/* i386-darwin.macho-upxmain.c -- loader hack for Mach-o i386

   This file is part of the UPX executable compressor.

   Copyright (C) 1996-2020 Markus Franz Xaver Johannes Oberhumer
   Copyright (C) 1996-2020 Laszlo Molnar
   Copyright (C) 2000-2020 John F. Reiser
   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>               <ml1050@users.sourceforge.net>

   John F. Reiser
   <jreiser@users.sourceforge.net>
 */

#define __WORDSIZE 32
#include <stdio.h>
#include <stdlib.h>
#include "include/darwin.h"

#ifndef DEBUG  /*{*/
#define DEBUG 0
#endif  /*}*/

/*************************************************************************
// configuration section
**************************************************************************/

// In order to make it much easier to move this code at runtime and execute
// it at an address different from it load address:  there must be no
// static data, and no string constants.

#if !DEBUG  /*{*/
#define DPRINTF(a) /* empty: no debug drivel */
#define DEBUG_STRCON(name, value) /* empty */
#else  /*}{ DEBUG */
extern int write(int, void const *, size_t);
#if 0
#include "stdarg.h"
#else
#define va_arg      __builtin_va_arg
#define va_end      __builtin_va_end
#define va_list     __builtin_va_list
#define va_start    __builtin_va_start
#endif

#if defined(__i386__) || defined(__x86_64__) /*{*/
#define PIC_STRING(value, var) \
    __asm__ __volatile__ ( \
        "call 0f; .asciz \"" value "\"; \
      0: pop %0;" : "=r"(var) : \
    )
#elif defined(__arm__)  /*}{*/
#define PIC_STRING(value, var) \
    __asm__ __volatile__ ( \
        "mov %0,pc; b 0f; \
        .asciz \"" value "\"; .balign 4; \
      0: " : "=r"(var) \
    )
#elif defined(__mips__)  /*}{*/
#define PIC_STRING(value, var) \
    __asm__ __volatile__ ( \
        ".set noreorder; bal 0f; move %0,$31; .set reorder; \
        .asciz \"" value "\"; .balign 4; \
      0: " \
        : "=r"(var) : : "ra" \
    )
#endif  /*}*/


#define DEBUG_STRCON(name, strcon) \
    static char const *name(void) { \
        register char const *rv; PIC_STRING(strcon, rv); \
        return rv; \
    }


#ifdef __arm__  /*{*/
extern unsigned div10(unsigned);
#else  /*}{*/
static unsigned
div10(unsigned x)
{
    return x / 10u;
}
#endif  /*}*/

static int
unsimal(unsigned x, char *ptr, int n)
{
    if (10<=x) {
        unsigned const q = div10(x);
        x -= 10 * q;
        n = unsimal(q, ptr, n);
    }
    ptr[n] = '0' + x;
    return 1+ n;
}

static int
decimal(int x, char *ptr, int n)
{
    if (x < 0) {
        x = -x;
        ptr[n++] = '-';
    }
    return unsimal(x, ptr, n);
}

DEBUG_STRCON(STR_hex, "0123456789abcdef");

static int
heximal(unsigned long x, char *ptr, int n)
{
    if (16<=x) {
        n = heximal(x>>4, ptr, n);
        x &= 0xf;
    }
    ptr[n] = STR_hex()[x];
    return 1+ n;
}


#define DPRINTF(a) my_printf a

static int
my_printf(char const *fmt, ...)
{
    char c;
    int n= 0;
    char *ptr;
    char buf[20];
    va_list va; va_start(va, fmt);
    ptr= &buf[0];
    while (0!=(c= *fmt++)) if ('%'!=c) goto literal;
    else switch (c= *fmt++) {
    default: {
literal:
        n+= write(2, fmt-1, 1);
    } break;
    case 0: goto done;  /* early */
    case 'u': {
        n+= write(2, buf, unsimal(va_arg(va, unsigned), buf, 0));
    } break;
    case 'd': {
        n+= write(2, buf, decimal(va_arg(va, int), buf, 0));
    } break;
    case 'p': {
        buf[0] = '0';
        buf[1] = 'x';
        n+= write(2, buf, heximal((unsigned long)va_arg(va, void *), buf, 2));
    } break;
    case 'x': {
        buf[0] = '0';
        buf[1] = 'x';
        n+= write(2, buf, heximal(va_arg(va, int), buf, 2));
    } break;
    }
done:
    va_end(va);
    return n;
}
#endif  /*}*/


