/* cto.h -- calltrick filter

   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>
 */

/*************************************************************************
// filter / scan
**************************************************************************/

static int F(Filter *f) {
#ifdef U
    // filter
    byte *b = f->buf;
#else
    // scan
    const byte *b = f->buf;
#endif
    const unsigned addvalue = f->addvalue;
    const unsigned size = f->buf_len;

    unsigned ic, jc, kc;
    unsigned calls = 0, noncalls = 0, noncalls2 = 0;
    unsigned lastnoncall = size, lastcall = 0;

    // find a 16 MiB large empty address space
    {
        unsigned char buf[256];
        memset(buf, 0, 256);

        // A call to a destination that is inside the buffer
        // will be rewritten and marked with cto8 as first byte.
        // So, a call to a destination that is outside the buffer
        // must not conflict with the mark.
        // Note that unsigned comparison checks both edges of buffer.
        for (ic = 0; ic < size - 5; ic++) {
            if (!COND(b, ic))
                continue;
            jc = get_le32(b + ic + 1) + ic + 1;
            if (jc < size) {
                if (jc + addvalue >= (1u << 24)) // hi 8 bits won't be cto8
                    return -1;
            } else
                buf[b[ic + 1]] |= 1;
        }

        if (getcto(f, buf) < 0)
            return -1;
    }
    const unsigned char cto8 = f->cto;
#ifdef U
    const unsigned cto = (unsigned) f->cto << 24;
#endif

    for (ic = 0; ic < size - 5; ic++) {
        if (!COND(b, ic))
            continue;
        jc = get_le32(b + ic + 1) + ic + 1;
        // try to detect 'real' calls only
        if (jc < size) {
            assert(jc + addvalue < (1u << 24)); // hi 8 bits won't be cto8
#ifdef U
            set_be32(b + ic + 1, jc + addvalue + cto);
#endif
            if (ic - lastnoncall < 5) {
                // check the last 4 bytes before this call
                for (kc = 4; kc; kc--)
                    if (COND(b, ic - kc) && b[ic - kc + 1] == cto8)
                        break;
                if (kc) {
#ifdef U
                    // restore original
                    set_le32(b + ic + 1, jc - ic - 1);
#endif
                    if (b[ic + 1] == cto8)
                        return 1; // fail - buffer not restored
                    lastnoncall = ic;
                    noncalls2++;
                    continue;
                }
            }
            calls++;
            ic += 4;
            lastcall = ic + 1;
        } else {
            assert(b[ic + 1] != cto8); // this should not happen
            lastnoncall = ic;
            noncalls++;
        }
    }

    f->calls = calls;
    f->noncalls = noncalls;
    f->lastcall = lastcall;

#if 0 || defined(TESTING)
    printf("\ncalls=%d noncalls=%d noncalls2=%d text_size=%x calltrickoffset=%x\n",calls,noncalls,noncalls2,size,cto);
#endif
    UNUSED(noncalls2);
    return 0;
}

/*************************************************************************
// unfilter
**************************************************************************/

#ifdef U
static int U(Filter *f) {
    byte *b = f->buf;
    const unsigned size5 = f->buf_len - 5;
    const unsigned addvalue = f->addvalue;
    const unsigned cto = (unsigned) f->cto << 24;

    unsigned ic, jc;

    for (ic = 0; ic < size5; ic++)
        if (COND(b, ic)) {
            jc = get_be32(b + ic + 1);
            if (b[ic + 1] == f->cto) {
                set_le32(b + ic + 1, jc - ic - 1 - addvalue - cto);
                f->calls++;
                ic += 4;
                f->lastcall = ic + 1;
            } else
                f->noncalls++;
        }
    return 0;
}
#endif

#undef F
#undef U

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