chore: call bpf_object__open_mem from go

This changes libbpfgo to call bpf_object__open_mem directly from go
instead of doing this via a C wrapper. What this means is that we
maintained opts creation in C, but the actual libbpf object open call
is done in go.

This creates two new functions in libbpfgo.h as helpers:
- bpf_object_open_opts_new()
- bpf_object_open_opts_free()

Context: #304

Additionally, this commit enforces the use of defer and resolves a
potential CKconfigPath leak when len(args.KConfigFilePath) is > 2.

libbpfgo.go

@@ -381,25 +381,31 @@ func NewModuleFromBufferArgs(args NewModuleArgs) (*Module, error) {
 	}
 
 	cBTFFilePath := C.CString(args.BTFObjPath)
+	defer C.free(unsafe.Pointer(cBTFFilePath))
 	cKconfigPath := C.CString(args.KConfigFilePath)
+	defer C.free(unsafe.Pointer(cKconfigPath))
 	cBPFObjName := C.CString(args.BPFObjName)
+	defer C.free(unsafe.Pointer(cBPFObjName))
 	cBPFBuff := unsafe.Pointer(C.CBytes(args.BPFObjBuff))
+	defer C.free(cBPFBuff)
 	cBPFBuffSize := C.size_t(len(args.BPFObjBuff))
 
 	if len(args.KConfigFilePath) <= 2 {
 		C.free(unsafe.Pointer(cKconfigPath))
 		cKconfigPath = nil
 	}
 
-	obj, errno := C.open_bpf_object(cBTFFilePath, cKconfigPath, cBPFObjName, cBPFBuff, cBPFBuffSize)
+	cOpts, errno := C.bpf_object_open_opts_new(cBTFFilePath, cKconfigPath, cBPFObjName)
+	if cOpts == nil {
+		return nil, fmt.Errorf("failed to create bpf_object_open_opts to %s: %w", args.BPFObjName, errno)
+	}
+	defer C.bpf_object_open_opts_free(cOpts)
+
+	obj, errno := C.bpf_object__open_mem(cBPFBuff, cBPFBuffSize, cOpts)
 	if obj == nil {
 		return nil, fmt.Errorf("failed to open BPF object %s: %w", args.BPFObjName, errno)
 	}
 
-	C.free(cBPFBuff)
-	C.free(unsafe.Pointer(cBPFObjName))
-	C.free(unsafe.Pointer(cBTFFilePath))
-
 	return &Module{
 		obj: obj,
 		elf: f,

libbpfgo.h

@@ -175,27 +175,25 @@ void bpf_iter_attach_opts_free(struct bpf_iter_attach_opts *opts)
     free(opts);
 }
 
-struct bpf_object *open_bpf_object(char *btf_file_path,
-                                   char *kconfig_path,
-                                   char *bpf_obj_name,
-                                   const void *obj_buf,
-                                   size_t obj_buf_size)
+struct bpf_object_open_opts *
+bpf_object_open_opts_new(char *btf_file_path, char *kconfig_path, char *bpf_obj_name)
 {
-    struct bpf_object_open_opts opts = {};
-    opts.btf_custom_path = btf_file_path;
-    opts.kconfig = kconfig_path;
-    opts.object_name = bpf_obj_name;
-    opts.sz = sizeof(opts);
-
-    struct bpf_object *obj = bpf_object__open_mem(obj_buf, obj_buf_size, &opts);
-    if (obj == NULL) {
-        int saved_errno = errno;
-        fprintf(stderr, "Failed to open bpf object: %s\n", strerror(errno));
-        errno = saved_errno;
+    struct bpf_object_open_opts *opts;
+    opts = calloc(1, sizeof(*opts));
+    if (!opts)
         return NULL;
-    }
 
-    return obj;
+    opts->sz = sizeof(*opts);
+    opts->btf_custom_path = btf_file_path;
+    opts->kconfig = kconfig_path;
+    opts->object_name = bpf_obj_name;
+
+    return opts;
+}
+
+void bpf_object_open_opts_free(struct bpf_object_open_opts *opts)
+{
+    free(opts);
 }
 
 #endif