/*************************************************************************
// "file" util
**************************************************************************/

typedef struct {
    size_t size;  // must be first to match size[0] uncompressed size
    void *buf;
} Extent;

DEBUG_STRCON(STR_xread, "xread %%p(%%x %%p) %%p %%x\\n")
DEBUG_STRCON(STR_xreadfail, "xreadfail %%p(%%x %%p) %%p %%x\\n")

static void
xread(Extent *x, void *buf, size_t count)
{
    unsigned char *p=x->buf, *q=buf;
    size_t j;
    DPRINTF((STR_xread(), x, x->size, x->buf, buf, count));
    if (x->size < count) {
        DPRINTF((STR_xreadfail(), x, x->size, x->buf, buf, count));
        exit(127);
    }
    for (j = count; 0!=j--; ++p, ++q) {
        *q = *p;
    }
    x->buf  += count;
    x->size -= count;
}


/*************************************************************************
// util
**************************************************************************/

#if 1  //{  save space
#define ERR_LAB error: exit(127);
#define err_exit(a) goto error
#else  //}{  save debugging time
#define ERR_LAB /*empty*/
DEBUG_STRCON(STR_exit, "err_exit %%x\\n");

static void
err_exit(int a)
{
    DPRINTF((STR_exit(), a));
    (void)a;  // debugging convenience
    exit(127);
}
#endif  //}


/*************************************************************************
// UPX & NRV stuff
**************************************************************************/

struct l_info { // 12-byte trailer for loader (after macho headers)
    unsigned l_checksum;
    unsigned l_magic;  // UPX_MAGIC_LE32
    unsigned short l_lsize;
    unsigned char l_version;
    unsigned char l_format;
};
struct p_info { // 12-byte packed program header
    unsigned p_progid;
    unsigned p_filesize;
    unsigned p_blocksize;
};

struct b_info { // 12-byte header before each compressed block
    unsigned sz_unc;  // uncompressed_size
    unsigned sz_cpr;  //   compressed_size
    unsigned char b_method;  // compression algorithm
    unsigned char b_ftid;  // filter id
    unsigned char b_cto8;  // filter parameter
    unsigned char b_unused;
};

typedef void f_unfilter(
    nrv_byte *,  // also addvalue
    nrv_uint,
    unsigned cto8, // junk in high 24 bits
    unsigned ftid
);
typedef int f_expand(
    const nrv_byte *, nrv_uint,
          nrv_byte *, nrv_uint *, unsigned );

DEBUG_STRCON(STR_unpackExtent,
        "unpackExtent in=%%p(%%x %%p)  out=%%p(%%x %%p)  %%p %%p\\n");
DEBUG_STRCON(STR_err5, "sz_cpr=%%x  sz_unc=%%x  xo->size=%%x\\n");

static void
unpackExtent(
    Extent *const xi,  // input
    Extent *const xo,  // output
    f_expand *const f_decompress,
    f_unfilter *f_unf
)
{
    DPRINTF((STR_unpackExtent(),
        xi, xi->size, xi->buf, xo, xo->size, xo->buf, f_decompress, f_unf));
    while (xo->size) {
        struct b_info h;
        //   Note: if h.sz_unc == h.sz_cpr then the block was not
        //   compressible and is stored in its uncompressed form.

