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.

Author: varun-r-mallya

BCC-Examples/disksnoop.ipynb

@@ -0,0 +1,122 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "c3520e58-e50f-4bc1-8f9d-a6fecbf6e9f0",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from vmlinux import struct_request, struct_pt_regs\n",
+    "from pythonbpf import bpf, section, bpfglobal, map, BPF\n",
+    "from pythonbpf.helper import ktime\n",
+    "from pythonbpf.maps import HashMap\n",
+    "from ctypes import c_int64, c_uint64, c_int32\n",
+    "\n",
+    "REQ_WRITE = 1\n",
+    "\n",
+    "\n",
+    "@bpf\n",
+    "@map\n",
+    "def start() -> HashMap:\n",
+    "    return HashMap(key=c_uint64, value=c_uint64, max_entries=10240)\n",
+    "\n",
+    "\n",
+    "@bpf\n",
+    "@section(\"kprobe/blk_mq_end_request\")\n",
+    "def trace_completion(ctx: struct_pt_regs) -> c_int64:\n",
+    "    # Get request pointer from first argument\n",
+    "    req_ptr = ctx.di\n",
+    "    req = struct_request(ctx.di)\n",
+    "    # Print: data_len, cmd_flags, latency_us\n",
+    "    data_len = req.__data_len\n",
+    "    cmd_flags = req.cmd_flags\n",
+    "    # Lookup start timestamp\n",
+    "    req_tsp = start.lookup(req_ptr)\n",
+    "    if req_tsp:\n",
+    "        # Calculate delta in nanoseconds\n",
+    "        delta = ktime() - req_tsp\n",
+    "\n",
+    "        # Convert to microseconds for printing\n",
+    "        delta_us = delta // 1000\n",
+    "\n",
+    "        print(f\"{data_len} {cmd_flags:x} {delta_us}\\n\")\n",
+    "\n",
+    "        # Delete the entry\n",
+    "        start.delete(req_ptr)\n",
+    "\n",
+    "    return c_int64(0)\n",
+    "\n",
+    "\n",
+    "@bpf\n",
+    "@section(\"kprobe/blk_mq_start_request\")\n",
+    "def trace_start(ctx1: struct_pt_regs) -> c_int32:\n",
+    "    req = ctx1.di\n",
+    "    ts = ktime()\n",
+    "    start.update(req, ts)\n",
+    "    return c_int32(0)\n",
+    "\n",
+    "\n",
+    "@bpf\n",
+    "@bpfglobal\n",
+    "def LICENSE() -> str:\n",
+    "    return \"GPL\"\n",
+    "\n",
+    "\n",
+    "b = BPF()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "97040f73-98e0-4993-94c6-125d1b42d931",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "b.load()\n",
+    "b.attach_all()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "b1bd4f51-fa25-42e1-877c-e48a2605189f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from pythonbpf import trace_pipe"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "96b4b59b-b0db-4952-9534-7a714f685089",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "trace_pipe()"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.12.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

BCC-Examples/disksnoop.py

@@ -0,0 +1,61 @@
+from vmlinux import struct_request, struct_pt_regs
+from pythonbpf import bpf, section, bpfglobal, compile_to_ir, compile, map
+from pythonbpf.helper import ktime
+from pythonbpf.maps import HashMap
+import logging
+from ctypes import c_int64, c_uint64, c_int32
+
+# Constants
+REQ_WRITE = 1  # from include/linux/blk_types.h
+
+
+@bpf
+@map
+def start() -> HashMap:
+    return HashMap(key=c_uint64, value=c_uint64, max_entries=10240)
+
+
+@bpf
+@section("kprobe/blk_mq_end_request")
+def trace_completion(ctx: struct_pt_regs) -> c_int64:
+    # Get request pointer from first argument
+    req_ptr = ctx.di
+    req = struct_request(ctx.di)
+    # Print: data_len, cmd_flags, latency_us
+    data_len = req.__data_len
+    cmd_flags = req.cmd_flags
+    # Lookup start timestamp
+    req_tsp = start.lookup(req_ptr)
+    if req_tsp:
+        # Calculate delta in nanoseconds
+        delta = ktime() - req_tsp
+
+        # Convert to microseconds for printing
+        delta_us = delta // 1000
+
+        print(f"{data_len} {cmd_flags:x} {delta_us}\n")
+
+        # Delete the entry
+        start.delete(req_ptr)
+
+    return c_int64(0)
+
+
+@bpf
+@section("kprobe/blk_mq_start_request")
+def trace_start(ctx1: struct_pt_regs) -> c_int32:
+    req = ctx1.di
+    ts = ktime()
+    start.update(req, ts)
+    return c_int32(0)
+
+
+@bpf
+@bpfglobal
+def LICENSE() -> str:
+    return "GPL"
+
+
+if __name__ == "__main__":
+    compile_to_ir("disksnoop.py", "disksnoop.ll", loglevel=logging.INFO)
+    compile()

