# Functions and classes for creating core dump from criu images.
# Code is inspired by outdated google coredumper(RIP) [1] and
# fs/binfmt_elf.h from Linux kernel [2].
#
# [1] https://code.google.com/p/google-coredumper/
#     probably already dead, so consider trying:
#     https://github.com/efiop/google-coredumper/
# [2] https://www.kernel.org/
#
# On my x86_64 systems with fresh kernel ~3.17 core dump looks like:
#
#    1) Elf file header;
#    2) PT_NOTE program header describing notes section;
#    3) PT_LOAD program headers for (almost?) each vma;
#    4) NT_PRPSINFO note with elf_prpsinfo inside;
#    5) An array of notes for each thread of the process:
#        NT_PRSTATUS note with elf_prstatus inside;
#        NT_FPREGSET note with elf_fpregset inside;
#        NT_X86_XSTATE note with x86 extended state using xsave;
#        NT_SIGINFO note with siginfo_t inside;
#    6) NT_AUXV note with auxv;
#    7) NT_FILE note with mapped files;
#    8) VMAs themselves;
#
# Or, you can represent it in less details as:
#    1) Elf file header;
#    2) Program table;
#    3) Notes;
#    4) VMAs contents;
#
import io
import sys
import ctypes

from pycriu import images
from . import elf


try:
    from itertools import ifilter as filter
except ImportError:
    pass

# Some memory-related constants
PAGESIZE = 4096
status = {
    "VMA_AREA_NONE": 0 << 0,
    "VMA_AREA_REGULAR": 1 << 0,
    "VMA_AREA_STACK": 1 << 1,
    "VMA_AREA_VSYSCALL": 1 << 2,
    "VMA_AREA_VDSO": 1 << 3,
    "VMA_FORCE_READ": 1 << 4,
    "VMA_AREA_HEAP": 1 << 5,
    "VMA_FILE_PRIVATE": 1 << 6,
    "VMA_FILE_SHARED": 1 << 7,
    "VMA_ANON_SHARED": 1 << 8,
    "VMA_ANON_PRIVATE": 1 << 9,
    "VMA_AREA_SYSVIPC": 1 << 10,
    "VMA_AREA_SOCKET": 1 << 11,
    "VMA_AREA_VVAR": 1 << 12,
    "VMA_AREA_AIORING": 1 << 13,
    "VMA_AREA_UNSUPP": 1 << 31
}

prot = {"PROT_READ": 0x1, "PROT_WRITE": 0x2, "PROT_EXEC": 0x4}


class elf_note:
    nhdr = None  # Elf_Nhdr;
    owner = None  # i.e. CORE or LINUX;
    data = None  # Ctypes structure with note data;


class coredump:
    """
    A class to keep elf core dump components inside and
    functions to properly write them to file.
    """
    ehdr = None  # Elf ehdr;
    phdrs = []  # Array of Phdrs;
    notes = []  # Array of elf_notes;
    vmas = []  # Array of BytesIO with memory content;

    # FIXME keeping all vmas in memory is a bad idea;

    def write(self, f):
        """
        Write core dump to file f.
        """
        buf = io.BytesIO()
        buf.write(self.ehdr)

        for phdr in self.phdrs:
            buf.write(phdr)

        for note in self.notes:
            buf.write(note.nhdr)
            buf.write(note.owner)
            buf.write(b"\0" * (8 - len(note.owner)))
            buf.write(note.data)

        offset = ctypes.sizeof(elf.Elf64_Ehdr())
        offset += (len(self.vmas) + 1) * ctypes.sizeof(elf.Elf64_Phdr())

        filesz = 0
        for note in self.notes:
            filesz += ctypes.sizeof(note.nhdr) + ctypes.sizeof(note.data) + 8

        note_align = PAGESIZE - ((offset + filesz) % PAGESIZE)

        if note_align == PAGESIZE:
            note_align = 0

        if note_align != 0:
            scratch = (ctypes.c_char * note_align)()
            ctypes.memset(ctypes.addressof(scratch), 0, ctypes.sizeof(scratch))
            buf.write(scratch)

        for vma in self.vmas:
            buf.write(vma.data)