        // Read and check block sizes.
        xread(xi, (unsigned char *)&h, sizeof(h));
        if (h.sz_unc == 0) {                     // uncompressed size 0 -> EOF
            if (h.sz_cpr != UPX_MAGIC_LE32)      // h.sz_cpr must be h->magic
                err_exit(2);
            if (xi->size != 0)                 // all bytes must be written
                err_exit(3);
            break;
        }
        if (h.sz_cpr <= 0) {
            err_exit(4);
ERR_LAB
        }
        if (h.sz_cpr > h.sz_unc
        ||  h.sz_unc > xo->size ) {
            DPRINTF((STR_err5(), h.sz_cpr, h.sz_unc, xo->size));
            err_exit(5);
        }
        // Now we have:
        //   assert(h.sz_cpr <= h.sz_unc);
        //   assert(h.sz_unc > 0 && h.sz_unc <= blocksize);
        //   assert(h.sz_cpr > 0 && h.sz_cpr <= blocksize);

        if (h.sz_cpr < h.sz_unc) { // Decompress block
            nrv_uint out_len = h.sz_unc;  // EOF for lzma
            int const j = (*f_decompress)(xi->buf, h.sz_cpr,
                xo->buf, &out_len, h.b_method);
            if (j != 0 || out_len != (nrv_uint)h.sz_unc)
                err_exit(7);
            if (h.b_ftid!=0 && f_unf) {  // have filter
                (*f_unf)(xo->buf, out_len, h.b_cto8, h.b_ftid);
            }
            xi->buf  += h.sz_cpr;
            xi->size -= h.sz_cpr;
        }
        else { // copy literal block
            xread(xi, xo->buf, h.sz_cpr);
        }
        xo->buf  += h.sz_unc;
        xo->size -= h.sz_unc;
    }
}

static void
upx_bzero(unsigned char *p, size_t len)
{
    if (len) do {
        *p++= 0;
    } while (--len);
}
#define bzero upx_bzero


// The PF_* and PROT_* bits are {1,2,4}; the conversion table fits in 32 bits.
#define REP8(x) \
    ((x)|((x)<<4)|((x)<<8)|((x)<<12)|((x)<<16)|((x)<<20)|((x)<<24)|((x)<<28))
#define EXP8(y) \
    ((1&(y)) ? 0xf0f0f0f0 : (2&(y)) ? 0xff00ff00 : (4&(y)) ? 0xffff0000 : 0)
#define PF_TO_PROT(pf) \
    ((PROT_READ|PROT_WRITE|PROT_EXEC) & ( \
        ( (REP8(PROT_EXEC ) & EXP8(PF_X)) \
         |(REP8(PROT_READ ) & EXP8(PF_R)) \
         |(REP8(PROT_WRITE) & EXP8(PF_W)) \
        ) >> ((pf & (PF_R|PF_W|PF_X))<<2) ))

typedef struct {
    unsigned magic;
    unsigned nfat_arch;
} Fat_header;
typedef struct {
    unsigned cputype;
    unsigned cpusubtype;
    unsigned offset;
    unsigned size;
    unsigned align;  /* shift count (log base 2) */
} Fat_arch;
    enum e8 {
        FAT_MAGIC = 0xcafebabe,
        FAT_CIGAM = 0xbebafeca
    };
    enum e9 {
        CPU_TYPE_I386      =          7,
        CPU_TYPE_AMD64     = 0x01000007,
        CPU_TYPE_ARM       =         12,
        CPU_TYPE_POWERPC   = 0x00000012,
        CPU_TYPE_POWERPC64 = 0x01000012
    };

typedef struct {
    unsigned magic;
    unsigned cputype;
    unsigned cpysubtype;
    unsigned filetype;
    unsigned ncmds;
    unsigned sizeofcmds;
    unsigned flags;
} Mach_header;
        enum e0 {
            MH_MAGIC   =   0xfeedface,
            MH_MAGIC64 = 1+0xfeedface
        };
        enum e2 {
            MH_EXECUTE = 2
        };
        enum e3 {
            MH_NOUNDEFS = 1
        };

typedef struct {
    unsigned cmd;
    unsigned cmdsize;
} Mach_load_command;
        enum e4 {
            LC_REQ_DYLD      = 0x80000000,  // OR'ed ==> must not ignore
            LC_SEGMENT       = 0x1,
            LC_SEGMENT_64    = 0x19,
            LC_THREAD        = 0x4,
            LC_UNIXTHREAD    = 0x5,
            LC_LOAD_DYLINKER = 0xe,
            LC_MAIN          = (0x28|LC_REQ_DYLD)
        };

