macho/research/custom_loader/b.cc

#include <mach-o/dyld.h>
#include <mach/mach.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

char *pwd;
uint32_t pwd_len;

int custom_strcmp(const char *p1, const char *p2) {
  const unsigned char *s1 = (const unsigned char *)p1;
  const unsigned char *s2 = (const unsigned char *)p2;
  unsigned char c1, c2;
  do {
    c1 = (unsigned char)*s1++;
    c2 = (unsigned char)*s2++;
    if (c1 == '\0')
      return c1 - c2;
  } while (c1 == c2);
  return c1 - c2;
}

void set_cwd(const char *const *envp) {
  while (*envp) {
    // PWD=
    if (0x3d445750 == *(uint32_t *)(*envp)) {
      break;
    }
    envp++;
  }
  pwd = (char *)(*envp + 4);
  for (; pwd[pwd_len] != 0; pwd_len++)
    ;
  printf("%s\n", pwd);
}

const uint32_t magic64 = 0xfeedfacf;
const uint32_t magic32 = 0xfeedface;

struct libcache_item {
  void *header;
  void *trie;
  uint32_t trie_size;
  uint32_t hash;

  uint64_t slide;

  // pointer to segment address
  uint32_t nsegment;
  uint64_t* segment;
};

struct libcache {
  struct libcache_item *libs;
  uint32_t size;

  void *main;
  void *thislib;
  void *libdyld;
};

// try these hashes
// https://gist.github.com/sgsfak/9ba382a0049f6ee885f68621ae86079b
uint32_t fnv_hash(const char *str) {
  unsigned char *s = (unsigned char *)str; /* unsigned string */

  /* See the FNV parameters at www.isthe.com/chongo/tech/comp/fnv/#FNV-param */
  const uint32_t FNV_32_PRIME = 0x01000193; /* 16777619 */

  uint32_t h = 0x811c9dc5; /* 2166136261 */
  while (*s != 0) {
    /* xor the bottom with the current octet */
    h ^= *s++;
    /* multiply by the 32 bit FNV magic prime mod 2^32 */
    h *= FNV_32_PRIME;
  }

  return h;
}

// calculate the hash to search
// _dyld_get_image_name returns the full path to the library
// while the static path in LC_DYLIB (and such) could be relative
// we should expand the path to fullpath to correctly compute the hash
//
// the hardest part is the @rpath, because there can be many LC_RPATH
// and @rpath can also reference @loader_path
uint32_t calculate_libname_hash(const libcache *cache, const char *name) {
  uint32_t hash;
  uint32_t (*hash_func)(const char *) = fnv_hash;
  if (name[0] == '.') {
    // resolve relative path with ./ ../ ../../ and so on
    char *p = realpath(name, 0);
    hash = hash_func(p);
    free(p);
  } else if (name[0] == '@') {
    // TODO: resolve @rpath
    // ohyeah this is gonna be wild
    // loop through all rpath and resolve that rpath
    // then resolve the full path for all rpath
    //
    // which rpath is correct can be done by checking if the cache has that hash
    printf("resolver for @rpath is not supported yet\n");
  } else {
    hash = hash_func(name);
  }
  return hash;
}

// dummy no sus function to look for dyld header
// i don't know if dyld_stub_binder should be better
// because if they are not familiar with dyld
// they would not suspect dyld_stub_binder inside modern macho
extern "C" uint32_t dyld_get_sdk_version(const mach_header *mh);
void exported_from_c();

void decode_uleb128(char *&addr, uint32_t *ret) {
  uint32_t result = 0;
  int shift = 0;

  while (1) {
    unsigned char byte = *(unsigned char *)(addr);
    addr++;

    result |= (byte & 0x7f) << shift;
    shift += 7;

    if (!(byte & 0x80))
      break;
  }

  *ret = result;
}

void *find_header(void *_func) {
  // Approach 1: (not stable)
  // we assume that text section is small enough to fit on 1 page
  // so the header should stay at the top of the page due to allocation logic
  // the slice/slide is random but always align 0x1000 so we test a few values
  // to see if the magic value is found
  //
  // Guaranteed to stop, but search range is small

  // const uint64_t page_size = 0x4000;
  // uint64_t func = (uint64_t)_func;
  // uint64_t potential_head = func + (0x4000 - (func % page_size));
  // void* head = 0;
  // for (uint64_t i = 0x1000; i < 0xf000; i+=0x1000) {
  //   uint32_t* x = (uint32_t*)(potential_head - i);
  //   if (*x == magic64 || *x == magic32) {
  //     head = (void*)x;
  //     break;
  //   }
  // }
  // return head;

