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Java example source code file (ps_core.c)

This example Java source code file (ps_core.c) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

elf_ehdr, elf_phdr, filemapheader, min, null, o_rdonly, priu64, prix64, ps_ok, pt_load, reading, seek_cur, seek_set, usesharedspaces

The ps_core.c Java example source code

/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include <jni.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <stddef.h>
#include "libproc_impl.h"

#ifdef __APPLE__
#include "sun_jvm_hotspot_debugger_amd64_AMD64ThreadContext.h"
#endif

// This file has the libproc implementation to read core files.
// For live processes, refer to ps_proc.c. Portions of this is adapted
// /modelled after Solaris libproc.so (in particular Pcore.c)

//----------------------------------------------------------------------
// ps_prochandle cleanup helper functions

// close all file descriptors
static void close_files(struct ps_prochandle* ph) {
  lib_info* lib = NULL;

  // close core file descriptor
  if (ph->core->core_fd >= 0)
    close(ph->core->core_fd);

  // close exec file descriptor
  if (ph->core->exec_fd >= 0)
    close(ph->core->exec_fd);

  // close interp file descriptor
  if (ph->core->interp_fd >= 0)
    close(ph->core->interp_fd);

  // close class share archive file
  if (ph->core->classes_jsa_fd >= 0)
    close(ph->core->classes_jsa_fd);

  // close all library file descriptors
  lib = ph->libs;
  while (lib) {
    int fd = lib->fd;
    if (fd >= 0 && fd != ph->core->exec_fd) {
      close(fd);
    }
    lib = lib->next;
  }
}

// clean all map_info stuff
static void destroy_map_info(struct ps_prochandle* ph) {
  map_info* map = ph->core->maps;
  while (map) {
    map_info* next = map->next;
    free(map);
    map = next;
  }

  if (ph->core->map_array) {
    free(ph->core->map_array);
  }

  // Part of the class sharing workaround
  map = ph->core->class_share_maps;
  while (map) {
    map_info* next = map->next;
    free(map);
    map = next;
  }
}

// ps_prochandle operations
static void core_release(struct ps_prochandle* ph) {
  if (ph->core) {
    close_files(ph);
    destroy_map_info(ph);
    free(ph->core);
  }
}

static map_info* allocate_init_map(int fd, off_t offset, uintptr_t vaddr, size_t memsz) {
  map_info* map;
  if ( (map = (map_info*) calloc(1, sizeof(map_info))) == NULL) {
    print_debug("can't allocate memory for map_info\n");
    return NULL;
  }

  // initialize map
  map->fd     = fd;
  map->offset = offset;
  map->vaddr  = vaddr;
  map->memsz  = memsz;
  return map;
}

// add map info with given fd, offset, vaddr and memsz
static map_info* add_map_info(struct ps_prochandle* ph, int fd, off_t offset,
                             uintptr_t vaddr, size_t memsz) {
  map_info* map;
  if ((map = allocate_init_map(fd, offset, vaddr, memsz)) == NULL) {
    return NULL;
  }

  // add this to map list
  map->next  = ph->core->maps;
  ph->core->maps   = map;
  ph->core->num_maps++;

  return map;
}

// Part of the class sharing workaround
static map_info* add_class_share_map_info(struct ps_prochandle* ph, off_t offset,
                             uintptr_t vaddr, size_t memsz) {
  map_info* map;
  if ((map = allocate_init_map(ph->core->classes_jsa_fd,
                               offset, vaddr, memsz)) == NULL) {
    return NULL;
  }

  map->next = ph->core->class_share_maps;
  ph->core->class_share_maps = map;
  return map;
}

// Return the map_info for the given virtual address.  We keep a sorted
// array of pointers in ph->map_array, so we can binary search.
static map_info* core_lookup(struct ps_prochandle *ph, uintptr_t addr) {
  int mid, lo = 0, hi = ph->core->num_maps - 1;
  map_info *mp;

  while (hi - lo > 1) {
    mid = (lo + hi) / 2;
    if (addr >= ph->core->map_array[mid]->vaddr) {
      lo = mid;
    } else {
      hi = mid;
    }
  }

  if (addr < ph->core->map_array[hi]->vaddr) {
    mp = ph->core->map_array[lo];
  } else {
    mp = ph->core->map_array[hi];
  }

  if (addr >= mp->vaddr && addr < mp->vaddr + mp->memsz) {
    return (mp);
  }


  // Part of the class sharing workaround
  // Unfortunately, we have no way of detecting -Xshare state.
  // Check out the share maps atlast, if we don't find anywhere.
  // This is done this way so to avoid reading share pages
  // ahead of other normal maps. For eg. with -Xshare:off we don't
  // want to prefer class sharing data to data from core.
  mp = ph->core->class_share_maps;
  if (mp) {
    print_debug("can't locate map_info at 0x%lx, trying class share maps\n", addr);
  }
  while (mp) {
    if (addr >= mp->vaddr && addr < mp->vaddr + mp->memsz) {
      print_debug("located map_info at 0x%lx from class share maps\n", addr);
      return (mp);
    }
    mp = mp->next;
  }

  print_debug("can't locate map_info at 0x%lx\n", addr);
  return (NULL);
}

//---------------------------------------------------------------
// Part of the class sharing workaround:
//
// With class sharing, pages are mapped from classes.jsa file.
// The read-only class sharing pages are mapped as MAP_SHARED,
// PROT_READ pages. These pages are not dumped into core dump.
// With this workaround, these pages are read from classes.jsa.

