libbpf: Allow decimal offset for kprobes

Allow to specify decimal offset in SEC macro, like:
  SEC("kprobe/bpf_fentry_test7+5")

Add selftest for that.
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20210721215810.889975-3-jolsa@kernel.org

tools/lib/bpf/libbpf.c

@@ -10424,7 +10424,7 @@ static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
 	func_name = prog->sec_name + sec->len;
 	opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;
 
-	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%lx", &func, &offset);
+	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
 	if (n < 1) {
 		err = -EINVAL;
 		pr_warn("kprobe name is invalid: %s\n", func_name);

tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c

@@ -17,6 +17,7 @@ void test_get_func_ip_test(void)
 	 */
 #ifndef __x86_64__
 	bpf_program__set_autoload(skel->progs.test6, false);
+	bpf_program__set_autoload(skel->progs.test7, false);
 #endif
 
 	err = get_func_ip_test__load(skel);
@@ -46,6 +47,7 @@ void test_get_func_ip_test(void)
 	ASSERT_EQ(skel->bss->test5_result, 1, "test5_result");
 #ifdef __x86_64__
 	ASSERT_EQ(skel->bss->test6_result, 1, "test6_result");
+	ASSERT_EQ(skel->bss->test7_result, 1, "test7_result");
 #endif
 
 cleanup:

tools/testing/selftests/bpf/progs/get_func_ip_test.c

@@ -11,6 +11,7 @@ extern const void bpf_fentry_test3 __ksym;
 extern const void bpf_fentry_test4 __ksym;
 extern const void bpf_modify_return_test __ksym;
 extern const void bpf_fentry_test6 __ksym;
+extern const void bpf_fentry_test7 __ksym;
 
 __u64 test1_result = 0;
 SEC("fentry/bpf_fentry_test1")
@@ -71,3 +72,13 @@ int test6(struct pt_regs *ctx)
 	test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
 	return 0;
 }
+
+__u64 test7_result = 0;
+SEC("kprobe/bpf_fentry_test7+5")
+int test7(struct pt_regs *ctx)
+{
+	__u64 addr = bpf_get_func_ip(ctx);
+
+	test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
+	return 0;
+}