  // Approach 2: (more stable)
  // We know that the header is 0x1000 aligned,
  // just loop until the magic value is found
  // Using while loop so ¯\_(ツ)_/¯
  const uint64_t page_size = 0x1000;
  uint64_t func = (uint64_t)_func;
  uint64_t potential_head = func + (0x1000 - (func % page_size));

  void *head = 0;
  uint32_t *x = (uint32_t *)(potential_head);
  while (*x != magic64 && *x != magic32) {
    x -= 0x1000 / 4;
  }
  return (void *)x;
}

uint64_t get_slide(const void *header) {
  const uint32_t magic = *(uint32_t *)header;
  char *ptr = (char *)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  uint64_t slice = 0;
  const uint32_t ncmds = *((uint32_t *)header + 4);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    if (cmd == LC_SEGMENT_64) {
      char *name = (char *)((uint64_t *)ptr + 1);
      uint64_t vmaddr = *((uint64_t *)ptr + 3);
      uint64_t fileoffset = *((uint64_t *)ptr + 5);
      if (custom_strcmp(name, "__TEXT") == 0) {
        slice = (uint64_t)header - vmaddr;
        return slice;
      }
    }
    ptr += cmdsize;
  }
  return 0;
}

void print_macho_summary(const void *header) {
  const uint32_t magic = *(uint32_t *)header;
  char *ptr = (char *)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  const uint32_t ncmds = *((uint32_t *)header + 4);
  printf("parsing macho at %p\n", header);
  printf("ncmds %x\n", ncmds);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    printf(" cmd %x %x\n", cmd, cmdsize);
    if (cmd == LC_DYLD_EXPORTS_TRIE) {
      const uint32_t offset = *((uint32_t *)ptr + 2);
      const uint32_t size = *((uint32_t *)ptr + 3);
      printf("  export trie: offset=0x%x size=0x%x\n", offset, size);
    }
    if (cmd == LC_SEGMENT_64) {
      char *name = (char *)((uint64_t *)ptr + 1);
      uint64_t vmaddr = *((uint64_t *)ptr + 3);
      uint64_t vmsize = *((uint64_t *)ptr + 4);
      uint64_t fileoffset = *((uint64_t *)ptr + 5);
      uint64_t filesize = *((uint64_t *)ptr + 6);
      if (custom_strcmp(name, "__TEXT") == 0) {
        uint64_t slide = (uint64_t)header - vmaddr;
        printf(" --- slide=0x%llx ---\n", slide);
      }
      printf("  Segment %s\n", name);
      printf("    vmaddr=0x%llx fileoffset=0x%llx\n", vmaddr, fileoffset);
      printf("    vmsize=0x%llx filesize=0x%llx\n", vmsize, filesize);

      uint64_t nsect = *((uint32_t *)ptr + 8*2);
      char* sections_ptr = (char*)((uint32_t*)ptr + 18);
      for (int sec = 0; sec < nsect; sec++) {
        char* secname = sections_ptr;
        uint64_t addr = *((uint64_t*)sections_ptr + 4);
        uint64_t size = *((uint64_t*)sections_ptr + 5);
        uint32_t fileoffset = *((uint32_t*)sections_ptr + 6*2);
        printf("    Section %s\n", sections_ptr);
        printf("      addr=0x%llx size=0x%llx fileoffset=0x%x\n", addr, size, fileoffset);
      }
    }
    if (cmd == LC_REEXPORT_DYLIB) {
      uint32_t name_offset = *((uint32_t *)ptr + 2);
      char *name = (char *)ptr + name_offset;
      printf("  reexport lib %s\n", name);
    }
    ptr += cmdsize;
  }
}

