/* p_com.cpp -- dos/com executable format

   This file is part of the UPX executable compressor.

   Copyright (C) Markus Franz Xaver Johannes Oberhumer

   Copyright (C) Laszlo Molnar

   All Rights Reserved.

   UPX and the UCL library are free software; you can redistribute them

   and/or modify them 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.,

   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

   Markus F.X.J. Oberhumer              Laszlo Molnar

   <markus@oberhumer.com>               <ezerotven+github@gmail.com>

 */

#include "conf.h"

#include "file.h"

#include "filter.h"

#include "packer.h"

#include "p_com.h"

#define WANT_EHDR_ENUM 1

#include "p_elf_enum.h"

#include "linker.h"

static const CLANG_FORMAT_DUMMY_STATEMENT

#include "stub/i086-dos16.com.h"

/*************************************************************************

//

**************************************************************************/

Linker *PackCom::newLinker() const { return new ElfLinkerX86(); }

const int *PackCom::getCompressionMethods(int method, int level) const {

    static const int m_nrv2b[] = {M_NRV2B_LE16, M_END};

    UNUSED(method);

    UNUSED(level);

    return m_nrv2b;

}

const int *PackCom::getFilters() const {

    // see class FilterImpl

    static const int filters[] = {0x06, 0x03, 0x04, 0x01, 0x05, 0x02, FT_END};

    return filters;

}

/*************************************************************************

//

**************************************************************************/

tribool PackCom::canPack() {

    byte buf[128];

    fi->readx(buf, sizeof(buf));

    if (memcmp(buf, "MZ", 2) == 0 || memcmp(buf, "ZM", 2) == 0) // .exe

        return false;

    if (memcmp(buf, "\xff\xff\xff\xff", 4) == 0) // .sys

        return false;

    if (!fn_has_ext(fi->getName(), "com")) // query file name

        return false;

    checkAlreadyPacked(buf, sizeof(buf));

    if (file_size < 1024)

        throwCantPack("file is too small for dos/com");

    if (file_size > 0xFF00)

        throwCantPack("file is too large for dos/com");

    return true;

}

/*************************************************************************

//

**************************************************************************/

void PackCom::addFilter16(int filter_id) {

    assert(filter_id > 0);

    assert(isValidFilter(filter_id));

    if (filter_id % 3 == 0) {

        // clang-format off

        addLoader("CALLTR16",

                  filter_id < 4 ? "CT16SUB0" : "",

                  filter_id < 4 ? "" : (opt->cpu_x86 == opt->CPU_8086 ? "CT16I086" : "CT16I286,CT16SUB0"),

                  "CALLTRI2",

                  getFormat() == UPX_F_DOS_COM ? "CORETURN" : "");

        // clang-format on

    } else {

        // clang-format off

        addLoader(filter_id % 3 == 1 ? "CT16E800" : "CT16E900",

                 "CALLTRI5",

                 getFormat() == UPX_F_DOS_COM ? "CT16JEND" : "CT16JUL2",

                 filter_id < 4 ? "CT16SUB1" : "",

                 filter_id < 4 ? "" : (opt->cpu_x86 == opt->CPU_8086 ? "CT16I087" : "CT16I287,CT16SUB1"),

                 "CALLTRI6");

        // clang-format on

    }

}

void PackCom::buildLoader(const Filter *ft) {

    initLoader(EM_386, stub_i086_dos16_com, sizeof(stub_i086_dos16_com));

    // clang-format off

    addLoader("COMMAIN1",

              ph.first_offset_found == 1 ? "COMSBBBP" : "",

              "COMPSHDI",

              ft->id ? "COMCALLT" : "",

              "COMMAIN2,UPX1HEAD,COMCUTPO,NRV2B160",

              ft->id ? "NRVDDONE" : "NRVDRETU",

              "NRVDECO1",

              ph.max_offset_found <= 0xd00 ? "NRVLED00" : "NRVGTD00",

              "NRVDECO2");

    // clang-format on

    if (ft->id) {

        assert(ft->calls > 0);

        addFilter16(ft->id);