        buf.seek(0)
        f.write(buf.read())


class coredump_generator:
    """
    Generate core dump from criu images.
    """
    coredumps = {}  # coredumps by pid;

    pstree = {}  # process info by pid;
    cores = {}  # cores by pid;
    mms = {}  # mm by pid;
    reg_files = None  # reg-files;
    pagemaps = {}  # pagemap by pid;

    def _img_open_and_strip(self, name, single=False, pid=None):
        """
        Load criu image and strip it from magic and redundant list.
        """
        path = self._imgs_dir + "/" + name
        if pid:
            path += "-" + str(pid)
        path += ".img"

        with open(path, 'rb') as f:
            img = images.load(f)

        if single:
            return img["entries"][0]
        else:
            return img["entries"]

    def __call__(self, imgs_dir):
        """
        Parse criu images stored in directory imgs_dir to fill core dumps.
        """
        self._imgs_dir = imgs_dir
        pstree = self._img_open_and_strip("pstree")

        for p in pstree:
            pid = p['pid']

            self.pstree[pid] = p
            for tid in p['threads']:
                self.cores[tid] = self._img_open_and_strip("core", True, tid)
            self.mms[pid] = self._img_open_and_strip("mm", True, pid)
            self.pagemaps[pid] = self._img_open_and_strip(
                "pagemap", False, pid)

        files = self._img_open_and_strip("files", False)
        self.reg_files = [x["reg"] for x in files if x["type"] == "REG"]

        for pid in self.pstree:
            self.coredumps[pid] = self._gen_coredump(pid)

        return self.coredumps

    def write(self, coredumps_dir, pid=None):
        """
        Write core dumpt to cores_dir directory. Specify pid to choose
        core dump of only one process.
        """
        for p in self.coredumps:
            if pid and p != pid:
                continue
            with open(coredumps_dir + "/" + "core." + str(p), 'wb+') as f:
                self.coredumps[p].write(f)

    def _gen_coredump(self, pid):
        """
        Generate core dump for pid.
        """
        cd = coredump()

        # Generate everything backwards so it is easier to calculate offset.
        cd.vmas = self._gen_vmas(pid)
        cd.notes = self._gen_notes(pid)
        cd.phdrs = self._gen_phdrs(pid, cd.notes, cd.vmas)
        cd.ehdr = self._gen_ehdr(pid, cd.phdrs)

        return cd

    def _gen_ehdr(self, pid, phdrs):
        """
        Generate elf header for process pid with program headers phdrs.
        """
        ehdr = elf.Elf64_Ehdr()

        ctypes.memset(ctypes.addressof(ehdr), 0, ctypes.sizeof(ehdr))
        ehdr.e_ident[elf.EI_MAG0] = elf.ELFMAG0
        ehdr.e_ident[elf.EI_MAG1] = elf.ELFMAG1
        ehdr.e_ident[elf.EI_MAG2] = elf.ELFMAG2
        ehdr.e_ident[elf.EI_MAG3] = elf.ELFMAG3
        ehdr.e_ident[elf.EI_CLASS] = elf.ELFCLASS64
        ehdr.e_ident[elf.EI_DATA] = elf.ELFDATA2LSB
        ehdr.e_ident[elf.EI_VERSION] = elf.EV_CURRENT

        ehdr.e_type = elf.ET_CORE
        ehdr.e_machine = elf.EM_X86_64
        ehdr.e_version = elf.EV_CURRENT
        ehdr.e_phoff = ctypes.sizeof(elf.Elf64_Ehdr())
        ehdr.e_ehsize = ctypes.sizeof(elf.Elf64_Ehdr())
        ehdr.e_phentsize = ctypes.sizeof(elf.Elf64_Phdr())
        # FIXME Case len(phdrs) > PN_XNUM should be handled properly.
        # See fs/binfmt_elf.c from linux kernel.
        ehdr.e_phnum = len(phdrs)

        return ehdr

    def _gen_phdrs(self, pid, notes, vmas):
        """
        Generate program headers for process pid.
        """
        phdrs = []

        offset = ctypes.sizeof(elf.Elf64_Ehdr())
        offset += (len(vmas) + 1) * ctypes.sizeof(elf.Elf64_Phdr())

        filesz = 0
        for note in notes:
            filesz += ctypes.sizeof(note.nhdr) + ctypes.sizeof(note.data) + 8