pythonbpf/allocation_pass.py

@@ -114,9 +114,22 @@ def _allocate_for_call(
         # Struct constructors
         elif call_type in structs_sym_tab:
             struct_info = structs_sym_tab[call_type]
-            var = builder.alloca(struct_info.ir_type, name=var_name)
-            local_sym_tab[var_name] = LocalSymbol(var, struct_info.ir_type, call_type)
-            logger.info(f"Pre-allocated {var_name} for struct {call_type}")
+            if len(rval.args) == 0:
+                # Zero-arg constructor: allocate the struct itself
+                var = builder.alloca(struct_info.ir_type, name=var_name)
+                local_sym_tab[var_name] = LocalSymbol(
+                    var, struct_info.ir_type, call_type
+                )
+                logger.info(f"Pre-allocated {var_name} for struct {call_type}")
+            else:
+                # Pointer cast: allocate as pointer to struct
+                ptr_type = ir.PointerType(struct_info.ir_type)
+                var = builder.alloca(ptr_type, name=var_name)
+                var.align = 8
+                local_sym_tab[var_name] = LocalSymbol(var, ptr_type, call_type)
+                logger.info(
+                    f"Pre-allocated {var_name} for struct pointer cast to {call_type}"
+                )
 
         elif VmlinuxHandlerRegistry.is_vmlinux_struct(call_type):
             # When calling struct_name(pointer), we're doing a cast, not construction
@@ -371,6 +384,7 @@ def _allocate_for_attribute(builder, var_name, rval, local_sym_tab, structs_sym_
                         f"Could not determine size for ctypes field {field_name}: {e}"
                     )
                     actual_ir_type = ir.IntType(64)
+                    field_size_bits = 64
 
             # Check if it's a nested vmlinux struct or complex type
             elif field.type.__module__ == "vmlinux":
@@ -379,23 +393,34 @@ def _allocate_for_attribute(builder, var_name, rval, local_sym_tab, structs_sym_
                     field.ctype_complex_type, ctypes._Pointer
                 ):
                     actual_ir_type = ir.IntType(64)  # Pointer is always 64-bit
+                    field_size_bits = 64
                 # For embedded structs, this is more complex - might need different handling
                 else:
                     logger.warning(
                         f"Field {field_name} is a nested vmlinux struct, using i64 for now"
                     )
                     actual_ir_type = ir.IntType(64)
+                    field_size_bits = 64
             else:
                 logger.warning(
                     f"Unknown field type module {field.type.__module__} for {field_name}"
                 )
                 actual_ir_type = ir.IntType(64)
+                field_size_bits = 64
+
+            # Pre-allocate the tmp storage used by load_struct_field (so we don't alloca inside handler)
+            tmp_name = f"{struct_var}_{field_name}_tmp"
+            tmp_ir_type = ir.IntType(field_size_bits)
+            tmp_var = builder.alloca(tmp_ir_type, name=tmp_name)
+            tmp_var.align = tmp_ir_type.width // 8
+            local_sym_tab[tmp_name] = LocalSymbol(tmp_var, tmp_ir_type)
+            logger.info(
+                f"Pre-allocated temp {tmp_name} (i{field_size_bits}) for vmlinux field read {vmlinux_struct_name}.{field_name}"
+            )
 
-            # Allocate with the actual IR type
+            # Allocate with the actual IR type for the destination var
             var = _allocate_with_type(builder, var_name, actual_ir_type)
-            local_sym_tab[var_name] = LocalSymbol(
-                var, actual_ir_type, field
-            )  # <-- Store Field metadata
+            local_sym_tab[var_name] = LocalSymbol(var, actual_ir_type, field)
 
             logger.info(
                 f"Pre-allocated {var_name} as {actual_ir_type} from vmlinux struct {vmlinux_struct_name}.{field_name}"

pythonbpf/assign_pass.py

@@ -174,6 +174,23 @@ def handle_variable_assignment(
                     f"Type mismatch: vmlinux struct pointer requires i64, got {var_type}"
                 )
                 return False
+        # Handle user-defined struct pointer casts
+        # val_type is a string (struct name), var_type is a pointer to the struct
+        if isinstance(val_type, str) and val_type in structs_sym_tab:
+            struct_info = structs_sym_tab[val_type]
+            expected_ptr_type = ir.PointerType(struct_info.ir_type)
+
+            # Check if var_type matches the expected pointer type
+            if isinstance(var_type, ir.PointerType) and var_type == expected_ptr_type:
+                # val is already the correct pointer type from inttoptr/bitcast
+                builder.store(val, var_ptr)
+                logger.info(f"Assigned user-defined struct pointer cast to {var_name}")
+                return True
+            else:
+                logger.error(
+                    f"Type mismatch: user-defined struct pointer cast requires pointer type, got {var_type}"
+                )
+                return False
         if isinstance(val_type, Field):
             logger.info("Handling assignment to struct field")
             # Special handling for struct_xdp_md i32 fields that are zero-extended to i64