post-W7 cleanup
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#!/usr/bin/env python3
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"""Validate a W2 UCE PIC unit wasm artifact.
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Checks intentionally stay small and explicit: section walk for dylink.0,
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uce.abi, imports/exports, plus llvm-nm for allocator definitions.
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"""
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from __future__ import annotations
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import argparse
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import shutil
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import subprocess
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import sys
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from pathlib import Path
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def read_u32leb(data: bytes, pos: int) -> tuple[int, int]:
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result = 0
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shift = 0
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while True:
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if pos >= len(data):
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raise ValueError("truncated leb128")
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b = data[pos]
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pos += 1
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result |= (b & 0x7F) << shift
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if (b & 0x80) == 0:
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return result, pos
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shift += 7
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if shift > 35:
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raise ValueError("oversized leb128")
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def read_name(data: bytes, pos: int) -> tuple[str, int]:
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n, pos = read_u32leb(data, pos)
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end = pos + n
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if end > len(data):
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raise ValueError("truncated name")
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return data[pos:end].decode("utf-8", "replace"), end
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def walk_sections(data: bytes):
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if not data.startswith(b"\0asm\x01\0\0\0"):
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raise ValueError("not a wasm v1 module")
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pos = 8
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while pos < len(data):
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section_id = data[pos]
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pos += 1
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size, pos = read_u32leb(data, pos)
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end = pos + size
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if end > len(data):
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raise ValueError("section extends past EOF")
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payload = data[pos:end]
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yield section_id, payload
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pos = end
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def parse_imports(payload: bytes):
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pos = 0
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count, pos = read_u32leb(payload, pos)
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imports = []
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for _ in range(count):
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module, pos = read_name(payload, pos)
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name, pos = read_name(payload, pos)
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if pos >= len(payload):
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raise ValueError("truncated import kind")
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kind = payload[pos]
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pos += 1
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# Skip type descriptors. We only need module/name/kind for W2 policy.
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if kind == 0: # func type index
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_, pos = read_u32leb(payload, pos)
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elif kind == 1: # table
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if pos >= len(payload): raise ValueError("truncated table import")
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pos += 1
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flags, pos = read_u32leb(payload, pos)
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_, pos = read_u32leb(payload, pos)
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if flags & 1: _, pos = read_u32leb(payload, pos)
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elif kind == 2: # memory
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flags, pos = read_u32leb(payload, pos)
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_, pos = read_u32leb(payload, pos)
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if flags & 1: _, pos = read_u32leb(payload, pos)
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elif kind == 3: # global
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pos += 2
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else:
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raise ValueError(f"unknown import kind {kind}")
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imports.append((module, name, kind))
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return imports
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def parse_exports(payload: bytes):
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pos = 0
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count, pos = read_u32leb(payload, pos)
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exports = []
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for _ in range(count):
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name, pos = read_name(payload, pos)
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if pos >= len(payload):
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raise ValueError("truncated export kind")
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kind = payload[pos]
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pos += 1
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_, pos = read_u32leb(payload, pos)
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exports.append((name, kind))
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return exports
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def collect(path: Path):
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data = path.read_bytes()
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customs: dict[str, list[bytes]] = {}
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imports = []
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exports = []
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for section_id, payload in walk_sections(data):
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if section_id == 0:
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name, pos = read_name(payload, 0)
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customs.setdefault(name, []).append(payload[pos:])
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elif section_id == 2:
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imports = parse_imports(payload)
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elif section_id == 7:
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exports = parse_exports(payload)
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return customs, imports, exports
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def dylink_has_valid_mem_info(payload: bytes) -> bool:
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pos = 0
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while pos < len(payload):
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subsection_id = payload[pos]
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pos += 1
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size, pos = read_u32leb(payload, pos)
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end = pos + size
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if end > len(payload):
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raise ValueError("dylink.0 subsection extends past section")
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if subsection_id == 1:
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mem_size, p = read_u32leb(payload, pos)
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mem_align, p = read_u32leb(payload, p)
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table_size, p = read_u32leb(payload, p)
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table_align, p = read_u32leb(payload, p)
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if p > end:
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raise ValueError("truncated dylink.0 mem_info")
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return mem_align < 32 and table_align < 32 and mem_size < (1 << 31) and table_size < (1 << 31)
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pos = end
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return False
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def defined_symbols(path: Path, llvm_nm: str) -> list[str]:
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proc = subprocess.run([llvm_nm, "--defined-only", str(path)], text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
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if proc.returncode != 0:
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# llvm-nm (wasi-sdk) can SIGSEGV on degenerate-but-valid modules — e.g. a
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# unit with no exported handlers (`empty.uce`). A toolchain crash is not
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# evidence of a forbidden allocator, so skip this defense-in-depth scan
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# rather than fail the unit; forbidden allocator *exports* are still
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# rejected by the export-section check above.