typedef struct {
    unsigned cmd;
    unsigned cmdsize;
    char segname[16];
    uint32_t vmaddr;
    uint32_t vmsize;
    uint32_t fileoff;
    uint32_t filesize;
    unsigned maxprot;
    unsigned initprot;
    unsigned nsects;
    unsigned flags;
} Mach_segment_command;
        enum e5 {
            VM_PROT_READ = 1,
            VM_PROT_WRITE = 2,
            VM_PROT_EXECUTE = 4
        };

typedef struct {
    char sectname[16];
    char segname[16];
    uint32_t addr;   /* memory address */
    uint32_t size;   /* size in bytes */
    unsigned offset; /* file offset */
    unsigned align;  /* power of 2 */
    unsigned reloff; /* file offset of relocation entries */
    unsigned nreloc; /* number of relocation entries */
    unsigned flags;  /* section type and attributes */
    unsigned reserved1;  /* for offset or index */
    unsigned reserved2;  /* for count or sizeof */
} Mach_section_command;

typedef struct {
    uint32_t cmd;  // LC_MAIN;  MH_EXECUTE only
    uint32_t cmdsize;  // 24
    uint64_t entryoff;  // file offset of main() [expected in __TEXT]
    uint64_t stacksize;  // non-default initial stack size
} Mach_main_command;

typedef struct {
    uint32_t eax, ebx, ecx, edx;
    uint32_t edi, esi, ebp;
    uint32_t esp, ss;
    uint32_t eflags;
    uint32_t eip, cs;
    uint32_t ds,es,fs,gs;
} Mach_i386_thread_state;

typedef struct {
    unsigned cmd;            /* LC_THREAD or  LC_UNIXTHREAD */
    unsigned cmdsize;        /* total size of this command */
    unsigned flavor;
    unsigned count;          /* sizeof(following_thread_state)/4 */
    Mach_i386_thread_state state;
} Mach_thread_command;
        enum e6 {
            x86_THREAD_STATE32 = 1
        };
        enum e7 {
            i386_THREAD_STATE_COUNT = sizeof(Mach_i386_thread_state)/4
        };

typedef union {
    unsigned offset;  /* from start of load command to string */
} Mach_lc_str;

#define MAP_FIXED     0x10
#define MAP_PRIVATE   0x02
#define MAP_ANON    0x1000
//#define MAP_ANON  0x20  // x86 DEBUG ONLY
#define PROT_READ      1
#define PROT_WRITE     2
#define PROT_EXEC      4
#define MAP_ANON_FD    -1
#define MAP_FAILED ((void *) -1)

extern void *mmap(void *, size_t, unsigned, unsigned, int, off_t);
ssize_t pread(int, void *, size_t, off_t);
extern void bswap(void *, unsigned);

DEBUG_STRCON(STR_mmap,
    "mmap  addr=%%p  len=%%p  prot=%%x  flags=%%x  fd=%%d  off=%%p\\n");
DEBUG_STRCON(STR_do_xmap,
    "do_xmap  fdi=%%x  mhdr=%%p  xi=%%p(%%x %%p) f_unf=%%p\\n")

static uint32_t  // entry address
do_xmap(
    Mach_header const *const mhdr,
    off_t const fat_offset,
    Extent *const xi,
    int const fdi,
    Mach_header **mhdrpp,
    f_expand *const f_decompress,
    f_unfilter *const f_unf
)
{
    Mach_segment_command const *sc = (Mach_segment_command const *)(1+ mhdr);
    Mach_segment_command const *segTEXT = 0;
    uint32_t entry = 0;
    unsigned long base = 0;
    unsigned j;

