feat: improve struct_ops codegen lifecycle and test coverage (#17)

* feat: enhance struct_ops implementation with additional functions and tests

- Added `undo_cwnd` function to `minimal_congestion_control` implementation.
- Updated test for struct_ops compilation completeness to verify direct calls.
- Introduced new test for ensuring internal calls remain direct instead of tail calls.

* tests: enhance struct_ops code generation tests with additional checks for runtime helpers and cleanup functions

* feat: enhance struct_ops handling with terminal return values and tail-call logic

Author: SiyuanSun0736

examples/struct_ops_simple.ks

@@ -12,6 +12,10 @@ impl minimal_congestion_control {
         return 16
     }
 
+    fn undo_cwnd(sk: *u8) -> u32 {
+        return ssthresh(sk)
+    }
+
     fn cong_avoid(sk: *u8, ack: u32, acked: u32) -> void {
         // Minimal TCP congestion avoidance implementation
         // In a real implementation, this would adjust the congestion window

src/ir_generator.ml

@@ -67,6 +67,7 @@ type ir_context = {
   map_origin_variables: (string, (string * ir_value * (ir_value_desc * ir_type))) Hashtbl.t; (* var_name -> (map_name, key, underlying_info) *)
   (* Track inferred variable types for proper lookups *)
   variable_types: (string, ir_type) Hashtbl.t; (* var_name -> ir_type *)
+  mutable current_program_type: program_type option;
 }
 
 (** Create new IR generation context *)
@@ -91,6 +92,7 @@ let create_context ?(global_variables = []) ?(helper_functions = []) symbol_tabl
                      tbl);
   map_origin_variables = Hashtbl.create 32;
   variable_types = Hashtbl.create 32;
+  current_program_type = None;
   helper_functions = (let tbl = Hashtbl.create 16 in
                      List.iter (fun helper_name -> Hashtbl.add tbl helper_name ()) helper_functions;
                      tbl);
@@ -349,6 +351,103 @@ let extract_struct_ops_kernel_name attributes =
     | _ -> acc
   ) "" attributes
 