// FIXME: !HACK ALERT!
// The format of sharing achive file header is needed to read shared heap
// file mappings. For now, I am hard coding portion of FileMapHeader here.
// Refer to filemap.hpp.

// FileMapHeader describes the shared space data in the file to be
// mapped.  This structure gets written to a file.  It is not a class,
// so that the compilers don't add any compiler-private data to it.

#define NUM_SHARED_MAPS 4

// Refer to FileMapInfo::_current_version in filemap.hpp
#define CURRENT_ARCHIVE_VERSION 1

struct FileMapHeader {
  int   _magic;              // identify file type.
  int   _version;            // (from enum, above.)
  size_t _alignment;         // how shared archive should be aligned

  struct space_info {
    int    _file_offset;     // sizeof(this) rounded to vm page size
    char*  _base;            // copy-on-write base address
    size_t _capacity;        // for validity checking
    size_t _used;            // for setting space top on read

    // 4991491 NOTICE These are C++ bool's in filemap.hpp and must match up with
    // the C type matching the C++ bool type on any given platform.
    // We assume the corresponding C type is char but licensees
    // may need to adjust the type of these fields.
    char   _read_only;       // read only space?
    char   _allow_exec;      // executable code in space?

  } _space[NUM_SHARED_MAPS];

  // Ignore the rest of the FileMapHeader. We don't need those fields here.
};

static bool read_jboolean(struct ps_prochandle* ph, uintptr_t addr, jboolean* pvalue) {
  jboolean i;
  if (ps_pread(ph, (psaddr_t) addr, &i, sizeof(i)) == PS_OK) {
    *pvalue = i;
    return true;
  } else {
    return false;
  }
}

static bool read_pointer(struct ps_prochandle* ph, uintptr_t addr, uintptr_t* pvalue) {
  uintptr_t uip;
  if (ps_pread(ph, (psaddr_t) addr, (char *)&uip, sizeof(uip)) == PS_OK) {
    *pvalue = uip;
    return true;
  } else {
    return false;
  }
}

// used to read strings from debuggee
static bool read_string(struct ps_prochandle* ph, uintptr_t addr, char* buf, size_t size) {
  size_t i = 0;
  char  c = ' ';

  while (c != '\0') {
    if (ps_pread(ph, (psaddr_t) addr, &c, sizeof(char)) != PS_OK) {
      return false;
    }
    if (i < size - 1) {
      buf[i] = c;
    } else {
      // smaller buffer
      return false;
    }
    i++; addr++;
  }
  buf[i] = '\0';
  return true;
}

#ifdef __APPLE__
#define USE_SHARED_SPACES_SYM "_UseSharedSpaces"
// mangled name of Arguments::SharedArchivePath
#define SHARED_ARCHIVE_PATH_SYM "_ZN9Arguments17SharedArchivePathE"
#define LIBJVM_NAME "/libjvm.dylib"
#else
#define USE_SHARED_SPACES_SYM "UseSharedSpaces"
// mangled name of Arguments::SharedArchivePath
#define SHARED_ARCHIVE_PATH_SYM "__ZN9Arguments17SharedArchivePathE"
#define LIBJVM_NAME "/libjvm.so"
#endif // __APPLE_

static bool init_classsharing_workaround(struct ps_prochandle* ph) {
  int m;
  size_t n;
  lib_info* lib = ph->libs;
  while (lib != NULL) {
    // we are iterating over shared objects from the core dump. look for
    // libjvm.so.
    const char *jvm_name = 0;
    if ((jvm_name = strstr(lib->name, LIBJVM_NAME)) != 0) {
      char classes_jsa[PATH_MAX];
      struct FileMapHeader header;
      int fd = -1;
      uintptr_t base = 0, useSharedSpacesAddr = 0;
      uintptr_t sharedArchivePathAddrAddr = 0, sharedArchivePathAddr = 0;
      jboolean useSharedSpaces = 0;

      memset(classes_jsa, 0, sizeof(classes_jsa));
      jvm_name = lib->name;
      useSharedSpacesAddr = lookup_symbol(ph, jvm_name, USE_SHARED_SPACES_SYM);
      if (useSharedSpacesAddr == 0) {
        print_debug("can't lookup 'UseSharedSpaces' flag\n");
        return false;
      }