        # PT_NOTE
        phdr = elf.Elf64_Phdr()
        ctypes.memset(ctypes.addressof(phdr), 0, ctypes.sizeof(phdr))
        phdr.p_type = elf.PT_NOTE
        phdr.p_offset = offset
        phdr.p_filesz = filesz

        phdrs.append(phdr)

        note_align = PAGESIZE - ((offset + filesz) % PAGESIZE)

        if note_align == PAGESIZE:
            note_align = 0

        offset += note_align

        # VMA phdrs

        for vma in vmas:
            offset += filesz
            filesz = vma.filesz
            phdr = elf.Elf64_Phdr()
            ctypes.memset(ctypes.addressof(phdr), 0, ctypes.sizeof(phdr))
            phdr.p_type = elf.PT_LOAD
            phdr.p_align = PAGESIZE
            phdr.p_paddr = 0
            phdr.p_offset = offset
            phdr.p_vaddr = vma.start
            phdr.p_memsz = vma.memsz
            phdr.p_filesz = vma.filesz
            phdr.p_flags = vma.flags

            phdrs.append(phdr)

        return phdrs

    def _gen_prpsinfo(self, pid):
        """
        Generate NT_PRPSINFO note for process pid.
        """
        pstree = self.pstree[pid]
        core = self.cores[pid]

        prpsinfo = elf.elf_prpsinfo()
        ctypes.memset(ctypes.addressof(prpsinfo), 0, ctypes.sizeof(prpsinfo))

        # FIXME TASK_ALIVE means that it is either running or sleeping, need to
        # teach criu to distinguish them.
        TASK_ALIVE = 0x1
        # XXX A bit of confusion here, as in ps "dead" and "zombie"
        # state are two separate states, and we use TASK_DEAD for zombies.
        TASK_DEAD = 0x2
        TASK_STOPPED = 0x3
        if core["tc"]["task_state"] == TASK_ALIVE:
            prpsinfo.pr_state = 0
        if core["tc"]["task_state"] == TASK_DEAD:
            prpsinfo.pr_state = 4
        if core["tc"]["task_state"] == TASK_STOPPED:
            prpsinfo.pr_state = 3
        # Don't even ask me why it is so, just borrowed from linux
        # source and made pr_state match.
        prpsinfo.pr_sname = b'.' if prpsinfo.pr_state > 5 else b"RSDTZW" [
            prpsinfo.pr_state]
        prpsinfo.pr_zomb = 1 if prpsinfo.pr_state == 4 else 0
        prpsinfo.pr_nice = core["thread_core"][
            "sched_prio"] if "sched_prio" in core["thread_core"] else 0
        prpsinfo.pr_flag = core["tc"]["flags"]
        prpsinfo.pr_uid = core["thread_core"]["creds"]["uid"]
        prpsinfo.pr_gid = core["thread_core"]["creds"]["gid"]
        prpsinfo.pr_pid = pid
        prpsinfo.pr_ppid = pstree["ppid"]
        prpsinfo.pr_pgrp = pstree["pgid"]
        prpsinfo.pr_sid = pstree["sid"]
        # prpsinfo.pr_psargs has a limit of 80 characters which means it will
        # fail here if the cmdline is longer than 80
        prpsinfo.pr_psargs = self._gen_cmdline(pid)[:80]
        if (sys.version_info > (3, 0)):
            prpsinfo.pr_fname = core["tc"]["comm"].encode()
        else:
            prpsinfo.pr_fname = core["tc"]["comm"]

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 5
        nhdr.n_descsz = ctypes.sizeof(elf.elf_prpsinfo())
        nhdr.n_type = elf.NT_PRPSINFO

        note = elf_note()
        note.data = prpsinfo
        note.owner = b"CORE"
        note.nhdr = nhdr

        return note

    def _gen_prstatus(self, pid, tid):
        """
        Generate NT_PRSTATUS note for thread tid of process pid.
        """
        core = self.cores[tid]
        regs = core["thread_info"]["gpregs"]
        pstree = self.pstree[pid]

        prstatus = elf.elf_prstatus()

        ctypes.memset(ctypes.addressof(prstatus), 0, ctypes.sizeof(prstatus))

