Python module to parse function declarations from a header file

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/mbedtls_dev/c_parsing_helper.py

@@ -0,0 +1,127 @@
+"""Helper functions to parse C code in heavily constrained scenarios.
+
+Currently supported functionality:
+
+* read_function_declarations: read function declarations from a header file.
+"""
+
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+
+import re
+from typing import Dict, Iterable, Iterator, List, Optional, Tuple
+
+
+class ArgumentInfo:
+    """Information about an argument to an API function."""
+    #pylint: disable=too-few-public-methods
+
+    _KEYWORDS = [
+        'const', 'register', 'restrict',
+        'int', 'long', 'short', 'signed', 'unsigned',
+    ]
+    _DECLARATION_RE = re.compile(
+        r'(?P<type>\w[\w\s*]*?)\s*' +
+        r'(?!(?:' + r'|'.join(_KEYWORDS) + r'))(?P<name>\b\w+\b)?' +
+        r'\s*(?P<suffix>\[[^][]*\])?\Z',
+        re.A | re.S)
+
+    @classmethod
+    def normalize_type(cls, typ: str) -> str:
+        """Normalize whitespace in a type."""
+        typ = re.sub(r'\s+', r' ', typ)
+        typ = re.sub(r'\s*\*', r' *', typ)
+        return typ
+
+    def __init__(self, decl: str) -> None:
+        self.decl = decl.strip()
+        m = self._DECLARATION_RE.match(self.decl)
+        if not m:
+            raise ValueError(self.decl)
+        self.type = self.normalize_type(m.group('type')) #type: str
+        self.name = m.group('name') #type: Optional[str]
+        self.suffix = m.group('suffix') if m.group('suffix') else '' #type: str
+
+
+class FunctionInfo:
+    """Information about an API function."""
+    #pylint: disable=too-few-public-methods
+
+    # Regex matching the declaration of a function that returns void.
+    VOID_RE = re.compile(r'\s*\bvoid\s*\Z', re.A)
+
+    def __init__(self, #pylint: disable=too-many-arguments
+                 filename: str,
+                 line_number: int,
+                 qualifiers: Iterable[str],
+                 return_type: str,
+                 name: str,
+                 arguments: List[str]) -> None:
+        self.filename = filename
+        self.line_number = line_number
+        self.qualifiers = frozenset(qualifiers)
+        self.return_type = return_type
+        self.name = name
+        self.arguments = [ArgumentInfo(arg) for arg in arguments]
+
+    def returns_void(self) -> bool:
+        """Whether the function returns void."""
+        return bool(self.VOID_RE.search(self.return_type))
+
+
+# Match one C comment.
+# Note that we match both comment types, so things like // in a /*...*/
+# comment are handled correctly.
+_C_COMMENT_RE = re.compile(r'//[^n]*|/\*.*?\*/', re.S)
+_NOT_NEWLINES_RE = re.compile(r'[^\n]+')
+
+def read_logical_lines(filename: str) -> Iterator[Tuple[int, str]]:
+    """Read logical lines from a file.
+
+    Logical lines are one or more physical line, with balanced parentheses.
+    """
+    with open(filename, encoding='utf-8') as inp:
+        content = inp.read()
+    # Strip comments, but keep newlines for line numbering
+    content = re.sub(_C_COMMENT_RE,
+                     lambda m: re.sub(_NOT_NEWLINES_RE, "", m.group(0)),
+                     content)
+    lines = enumerate(content.splitlines(), 1)
+    for line_number, line in lines:
+        # Read a logical line, containing balanced parentheses.
+        # We assume that parentheses are balanced (this should be ok
+        # since comments have been stripped), otherwise there will be
+        # a gigantic logical line at the end.
+        paren_level = line.count('(') - line.count(')')
+        while paren_level > 0:
+            _, more = next(lines) #pylint: disable=stop-iteration-return
+            paren_level += more.count('(') - more.count(')')
+            line += '\n' + more
+        yield line_number, line
+
+_C_FUNCTION_DECLARATION_RE = re.compile(
+    r'(?P<qualifiers>(?:(?:extern|inline|static)\b\s*)*)'
+    r'(?P<return_type>\w[\w\s*]*?)\s*' +
+    r'\b(?P<name>\w+)' +
+    r'\s*\((?P<arguments>.*)\)\s*;',
+    re.A | re.S)
+
+def read_function_declarations(functions: Dict[str, FunctionInfo],
+                               filename: str) -> None:
+    """Collect function declarations from a C header file."""
+    for line_number, line in read_logical_lines(filename):
+        m = _C_FUNCTION_DECLARATION_RE.match(line)
+        if not m:
+            continue
+        qualifiers = m.group('qualifiers').split()
+        return_type = m.group('return_type')
+        name = m.group('name')
+        arguments = m.group('arguments').split(',')
+        if len(arguments) == 1 and re.match(FunctionInfo.VOID_RE, arguments[0]):
+            arguments = []
+        # Note: we replace any existing declaration for the same name.
+        functions[name] = FunctionInfo(filename, line_number,
+                                       qualifiers,
+                                       return_type,
+                                       name,
+                                       arguments)