Fix attach_uprobe_multi_with_opts opts

Currently `func_pattern` is mandatory in `attach_uprobe_multi_with_opts`
Although in the C api it is optional, and mutually exclusive with some
other options. The rust api didn't allow passing null pointer, which
made it impossible to use `syms`/`offsets`/`ref_ctr_offsets`/`cookies`
from `opts` because of the following check -
https://github.com/libbpf/libbpf/blob/3b4f0ef5a6fa247ce1958d909c0e85e760249840/src/libbpf.c#L12172

Change was intentionally made in a way that doesn't break the existing
interface - interpret empty `func_pattern` string as non-existant
pattern. A more correct fix would probably be using an `Option` as this
is truely optional value, or structuring the api in a way that won't
allow passing mutually exclusive parameters.

Signed-off-by: Omer Kattan <omer.kattan@wiz.io>

Author: gadol21

libbpf-rs/src/program.rs

@@ -1107,7 +1107,11 @@ impl<'obj> ProgramMut<'obj> {
         } = opts;
 
         let pattern = util::str_to_cstring(func_pattern.as_ref())?;
-        let pattern_ptr = pattern.as_ptr();
+        let pattern_ptr = if pattern.is_empty() {
+            ptr::null()
+        } else {
+            pattern.as_ptr()
+        };
 
         let syms_cstrings = syms
             .iter()

libbpf-rs/tests/bin/src/uprobe_multi.bpf.c

@@ -42,4 +42,20 @@ int handle__uprobe_multi_with_opts(void *ctx)
     return 0;
 }
 
+SEC("uprobe.multi")
+int handle__uprobe_multi_with_non_default_opts(void *ctx)
+{
+    const int key = 1, init_val = 1;
+
+    int *val = bpf_map_lookup_elem(&hash_map, &key);
+    if (val) {
+        __sync_fetch_and_add(val, 1);
+        bpf_printk("handle__uprobe_multi_with_non_default_opts: val=%d\n", *val);
+    } else {
+        bpf_map_update_elem(&hash_map, &key, &init_val, BPF_ANY);
+    }
+
+    return 0;
+}
+
 char LICENSE[] SEC("license") = "GPL";

libbpf-rs/tests/test.rs

@@ -1987,6 +1987,20 @@ extern "C" fn multi_uprobe_func_with_opts_func_2() -> usize {
     hint::black_box(45)
 }
 
+#[inline(never)]
+#[no_mangle]
+extern "C" fn non_default_opts_multi_uprobe_func_with_opts_func_1() -> usize {
+    // Use `black_box` here as an additional barrier to inlining.
+    hint::black_box(46)
+}
+
+#[inline(never)]
+#[no_mangle]
+extern "C" fn non_default_opts_multi_uprobe_func_with_opts_func_2() -> usize {
+    // Use `black_box` here as an additional barrier to inlining.
+    hint::black_box(47)
+}
+
 #[tag(root)]
 #[test]
 fn test_object_uprobe_multi_with_opts() {
@@ -2021,6 +2035,46 @@ fn test_object_uprobe_multi_with_opts() {
     assert_eq!(result, 2);
 }
 
+#[tag(root)]
+#[test]
+fn test_object_uprobe_multi_with_non_default_opts() {
+    let mut obj = get_test_object("uprobe_multi.bpf.o");
+    let prog = get_prog_mut(&mut obj, "handle__uprobe_multi_with_non_default_opts");
+    let func_pattern = "";
+
+    let pid = unsafe { libc::getpid() };
+    let path = current_exe().expect("failed to find executable name");
+    let opts = UprobeMultiOpts {
+        syms: vec![
+            "non_default_opts_multi_uprobe_func_with_opts_func_1".to_string(),
+            "non_default_opts_multi_uprobe_func_with_opts_func_2".to_string(),
+        ],
+      ..Default::default()
+    };
+
+    let _link = prog
+        .attach_uprobe_multi_with_opts(pid, path, func_pattern, opts)
+        .expect("failed to attach uprobe multi");
+
+    non_default_opts_multi_uprobe_func_with_opts_func_1();
+    non_default_opts_multi_uprobe_func_with_opts_func_2();
+
+    let map = get_map_mut(&mut obj, "hash_map");
+    let result_bytes = map
+        .lookup(&(1_u32).to_ne_bytes(), MapFlags::ANY)
+        .expect("failed to lookup")
+        .expect("failed to find value for key");
+
+    let result = i32::from_ne_bytes(
+        result_bytes
+            .as_slice()
+            .try_into()
+            .expect("invalid value size"),
+    );
+
+    assert_eq!(result, 2);
+}
+
 #[tag(root)]
 #[test]
 fn test_object_uprobe_multi() {