      // Hotspot vm types are not exported to build this library. So
      // using equivalent type jboolean to read the value of
      // UseSharedSpaces which is same as hotspot type "bool".
      if (read_jboolean(ph, useSharedSpacesAddr, &useSharedSpaces) != true) {
        print_debug("can't read the value of 'UseSharedSpaces' flag\n");
        return false;
      }

      if ((int)useSharedSpaces == 0) {
        print_debug("UseSharedSpaces is false, assuming -Xshare:off!\n");
        return true;
      }

      sharedArchivePathAddrAddr = lookup_symbol(ph, jvm_name, SHARED_ARCHIVE_PATH_SYM);
      if (sharedArchivePathAddrAddr == 0) {
        print_debug("can't lookup shared archive path symbol\n");
        return false;
      }

      if (read_pointer(ph, sharedArchivePathAddrAddr, &sharedArchivePathAddr) != true) {
        print_debug("can't read shared archive path pointer\n");
        return false;
      }

      if (read_string(ph, sharedArchivePathAddr, classes_jsa, sizeof(classes_jsa)) != true) {
        print_debug("can't read shared archive path value\n");
        return false;
      }

      print_debug("looking for %s\n", classes_jsa);
      // open the class sharing archive file
      fd = pathmap_open(classes_jsa);
      if (fd < 0) {
        print_debug("can't open %s!\n", classes_jsa);
        ph->core->classes_jsa_fd = -1;
        return false;
      } else {
        print_debug("opened %s\n", classes_jsa);
      }

      // read FileMapHeader from the file
      memset(&header, 0, sizeof(struct FileMapHeader));
      if ((n = read(fd, &header, sizeof(struct FileMapHeader)))
           != sizeof(struct FileMapHeader)) {
        print_debug("can't read shared archive file map header from %s\n", classes_jsa);
        close(fd);
        return false;
      }

      // check file magic
      if (header._magic != 0xf00baba2) {
        print_debug("%s has bad shared archive file magic number 0x%x, expecing 0xf00baba2\n",
                     classes_jsa, header._magic);
        close(fd);
        return false;
      }

      // check version
      if (header._version != CURRENT_ARCHIVE_VERSION) {
        print_debug("%s has wrong shared archive file version %d, expecting %d\n",
                     classes_jsa, header._version, CURRENT_ARCHIVE_VERSION);
        close(fd);
        return false;
      }

      ph->core->classes_jsa_fd = fd;
      // add read-only maps from classes.jsa to the list of maps
      for (m = 0; m < NUM_SHARED_MAPS; m++) {
        if (header._space[m]._read_only) {
          base = (uintptr_t) header._space[m]._base;
          // no need to worry about the fractional pages at-the-end.
          // possible fractional pages are handled by core_read_data.
          add_class_share_map_info(ph, (off_t) header._space[m]._file_offset,
                                   base, (size_t) header._space[m]._used);
          print_debug("added a share archive map at 0x%lx\n", base);
        }
      }
      return true;
   }
   lib = lib->next;
  }
  return true;
}

//---------------------------------------------------------------------------
// functions to handle map_info

// Order mappings based on virtual address.  We use this function as the
// callback for sorting the array of map_info pointers.
static int core_cmp_mapping(const void *lhsp, const void *rhsp)
{
  const map_info *lhs = *((const map_info **)lhsp);
  const map_info *rhs = *((const map_info **)rhsp);

  if (lhs->vaddr == rhs->vaddr) {
    return (0);
  }

  return (lhs->vaddr < rhs->vaddr ? -1 : 1);
}

// we sort map_info by starting virtual address so that we can do
// binary search to read from an address.
static bool sort_map_array(struct ps_prochandle* ph) {
  size_t num_maps = ph->core->num_maps;
  map_info* map = ph->core->maps;
  int i = 0;

  // allocate map_array
  map_info** array;
  if ( (array = (map_info**) malloc(sizeof(map_info*) * num_maps)) == NULL) {
    print_debug("can't allocate memory for map array\n");
    return false;
  }

  // add maps to array
  while (map) {
    array[i] = map;
    i++;
    map = map->next;
  }

  // sort is called twice. If this is second time, clear map array
  if (ph->core->map_array) {
    free(ph->core->map_array);
  }
  ph->core->map_array = array;
  // sort the map_info array by base virtual address.
  qsort(ph->core->map_array, ph->core->num_maps, sizeof (map_info*),
        core_cmp_mapping);

  // print map
  if (is_debug()) {
    int j = 0;
    print_debug("---- sorted virtual address map ----\n");
    for (j = 0; j < ph->core->num_maps; j++) {
      print_debug("base = 0x%lx\tsize = %d\n", ph->core->map_array[j]->vaddr,
                  ph->core->map_array[j]->memsz);
    }
  }

  return true;
}

#ifndef MIN
#define MIN(x, y) (((x) < (y))? (x): (y))
#endif

static bool core_read_data(struct ps_prochandle* ph, uintptr_t addr, char *buf, size_t size) {
   ssize_t resid = size;
   int page_size=sysconf(_SC_PAGE_SIZE);
   while (resid != 0) {
      map_info *mp = core_lookup(ph, addr);
      uintptr_t mapoff;
      ssize_t len, rem;
      off_t off;
      int fd;

      if (mp == NULL) {
         break;  /* No mapping for this address */
      }

      fd = mp->fd;
      mapoff = addr - mp->vaddr;
      len = MIN(resid, mp->memsz - mapoff);
      off = mp->offset + mapoff;

      if ((len = pread(fd, buf, len, off)) <= 0) {
         break;
      }

      resid -= len;
      addr += len;
      buf = (char *)buf + len;

