Merge pull request #94 from pythonbpf/fix/probe-read-ctx-not-found

register ctx in the local_sym_tab with the type `void *` if no struct annotation is given

Author: varun-r-mallya

pythonbpf/allocation_pass.py

@@ -340,9 +340,15 @@ def _allocate_for_attribute(
 
     struct_type: type = local_sym_tab[struct_var].metadata
     if not struct_type or struct_type not in structs_sym_tab:
-        if VmlinuxHandlerRegistry.is_vmlinux_struct(struct_type.__name__):
+        # `metadata` only names a struct for struct-typed symbols. For anything
+        # else (None, an IR type, or a plain ctypes class such as a `c_void_p`
+        # context parameter) there is no vmlinux struct name to look up, so guard
+        # the attribute access instead of blowing up with an AttributeError.
+        vmlinux_struct_name = getattr(struct_type, "__name__", None)
+        if vmlinux_struct_name and VmlinuxHandlerRegistry.is_vmlinux_struct(
+            vmlinux_struct_name
+        ):
             # Handle vmlinux struct field access
-            vmlinux_struct_name = struct_type.__name__
             if not VmlinuxHandlerRegistry.has_field(vmlinux_struct_name, field_name):
                 logger.error(
                     f"Field '{field_name}' not found in vmlinux struct '{vmlinux_struct_name}'"

pythonbpf/functions/functions_pass.py

@@ -1,11 +1,12 @@
 from llvmlite import ir
 import ast
+import ctypes
 import logging
 
 from pythonbpf.helper import (
     HelperHandlerRegistry,
 )
-from pythonbpf.type_deducer import ctypes_to_ir
+from pythonbpf.type_deducer import ctypes_to_ir, is_ctypes
 from pythonbpf.expr import (
     eval_expr,
     handle_expr,
@@ -325,13 +326,28 @@ def process_func_body(
                     f"Unsupported annotation type: {ast.dump(context_arg.annotation)}"
                 )
 
+            # NOTE: `var` is None for the context parameter. It is the sentinel
+            # that tells consumers the symbol is an incoming function argument
+            # (`func.args[0]`) rather than a stack slot they can load from.
             if VmlinuxHandlerRegistry.is_vmlinux_struct(context_type_name):
                 resolved_type = VmlinuxHandlerRegistry.get_struct_type(
                     context_type_name
                 )
                 context_type = LocalSymbol(None, None, resolved_type)
                 local_sym_tab[context_name] = context_type
                 logger.info(f"Added argument '{context_name}' to local symbol table")
+            elif is_ctypes(context_type_name):
+                # Plain ctypes annotation, e.g. `ctx: c_void_p`. Register it so
+                # helpers that take the raw context (probe_read, ...) can resolve
+                # the name. Metadata is the annotated Python type, mirroring the
+                # vmlinux branch above.
+                context_type = LocalSymbol(
+                    None,
+                    ir.PointerType(),
+                    getattr(ctypes, context_type_name, None),
+                )
+                local_sym_tab[context_name] = context_type
+                logger.info(f"Added argument '{context_name}' to local symbol table")
 
     # pre-allocate dynamic variables
     local_sym_tab = allocate_mem(

pythonbpf/helper/helper_utils.py

@@ -52,8 +52,20 @@ def get_or_create_ptr_from_arg(
     logger.info(f"Getting pointer from arg: {ast.dump(arg)}")
     sz = None
     if isinstance(arg, ast.Name):
-        # Stack space is already allocated
-        ptr = get_var_ptr_from_name(arg.id, local_sym_tab)
+        symbol = local_sym_tab.get(arg.id) if local_sym_tab else None
+        if symbol is not None and symbol.var is None:
+            # A None `var` marks the context parameter (see process_func_body):
+            # it arrives as the function's first argument, not as a stack slot,
+            # so there is no alloca to hand back. Use the argument itself.
+            if not func.args:
+                raise ValueError(
+                    f"'{arg.id}' is the context parameter but "
+                    f"'{func.name}' takes no arguments"
+                )
+            ptr = builder.bitcast(func.args[0], ir.PointerType())
+        else:
+            # 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):
         int_width = 64  # Default to i64
         if expected_type and isinstance(expected_type, ir.IntType):