+let ast_struct_has_field ast struct_name field_name =
+  List.exists (function
+    | Ast.StructDecl struct_def when struct_def.Ast.struct_name = struct_name ->
+        List.exists (fun (name, _) -> name = field_name) struct_def.Ast.struct_fields
+    | _ -> false
+  ) ast
+
+let impl_block_has_static_field impl_block field_name =
+  List.exists (function
+    | Ast.ImplStaticField (name, _) when name = field_name -> true
+    | _ -> false
+  ) impl_block.Ast.impl_items
+
+let normalize_struct_ops_instance_name name =
+  let buffer = Buffer.create (String.length name * 2) in
+  let is_uppercase ch = ch >= 'A' && ch <= 'Z' in
+  let is_lowercase ch = ch >= 'a' && ch <= 'z' in
+  let is_digit ch = ch >= '0' && ch <= '9' in
+  let add_separator_if_needed idx ch =
+    if idx > 0 && is_uppercase ch then
+      let prev = name.[idx - 1] in
+      let next_is_lowercase = idx + 1 < String.length name && is_lowercase name.[idx + 1] in
+      if is_lowercase prev || is_digit prev || (is_uppercase prev && next_is_lowercase) then
+        Buffer.add_char buffer '_'
+  in
+  String.iteri (fun idx ch ->
+    add_separator_if_needed idx ch;
+    let normalized =
+      if is_uppercase ch then Char.lowercase_ascii ch
+      else if is_lowercase ch || is_digit ch || ch = '_' then ch
+      else '_'
+    in
+    Buffer.add_char buffer normalized
+  ) name;
+  Buffer.contents buffer
+
+let generate_default_struct_ops_name instance_name =
+  (* BPF_OBJ_NAME_LEN is 16 bytes including the NUL terminator, so the
+     usable name length is 15 characters. *)
+  let max_len = 15 in
+  let normalized = normalize_struct_ops_instance_name instance_name in
+  if String.length normalized <= max_len then normalized
+  else
+    let parts = List.filter (fun part -> part <> "") (String.split_on_char '_' normalized) in
+    match parts with
+    | [] -> String.sub normalized 0 max_len
+    | first :: rest ->
+        let abbreviated =
+          match rest with
+          | [] -> first
+          | _ ->
+              let initials = rest |> List.map (fun part -> String.make 1 part.[0]) |> String.concat "" in
+              first ^ "_" ^ initials
+        in
+        if String.length abbreviated <= max_len then abbreviated
+        else String.sub abbreviated 0 max_len
+
+(* Decide whether a tail-call return (IRReturnCall) should be emitted for a
+   call to [name] in the current context.
+
+   Two intentional behaviour changes vs. the previous per-site inline logic:
+
+   1. [is_function_pointer] now checks for [IRFunctionPointer] specifically
+      instead of [Hashtbl.mem ctx.variable_types name].  The old check was
+      too broad: any local variable (int, pointer, …) with the same name
+      would be treated as a function pointer and block tail-call lowering.
+
+   2. A tail call is only emitted when [current_program_type] is set to a
+      known attributed type (e.g. XDP, TC, kprobe).  Helper functions that
+      are lowered outside of an attributed program context therefore never
+      produce tail calls, which is correct because they have no prog_array
+      to dispatch into.  struct_ops methods are explicitly excluded via the
+      [StructOps] branch. *)
+let should_lower_as_implicit_tail_call ctx name =
+  let is_function_pointer =
+    Hashtbl.mem ctx.function_parameters name ||
+    match Hashtbl.find_opt ctx.variable_types name with
+    | Some (IRFunctionPointer _) -> true
+    | _ -> false
+  in
+  if is_function_pointer || Hashtbl.mem ctx.helper_functions name then
+    false
+  else
+    match ctx.current_function, ctx.current_program_type with
+    | Some _, Some Ast.StructOps -> false
+    | Some current_func_name, Some _ ->
+        let caller_is_attributed =
+          try Symbol_table.lookup_function ctx.symbol_table current_func_name <> None
+          with _ -> false
+        in
+        let target_is_attributed =
+          try Symbol_table.lookup_function ctx.symbol_table name <> None
+          with _ -> false
+        in
+        caller_is_attributed && target_is_attributed
+    | _ -> false
+
 