      // mappings always start at page boundary. But, may end in fractional
      // page. fill zeros for possible fractional page at the end of a mapping.
      rem = mp->memsz % page_size;
      if (rem > 0) {
         rem = page_size - rem;
         len = MIN(resid, rem);
         resid -= len;
         addr += len;
         // we are not assuming 'buf' to be zero initialized.
         memset(buf, 0, len);
         buf += len;
      }
   }

   if (resid) {
      print_debug("core read failed for %d byte(s) @ 0x%lx (%d more bytes)\n",
              size, addr, resid);
      return false;
   } else {
      return true;
   }
}

// null implementation for write
static bool core_write_data(struct ps_prochandle* ph,
                             uintptr_t addr, const char *buf , size_t size) {
   return false;
}

static bool core_get_lwp_regs(struct ps_prochandle* ph, lwpid_t lwp_id,
                          struct reg* regs) {
   // for core we have cached the lwp regs after segment parsed
   sa_thread_info* thr = ph->threads;
   while (thr) {
     if (thr->lwp_id == lwp_id) {
       memcpy(regs, &thr->regs, sizeof(struct reg));
       return true;
     }
     thr = thr->next;
   }
   return false;
}

static bool core_get_lwp_info(struct ps_prochandle *ph, lwpid_t id, void *info) {
   print_debug("core_get_lwp_info not implemented\n");
   return false;
}

static ps_prochandle_ops core_ops = {
   .release=  core_release,
   .p_pread=  core_read_data,
   .p_pwrite= core_write_data,
   .get_lwp_regs= core_get_lwp_regs,
   .get_lwp_info= core_get_lwp_info
};

// from this point, mainly two blocks divided by def __APPLE__
// one for Macosx, the other for regular Bsd

#ifdef __APPLE__

void print_thread(sa_thread_info *threadinfo) {
  print_debug("thread added: %d\n", threadinfo->lwp_id);
  print_debug("registers:\n");
  print_debug("  r_r15: 0x%" PRIx64 "\n", threadinfo->regs.r_r15);
  print_debug("  r_r14: 0x%" PRIx64 "\n", threadinfo->regs.r_r14);
  print_debug("  r_r13: 0x%" PRIx64 "\n", threadinfo->regs.r_r13);
  print_debug("  r_r12: 0x%" PRIx64 "\n", threadinfo->regs.r_r12);
  print_debug("  r_r11: 0x%" PRIx64 "\n", threadinfo->regs.r_r11);
  print_debug("  r_r10: 0x%" PRIx64 "\n", threadinfo->regs.r_r10);
  print_debug("  r_r9:  0x%" PRIx64 "\n", threadinfo->regs.r_r9);
  print_debug("  r_r8:  0x%" PRIx64 "\n", threadinfo->regs.r_r8);
  print_debug("  r_rdi: 0x%" PRIx64 "\n", threadinfo->regs.r_rdi);
  print_debug("  r_rsi: 0x%" PRIx64 "\n", threadinfo->regs.r_rsi);
  print_debug("  r_rbp: 0x%" PRIx64 "\n", threadinfo->regs.r_rbp);
  print_debug("  r_rbx: 0x%" PRIx64 "\n", threadinfo->regs.r_rbx);
  print_debug("  r_rdx: 0x%" PRIx64 "\n", threadinfo->regs.r_rdx);
  print_debug("  r_rcx: 0x%" PRIx64 "\n", threadinfo->regs.r_rcx);
  print_debug("  r_rax: 0x%" PRIx64 "\n", threadinfo->regs.r_rax);
  print_debug("  r_fs:  0x%" PRIx32 "\n", threadinfo->regs.r_fs);
  print_debug("  r_gs:  0x%" PRIx32 "\n", threadinfo->regs.r_gs);
  print_debug("  r_rip  0x%" PRIx64 "\n", threadinfo->regs.r_rip);
  print_debug("  r_cs:  0x%" PRIx64 "\n", threadinfo->regs.r_cs);
  print_debug("  r_rsp: 0x%" PRIx64 "\n", threadinfo->regs.r_rsp);
  print_debug("  r_rflags: 0x%" PRIx64 "\n", threadinfo->regs.r_rflags);
}

// read all segments64 commands from core file
// read all thread commands from core file
static bool read_core_segments(struct ps_prochandle* ph) {
  int i = 0;
  int num_threads = 0;
  int fd = ph->core->core_fd;
  off_t offset = 0;
  mach_header_64      fhead;
  load_command        lcmd;
  segment_command_64  segcmd;
  // thread_command      thrcmd;