    DPRINTF((STR_do_xmap(),
        fdi, mhdr, xi, (xi? xi->size: 0), (xi? xi->buf: 0), f_unf));

    for ( j=0; j < mhdr->ncmds; ++j,
        (sc = (Mach_segment_command const *)(sc->cmdsize + (void const *)sc))
    ) if (LC_SEGMENT==sc->cmd && sc->vmsize!=0) {
        Extent xo;
        size_t mlen = xo.size = sc->filesize;
        unsigned char  *addr = xo.buf  = base + (unsigned char *)sc->vmaddr;
        unsigned char *haddr =     sc->vmsize +                        addr;
        size_t frag = (int)(uint32_t)addr &~ PAGE_MASK;
        addr -= frag;
        mlen += frag;

        if (0!=mlen) { // In particular, omitted for __PAGEZERO
            // Decompressor can overrun the destination by 3 bytes.  [x86 only]
            size_t const mlen3 = mlen + (xi ? 3 : 0);
            unsigned const prot = VM_PROT_READ | VM_PROT_WRITE;
            unsigned const flags = (addr ? MAP_FIXED : 0) | MAP_PRIVATE |
                        ((xi || 0==sc->filesize) ? MAP_ANON : 0);
            int const fdm = ((0==sc->filesize) ? MAP_ANON_FD : fdi);
            off_t const offset = sc->fileoff + fat_offset;

            DPRINTF((STR_mmap(),       addr, mlen3, prot, flags, fdm, offset));
            unsigned char *mapa = mmap(addr, mlen3, prot, flags, fdm, offset);
            if (MAP_FAILED == mapa) {
                err_exit(8);
            }
            if (0 == addr) { // dyld auto-relocate
                base = (unsigned long)mapa;  // relocation constant
            }
            addr = mapa;
        }
        if (xi && 0!=sc->filesize) {
            if (0==sc->fileoff /*&& 0!=mhdrpp*/) {
                segTEXT = sc;
                *mhdrpp = (Mach_header *)(void *)addr;
            }
            unpackExtent(xi, &xo, f_decompress, f_unf);
        }
        /*bzero(addr, frag);*/  // fragment at lo end
        frag = (-mlen) &~ PAGE_MASK;  // distance to next page boundary
        bzero(mlen+addr, frag);  // fragment at hi end
        if (0!=mlen && 0!=mprotect(addr, mlen, sc->initprot)) {
            err_exit(10);
ERR_LAB
        }
        addr += mlen + frag;  /* page boundary on hi end */
        if (
#if defined(SIMULATE_ON_LINUX_EABI4)  /*{*/
            0!=addr &&
#endif  /*}*/
                        addr < haddr) { // need pages for .bss
            if (0!=addr && addr != mmap(addr, haddr - addr, sc->initprot,
                    MAP_FIXED | MAP_PRIVATE | MAP_ANON, MAP_ANON_FD, 0 ) ) {
                err_exit(9);
            }
        }
        else if (xi) { // cleanup if decompressor overrun crosses page boundary
            mlen = ~PAGE_MASK & (3+ mlen);
            if (mlen<=3) { // page fragment was overrun buffer only
                munmap((char *)addr, mlen);
            }
        }
    }
    else if (LC_UNIXTHREAD==sc->cmd || LC_THREAD==sc->cmd) {
        Mach_thread_command const *const thrc = (Mach_thread_command const *)sc;
        if (x86_THREAD_STATE32      ==thrc->flavor
        &&  i386_THREAD_STATE_COUNT ==thrc->count ) {
            entry = thrc->state.eip + base;  // JMP
        }
    }
    else if (LC_MAIN==sc->cmd) {
        entry = ((Mach_main_command const *)sc)->entryoff;
        if (segTEXT->fileoff <= entry && entry < segTEXT->filesize) {
            entry += segTEXT->vmaddr;  // CALL
        }
        // XXX FIXME TODO: if entry not in segTEXT?
        // XXX FIXME TODO: LC_MAIN is a CALL; LC_*THREAD is a JMP
    }
    return entry;
}

static off_t
fat_find(Fat_header *fh) // *fh suffers bswap()
{
    Fat_arch *fa = (Fat_arch *)(1+ fh);
    bswap(fh, sizeof(*fh) + (fh->nfat_arch>>24)*sizeof(*fa));
    unsigned j;
    for (j= 0; j < fh->nfat_arch; ++j, ++fa) {
        if (CPU_TYPE_I386==fa->cputype) {
            return fa->offset;  // should not be 0 because of header
        }
    }
    return 0;
}

