/* cto.h -- calltrick filter

   This file is part of the UPX executable compressor.

   Copyright (C) 1996-2024 Markus Franz Xaver Johannes Oberhumer
   Copyright (C) 1996-2024 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: */