void *get_export_trie(const void *header, uint32_t &size) {
  const uint32_t magic = *(uint32_t *)header;
  char *ptr = (char *)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  uint64_t slice = 0;
  uint64_t linkedit_vmaddr = 0;
  uint64_t linkedit_fileoffset = 0;
  const uint32_t ncmds = *((uint32_t *)header + 4);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    if (cmd == LC_DYLD_EXPORTS_TRIE) {
      const uint32_t offset = *((uint32_t *)ptr + 2);
      size = *((uint32_t *)ptr + 3);
      uint64_t offset_in_linkedit = (uint64_t)offset - linkedit_fileoffset;
      return (void *)(linkedit_vmaddr + slice + offset_in_linkedit);
    }
    if (cmd == LC_DYLD_INFO_ONLY) {
      const uint32_t offset = *((uint32_t *)ptr + 10);
      size = *((uint32_t *)ptr + 11);
      uint64_t offset_in_linkedit = (uint64_t)offset - linkedit_fileoffset;
      return (void *)(linkedit_vmaddr + slice + offset_in_linkedit);
    }
    if (cmd == LC_SEGMENT_64) {
      char *name = (char *)((uint64_t *)ptr + 1);
      uint64_t vmaddr = *((uint64_t *)ptr + 3);
      uint64_t fileoffset = *((uint64_t *)ptr + 5);
      if (custom_strcmp(name, "__TEXT") == 0) {
        slice = (uint64_t)header - vmaddr;
      } else if (custom_strcmp(name, "__LINKEDIT") == 0) {
        linkedit_vmaddr = vmaddr;
        linkedit_fileoffset = fileoffset;
      }
    }
    ptr += cmdsize;
  }
  return 0;
}

uint32_t should_follow_symbol(char *&buffer, char *&_find) {
  // printf("follow check %s has prefix: %s\n", _find, buffer);
  char *find = _find;
  char is_prefix = true;
  while (1) {
    int find_end = *find == 0;
    int buffer_end = *buffer == 0;
    int check = *buffer == *find;
    // printf("check is %x == %x\n", *buffer, *find);

    if (buffer_end) {
      // we must always run to the end of buffer, marked 0x00
      buffer++;
      break;
    }
    if (find_end) {
      // symbol to find is shorter than current buffer string
      // but we still need to run to the end of buffer
      // so just set not prefix
      is_prefix = false;
    }
    if (!check) {
      is_prefix = false;
    }
    buffer++;
    find++;
  }
  // only move forward if is_prefix
  if (is_prefix) {
    _find = find;
    // printf("prefix is found\n");
  }
  return is_prefix;
}

void *find_in_export_trie(const void *header, void *trie, const char *symbol) {
  uint32_t func = 0;

  char *ptr = (char *)trie;
  char *find = (char *)symbol;
  while (1) {
    // terminal node will have data
    uint32_t data_count = 0;
    decode_uleb128(ptr, &data_count);
    if (data_count != 0 && *find == 0) {
      // printf("reached terminal node\n");
      break;
    } else if (data_count) {
      // still need to follow the branch
      ptr += data_count;
    }
    char num_child = ptr[0];
    ptr++;

    int still_following = 0;
    for (char i = 0; i < num_child; i++) {
      still_following = should_follow_symbol(ptr, find);
      uint32_t follow_offset;
      decode_uleb128(ptr, &follow_offset);
      if (still_following) {
        ptr = (char *)trie + follow_offset;
        break;
      }
    }

    if (!still_following) {
      // symbol not found
      return 0;
    }
  }

  char count = *(ptr - 1);
  ptr++; // flags
  // uleb128 offset
  decode_uleb128(ptr, &func);
  return (void *)((char *)header + func);
}

void *find_in_lib(struct libcache *cache, struct libcache_item *lib,
                  const char *symbol);

void *find_in_reexport(struct libcache *cache, struct libcache_item *lib,
                       const char *symbol) {
  void *header = lib->header;
  const uint32_t magic = *(uint32_t *)header;
  char *ptr = (char *)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  const uint32_t ncmds = *((uint32_t *)header + 4);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    if (cmd != LC_REEXPORT_DYLIB) {
      ptr += cmdsize;
      continue;
    }
    uint32_t name_offset = *((uint32_t *)ptr + 2);
    char *name = (char *)ptr + name_offset;
    uint32_t hash = calculate_libname_hash(cache, name);
    for (int j = 0; j < cache->size; j++) {
      struct libcache_item reexport = cache->libs[j];
      if (reexport.hash != hash) {
        continue;
      }
      void *found = find_in_lib(cache, &reexport, symbol);
      if (found)
        return found;
    }
    ptr += cmdsize;
  }
  return 0;
}

void *find_in_lib(struct libcache *cache, struct libcache_item *lib,
                  const char *symbol) {
  void *direct = find_in_export_trie(lib->header, lib->trie, symbol);
  if (direct)
    return direct;
  // cannot find in directly exported trie, loop through all reexport libs
  return find_in_reexport(cache, lib, symbol);
}