        # FIXME setting only some of the fields for now. Revisit later.
        prstatus.pr_pid = tid
        prstatus.pr_ppid = pstree["ppid"]
        prstatus.pr_pgrp = pstree["pgid"]
        prstatus.pr_sid = pstree["sid"]

        prstatus.pr_reg.r15 = regs["r15"]
        prstatus.pr_reg.r14 = regs["r14"]
        prstatus.pr_reg.r13 = regs["r13"]
        prstatus.pr_reg.r12 = regs["r12"]
        prstatus.pr_reg.rbp = regs["bp"]
        prstatus.pr_reg.rbx = regs["bx"]
        prstatus.pr_reg.r11 = regs["r11"]
        prstatus.pr_reg.r10 = regs["r10"]
        prstatus.pr_reg.r9 = regs["r9"]
        prstatus.pr_reg.r8 = regs["r8"]
        prstatus.pr_reg.rax = regs["ax"]
        prstatus.pr_reg.rcx = regs["cx"]
        prstatus.pr_reg.rdx = regs["dx"]
        prstatus.pr_reg.rsi = regs["si"]
        prstatus.pr_reg.rdi = regs["di"]
        prstatus.pr_reg.orig_rax = regs["orig_ax"]
        prstatus.pr_reg.rip = regs["ip"]
        prstatus.pr_reg.cs = regs["cs"]
        prstatus.pr_reg.eflags = regs["flags"]
        prstatus.pr_reg.rsp = regs["sp"]
        prstatus.pr_reg.ss = regs["ss"]
        prstatus.pr_reg.fs_base = regs["fs_base"]
        prstatus.pr_reg.gs_base = regs["gs_base"]
        prstatus.pr_reg.ds = regs["ds"]
        prstatus.pr_reg.es = regs["es"]
        prstatus.pr_reg.fs = regs["fs"]
        prstatus.pr_reg.gs = regs["gs"]

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 5
        nhdr.n_descsz = ctypes.sizeof(elf.elf_prstatus())
        nhdr.n_type = elf.NT_PRSTATUS

        note = elf_note()
        note.data = prstatus
        note.owner = b"CORE"
        note.nhdr = nhdr

        return note

    def _gen_fpregset(self, pid, tid):
        """
        Generate NT_FPREGSET note for thread tid of process pid.
        """
        core = self.cores[tid]
        regs = core["thread_info"]["fpregs"]

        fpregset = elf.elf_fpregset_t()
        ctypes.memset(ctypes.addressof(fpregset), 0, ctypes.sizeof(fpregset))

        fpregset.cwd = regs["cwd"]
        fpregset.swd = regs["swd"]
        fpregset.ftw = regs["twd"]
        fpregset.fop = regs["fop"]
        fpregset.rip = regs["rip"]
        fpregset.rdp = regs["rdp"]
        fpregset.mxcsr = regs["mxcsr"]
        fpregset.mxcr_mask = regs["mxcsr_mask"]
        fpregset.st_space = (ctypes.c_uint * len(regs["st_space"]))(
            *regs["st_space"])
        fpregset.xmm_space = (ctypes.c_uint * len(regs["xmm_space"]))(
            *regs["xmm_space"])

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 5
        nhdr.n_descsz = ctypes.sizeof(elf.elf_fpregset_t())
        nhdr.n_type = elf.NT_FPREGSET

        note = elf_note()
        note.data = fpregset
        note.owner = b"CORE"
        note.nhdr = nhdr

        return note

    def _gen_x86_xstate(self, pid, tid):
        """
        Generate NT_X86_XSTATE note for thread tid of process pid.
        """
        core = self.cores[tid]
        fpregs = core["thread_info"]["fpregs"]

        data = elf.elf_xsave_struct()
        ctypes.memset(ctypes.addressof(data), 0, ctypes.sizeof(data))

