[RFC PATCH bpf-next 1/2] libbpf: Try get fentry func addr from available_filter_functions_addr

[Tao Chen <chen.dylane@linux.dev>]

Try to get the real kernel func addr from available_filter_functions_addr,
in case of the function name is optimized by the compiler and a suffix
such as ".isra.0" is added, which will be used in the next patch.

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 tools/include/uapi/linux/bpf.h |  1 +
 tools/lib/bpf/bpf.c            |  1 +
 tools/lib/bpf/bpf.h            |  1 +
 tools/lib/bpf/gen_loader.c     |  1 +
 tools/lib/bpf/libbpf.c         | 53 ++++++++++++++++++++++++++++++++++
 5 files changed, 57 insertions(+)

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 07ee73cdf9..7016e47a70 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1577,6 +1577,7 @@ union bpf_attr {
 		 * If provided, prog_flags should have BPF_F_TOKEN_FD flag set.
 		 */
 		__s32		prog_token_fd;
+		__aligned_u64	fentry_func;
 		/* The fd_array_cnt can be used to pass the length of the
 		 * fd_array array. In this case all the [map] file descriptors
 		 * passed in this array will be bound to the program, even if
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index a9c3e33d0f..639a6b54e8 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -312,6 +312,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
 
 	attr.fd_array = ptr_to_u64(OPTS_GET(opts, fd_array, NULL));
 	attr.fd_array_cnt = OPTS_GET(opts, fd_array_cnt, 0);
+	attr.fentry_func = OPTS_GET(opts, fentry_func, 0);
 
 	if (log_level) {
 		attr.log_buf = ptr_to_u64(log_buf);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 777627d33d..b3340bcf7b 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -83,6 +83,7 @@ struct bpf_prog_load_opts {
 	__u32 attach_btf_id;
 	__u32 attach_prog_fd;
 	__u32 attach_btf_obj_fd;
+	__u64 fentry_func;
 
 	const int *fd_array;
 
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index 113ae4abd3..d90874b746 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -1023,6 +1023,7 @@ void bpf_gen__prog_load(struct bpf_gen *gen,
 	attr.kern_version = 0;
 	attr.insn_cnt = tgt_endian((__u32)insn_cnt);
 	attr.prog_flags = tgt_endian(load_attr->prog_flags);
+	attr.fentry_func = tgt_endian(load_attr->fentry_func);
 
 	attr.func_info_rec_size = tgt_endian(load_attr->func_info_rec_size);
 	attr.func_info_cnt = tgt_endian(load_attr->func_info_cnt);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 37d563e140..624e75cf2f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7456,6 +7456,50 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
 }
 
 static void fixup_verifier_log(struct bpf_program *prog, char *buf, size_t buf_sz);
+static const char *tracefs_available_filter_functions_addrs(void);
+
+static void try_get_fentry_func_addr(const char *func_name, struct bpf_prog_load_opts *load_attr)
+{
+	const char *available_functions_file = tracefs_available_filter_functions_addrs();
+	char sym_name[500];
+	FILE *f;
+	char *suffix;
+	int ret;
+	unsigned long long sym_addr;
+
+	f = fopen(available_functions_file, "re");
+	if (!f) {
+		pr_warn("failed to open %s: %s\n", available_functions_file, errstr(errno));
+		return;
+	}
+
+	while (true) {
+		ret = fscanf(f, "%llx %499s%*[^\n]\n", &sym_addr, sym_name);
+		if (ret == EOF && feof(f))
+			break;
+
+		if (ret != 2) {
+			pr_warn("failed to parse available_filter_functions_addrs entry: %d\n",
+				ret);
+			goto cleanup;
+		}
+
+		if (strcmp(func_name, sym_name) == 0) {
+			load_attr->fentry_func = sym_addr;
+			break;
+		}
+		/* find [func_name] optimized by compiler like [func_name].isra.0 */
+		suffix = strstr(sym_name, ".");
+		if (suffix && strncmp(sym_name, func_name,
+					strlen(sym_name) - strlen(suffix)) == 0) {
+			load_attr->fentry_func = sym_addr;
+			break;
+		}
+	}
+
+cleanup:
+	fclose(f);
+}
 
 static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog,
 				struct bpf_insn *insns, int insns_cnt,
@@ -7504,6 +7548,15 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
 	load_attr.prog_ifindex = prog->prog_ifindex;
 	load_attr.expected_attach_type = prog->expected_attach_type;
 
+	if (load_attr.expected_attach_type == BPF_TRACE_FENTRY ||
+		load_attr.expected_attach_type == BPF_TRACE_FEXIT) {
+		const char *func_name;
+
+		func_name = strchr(prog->sec_name, '/');
+		if (func_name)
+			try_get_fentry_func_addr(++func_name, &load_attr);
+	}
+
 	/* specify func_info/line_info only if kernel supports them */
 	if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
 		load_attr.prog_btf_fd = btf__fd(obj->btf);
-- 
2.43.0