  lseek(fd, offset, SEEK_SET);
  if(read(fd, (void *)&fhead, sizeof(mach_header_64)) != sizeof(mach_header_64)) {
     goto err;
  }
  print_debug("total commands: %d\n", fhead.ncmds);
  offset += sizeof(mach_header_64);
  for (i = 0; i < fhead.ncmds; i++) {
    lseek(fd, offset, SEEK_SET);
    if (read(fd, (void *)&lcmd, sizeof(load_command)) != sizeof(load_command)) {
      goto err;
    }
    offset += lcmd.cmdsize;    // next command position
    if (lcmd.cmd == LC_SEGMENT_64) {
      lseek(fd, -sizeof(load_command), SEEK_CUR);
      if (read(fd, (void *)&segcmd, sizeof(segment_command_64)) != sizeof(segment_command_64)) {
        print_debug("failed to read LC_SEGMENT_64 i = %d!\n", i);
        goto err;
      }
      if (add_map_info(ph, fd, segcmd.fileoff, segcmd.vmaddr, segcmd.vmsize) == NULL) {
        print_debug("Failed to add map_info at i = %d\n", i);
        goto err;
      }
      print_debug("segment added: %" PRIu64 " 0x%" PRIx64 " %d\n",
                   segcmd.fileoff, segcmd.vmaddr, segcmd.vmsize);
    } else if (lcmd.cmd == LC_THREAD || lcmd.cmd == LC_UNIXTHREAD) {
      typedef struct thread_fc {
        uint32_t  flavor;
        uint32_t  count;
      } thread_fc;
      thread_fc fc;
      uint32_t size = sizeof(load_command);
      while (size < lcmd.cmdsize) {
        if (read(fd, (void *)&fc, sizeof(thread_fc)) != sizeof(thread_fc)) {
          printf("Reading flavor, count failed.\n");
          goto err;
        }
        size += sizeof(thread_fc);
        if (fc.flavor == x86_THREAD_STATE) {
          x86_thread_state_t thrstate;
          if (read(fd, (void *)&thrstate, sizeof(x86_thread_state_t)) != sizeof(x86_thread_state_t)) {
            printf("Reading flavor, count failed.\n");
            goto err;
          }
          size += sizeof(x86_thread_state_t);
          // create thread info list, update lwp_id later
          sa_thread_info* newthr = add_thread_info(ph, (pthread_t) -1, (lwpid_t) num_threads++);
          if (newthr == NULL) {
            printf("create thread_info failed\n");
            goto err;
          }

          // note __DARWIN_UNIX03 depengs on other definitions
#if __DARWIN_UNIX03
#define get_register_v(regst, regname) \
  regst.uts.ts64.__##regname
#else
#define get_register_v(regst, regname) \
  regst.uts.ts64.##regname
#endif // __DARWIN_UNIX03
          newthr->regs.r_rax = get_register_v(thrstate, rax);
          newthr->regs.r_rbx = get_register_v(thrstate, rbx);
          newthr->regs.r_rcx = get_register_v(thrstate, rcx);
          newthr->regs.r_rdx = get_register_v(thrstate, rdx);
          newthr->regs.r_rdi = get_register_v(thrstate, rdi);
          newthr->regs.r_rsi = get_register_v(thrstate, rsi);
          newthr->regs.r_rbp = get_register_v(thrstate, rbp);
          newthr->regs.r_rsp = get_register_v(thrstate, rsp);
          newthr->regs.r_r8  = get_register_v(thrstate, r8);
          newthr->regs.r_r9  = get_register_v(thrstate, r9);
          newthr->regs.r_r10 = get_register_v(thrstate, r10);
          newthr->regs.r_r11 = get_register_v(thrstate, r11);
          newthr->regs.r_r12 = get_register_v(thrstate, r12);
          newthr->regs.r_r13 = get_register_v(thrstate, r13);
          newthr->regs.r_r14 = get_register_v(thrstate, r14);
          newthr->regs.r_r15 = get_register_v(thrstate, r15);
          newthr->regs.r_rip = get_register_v(thrstate, rip);
          newthr->regs.r_rflags = get_register_v(thrstate, rflags);
          newthr->regs.r_cs  = get_register_v(thrstate, cs);
          newthr->regs.r_fs  = get_register_v(thrstate, fs);
          newthr->regs.r_gs  = get_register_v(thrstate, gs);
          print_thread(newthr);
        } else if (fc.flavor == x86_FLOAT_STATE) {
          x86_float_state_t flstate;
          if (read(fd, (void *)&flstate, sizeof(x86_float_state_t)) != sizeof(x86_float_state_t)) {
            print_debug("Reading flavor, count failed.\n");
            goto err;
          }
          size += sizeof(x86_float_state_t);
        } else if (fc.flavor == x86_EXCEPTION_STATE) {
          x86_exception_state_t excpstate;
          if (read(fd, (void *)&excpstate, sizeof(x86_exception_state_t)) != sizeof(x86_exception_state_t)) {
            printf("Reading flavor, count failed.\n");
            goto err;
          }
          size += sizeof(x86_exception_state_t);
        }
      }
    }
  }
  return true;
err:
  return false;
}

/**local function **/
bool exists(const char *fname)
{
  int fd;
  if ((fd = open(fname, O_RDONLY)) > 0) {
    close(fd);
    return true;
  }
  return false;
}

