/* 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: */