        data.i387.cwd = fpregs["cwd"]
        data.i387.swd = fpregs["swd"]
        data.i387.twd = fpregs["twd"]
        data.i387.fop = fpregs["fop"]
        data.i387.rip = fpregs["rip"]
        data.i387.rdp = fpregs["rdp"]
        data.i387.mxcsr = fpregs["mxcsr"]
        data.i387.mxcsr_mask = fpregs["mxcsr_mask"]
        data.i387.st_space = (ctypes.c_uint * len(fpregs["st_space"]))(
            *fpregs["st_space"])
        data.i387.xmm_space = (ctypes.c_uint * len(fpregs["xmm_space"]))(
            *fpregs["xmm_space"])

        if "xsave" in fpregs:
            data.xsave_hdr.xstate_bv = fpregs["xsave"]["xstate_bv"]
            data.ymmh.ymmh_space = (ctypes.c_uint *
                                    len(fpregs["xsave"]["ymmh_space"]))(
                                        *fpregs["xsave"]["ymmh_space"])

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 6
        nhdr.n_descsz = ctypes.sizeof(data)
        nhdr.n_type = elf.NT_X86_XSTATE

        note = elf_note()
        note.data = data
        note.owner = b"LINUX"
        note.nhdr = nhdr

        return note

    def _gen_siginfo(self, pid, tid):
        """
        Generate NT_SIGINFO note for thread tid of process pid.
        """
        siginfo = elf.siginfo_t()
        # FIXME zeroify everything for now
        ctypes.memset(ctypes.addressof(siginfo), 0, ctypes.sizeof(siginfo))

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 5
        nhdr.n_descsz = ctypes.sizeof(elf.siginfo_t())
        nhdr.n_type = elf.NT_SIGINFO

        note = elf_note()
        note.data = siginfo
        note.owner = b"CORE"
        note.nhdr = nhdr

        return note

    def _gen_auxv(self, pid):
        """
        Generate NT_AUXV note for thread tid of process pid.
        """
        mm = self.mms[pid]
        num_auxv = len(mm["mm_saved_auxv"]) // 2

        class elf_auxv(ctypes.Structure):
            _fields_ = [("auxv", elf.Elf64_auxv_t * num_auxv)]

        auxv = elf_auxv()
        for i in range(num_auxv):
            auxv.auxv[i].a_type = mm["mm_saved_auxv"][i]
            auxv.auxv[i].a_val = mm["mm_saved_auxv"][i + 1]

        nhdr = elf.Elf64_Nhdr()
        nhdr.n_namesz = 5
        nhdr.n_descsz = ctypes.sizeof(elf_auxv())
        nhdr.n_type = elf.NT_AUXV

        note = elf_note()
        note.data = auxv
        note.owner = b"CORE"
        note.nhdr = nhdr

        return note

    def _gen_files(self, pid):
        """
        Generate NT_FILE note for process pid.
        """
        mm = self.mms[pid]

        class mmaped_file_info:
            start = None
            end = None
            file_ofs = None
            name = None

        infos = []
        for vma in mm["vmas"]:
            if vma["shmid"] == 0:
                # shmid == 0 means that it is not a file
                continue

            shmid = vma["shmid"]
            off = vma["pgoff"] // PAGESIZE

            files = self.reg_files
            fname = next(filter(lambda x: x["id"] == shmid, files))["name"]

            info = mmaped_file_info()
            info.start = vma["start"]
            info.end = vma["end"]
            info.file_ofs = off
            info.name = fname

            infos.append(info)