// we check: 1. lib
//           2. lib/server
//           3. jre/lib
//           4. jre/lib/server
// from: 1. exe path
//       2. JAVA_HOME
//       3. DYLD_LIBRARY_PATH
static bool get_real_path(struct ps_prochandle* ph, char *rpath) {
  /** check if they exist in JAVA ***/
  char* execname = ph->core->exec_path;
  char  filepath[4096];
  char* filename = strrchr(rpath, '/');               // like /libjvm.dylib
  if (filename == NULL) {
    return false;
  }

  char* posbin = strstr(execname, "/bin/java");
  if (posbin != NULL) {
    memcpy(filepath, execname, posbin - execname);    // not include trailing '/'
    filepath[posbin - execname] = '\0';
  } else {
    char* java_home = getenv("JAVA_HOME");
    if (java_home != NULL) {
      strcpy(filepath, java_home);
    } else {
      char* dyldpath = getenv("DYLD_LIBRARY_PATH");
      char* dypath = strtok(dyldpath, ":");
      while (dypath != NULL) {
        strcpy(filepath, dypath);
        strcat(filepath, filename);
        if (exists(filepath)) {
           strcpy(rpath, filepath);
           return true;
        }
        dypath = strtok(dyldpath, ":");
      }
      // not found
      return false;
    }
  }
  // for exec and java_home, jdkpath now is filepath
  size_t filepath_base_size = strlen(filepath);

  // first try /lib/ and /lib/server
  strcat(filepath, "/lib");
  strcat(filepath, filename);
  if (exists(filepath)) {
    strcpy(rpath, filepath);
    return true;
  }
  char* pos = strstr(filepath, filename);    // like /libjvm.dylib
  *pos = '\0';
  strcat(filepath, "/server");
  strcat(filepath, filename);
  if (exists(filepath)) {
    strcpy(rpath, filepath);
    return true;
  }

  // then try /jre/lib/ and /jre/lib/server
  filepath[filepath_base_size] = '\0';
  strcat(filepath, "/jre/lib");
  strcat(filepath, filename);
  if (exists(filepath)) {
    strcpy(rpath, filepath);
    return true;
  }
  pos = strstr(filepath, filename);
  *pos = '\0';
  strcat(filepath, "/server");
  strcat(filepath, filename);
  if (exists(filepath)) {
    strcpy(rpath, filepath);
    return true;
  }

  return false;
}

static bool read_shared_lib_info(struct ps_prochandle* ph) {
  static int pagesize = 0;
  int fd = ph->core->core_fd;
  int i = 0, j;
  uint32_t  v;
  mach_header_64 header;        // used to check if a file header in segment
  load_command lcmd;
  dylib_command dylibcmd;

  char name[BUF_SIZE];  // use to store name

  if (pagesize == 0) {
    pagesize = getpagesize();
    print_debug("page size is %d\n", pagesize);
  }
  for (j = 0; j < ph->core->num_maps; j++) {
    map_info *iter = ph->core->map_array[j];   // head
    off_t fpos = iter->offset;
    if (iter->fd != fd) {
      // only search core file!
      continue;
    }
    print_debug("map_info %d: vmaddr = 0x%016" PRIx64 "  fileoff = %" PRIu64 "  vmsize = %" PRIu64 "\n",
                           j, iter->vaddr, iter->offset, iter->memsz);
    lseek(fd, fpos, SEEK_SET);
    // we assume .dylib loaded at segment address --- which is true for JVM libraries
    // multiple files may be loaded in one segment.
    // if first word is not a magic word, means this segment does not contain lib file.
    if (read(fd, (void *)&v, sizeof(uint32_t)) == sizeof(uint32_t)) {
      if (v != MH_MAGIC_64) {
        continue;
      }
    } else {
      // may be encountered last map, which is not readable
      continue;
    }
    while (ltell(fd) - iter->offset < iter->memsz) {
      lseek(fd, fpos, SEEK_SET);
      if (read(fd, (void *)&v, sizeof(uint32_t)) != sizeof(uint32_t)) {
        break;
      }
      if (v != MH_MAGIC_64) {
        fpos = (ltell(fd) + pagesize -1)/pagesize * pagesize;
        continue;
      }
      lseek(fd, -sizeof(uint32_t), SEEK_CUR);
      // this is the file begining to core file.
      if (read(fd, (void *)&header, sizeof(mach_header_64)) != sizeof(mach_header_64)) {
        goto err;
      }
      fpos = ltell(fd);

      // found a mach-o file in this segment
      for (i = 0; i < header.ncmds; i++) {
        // read commands in this "file"
        // LC_ID_DYLIB is the file itself for a .dylib
        lseek(fd, fpos, SEEK_SET);
        if (read(fd, (void *)&lcmd, sizeof(load_command)) != sizeof(load_command)) {
          return false;   // error
        }
        fpos += lcmd.cmdsize;  // next command position
        // make sure still within seg size.
        if (fpos  - lcmd.cmdsize - iter->offset > iter->memsz) {
          print_debug("Warning: out of segement limit: %ld \n", fpos  - lcmd.cmdsize - iter->offset);
          break;  // no need to iterate all commands
        }
        if (lcmd.cmd == LC_ID_DYLIB) {
          lseek(fd, -sizeof(load_command), SEEK_CUR);
          if (read(fd, (void *)&dylibcmd, sizeof(dylib_command)) != sizeof(dylib_command)) {
            return false;
          }
          /**** name stored at dylib_command.dylib.name.offset, is a C string  */
          lseek(fd, dylibcmd.dylib.name.offset - sizeof(dylib_command), SEEK_CUR);
          int j = 0;
          while (j < BUF_SIZE) {
            read(fd, (void *)(name + j), sizeof(char));
            if (name[j] == '\0') break;
            j++;
          }
          print_debug("%s\n", name);
          // changed name from @rpath/xxxx.dylib to real path
          if (strrchr(name, '@')) {
            get_real_path(ph, name);
            print_debug("get_real_path returned: %s\n", name);
          }
          add_lib_info(ph, name, iter->vaddr);
          break;
        }
      }
      // done with the file, advanced to next page to search more files
      fpos = (ltell(fd) + pagesize - 1) / pagesize * pagesize;
    }
  }
  return true;
err:
  return false;
}