/*************************************************************************
// upx_main - called by our entry code
//
**************************************************************************/

DEBUG_STRCON(STR_upx_main,
    "upx_main szc=%%x  f_dec=%%p  f_unf=%%p  "
    "  xo=%%p(%%x %%p)  xi=%%p(%%x %%p)  mhdrpp=%%p\\n")

uint32_t // entry address
upx_main(
    struct l_info const *const li,
    size_t volatile sz_compressed,  // total length
    Mach_header *const mhdr,  // temp char[sz_mhdr] for decompressing
    size_t const sz_mhdr,
    f_expand *const f_decompress,
    f_unfilter *const f_unf,
    Mach_header **const mhdrpp  // Out: *mhdrpp= &real Mach_header
)
{
    uint32_t entry;
    off_t fat_offset = 0;
    Extent xi, xo, xi0;
    xi.buf  = CONST_CAST(unsigned char *, 1+ (struct p_info const *)(1+ li));  // &b_info
    xi.size = sz_compressed - (sizeof(struct l_info) + sizeof(struct p_info));
    xo.buf  = (unsigned char *)mhdr;
    xo.size = ((struct b_info const *)(void const *)xi.buf)->sz_unc;
    xi0 = xi;

    DPRINTF((STR_upx_main(),
        sz_compressed, f_decompress, f_unf, &xo, xo.size, xo.buf,
        &xi, xi.size, xi.buf, mhdrpp));

    // Uncompress Macho headers
    unpackExtent(&xi, &xo, f_decompress, 0);  // never filtered?

    entry = do_xmap(mhdr, fat_offset, &xi0, MAP_ANON_FD, mhdrpp, f_decompress, f_unf);

  { // Map dyld dynamic loader
    Mach_load_command const *lc = (Mach_load_command const *)(1+ mhdr);
    unsigned j;

    for (j=0; j < mhdr->ncmds; ++j,
        (lc = (Mach_load_command const *)(lc->cmdsize + (void const *)lc))
    ) if (LC_LOAD_DYLINKER==lc->cmd) {
        char const *const dyld_name = ((Mach_lc_str const *)(1+ lc))->offset +
            (char const *)lc;
        int const fdi = open(dyld_name, O_RDONLY, 0);
        if (0 > fdi) {
            err_exit(18);
        }
        for (;;) { // possibly 2 times for 'fat' binary
            if (sz_mhdr!=pread(fdi, (void *)mhdr, sz_mhdr, fat_offset)) {
ERR_LAB
                err_exit(19);
            }
            switch (mhdr->magic) {
            case MH_MAGIC: break;  // i686 on x86_64 ?
            case MH_MAGIC64: break;

            case FAT_CIGAM:
            case FAT_MAGIC: {
                // stupid Apple: waste code and a page fault on EVERY execve
                fat_offset = fat_find((Fat_header *)mhdr);
                if (fat_offset) {
                    continue;  // the 'for' loop
                }
                err_exit(20);  // no other choice
            } break;
            } // switch
            break;
        }
        entry = do_xmap(mhdr, fat_offset, 0, fdi, 0, 0, 0);
        close(fdi);
        break;
    }
  }

    return entry;
}

typedef struct {
    uint32_t cmd;
    uint32_t cmdsize;
    uint32_t data[2];  // because cmdsize >= 16
} Mach_command;  // generic prefix

//
// Build on Mac OS X: (where gcc is really clang)
// gcc -o i386-darwin.macho-upxmain.exe \
//    -Os -fPIC -fno-stack-protector \
//    i386-darwin.macho-upxmain.c \
//    i386-darwin.macho-upxsubr.S \
//    -Wl,-pagezero_size,0x1000 \
//    -Wl,-no_pie \
//    -Wl,-no_uuid \
//    -Wl,-no_function_starts \
//    -Wl,-bind_at_load \
//    -Wl,-headerpad,0x400 \
//
//#    -Wl,-unexported_symbols_list unexport-upxload.txt \
//# strip -u -r i386-darwin.macho-upxmain.exe