        # /*
        #  * Format of NT_FILE note:
        #  *
        #  * long count     -- how many files are mapped
        #  * long page_size -- units for file_ofs
        #  * array of [COUNT] elements of
        #  *   long start
        #  *   long end
        #  *   long file_ofs
        #  * followed by COUNT filenames in ASCII: "FILE1" NUL "FILE2" NUL...
        #  */
        fields = []
        fields.append(("count", ctypes.c_long))
        fields.append(("page_size", ctypes.c_long))
        for i in range(len(infos)):
            fields.append(("start" + str(i), ctypes.c_long))
            fields.append(("end" + str(i), ctypes.c_long))
            fields.append(("file_ofs" + str(i), ctypes.c_long))
        for i in range(len(infos)):
            fields.append(
                ("name" + str(i), ctypes.c_char * (len(infos[i].name) + 1)))

        class elf_files(ctypes.Structure):
            _fields_ = fields

        data = elf_files()
        data.count = len(infos)
        data.page_size = PAGESIZE
        for i in range(len(infos)):
            info = infos[i]
            setattr(data, "start" + str(i), info.start)
            setattr(data, "end" + str(i), info.end)
            setattr(data, "file_ofs" + str(i), info.file_ofs)
            if (sys.version_info > (3, 0)):
                setattr(data, "name" + str(i), info.name.encode())
            else:
                setattr(data, "name" + str(i), info.name)

        nhdr = elf.Elf64_Nhdr()

        nhdr.n_namesz = 5  # strlen + 1
        nhdr.n_descsz = ctypes.sizeof(elf_files())
        nhdr.n_type = elf.NT_FILE

        note = elf_note()
        note.nhdr = nhdr
        note.owner = b"CORE"
        note.data = data

        return note

    def _gen_thread_notes(self, pid, tid):
        notes = []

        notes.append(self._gen_prstatus(pid, tid))
        notes.append(self._gen_fpregset(pid, tid))
        notes.append(self._gen_x86_xstate(pid, tid))
        notes.append(self._gen_siginfo(pid, tid))

        return notes

    def _gen_notes(self, pid):
        """
        Generate notes for core dump of process pid.
        """
        notes = []

        notes.append(self._gen_prpsinfo(pid))

        threads = self.pstree[pid]["threads"]

        # Main thread first
        notes += self._gen_thread_notes(pid, pid)

        # Then other threads
        for tid in threads:
            if tid == pid:
                continue

            notes += self._gen_thread_notes(pid, tid)

        notes.append(self._gen_auxv(pid))
        notes.append(self._gen_files(pid))

        return notes

    def _get_page(self, pid, page_no):
        """
        Try to find memory page page_no in pages.img image for process pid.
        """
        pagemap = self.pagemaps[pid]

        # First entry is pagemap_head, we will need it later to open
        # proper pages.img.
        pages_id = pagemap[0]["pages_id"]
        off = 0  # in pages
        for m in pagemap[1:]:
            found = False
            for i in range(m["nr_pages"]):
                if m["vaddr"] + i * PAGESIZE == page_no * PAGESIZE:
                    found = True
                    break
                off += 1

            if not found:
                continue

            if "in_parent" in m and m["in_parent"]:
                ppid = self.pstree[pid]["ppid"]
                return self._get_page(ppid, page_no)
            else:
                with open(self._imgs_dir + "/pages-%s.img" % pages_id, 'rb') as f:
                    f.seek(off * PAGESIZE)
                    return f.read(PAGESIZE)

        return None

    def _gen_mem_chunk(self, pid, vma, size):
        """
        Obtain vma contents for process pid.
        """
        f = None

        if size == 0:
            return b""

        if vma["status"] & status["VMA_AREA_VVAR"]:
            # FIXME this is what gdb does, as vvar vma
            # is not readable from userspace?
            return b"\0" * size
        elif vma["status"] & status["VMA_AREA_VSYSCALL"]:
            # FIXME need to dump it with criu or read from
            # current process.
            return b"\0" * size

        if vma["status"] & status["VMA_FILE_SHARED"] or \
           vma["status"] & status["VMA_FILE_PRIVATE"]:
            # Open file before iterating vma pages
            shmid = vma["shmid"]
            off = vma["pgoff"]

            files = self.reg_files
            fname = next(filter(lambda x: x["id"] == shmid, files))["name"]

            try:
                f = open(fname, 'rb')
            except FileNotFoundError:
                sys.exit('Required file %s not found.' % fname)

            f.seek(off)