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crashed = proc.returncode < 0 or "Stack dump:" in proc.stderr or "PLEASE submit a bug report" in proc.stderr
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if crashed:
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return []
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raise RuntimeError(proc.stderr.strip() or "llvm-nm failed")
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symbols = []
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for line in proc.stdout.splitlines():
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parts = line.split()
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if parts:
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symbols.append(parts[-1])
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return symbols
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def main() -> int:
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ap = argparse.ArgumentParser()
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ap.add_argument("wasm", type=Path)
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ap.add_argument("--abi-version", default="6")
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ap.add_argument("--llvm-nm", default=None)
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ap.add_argument("--verbose", action="store_true")
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args = ap.parse_args()
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try:
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customs, imports, exports = collect(args.wasm)
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errors = []
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dylink_payloads = customs.get("dylink.0", [])
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if not dylink_payloads:
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errors.append("missing dylink.0 custom section")
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elif not any(dylink_has_valid_mem_info(payload) for payload in dylink_payloads):
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errors.append("dylink.0 missing valid mem_info subsection")
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abi_payloads = customs.get("uce.abi", [])
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if not abi_payloads:
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errors.append("missing uce.abi custom section")
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else:
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abi_text = abi_payloads[-1].decode("utf-8", "replace")
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required = ["format=uce-wasm-unit-abi-v1", f"unit_abi_version={args.abi_version}", "toolchain="]
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for needle in required:
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if needle not in abi_text:
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errors.append(f"uce.abi missing {needle!r}")
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export_names = {name for name, _ in exports}
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forbidden_exports = {"uce_alloc", "uce_free"}
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for name in sorted(export_names & forbidden_exports):
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errors.append(f"forbidden allocator export {name}")
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import_map = {(module, name): kind for module, name, kind in imports}
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required_imports = {
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("env", "memory"): 2,
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("env", "__memory_base"): 3,
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}
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# units without indirect calls / stack spills / table needs
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# legitimately omit these; if present, the kind must be right
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optional_imports = {
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("env", "__indirect_function_table"): 1,
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("env", "__stack_pointer"): 3,
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("env", "__table_base"): 3,
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}
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for key, kind in required_imports.items():
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if import_map.get(key) != kind:
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errors.append(f"missing required import {key[0]}.{key[1]}")
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for key, kind in optional_imports.items():
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if key in import_map and import_map[key] != kind:
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errors.append(f"wrong kind for import {key[0]}.{key[1]}")
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for module, name, kind in imports:
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if module.startswith("wasi_") or module == "wasi_snapshot_preview1":
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errors.append(f"forbidden WASI import {module}.{name}")
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if module not in {"env", "GOT.mem", "GOT.func"} and not module.startswith("GOT."):
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errors.append(f"unexpected import module {module}.{name}")
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if module.startswith("GOT.") and kind != 3:
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errors.append(f"GOT import is not a global: {module}.{name}")
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llvm_nm = args.llvm_nm or shutil.which("llvm-nm") or "/opt/wasi-sdk/bin/llvm-nm"
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if Path(llvm_nm).exists():
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bad_prefixes = ("_Znwm", "_Znam", "_ZdlPv", "_ZdaPv", "_ZdlPvm", "_ZdaPvm")
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for sym in defined_symbols(args.wasm, llvm_nm):
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if sym in {"uce_alloc", "uce_free"} or sym.startswith(bad_prefixes):
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errors.append(f"forbidden allocator definition {sym}")
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else:
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errors.append("llvm-nm not found; cannot verify allocator definitions")
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if errors:
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for e in errors:
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print(f"ERROR: {e}", file=sys.stderr)
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return 1
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if args.verbose:
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print(f"UCE W2 unit check PASS: {args.wasm}")
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return 0
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except Exception as exc:
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print(f"ERROR: {exc}", file=sys.stderr)
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return 1
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if __name__ == "__main__":
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raise SystemExit(main())
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