// Makefile:
//# Compile i386-darwin.macho-upxmain.c on MacOS 10.9 (Mavericks) or later,
//# to get smaller code.  Then copy i386-darwin.macho-upxmain.o to MacOS 10.6.x,
//# and static link, to get runtime conventions straight [??]
//#\tgcc -m32 -c -I $PWD \
//#\t    -Os -fPIC -fno-stack-protector -fno-unwind-tables \
//#\t    i386-darwin.macho-upxmain.c
//
//i386-darwin.macho-upxmain.exe: Makefile
//i386-darwin.macho-upxmain.exe: start.S
//i386-darwin.macho-upxmain.exe: i386-darwin.macho-upxsubr.S
//i386-darwin.macho-upxmain.exe: i386-darwin.macho-upxmain.o
//\tgcc -c start.S i386-darwin.macho-upxsubr.S
//\tgcc -o $@ -I $PWD \
//\t    -O -nostartfiles -fno-stack-protector -fno-unwind-tables \
//\t    start.o \
//\t    i386-darwin.macho-upxmain.o \
//\t    i386-darwin.macho-upxsubr.o \
//\t    -Wl,-pagezero_size,0x1000 \
//\t    -Wl,-no_uuid \
//\t    -Wl,-bind_at_load \
//\t    -Wl,-headerpad,0x400
//\tstrip -u -r -S -x $@
//\totool -hl $@ >upxmain-new.otool

// History: Originally this file i386-darwin.macho-upxmain.c was the entry point
// of the compressed program.  The output i386-darwin.macho-upxmain.exe was used
// as a prototype for LC_* commands.  The start address was in LC_UNIXTHREAD.
// The decompressor upx_main() i386-darwin.macho-main.c itself was not compressed.
//
// Then MacOS 10.7 ("Lion") supported 64-bit x86_64, and things began to change.
// The start address (for anything except the dynamic linker) is in LC_MAIN.
// We still use LC_UNIXTHREAD because we are "dynamic linker".
// Because no program on MacOS uses brk(0), then the compressed program and stub
// could above the space for un-compressed program, saving a copy-and-relocate.
// The run-time decompression could be more like on Linux, using: macho-entry.S,
// macho-fold.S, macho-main.c

int
main(int argc, char *argv[])
{
    // Entry via JMP (with no parameters) instead of CALL
    asm("movl 1*4(%%ebp),%0; lea 2*4(%%ebp),%1" : "=r" (argc), "=r" (argv) : );

    Mach_header const *mhdr0 = (Mach_header const *)((~0ul<<12) & (unsigned long)&main);
    Mach_command const *ptr = (Mach_command const *)(1+ mhdr0);
    f_unfilter *f_unf;
    f_expand *f_exp;
    char *payload;
    size_t paysize;

    unsigned j;
    for (j=0; j < mhdr0->ncmds; ++j,
            ptr = (Mach_command const *)(ptr->cmdsize + (char const *)ptr))
    if (LC_SEGMENT==ptr->cmd) {
        Mach_segment_command const *const seg = (Mach_segment_command const *)ptr;
        // Compare 8 characters
        if (*(uint64_t const *)(&"__LINKEDIT"[2]) == *(uint64_t const *)(&seg->segname[2])) {
            f_unf = (f_unfilter *)(sizeof(unsigned short)             + seg->vmaddr);
            f_exp = (f_expand *)(*(unsigned short const *)seg->vmaddr + seg->vmaddr);
            unsigned const *q = (unsigned const *)seg->vmaddr;
            while (!(paysize = *--q)) /*empty*/ ;
            payload = (char *)(-paysize + (char const *)q);
            break;
        }
    }
    char mhdr[16384];
    uint32_t entry = upx_main((struct l_info const *)payload, paysize,
        (Mach_header *)mhdr, sizeof(mhdr),
        f_exp, f_unf, (Mach_header **)&argv[-2]);

    munmap(payload, paysize);  // leaving __LINKEDIT
    argv[-1] = (char *)(long)argc;
    asm("lea -2*4(%1),%%esp; jmp *%0" : : "r" (entry), "r" (argv));
    return 0;
}

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