bool read_macho64_header(int fd, mach_header_64* core_header) {
  bool is_macho = false;
  if (fd < 0) return false;
  off_t pos = ltell(fd);
  lseek(fd, 0, SEEK_SET);
  if (read(fd, (void *)core_header, sizeof(mach_header_64)) != sizeof(mach_header_64)) {
    is_macho = false;
  } else {
    is_macho = (core_header->magic ==  MH_MAGIC_64 || core_header->magic ==  MH_CIGAM_64);
  }
  lseek(fd, pos, SEEK_SET);
  return is_macho;
}

// the one and only one exposed stuff from this file
struct ps_prochandle* Pgrab_core(const char* exec_file, const char* core_file) {
  mach_header_64 core_header;
  mach_header_64 exec_header;

  struct ps_prochandle* ph = (struct ps_prochandle*) calloc(1, sizeof(struct ps_prochandle));
  if (ph == NULL) {
    print_debug("cant allocate ps_prochandle\n");
    return NULL;
  }

  if ((ph->core = (struct core_data*) calloc(1, sizeof(struct core_data))) == NULL) {
    free(ph);
    print_debug("can't allocate ps_prochandle\n");
    return NULL;
  }

  // initialize ph
  ph->ops = &core_ops;
  ph->core->core_fd   = -1;
  ph->core->exec_fd   = -1;
  ph->core->interp_fd = -1;

  print_debug("exec: %s   core: %s", exec_file, core_file);

  strncpy(ph->core->exec_path, exec_file, sizeof(ph->core->exec_path));

  // open the core file
  if ((ph->core->core_fd = open(core_file, O_RDONLY)) < 0) {
    print_error("can't open core file\n");
    goto err;
  }

  // read core file header
  if (read_macho64_header(ph->core->core_fd, &core_header) != true || core_header.filetype != MH_CORE) {
    print_debug("core file is not a valid Mach-O file\n");
    goto err;
  }

  if ((ph->core->exec_fd = open(exec_file, O_RDONLY)) < 0) {
    print_error("can't open executable file\n");
    goto err;
  }

  if (read_macho64_header(ph->core->exec_fd, &exec_header) != true ||
                          exec_header.filetype != MH_EXECUTE) {
    print_error("executable file is not a valid Mach-O file\n");
    goto err;
  }

  // process core file segments
  if (read_core_segments(ph) != true) {
    print_error("failed to read core segments\n");
    goto err;
  }

  // allocate and sort maps into map_array, we need to do this
  // here because read_shared_lib_info needs to read from debuggee
  // address space
  if (sort_map_array(ph) != true) {
    print_error("failed to sort segment map array\n");
    goto err;
  }

  if (read_shared_lib_info(ph) != true) {
    print_error("failed to read libraries\n");
    goto err;
  }

  // sort again because we have added more mappings from shared objects
  if (sort_map_array(ph) != true) {
    print_error("failed to sort segment map array\n");
    goto err;
  }

  if (init_classsharing_workaround(ph) != true) {
    print_error("failed to workaround classshareing\n");
    goto err;
  }

  print_debug("Leave Pgrab_core\n");
  return ph;

err:
  Prelease(ph);
  return NULL;
}

#else // __APPLE__ (none macosx)

// read regs and create thread from core file
static bool core_handle_prstatus(struct ps_prochandle* ph, const char* buf, size_t nbytes) {
   // we have to read prstatus_t from buf
   // assert(nbytes == sizeof(prstaus_t), "size mismatch on prstatus_t");
   prstatus_t* prstat = (prstatus_t*) buf;
   sa_thread_info* newthr;
   print_debug("got integer regset for lwp %d\n", prstat->pr_pid);
   // we set pthread_t to -1 for core dump
   if((newthr = add_thread_info(ph, (pthread_t) -1,  prstat->pr_pid)) == NULL)
      return false;

   // copy regs
   memcpy(&newthr->regs, &prstat->pr_reg, sizeof(struct reg));

   if (is_debug()) {
      print_debug("integer regset\n");
#ifdef i386
      // print the regset
      print_debug("\teax = 0x%x\n", newthr->regs.r_eax);
      print_debug("\tebx = 0x%x\n", newthr->regs.r_ebx);
      print_debug("\tecx = 0x%x\n", newthr->regs.r_ecx);
      print_debug("\tedx = 0x%x\n", newthr->regs.r_edx);
      print_debug("\tesp = 0x%x\n", newthr->regs.r_esp);
      print_debug("\tebp = 0x%x\n", newthr->regs.r_ebp);
      print_debug("\tesi = 0x%x\n", newthr->regs.r_esi);
      print_debug("\tedi = 0x%x\n", newthr->regs.r_edi);
      print_debug("\teip = 0x%x\n", newthr->regs.r_eip);
#endif

