Merge pull request #74 from pythonbpf/fix-vmlinux-ir-gen

Fix some issues with vmlinux struct usage in syntax
TODO: THIS DOES NOT FIX the XDP example. 
The issue with the XDP example here is that the range is not being tracked due to multiple loads from stack which is making the verifier lose track of the range on that value.

pythonbpf/expr/expr_pass.py

@@ -168,7 +168,11 @@ def get_operand_value(
             var_type = var.type
             base_type, depth = get_base_type_and_depth(var_type)
             logger.info(f"var is {var}, base_type is {base_type}, depth is {depth}")
-            val = deref_to_depth(func, builder, var, depth)
+            if depth == 1:
+                val = builder.load(var)
+                return val
+            else:
+                val = deref_to_depth(func, builder, var, depth)
             return val
         else:
             # Check if it's a vmlinux enum/constant
@@ -545,7 +549,7 @@ def _handle_boolean_op(
 
 
 # ============================================================================
-# VMLinux casting
+# Struct casting (including vmlinux struct casting)
 # ============================================================================
 
 
@@ -593,17 +597,85 @@ def _handle_vmlinux_cast(
     # Cast the integer/value to a pointer to the struct
     # If arg_val is an integer type, we need to inttoptr it
     ptr_type = ir.PointerType()
-    # TODO: add a integer check here later
-    if ctypes_to_ir(arg_type.type.__name__):
-        # Cast integer to pointer
-        casted_ptr = builder.inttoptr(arg_val, ptr_type)
+    # TODO: add a field value type check here
+    # print(arg_type)
+    if isinstance(arg_type, Field):
+        if ctypes_to_ir(arg_type.type.__name__):
+            # Cast integer to pointer
+            casted_ptr = builder.inttoptr(arg_val, ptr_type)
+        else:
+            logger.error(f"Unsupported type for vmlinux cast: {arg_type}")
+            return None
     else:
-        logger.error(f"Unsupported type for vmlinux cast: {arg_type}")
-        return None
+        casted_ptr = builder.inttoptr(arg_val, ptr_type)
 
     return casted_ptr, vmlinux_struct_type
 
 
+def _handle_user_defined_struct_cast(
+    func,
+    module,
+    builder,
+    expr,
+    local_sym_tab,
+    map_sym_tab,
+    structs_sym_tab,
+):
+    """Handle user-defined struct cast expressions like iphdr(nh).
+
+    This casts a pointer/integer value to a pointer to the user-defined struct,
+    similar to how vmlinux struct casts work but for user-defined @struct types.
+    """
+    if len(expr.args) != 1:
+        logger.info("User-defined struct cast takes exactly one argument")
+        return None
+
+    # Get the struct name
+    struct_name = expr.func.id
+
+    if struct_name not in structs_sym_tab:
+        logger.error(f"Struct {struct_name} not found in structs_sym_tab")
+        return None
+
+    struct_info = structs_sym_tab[struct_name]
+
+    # Evaluate the argument (e.g.,
+    # an address/pointer value)
+    arg_result = eval_expr(
+        func,
+        module,
+        builder,
+        expr.args[0],
+        local_sym_tab,
+        map_sym_tab,
+        structs_sym_tab,
+    )
+
+    if arg_result is None:
+        logger.info("Failed to evaluate argument to user-defined struct cast")
+        return None
+
+    arg_val, arg_type = arg_result
+
+    # Cast the integer/pointer value to a pointer to the struct type
+    # The struct pointer type is a pointer to the struct's IR type
+    struct_ptr_type = ir.PointerType(struct_info.ir_type)
+
+    # If arg_val is an integer type (like i64), convert to pointer using inttoptr
+    if isinstance(arg_val.type, ir.IntType):
+        casted_ptr = builder.inttoptr(arg_val, struct_ptr_type)
+        logger.info(f"Cast integer to pointer for struct {struct_name}")
+    elif isinstance(arg_val.type, ir.PointerType):
+        # If already a pointer, bitcast to the struct pointer type
+        casted_ptr = builder.bitcast(arg_val, struct_ptr_type)
+        logger.info(f"Bitcast pointer to struct pointer for {struct_name}")
+    else:
+        logger.error(f"Unsupported type for user-defined struct cast: {arg_val.type}")
+        return None
+
+    return casted_ptr, struct_name
+
+
 # ============================================================================
 # Expression Dispatcher
 # ============================================================================
@@ -649,6 +721,16 @@ def eval_expr(
                 map_sym_tab,
                 structs_sym_tab,
             )
+        if isinstance(expr.func, ast.Name) and (expr.func.id in structs_sym_tab):
+            return _handle_user_defined_struct_cast(
+                func,
+                module,
+                builder,
+                expr,
+                local_sym_tab,
+                map_sym_tab,
+                structs_sym_tab,
+            )
 
         result = CallHandlerRegistry.handle_call(
             expr, module, builder, func, local_sym_tab, map_sym_tab, structs_sym_tab