        start = vma["start"]
        end = vma["start"] + size

        # Split requested memory chunk into pages, so it could be
        # pictured as:
        #
        # "----" -- part of page with memory outside of our vma;
        # "XXXX" -- memory from our vma;
        #
        #  Start page     Pages in the middle        End page
        # [-----XXXXX]...[XXXXXXXXXX][XXXXXXXXXX]...[XXX-------]
        #
        # Each page could be found in pages.img or in a standalone
        # file described by shmid field in vma entry and
        # corresponding entry in reg-files.img.
        # For VMA_FILE_PRIVATE vma, unchanged pages are taken from
        # a file, and changed ones -- from pages.img.
        # Finally, if no page is found neither in pages.img nor
        # in file, hole in inserted -- a page filled with zeroes.
        start_page = start // PAGESIZE
        end_page = end // PAGESIZE

        buf = b""
        for page_no in range(start_page, end_page + 1):
            page = None

            # Search for needed page in pages.img and reg-files.img
            # and choose appropriate.
            page_mem = self._get_page(pid, page_no)

            if f is not None:
                page = f.read(PAGESIZE)

            if page_mem is not None:
                # Page from pages.img has higher priority
                # than one from mapped file on disk.
                page = page_mem

            if page is None:
                # Hole
                page = PAGESIZE * b"\0"

            # If it is a start or end page, we need to read
            # only part of it.
            if page_no == start_page:
                n_skip = start - page_no * PAGESIZE
                if start_page == end_page:
                    n_read = size
                else:
                    n_read = PAGESIZE - n_skip
            elif page_no == end_page:
                n_skip = 0
                n_read = end - page_no * PAGESIZE
            else:
                n_skip = 0
                n_read = PAGESIZE

            buf += page[n_skip:n_skip + n_read]

        # Don't forget to close file.
        if f is not None:
            f.close()

        return buf

    def _gen_cmdline(self, pid):
        """
        Generate full command with arguments.
        """
        mm = self.mms[pid]

        vma = {}
        vma["start"] = mm["mm_arg_start"]
        vma["end"] = mm["mm_arg_end"]
        # Dummy flags and status.
        vma["flags"] = 0
        vma["status"] = 0
        size = vma["end"] - vma["start"]

        chunk = self._gen_mem_chunk(pid, vma, size)

        # Replace all '\0's with spaces.
        return chunk.replace(b'\0', b' ')

    def _get_vma_dump_size(self, vma):
        """
        Calculate amount of vma to put into core dump.
        """
        if (vma["status"] & status["VMA_AREA_VVAR"] or
                vma["status"] & status["VMA_AREA_VSYSCALL"] or
                vma["status"] & status["VMA_AREA_VDSO"]):
            size = vma["end"] - vma["start"]
        elif vma["prot"] == 0:
            size = 0
        elif (vma["prot"] & prot["PROT_READ"] and
              vma["prot"] & prot["PROT_EXEC"]):
            size = PAGESIZE
        elif (vma["status"] & status["VMA_ANON_SHARED"] or
              vma["status"] & status["VMA_FILE_SHARED"] or
              vma["status"] & status["VMA_ANON_PRIVATE"] or
              vma["status"] & status["VMA_FILE_PRIVATE"]):
            size = vma["end"] - vma["start"]
        else:
            size = 0

        return size

    def _get_vma_flags(self, vma):
        """
        Convert vma flags int elf flags.
        """
        flags = 0

        if vma['prot'] & prot["PROT_READ"]:
            flags = flags | elf.PF_R

        if vma['prot'] & prot["PROT_WRITE"]:
            flags = flags | elf.PF_W

        if vma['prot'] & prot["PROT_EXEC"]:
            flags = flags | elf.PF_X

        return flags

    def _gen_vmas(self, pid):
        """
        Generate vma contents for core dump for process pid.
        """
        mm = self.mms[pid]

        class vma_class:
            data = None
            filesz = None
            memsz = None
            flags = None
            start = None

        vmas = []
        for vma in mm["vmas"]:
            v = vma_class()
            v.filesz = self._get_vma_dump_size(vma)
            v.data = self._gen_mem_chunk(pid, vma, v.filesz)
            v.memsz = vma["end"] - vma["start"]
            v.start = vma["start"]
            v.flags = self._get_vma_flags(vma)

            vmas.append(v)

        return vmas
