# FRR DWARF structure definition extractor
#
# Copyright (C) 2020  David Lamparter for NetDEF, Inc.
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 2 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; see the file COPYING; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

import sys
import os
import subprocess
import re
import argparse
import json

structs = ['xref', 'xref_logmsg', 'xref_threadsched', 'xref_install_element', 'xrefdata', 'xrefdata_logmsg', 'cmd_element']

def extract(filename='lib/.libs/libfrr.so'):
    '''
    Convert output from "pahole" to JSON.

    Example pahole output:
    $ pahole -C xref lib/.libs/libfrr.so
    struct xref {
        struct xrefdata *          xrefdata;             /*     0     8 */
        enum xref_type             type;                 /*     8     4 */
        int                        line;                 /*    12     4 */
        const char  *              file;                 /*    16     8 */
        const char  *              func;                 /*    24     8 */

        /* size: 32, cachelines: 1, members: 5 */
        /* last cacheline: 32 bytes */
    };
    '''
    pahole = subprocess.check_output(['pahole', '-C', ','.join(structs), filename]).decode('UTF-8')

    struct_re = re.compile(r'^struct ([^ ]+) \{([^\}]+)};', flags=re.M | re.S)
    field_re = re.compile(r'^\s*(?P<type>[^;\(]+)\s+(?P<name>[^;\[\]]+)(?:\[(?P<array>\d+)\])?;\s*\/\*(?P<comment>.*)\*\/\s*$')
    comment_re = re.compile(r'^\s*\/\*.*\*\/\s*$')

    pastructs = struct_re.findall(pahole)
    out = {}

    for sname, data in pastructs:
        this = out.setdefault(sname, {})
        fields = this.setdefault('fields', [])

        lines = data.strip().splitlines()

        next_offs = 0

        for line in lines:
            if line.strip() == '':
                continue
            m = comment_re.match(line)
            if m is not None:
                continue

            m = field_re.match(line)
            if m is not None:
                offs, size = m.group('comment').strip().split()
                offs = int(offs)
                size = int(size)
                typ_ = m.group('type').strip()
                name = m.group('name')

                if name.startswith('(*'):
                    # function pointer
                    typ_ = typ_ + ' *'
                    name = name[2:].split(')')[0]

                data = {
                    'name': name,
                    'type': typ_,
                #   'offset': offs,
                #   'size': size,
                }
                if m.group('array'):
                    data['array'] = int(m.group('array'))

                fields.append(data)
                if offs != next_offs:
                    raise ValueError('%d padding bytes before struct %s.%s' % (offs - next_offs, sname, name))
                next_offs = offs + size
                continue

            raise ValueError('cannot process line: %s' % line)

    return out

class FieldApplicator(object):
    '''
    Fill ELFDissectStruct fields list from pahole/JSON

    Uses the JSON file created by the above code to fill in the struct fields
    in subclasses of ELFDissectStruct.
    '''

    # only what we really need.  add more as needed.
    packtypes = {
        'int': 'i',
        'uint8_t': 'B',
        'uint16_t': 'H',
        'uint32_t': 'I',
        'char': 's',
    }

    def __init__(self, data):
        self.data = data
        self.classes = []
        self.clsmap = {}

    def add(self, cls):
        self.classes.append(cls)
        self.clsmap[cls.struct] = cls

    def resolve(self, cls):
        out = []
        #offset = 0

        fieldrename = getattr(cls, 'fieldrename', {})
        def mkname(n):
            return (fieldrename.get(n, n),)

        for field in self.data[cls.struct]['fields']:
            typs = field['type'].split()
            typs = [i for i in typs if i not in ['const']]

            # this will break reuse of xrefstructs.json across 32bit & 64bit
            # platforms

            #if field['offset'] != offset:
            #    assert offset < field['offset']
            #    out.append(('_pad', '%ds' % (field['offset'] - offset,)))

            # pretty hacky C types handling, but covers what we need

            ptrlevel = 0
            while typs[-1] == '*':
                typs.pop(-1)
                ptrlevel += 1

            if ptrlevel > 0:
                packtype = ('P', None)
                if ptrlevel == 1:
                    if typs[0] == 'char':
                        packtype = ('P', str)
                    elif typs[0] == 'struct' and typs[1] in self.clsmap:
                        packtype = ('P', self.clsmap[typs[1]])
            elif typs[0] == 'enum':
                packtype = ('I',)
            elif typs[0] in self.packtypes:
                packtype = (self.packtypes[typs[0]],)
            elif typs[0] == 'struct':
                if typs[1] in self.clsmap:
                    packtype = (self.clsmap[typs[1]],)
                else:
                    raise ValueError('embedded struct %s not in extracted data' % (typs[1],))
            else:
                raise ValueError('cannot decode field %s in struct %s (%s)' % (
                        cls.struct, field['name'], field['type']))

            if 'array' in field and typs[0] == 'char':
                packtype = ('%ds' % field['array'],)
                out.append(mkname(field['name']) + packtype)
            elif 'array' in field:
                for i in range(0, field['array']):
                    out.append(mkname('%s_%d' % (field['name'], i)) + packtype)
            else:
                out.append(mkname(field['name']) + packtype)

            #offset = field['offset'] + field['size']

        cls.fields = out

    def __call__(self):
        for cls in self.classes:
            self.resolve(cls)

def main():
    argp = argparse.ArgumentParser(description = 'FRR DWARF structure extractor')
    argp.add_argument('-o', dest='output', type=str, help='write JSON output', default='python/xrefstructs.json')
    argp.add_argument('-i', dest='input',  type=str, help='ELF file to read',  default='lib/.libs/libfrr.so')
    args = argp.parse_args()

    out = extract(args.input)
    with open(args.output + '.tmp', 'w') as fd:
        json.dump(out, fd, indent=2, sort_keys=True)
    os.rename(args.output + '.tmp', args.output)

if __name__ == '__main__':
    main()