check-structs

#! /usr/bin/python3

import os.path
import sys
import re

macros = {}

anyWarnings = False

types = {}
types['char'] = {"size": 1, "alignment": 1}
types['uint8_t'] = {"size": 1, "alignment": 1}
types['ovs_be16'] = {"size": 2, "alignment": 2}
types['ovs_be32'] = {"size": 4, "alignment": 4}
types['ovs_be64'] = {"size": 8, "alignment": 8}
types['ovs_32aligned_be64'] = {"size": 8, "alignment": 4}
types['struct eth_addr'] = {"size": 6, "alignment": 2}
types['struct eth_addr64'] = {"size": 8, "alignment": 2}

token = None
line = ""
idRe = "[a-zA-Z_][a-zA-Z_0-9]*"
tokenRe = "#?" + idRe + "|[0-9]+|."
includeRe = re.compile(r'\s*#include\s+<(openflow/[^#]+)>')
includePath = ''
inComment = False
inDirective = False
inputStack = []
def getToken():
    global token
    global line
    global inComment
    global inDirective
    global inputFile
    global fileName
    while True:
        line = line.lstrip()
        if line != "":
            if line.startswith("/*"):
                inComment = True
                line = line[2:]
            elif inComment:
                commentEnd = line.find("*/")
                if commentEnd < 0:
                    line = ""
                else:
                    inComment = False
                    line = line[commentEnd + 2:]
            else:
                match = re.match(tokenRe, line)
                token = match.group(0)
                line = line[len(token):]
                if token.startswith('#'):
                    inDirective = True
                elif token in macros and not inDirective:
                    line = macros[token] + line
                    continue
                return True
        elif inDirective:
            token = "$"
            inDirective = False
            return True
        else:
            global lineNumber
            while True:
                line = inputFile.readline()
                lineNumber += 1
                while line.endswith("\\\n"):
                    line = line[:-2] + inputFile.readline()
                    lineNumber += 1
                match = includeRe.match(line)
                if match:
                    inputStack.append((fileName, inputFile, lineNumber))
                    inputFile = open(includePath + match.group(1))
                    lineNumber = 0
                    continue
                if line == "":
                    if inputStack:
                        fileName, inputFile, lineNumber = inputStack.pop()
                        continue
                    if token == None:
                        fatal("unexpected end of input")
                    token = None
                    return False
                break
    
def fatal(msg):
    sys.stderr.write("%s:%d: error at \"%s\": %s\n" % (fileName, lineNumber, token, msg))
    sys.exit(1)
    
def warn(msg):
    global anyWarnings
    anyWarnings = True
    sys.stderr.write("%s:%d: warning: %s\n" % (fileName, lineNumber, msg))

def skipDirective():
    getToken()
    while token != '$':
        getToken()

def isId(s):
    return re.match(idRe + "$", s) != None

def forceId():
    if not isId(token):
        fatal("identifier expected")

def forceInteger():
    if not re.match('[0-9]+$', token):
        fatal("integer expected")

def match(t):
    if token == t:
        getToken()
        return True
    else:
        return False

def forceMatch(t):
    if not match(t):
        fatal("%s expected" % t)

def parseTaggedName():
    assert token in ('struct', 'union')
    name = token
    getToken()
    forceId()
    name = "%s %s" % (name, token)
    getToken()
    return name

def parseTypeName():
    if token in ('struct', 'union'):
        name = parseTaggedName()
    elif isId(token):
        name = token
        getToken()
    else:
        fatal("type name expected")

    if name in types:
        return name
    else:
        fatal("unknown type \"%s\"" % name)

def parseStruct():
    isStruct = token == 'struct'
    structName = parseTaggedName()
    if token == ";":
        return

    ofs = size = 0
    alignment = 4               # ARM has minimum 32-bit alignment
    forceMatch('{')
    while not match('}'):
        typeName = parseTypeName()
        typeSize = types[typeName]['size']
        typeAlignment = types[typeName]['alignment']

        forceId()
        memberName = token
        getToken()

        if match('['):
            if token == ']':
                count = 0
            else:
                forceInteger()
                count = int(token)
                getToken()
            forceMatch(']')
        else:
            count = 1

        nBytes = typeSize * count
        if isStruct:
            if ofs % typeAlignment:
                shortage = typeAlignment - (ofs % typeAlignment)
                warn("%s member %s is %d bytes short of %d-byte alignment"
                     % (structName, memberName, shortage, typeAlignment))
                size += shortage
                ofs += shortage
            size += nBytes
            ofs += nBytes
        else:
            if nBytes > size:
                size = nBytes
        if typeAlignment > alignment:
            alignment = typeAlignment

        forceMatch(';')
    if size % alignment:
        shortage = alignment - (size % alignment)
        if (structName == "struct ofp10_packet_in" and
            shortage == 2 and
            memberName == 'data' and
            count == 0):
            # This is intentional
            pass
        else:
            warn("%s needs %d bytes of tail padding" % (structName, shortage))
        size += shortage
    types[structName] = {"size": size, "alignment": alignment}
    return structName

def checkStructs():
    if len(sys.argv) < 2:
        sys.stderr.write("at least one non-option argument required; "
                         "use --help for help")
        sys.exit(1)

    if '--help' in sys.argv:
        argv0 = os.path.basename(sys.argv[0])
        print('''\
%(argv0)s, for checking struct and struct member alignment
usage: %(argv0)s -Ipath HEADER [HEADER]...

This program reads the header files specified on the command line and
verifies that all struct members are aligned on natural boundaries
without any need for the compiler to add additional padding.  It also
verifies that each struct's size is a multiple of 32 bits (because
some ABIs for ARM require all structs to be a multiple of 32 bits), or
64 bits if the struct has any 64-bit members, again without the
compiler adding additional padding.  Finally, it checks struct size
assertions using OFP_ASSERT.

This program is specialized for reading Open vSwitch's OpenFlow header
files.  It will not work on arbitrary header files without extensions.\
''' % {"argv0": argv0})
        sys.exit(0)

    global fileName
    for fileName in sys.argv[1:]:
        if fileName.startswith('-I'):
            global includePath
            includePath = fileName[2:]
            if not includePath.endswith('/'):
                includePath += '/'
            continue
        global inputFile
        global lineNumber
        inputFile = open(fileName)
        lineNumber = 0
        lastStruct = None
        while getToken():
            if token in ("#ifdef", "#ifndef", "#include",
                         "#endif", "#elif", "#else"):
                skipDirective()
            elif token == "#define":
                getToken()
                name = token
                if line.startswith('('):
                    skipDirective()
                else:
                    definition = ""
                    getToken()
                    while token != '$':
                        definition += token
                        getToken()
                    macros[name] = definition
            elif token == "enum":
                while token != ';':
                    getToken()
            elif token in ('struct', 'union'):
                lastStruct = parseStruct()
            elif match('OFP_ASSERT') or match('BOOST_STATIC_ASSERT'):
                forceMatch('(')
                forceMatch('sizeof')
                forceMatch('(')
                typeName = parseTypeName()
                if typeName != lastStruct:
                    warn("checking size of %s but %s was most recently defined"
                         % (typeName, lastStruct))
                forceMatch(')')
                forceMatch('=')
                forceMatch('=')
                forceInteger()
                size = int(token)
                getToken()
                forceMatch(')')
                if types[typeName]['size'] != size:
                    warn("%s is %d bytes long but declared as %d" % (
                            typeName, types[typeName]['size'], size))
            else:
                fatal("parse error")
        inputFile.close()
    if anyWarnings:
        sys.exit(1)

if __name__ == '__main__':
    checkStructs()