void *custom_dlsym(struct libcache *cache, const char *libname,
                   const char *symbol) {
  uint32_t hash = calculate_libname_hash(cache, libname);
  for (int i = 0; i < cache->size; i++) {
    struct libcache_item cache_lib = cache->libs[i];
    if (cache_lib.hash == hash) {
      return find_in_lib(cache, &cache_lib, symbol);
    }
  }
  printf("cannot find lib with hash 0x%x\n", hash);
  return 0;
}

void *custom_dlsym(struct libcache *cache, uint32_t hash, const char *symbol) {
  for (int i = 0; i < cache->size; i++) {
    struct libcache_item cache_lib = cache->libs[i];
    if (cache_lib.hash == hash) {
      return find_in_lib(cache, &cache_lib, symbol);
    }
  }
  return 0;
}

void bootstrap_libcache_item(struct libcache_item* item, const void* header, const char* name) {
  item->header = (void*)header;
  item->trie = get_export_trie(header, item->trie_size);

  const uint32_t magic = *(uint32_t *)header;
  char *ptr = (char *)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  const uint32_t ncmds = *((uint32_t *)header + 4);
  char* command_ptr = ptr;

  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    if (cmd == LC_SEGMENT_64) {
      char *name = (char *)((uint64_t *)ptr + 1);
      if (custom_strcmp(name, "__TEXT") == 0) {
        uint64_t vmaddr = *((uint64_t *)ptr + 3);
        item->slide = (uint64_t)header - vmaddr;
      }
      item->nsegment++;
    }
    ptr += cmdsize;
  }

  ptr = command_ptr;
  item->segment = (uint64_t*)malloc(sizeof(uint64_t) * item->nsegment);
  for (int i = 0, segment_i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t *)ptr + 0);
    const uint32_t cmdsize = *((uint32_t *)ptr + 1);
    if (cmd == LC_SEGMENT_64) {
      uint64_t vmaddr = *((uint64_t *)ptr + 3);
      item->segment[segment_i++] = (vmaddr + item->slide);
    }
    ptr += cmdsize;
  }
  return;

}

struct libcache_item* get_libcache_with_name(struct libcache* cache, const char* name) {
  uint32_t hash = calculate_libname_hash(cache, name);
  for (int i = 0; i < cache->size; i++) {
    struct libcache_item* cache_lib = &cache->libs[i];
    if (cache_lib->hash == hash) {
      return cache_lib;
    }
  }
  return 0;
}

void dump_export_trie(const void* trie, uint32_t size, const char* filename) {
  FILE *outfile = fopen(filename, "wb");
  fwrite((char*)trie, size, 1, outfile);
  fclose(outfile);
}

void dump_export_trie_of(const char* libname, const libcache* cache, const char* filename) {
  uint32_t hash = calculate_libname_hash(cache, libname);
  for (int i = 0; i < cache->size; i++) {
    struct libcache_item cache_lib = cache->libs[i];
    if (cache_lib.hash == hash) {
      return dump_export_trie(cache_lib.trie, cache_lib.trie_size, filename);
    }
  }
}

int hook_printf(const char *format, ...) {
  va_list args;
  va_start(args, format);

  printf("HOOKED BEGIN LOL\n");
  int status = printf(format, args);
  printf("HOOKED  END  LOL\n");

  va_end(args);
  return status;
}

struct ProgramVars {
  void *mh; // mach_header or mach_header64
  int *NXArgcPtr;
  const char ***NXArgvPtr;
  const char ***environPtr;
  const char **__prognamePtr;
};

void build_cache(struct libcache& cache, void* main);
void fix(struct libcache& cache);

void test(struct libcache& cache);

__attribute__((constructor)) static void
bruh(int argc, const char *const argv[], const char *const envp[],
     const char *const apple[], const struct ProgramVars *vars) {
  set_cwd(envp);

  // ProgramVars contains pointer to main executable (mapped) file

  struct libcache cache;
  build_cache(cache, (void *)(vars->mh));

  // dump_export_trie_of(
  //   "/usr/lib/system/libsystem_c.dylib", &cache,
  //   "../scripts/libsystem_c_export_trie.bin");

  // test(cache);