    }

}

void PackCom::patchLoader(OutputFile *fo, byte *loader, int lsize, unsigned calls) {

    const int e_len = getLoaderSectionStart("COMCUTPO");

    const int d_len = lsize - e_len;

    assert(e_len > 0 && e_len < 128);

    assert(d_len > 0 && d_len < 256);

    const unsigned upper_end = ph.u_len + ph.overlap_overhead + d_len + 0x100;

    unsigned stacksize = 0x60;

    if (upper_end + stacksize > 0xfffe)

        stacksize = 0x56;

    if (upper_end + stacksize > 0xfffe)

        throwCantPack("file is too large for dos/com");

    linker->defineSymbol("calltrick_calls", calls);

    linker->defineSymbol("sp_limit", upper_end + stacksize);

    linker->defineSymbol("bytes_to_copy", ph.c_len + lsize);

    linker->defineSymbol("copy_source", ph.c_len + lsize + 0x100);

    linker->defineSymbol("copy_destination", upper_end);

    linker->defineSymbol("neg_e_len", 0 - e_len);

    linker->defineSymbol("NRV2B160", ph.u_len + ph.overlap_overhead);

    relocateLoader();

    loader = getLoader();

    // some day we could use the relocation stuff for patchPackHeader too..

    patchPackHeader(loader, e_len);

    // write loader + compressed file

    fo->write(loader, e_len);         // entry

    fo->write(obuf, ph.c_len);        // compressed

    fo->write(loader + e_len, d_len); // decompressor

    NO_printf("%-13s: entry        : %8u bytes\n", getName(), e_len);

    NO_printf("%-13s: compressed   : %8u bytes\n", getName(), ph.c_len);

    NO_printf("%-13s: decompressor : %8u bytes\n", getName(), d_len);

}

/*************************************************************************

//

**************************************************************************/

void PackCom::pack(OutputFile *fo) {

    // read file

    ibuf.alloc(file_size);

    obuf.allocForCompression(file_size);

    fi->seek(0, SEEK_SET);

    fi->readx(ibuf, file_size);

    // prepare packheader

    ph.u_len = file_size;

    // prepare filter

    Filter ft(ph.level);

    ft.addvalue = getCallTrickOffset();

    // compress

    const unsigned overlap_range = ph.u_len < 0xFE00 - ft.addvalue ? 32 : 0;

    compressWithFilters(&ft, overlap_range, NULL_cconf);

    const int lsize = getLoaderSize();

    MemBuffer loader(lsize);

    memcpy(loader, getLoader(), lsize);

    const unsigned calls = ft.id % 3 ? ft.lastcall - 2 * ft.calls : ft.calls;

    patchLoader(fo, loader, lsize, calls);

    // verify

    verifyOverlappingDecompression();

    // finally check the compression ratio

    if (!checkFinalCompressionRatio(fo))

        throwNotCompressible();

}

/*************************************************************************

//

**************************************************************************/

tribool PackCom::canUnpack() {

    if (!readPackHeader(128)) // read "ph"

        return false;

    if (file_size_u <= ph.c_len)

        return false;

    return true;

}

/*************************************************************************

//

**************************************************************************/

void PackCom::unpack(OutputFile *fo) {

    ibuf.alloc(file_size);

    obuf.allocForDecompression(ph.u_len);

    // read whole file

    fi->seek(0, SEEK_SET);

    fi->readx(ibuf, file_size);

    // get compressed data offset

    unsigned e_len = ph.buf_offset + ph.getPackHeaderSize();

    if (file_size_u <= e_len + ph.c_len)

        throwCantUnpack("file damaged");

    // decompress

    decompress(ibuf + e_len, obuf);

    // unfilter

    Filter ft(ph.level);

    ft.init(ph.filter, getCallTrickOffset());

    ft.unfilter(obuf, ph.u_len);

    // write decompressed file

    if (fo)

        fo->write(obuf, ph.u_len);

}

/* vim:set ts=4 sw=4 et: */