf_attach_type {
 	BPF_CGROUP_GETSOCKOPT,
 	BPF_CGROUP_SETSOCKOPT,
 	BPF_TRACE_RAW_TP,
+	BPF_TRACE_FENTRY,
+	BPF_TRACE_FEXIT,
 	__MAX_BPF_ATTACH_TYPE
 };
 
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index be4af95d5a2c..4baaa14b4ca0 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3859,8 +3859,6 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
 	return 0;
 }
 
-static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id);
-
 static struct bpf_object *
 __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 		   struct bpf_object_open_opts *opts)
@@ -3926,7 +3924,9 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 		bpf_program__set_type(prog, prog_type);
 		bpf_program__set_expected_attach_type(prog, attach_type);
 		if (prog_type == BPF_PROG_TYPE_TRACING) {
-			err = libbpf_attach_btf_id_by_name(prog->section_name, &btf_id);
+			err = libbpf_attach_btf_id_by_name(prog->section_name,
+							   attach_type,
+							   &btf_id);
 			if (err)
 				goto out;
 			prog->attach_btf_id = btf_id;
@@ -4928,6 +4928,10 @@ static const struct {
 	BPF_PROG_SEC("raw_tp/",			BPF_PROG_TYPE_RAW_TRACEPOINT),
 	BPF_PROG_BTF("tp_btf/",			BPF_PROG_TYPE_TRACING,
 						BPF_TRACE_RAW_TP),
+	BPF_PROG_BTF("fentry/",			BPF_PROG_TYPE_TRACING,
+						BPF_TRACE_FENTRY),
+	BPF_PROG_BTF("fexit/",			BPF_PROG_TYPE_TRACING,
+						BPF_TRACE_FEXIT),
 	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
 	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
@@ -5045,12 +5049,15 @@ int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 }
 
 #define BTF_PREFIX "btf_trace_"
-static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id)
+int libbpf_attach_btf_id_by_name(const char *name,
+				 enum bpf_attach_type attach_type,
+				 __u32 *btf_id)
 {
 	struct btf *btf = bpf_core_find_kernel_btf();
 	char raw_tp_btf_name[128] = BTF_PREFIX;
 	char *dst = raw_tp_btf_name + sizeof(BTF_PREFIX) - 1;
 	int ret, i, err = -EINVAL;
+	const char *btf_name;
 
 	if (IS_ERR(btf)) {
 		pr_warn("vmlinux BTF is not found\n");
@@ -5065,12 +5072,17 @@ static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id)
 			continue;
 		if (strncmp(name, section_names[i].sec, section_names[i].len))
 			continue;
-		/* prepend "btf_trace_" prefix per kernel convention */
-		strncat(dst, name + section_names[i].len,
-			sizeof(raw_tp_btf_name) - sizeof(BTF_PREFIX));
-		ret = btf__find_by_name(btf, raw_tp_btf_name);
+		if (attach_type == BPF_TRACE_RAW_TP) {
+			/* prepend "btf_trace_" prefix per kernel convention */
+			strncat(dst, name + section_names[i].len,
+				sizeof(raw_tp_btf_name) - sizeof(BTF_PREFIX));
+			btf_name = raw_tp_btf_name;
+		} else {
+			btf_name = name + section_names[i].len;
+		}
+		ret = btf__find_by_name(btf, btf_name);
 		if (ret <= 0) {
-			pr_warn("%s is not found in vmlinux BTF\n", dst);
+			pr_warn("%s is not found in vmlinux BTF\n", btf_name);
 			goto out;
 		}
 		*btf_id = ret;
@@ -5709,6 +5721,37 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
 	return (struct bpf_link *)link;
 }
 
+struct bpf_link *bpf_program__attach_trace(struct bpf_program *prog)
+{
+	char errmsg[STRERR_BUFSIZE];
+	struct bpf_link_fd *link;
+	int prog_fd, pfd;
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("program '%s': can't attach before loaded\n",
+			bpf_program__title(prog, false));
+		return ERR_PTR(-EINVAL);
+	}
+
+	link = malloc(sizeof(*link));
+	if (!link)
+		return ERR_PTR(-ENOMEM);
+	link->link.destroy = &bpf_link__destroy_fd;
+
+	pfd = bpf_raw_tracepoint_open(NULL, prog_fd);
+	if (pfd < 0) {
+		pfd = -errno;
+		free(link);
+		pr_warn("program '%s': failed to attach to trace: %s\n",
+			bpf_program__title(prog, false),
+			libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+		return ERR_PTR(pfd);
+	}
+	link->fd = pfd;
+	return (struct bpf_link *)link;
+}
+
 enum bpf_perf_event_ret
 bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
 			   void **copy_mem, size_t *copy_size,
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 6ddc0419337b..9576aeadc421 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -188,6 +188,9 @@ libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 			 enum bpf_attach_type *expected_attach_type);
 LIBBPF_API int libbpf_attach_type_by_name(const char *name,
 					  enum bpf_attach_type *attach_type);
+LIBBPF_API int libbpf_attach_btf_id_by_name(const char *name,
+					    enum bpf_attach_type attach_type,
+					    __u32 *btf_id);
 
 /* Accessors of bpf_program */
 struct bpf_program;
@@ -248,6 +251,8 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
 				   const char *tp_name);
 
+LIBBPF_API struct bpf_link *
+bpf_program__attach_trace(struct bpf_program *prog);
 struct bpf_insn;
 
 /*
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 86173cbb159d..3a7ea739bb2a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -198,8 +198,10 @@ LIBBPF_0.0.6 {
 		bpf_map__set_pin_path;
 		bpf_object__open_file;
 		bpf_object__open_mem;
+		bpf_program__attach_trace;
 		bpf_program__get_expected_attach_type;
 		bpf_program__get_type;
 		bpf_program__is_tracing;
 		bpf_program__set_tracing;
+		libbpf_attach_btf_id_by_name;
 } LIBBPF_0.0.5;
-- 
2.23.0