  // ATTENTION:
  // If we choose to resolve **this** lib
  // Before resolve is complete, **DO NOT** call any library function
  //
  // The following functions can be used:
  // (we do not remove them for **our lib**)
  // - malloc
  // - free
  fix(cache);

  for (int i = 0; i < cache.size; i++) {
    free(cache.libs[i].segment);
  }
  free(cache.libs);
}

void build_cache(struct libcache& cache, void* main) {
  const uint64_t main_slide = get_slide(main);
  // Find our lib (mapped) file
  const void *thislib = find_header((void *)bruh);
  // Find dyld lib (mapped) file using a no-sus function
  const void *libdyld = find_header((void *)dyld_get_sdk_version);

  cache.main = (void*)main;
  cache.thislib = (void*)thislib;
  cache.libdyld = (void*)libdyld;
  uint32_t libsystem_hash =
      calculate_libname_hash(&cache, "/usr/lib/libSystem.B.dylib");

  // From libdyld header, we can list exports table
  // to find all function we want to use
  //
  // This way there is no leakage of functions we use to do our trick
  // mostly to hide
  //  - _dyld_image_count
  //  - _dyld_get_image_name
  //  - _dyld_get_image_header
  //  - _dyld_get_image_vmaddr_slide

  // The above functions are crucial to find all libraries loaded
  // From which we will traverse the exports table to replace
  // _got and _la_symbol_pointer data

  // Our lib can hide more details too
  // We can resolve all functions we use
  // before resolving the main executable imports
  //
  // This will make our lib use only dyld_get_sdk_version
  // For the main executable, imports are empty due to manual resolve

  printf("executable header at %p\n", main);
  printf("lib header at %p\n", thislib);
  printf("libdyld header at %p\n", libdyld);

  // print_macho_summary(main);
  // print_macho_summary(thislib);

  uint32_t trie_size;
  void *libdyld_export_trie = get_export_trie(libdyld, trie_size);

  // we have to traverse the trie to find these symbols
  // because if we self-rebuild import table for **this** lib,
  // these symbols aren't resolved
  // so we have to resolve ourselves and then rebuild the symbols for others
  typedef int (*dyld_image_count_t)(void);
  typedef char *(*dyld_get_image_name_t)(int);
  typedef void *(*dyld_get_image_header_t)(int);
  int (*dyld_image_count_func)(void) = (dyld_image_count_t)find_in_export_trie(
      libdyld, libdyld_export_trie, "__dyld_image_count");
  void *(*dyld_get_image_header_func)(int) =
      (dyld_get_image_header_t)find_in_export_trie(libdyld, libdyld_export_trie,
                                                   "__dyld_get_image_header");
  char *(*dyld_get_image_name_func)(int) =
      (dyld_get_image_name_t)find_in_export_trie(libdyld, libdyld_export_trie,
                                                 "__dyld_get_image_name");

  cache.size = dyld_image_count_func();
  cache.libs =
      (struct libcache_item *)malloc(sizeof(struct libcache_item) * cache.size);
  for (int i = 0; i < cache.size; i++) {
    void *header = dyld_get_image_header_func(i);
    char *name = dyld_get_image_name_func(i);
    bootstrap_libcache_item(&cache.libs[i], header, name);
    cache.libs[i].hash = calculate_libname_hash(&cache, name);
    // printf("%p %s\n", header, name);
  }
}

void fix(struct libcache& cache) {
  // now we have function to find exported symbols
  // it supports full name search or hash search
  // to reserve space, we use the hash search
  //
  // so we will collect all imported symbols, and its offset to fix
  // with legacy symbol resolve
  //    __got always has dyld_stub_binder
  //    __la_symbol_ptr
  // with modern symbol resolve
  //    __got now contains full rebase/bind opcode
  //
  // the list of all imported symbols should be
  // [(offset, name, libhash)]
  // if we want to also fix framework/libraries used by the main executable,
  // (only those that are not governed by the system)
  // we should also have extra list(s) for that lib to resolve ourselves
  //
  // main: [(offset, name, libhash)]
  // libA: [(offset, name, libhash)]
  // libB: [(offset, name, libhash)]
  //
  // using the list is temporary for PoC
  // we know that many symbols are exported from 1 lib
  // so we can build a trie (yes, more trie)
  // where the symbols are now concatenated with libhash 4 bytes as prefix
  // and the offset is at the terminal node
  //
  // this way, we can reduce the libhash, although we need to build a trie
  // build the trie is harder than traversing it
  //
  // just an idea, if we can somehow reduce the datasize then it would be better

  // NOTES:
  // mach_task_self() has a conflicting symbol or something,
  // in symbol table it's: _mach_task_self_
  // but have to search with: _mach_task_self
  //
  // so future replacement into mach_task_self has to use _mach_task_self
  // despite the symbol is _mach_task_self_
  //
  // may need to look into why this happens so we can deal with this more
  // generic

  uint32_t libsystem_hash =
      calculate_libname_hash(&cache, "/usr/lib/libSystem.B.dylib");

