Move get_struct_char_array_ptr from helper/printk_formatter to helper/helper_utils, enable array to ptr conversion in skb_store_bytes

Author: r41k0u

pythonbpf/helper/helper_utils.py

@@ -85,6 +85,52 @@ def create_int_constant_ptr(value, builder, local_sym_tab, int_width=64):
     return ptr
 
 
+def get_struct_char_array_ptr(expr, builder, local_sym_tab, struct_sym_tab):
+    """Get pointer to first element of char array in struct field, or None."""
+    if not (isinstance(expr, ast.Attribute) and isinstance(expr.value, ast.Name)):
+        return None
+
+    var_name = expr.value.id
+    field_name = expr.attr
+
+    # Check if it's a valid struct field
+    if not (
+        local_sym_tab
+        and var_name in local_sym_tab
+        and struct_sym_tab
+        and local_sym_tab[var_name].metadata in struct_sym_tab
+    ):
+        return None
+
+    struct_type = local_sym_tab[var_name].metadata
+    struct_info = struct_sym_tab[struct_type]
+
+    if field_name not in struct_info.fields:
+        return None
+
+    field_type = struct_info.field_type(field_name)
+
+    # Check if it's a char array
+    is_char_array = (
+        isinstance(field_type, ir.ArrayType)
+        and isinstance(field_type.element, ir.IntType)
+        and field_type.element.width == 8
+    )
+
+    if not is_char_array:
+        return None
+
+    # Get field pointer and GEP to first element: [N x i8]* -> i8*
+    struct_ptr = local_sym_tab[var_name].var
+    field_ptr = struct_info.gep(builder, struct_ptr, field_name)
+
+    return builder.gep(
+        field_ptr,
+        [ir.Constant(ir.IntType(32), 0), ir.Constant(ir.IntType(32), 0)],
+        inbounds=True,
+    )
+
+
 def get_or_create_ptr_from_arg(
     func,
     module,
@@ -97,13 +143,47 @@ def get_or_create_ptr_from_arg(
 ):
     """Extract or create pointer from the call arguments."""
 
+    logger.info(f"Getting pointer from arg: {ast.dump(arg)}")
     if isinstance(arg, ast.Name):
         # Stack space is already allocated
         ptr = get_var_ptr_from_name(arg.id, local_sym_tab)
     elif isinstance(arg, ast.Constant) and isinstance(arg.value, int):
         if expected_type and isinstance(expected_type, ir.IntType):
             int_width = expected_type.width
         ptr = create_int_constant_ptr(arg.value, builder, local_sym_tab, int_width)
+    elif isinstance(arg, ast.Attribute):
+        # A struct field
+        struct_name = arg.value.id
+        field_name = arg.attr
+
+        if not local_sym_tab or struct_name not in local_sym_tab:
+            raise ValueError(f"Struct '{struct_name}' not found")
+
+        struct_type = local_sym_tab[struct_name].metadata
+        if not struct_sym_tab or struct_type not in struct_sym_tab:
+            raise ValueError(f"Struct type '{struct_type}' not found")
+
+        struct_info = struct_sym_tab[struct_type]
+        if field_name not in struct_info.fields:
+            raise ValueError(
+                f"Field '{field_name}' not found in struct '{struct_name}'"
+            )
+
+        field_type = struct_info.field_type(field_name)
+        struct_ptr = local_sym_tab[struct_name].var
+
+        # Special handling for char arrays
+        if (
+            isinstance(field_type, ir.ArrayType)
+            and isinstance(field_type.element, ir.IntType)
+            and field_type.element.width == 8
+        ):
+            ptr = get_struct_char_array_ptr(arg, builder, local_sym_tab, struct_sym_tab)
+            if not ptr:
+                raise ValueError("Failed to get char array pointer from struct field")
+        else:
+            ptr = struct_info.gep(builder, struct_ptr, field_name)
+
     else:
         # NOTE: For any integer expression reaching this branch, it is probably a struct field or a binop
         # Evaluate the expression and store the result in a temp variable

pythonbpf/helper/printk_formatter.py

@@ -4,6 +4,7 @@
 from llvmlite import ir
 from pythonbpf.expr import eval_expr, get_base_type_and_depth, deref_to_depth
 from pythonbpf.expr.vmlinux_registry import VmlinuxHandlerRegistry
+from pythonbpf.helper.helper_utils import get_struct_char_array_ptr
 
 logger = logging.getLogger(__name__)
 
@@ -219,7 +220,7 @@ def _prepare_expr_args(expr, func, module, builder, local_sym_tab, struct_sym_ta
     """Evaluate and prepare an expression to use as an arg for bpf_printk."""
 
     # Special case: struct field char array needs pointer to first element
-    char_array_ptr = _get_struct_char_array_ptr(
+    char_array_ptr = get_struct_char_array_ptr(
         expr, builder, local_sym_tab, struct_sym_tab
     )
     if char_array_ptr:
@@ -242,52 +243,6 @@ def _prepare_expr_args(expr, func, module, builder, local_sym_tab, struct_sym_ta
         return ir.Constant(ir.IntType(64), 0)
 
 
-def _get_struct_char_array_ptr(expr, builder, local_sym_tab, struct_sym_tab):
-    """Get pointer to first element of char array in struct field, or None."""
-    if not (isinstance(expr, ast.Attribute) and isinstance(expr.value, ast.Name)):
-        return None
-
-    var_name = expr.value.id
-    field_name = expr.attr
-
-    # Check if it's a valid struct field
-    if not (
-        local_sym_tab
-        and var_name in local_sym_tab
-        and struct_sym_tab
-        and local_sym_tab[var_name].metadata in struct_sym_tab
-    ):
-        return None
-
-    struct_type = local_sym_tab[var_name].metadata
-    struct_info = struct_sym_tab[struct_type]
-
-    if field_name not in struct_info.fields:
-        return None
-
-    field_type = struct_info.field_type(field_name)
-
-    # Check if it's a char array
-    is_char_array = (
-        isinstance(field_type, ir.ArrayType)
-        and isinstance(field_type.element, ir.IntType)
-        and field_type.element.width == 8
-    )
-
-    if not is_char_array:
-        return None
-
-    # Get field pointer and GEP to first element: [N x i8]* -> i8*
-    struct_ptr = local_sym_tab[var_name].var
-    field_ptr = struct_info.gep(builder, struct_ptr, field_name)
-
-    return builder.gep(
-        field_ptr,
-        [ir.Constant(ir.IntType(32), 0), ir.Constant(ir.IntType(32), 0)],
-        inbounds=True,
-    )
-
-
 def _handle_pointer_arg(val, func, builder):
     """Convert pointer type for bpf_printk."""
     target, depth = get_base_type_and_depth(val.type)