 (** Map struct names to their corresponding context types *)
 let struct_name_to_context_type = function
@@ -1659,14 +1758,12 @@ and lower_statement ctx stmt =
                               (* Check if this is a simple function call that could be a tail call *)
                               (match callee_expr.expr_desc with
                                | Ast.Identifier name ->
-                                   (* Check if this is a helper function - if so, treat as regular call *)
-                                   if Hashtbl.mem ctx.helper_functions name then
-                                     let ret_val = lower_expression ctx expr in
-                                     IRReturnValue ret_val
-                                   else
-                                     (* This will be converted to tail call by tail call analyzer *)
+                                     if should_lower_as_implicit_tail_call ctx name then
                                      let arg_vals = List.map (lower_expression ctx) args in
                                      IRReturnCall (name, arg_vals)
+                                     else
+                                       let ret_val = lower_expression ctx expr in
+                                       IRReturnValue ret_val
                                | _ ->
                                    (* Function pointer call - treat as regular return *)
                                    let ret_val = lower_expression ctx expr in
@@ -1689,13 +1786,12 @@ and lower_statement ctx stmt =
                                     (* Check if this is a simple function call that could be a tail call *)
                                     (match callee_expr.expr_desc with
                                      | Ast.Identifier name ->
-                                         (* Check if this is a helper function - if so, treat as regular call *)
-                                         if Hashtbl.mem ctx.helper_functions name then
-                                           let ret_val = lower_expression ctx return_expr in
-                                           IRReturnValue ret_val
-                                         else
+                                           if should_lower_as_implicit_tail_call ctx name then
                                            let arg_vals = List.map (lower_expression ctx) args in
                                            IRReturnCall (name, arg_vals)
+                                           else
+                                             let ret_val = lower_expression ctx return_expr in
+                                             IRReturnValue ret_val
                                      | _ ->
                                          (* Function pointer call - treat as regular return *)
                                          let ret_val = lower_expression ctx return_expr in
@@ -1712,13 +1808,12 @@ and lower_statement ctx stmt =
                                 | Ast.Call (callee_expr, args) ->
                                     (match callee_expr.expr_desc with
                                      | Ast.Identifier name ->
-                                         (* Check if this is a helper function - if so, treat as regular call *)
-                                         if Hashtbl.mem ctx.helper_functions name then
-                                           let ret_val = lower_expression ctx expr in
-                                           IRReturnValue ret_val
-                                         else
+                                         if should_lower_as_implicit_tail_call ctx name then
                                            let arg_vals = List.map (lower_expression ctx) args in
                                            IRReturnCall (name, arg_vals)
+                                         else
+                                           let ret_val = lower_expression ctx expr in
+                                           IRReturnValue ret_val
                                      | _ ->
                                          let ret_val = lower_expression ctx expr in
                                          IRReturnValue ret_val)
@@ -1761,47 +1856,7 @@ and lower_statement ctx stmt =
                  (* Check if this is a simple function call that could be a tail call *)
                  (match callee_expr.expr_desc with
                   | Ast.Identifier name ->
-                      (* Check if this should be a tail call *)
-                      let should_be_tail_call = 
-                        (* First check if the identifier is a function parameter or variable (function pointer) *)
-                        let is_function_pointer = 
-                          Hashtbl.mem ctx.function_parameters name || 
-                          Hashtbl.mem ctx.variable_types name
-                        in
-                        
-                        if is_function_pointer then
-                          (* Function pointer calls should never be tail calls *)
-                          false
-                        else
-                          (* Check if we're in an attributed function context *)
-                          match ctx.current_function with
-                          | Some current_func_name ->
-                              (* Check if caller is attributed (has eBPF attributes) *)
-                              let caller_is_attributed = 
-                                try
-                                  let caller_symbol = Symbol_table.lookup_function ctx.symbol_table current_func_name in
-                                  (* TODO: Check if caller has eBPF attributes like @xdp, @tc, etc. *)
-                                  (* For now, assume attributed functions are defined in symbol table *)
-                                  caller_symbol <> None
-                                with _ -> false
-                              in
-                              
-                              (* Check if target function is an attributed function *)
-                              let target_is_attributed = 
-                                try
-                                  let target_symbol = Symbol_table.lookup_function ctx.symbol_table name in
-                                  (* TODO: Check if target has eBPF attributes like @xdp, @tc, etc. *)
-                                  (* For now, assume attributed functions are defined in symbol table *)
-                                  target_symbol <> None
-                                with _ -> false
-                              in
-                              
-                              (* Only allow tail calls between attributed functions *)
-                              caller_is_attributed && target_is_attributed
-                          | None -> false
-                      in
-                      
-                      if should_be_tail_call then
+                      if should_lower_as_implicit_tail_call ctx name then
                         (* Generate tail call instruction *)
                         let arg_vals = List.map (lower_expression ctx) args in
                         let tail_call_index = 0 in  (* This will be set by tail call analyzer *)
@@ -2356,6 +2411,7 @@ let convert_match_return_calls_to_tail_calls ir_function =
 (** Lower AST function to IR function *)
 let lower_function ctx prog_name ?(program_type : program_type option = None) ?(func_target = None) (func_def : Ast.function_def) =
   ctx.current_function <- Some func_def.func_name;
+  ctx.current_program_type <- program_type;
 
   (* Reset for new function *)
   Hashtbl.clear ctx.variable_types;
@@ -3125,6 +3181,19 @@ let lower_multi_program ast symbol_table source_name =
           in
           Some (field_name, field_val)
     ) impl_block.impl_items in
+    let ir_instance_fields =
+      if ast_struct_has_field ast kernel_struct_name "name" && not (impl_block_has_static_field impl_block "name") then
+        let generated_name = generate_default_struct_ops_name impl_block.impl_name in
+        let generated_name_val =
+          make_ir_value
+            (IRLiteral (StringLit generated_name))
+            (IRStr (String.length generated_name + 1))
+            impl_block.impl_pos
+        in
+        ir_instance_fields @ [("name", generated_name_val)]
+      else
+        ir_instance_fields
+    in
     let ir_instance = make_ir_struct_ops_instance
       impl_block.impl_name
       kernel_struct_name