  // this is just for now,
  // in the future we will self fix our lib so our lib also has no import
  typedef void *(*vm_protect_t)(void *, uint64_t, uint64_t, int, int);
  typedef void *(*mach_task_self_t)();
  mach_task_self_t mach_task_self_func =
      (mach_task_self_t)custom_dlsym(&cache, libsystem_hash, "_mach_task_self");
  vm_protect_t vm_protect_func =
      (vm_protect_t)custom_dlsym(&cache, libsystem_hash, "_vm_protect");

  int npage_rw_fixed = 0;
  uint64_t page_rw_fixed[10]; // should be dynamic, but works for now

#include "out/b.h"
  // think of a way to get what binary to fix
  // so we can iterate through them
  struct libcache_item* libfixing = get_libcache_with_name(&cache, "./out/a");
  // print_macho_summary(libfixing->header);
  for (int i = 0; i < nimports; i++) {
    struct imported_symbol symbol = imported_table[i];
    uint64_t fix_at = symbol.offset + libfixing->segment[symbol.segment_i];

    int need_rw_fix = true;
    for (int j = 0; j < npage_rw_fixed; j++) {
      if (page_rw_fixed[j] <= fix_at &&
          page_rw_fixed[j] + 0x1000 > fix_at) {
        need_rw_fix = false;
      }
    }
    if (need_rw_fix) {
      uint64_t start_page = fix_at - (fix_at % 0x1000);
      vm_protect_func(mach_task_self_func(), start_page, 0x1000, 0,
                      VM_PROT_READ | VM_PROT_WRITE);
      page_rw_fixed[npage_rw_fixed++] = start_page;
      printf("modify page starts at 0x%llx to RW\n", start_page);
    }

    void *resolved;
    // search with hash is faster
    resolved = custom_dlsym(&cache, symbol.hash, symbol.name);
    if (resolved == 0) {
      // but fuck apple they have relative path and rpath
      resolved = custom_dlsym(&cache, symbol.lib, symbol.name);
    }
    *(uint64_t *)fix_at = (uint64_t)resolved;

    printf("imports need to fix: (0x%x)%s at 0x%llx\n", symbol.hash,
           symbol.name, fix_at);
    printf("  from=%s\n", symbol.lib);
    printf("  segment id=%d; offset=0x%llx;", symbol.segment_i, symbol.offset);
    printf("  resolved=%p\n", resolved);
  }

  for (int j = 0; j < npage_rw_fixed; j++) {
    uint64_t start_page = page_rw_fixed[j];
    vm_protect_func(mach_task_self_func(), start_page, 0x4000, 0, VM_PROT_READ);
  }
}

void test(struct libcache& cache) {
  uint32_t libsystem_hash =
      calculate_libname_hash(&cache, "/usr/lib/libSystem.B.dylib");
  if (false) { // test search using name
    void *printf_func =
        custom_dlsym(&cache, "/usr/lib/libSystem.B.dylib", "_printf");
    printf("Indirect search: Found=%p Expected=%p\n", printf_func, printf);

    void *vm_protect_func =
        custom_dlsym(&cache, "/usr/lib/libSystem.B.dylib", "_vm_protect");
    printf("Indirect search: Found=%p Expected=%p\n", vm_protect_func,
           vm_protect);

    // using relative path
    void *func_c_1 =
        custom_dlsym(&cache, "./out/libb.dylib", "__Z15exported_from_cv");
    printf("Indirect search: Found=%p Expected=%p\n", func_c_1,
           exported_from_c);

    // using rpath
    void *func_c_2 =
        custom_dlsym(&cache, "@rpath/libb.dylib", "__Z15exported_from_cv");
    printf("Indirect search: Found=%p Expected=%p\n", func_c_2,
           exported_from_c);
  }

  if (false) { // test search using hash of name
    void *printf_func = custom_dlsym(&cache, libsystem_hash, "_printf");
    printf("Indirect search: Found=%p Expected=%p\n", printf_func, printf);

    void *vm_protect_func = custom_dlsym(&cache, libsystem_hash, "_vm_protect");
    printf("Indirect search: Found=%p Expected=%p\n", vm_protect_func,
           vm_protect);

    void *realpath_func = custom_dlsym(&cache, libsystem_hash, "_realpath$DARWIN_EXTSN");
    printf("Indirect search: Found=%p Expected=%p\n", realpath_func, realpath);
  }
}