#if defined(amd64) || defined(x86_64)
      // print the regset
      print_debug("\tr15 = 0x%lx\n", newthr->regs.r_r15);
      print_debug("\tr14 = 0x%lx\n", newthr->regs.r_r14);
      print_debug("\tr13 = 0x%lx\n", newthr->regs.r_r13);
      print_debug("\tr12 = 0x%lx\n", newthr->regs.r_r12);
      print_debug("\trbp = 0x%lx\n", newthr->regs.r_rbp);
      print_debug("\trbx = 0x%lx\n", newthr->regs.r_rbx);
      print_debug("\tr11 = 0x%lx\n", newthr->regs.r_r11);
      print_debug("\tr10 = 0x%lx\n", newthr->regs.r_r10);
      print_debug("\tr9 = 0x%lx\n", newthr->regs.r_r9);
      print_debug("\tr8 = 0x%lx\n", newthr->regs.r_r8);
      print_debug("\trax = 0x%lx\n", newthr->regs.r_rax);
      print_debug("\trcx = 0x%lx\n", newthr->regs.r_rcx);
      print_debug("\trdx = 0x%lx\n", newthr->regs.r_rdx);
      print_debug("\trsi = 0x%lx\n", newthr->regs.r_rsi);
      print_debug("\trdi = 0x%lx\n", newthr->regs.r_rdi);
      //print_debug("\torig_rax = 0x%lx\n", newthr->regs.orig_rax);
      print_debug("\trip = 0x%lx\n", newthr->regs.r_rip);
      print_debug("\tcs = 0x%lx\n", newthr->regs.r_cs);
      //print_debug("\teflags = 0x%lx\n", newthr->regs.eflags);
      print_debug("\trsp = 0x%lx\n", newthr->regs.r_rsp);
      print_debug("\tss = 0x%lx\n", newthr->regs.r_ss);
      //print_debug("\tfs_base = 0x%lx\n", newthr->regs.fs_base);
      //print_debug("\tgs_base = 0x%lx\n", newthr->regs.gs_base);
      //print_debug("\tds = 0x%lx\n", newthr->regs.ds);
      //print_debug("\tes = 0x%lx\n", newthr->regs.es);
      //print_debug("\tfs = 0x%lx\n", newthr->regs.fs);
      //print_debug("\tgs = 0x%lx\n", newthr->regs.gs);
#endif
   }

   return true;
}

#define ROUNDUP(x, y)  ((((x)+((y)-1))/(y))*(y))

// read NT_PRSTATUS entries from core NOTE segment
static bool core_handle_note(struct ps_prochandle* ph, ELF_PHDR* note_phdr) {
   char* buf = NULL;
   char* p = NULL;
   size_t size = note_phdr->p_filesz;

   // we are interested in just prstatus entries. we will ignore the rest.
   // Advance the seek pointer to the start of the PT_NOTE data
   if (lseek(ph->core->core_fd, note_phdr->p_offset, SEEK_SET) == (off_t)-1) {
      print_debug("failed to lseek to PT_NOTE data\n");
      return false;
   }

   // Now process the PT_NOTE structures.  Each one is preceded by
   // an Elf{32/64}_Nhdr structure describing its type and size.
   if ( (buf = (char*) malloc(size)) == NULL) {
      print_debug("can't allocate memory for reading core notes\n");
      goto err;
   }

   // read notes into buffer
   if (read(ph->core->core_fd, buf, size) != size) {
      print_debug("failed to read notes, core file must have been truncated\n");
      goto err;
   }

   p = buf;
   while (p < buf + size) {
      ELF_NHDR* notep = (ELF_NHDR*) p;
      char* descdata  = p + sizeof(ELF_NHDR) + ROUNDUP(notep->n_namesz, 4);
      print_debug("Note header with n_type = %d and n_descsz = %u\n",
                                   notep->n_type, notep->n_descsz);

      if (notep->n_type == NT_PRSTATUS) {
        if (core_handle_prstatus(ph, descdata, notep->n_descsz) != true) {
          return false;
        }
      }
      p = descdata + ROUNDUP(notep->n_descsz, 4);
   }

   free(buf);
   return true;

err:
   if (buf) free(buf);
   return false;
}

// read all segments from core file
static bool read_core_segments(struct ps_prochandle* ph, ELF_EHDR* core_ehdr) {
   int i = 0;
   ELF_PHDR* phbuf = NULL;
   ELF_PHDR* core_php = NULL;

   if ((phbuf =  read_program_header_table(ph->core->core_fd, core_ehdr)) == NULL)
      return false;

   /*
    * Now iterate through the program headers in the core file.
    * We're interested in two types of Phdrs: PT_NOTE (which
    * contains a set of saved /proc structures), and PT_LOAD (which
    * represents a memory mapping from the process's address space).
    *
    * Difference b/w Solaris PT_NOTE and Linux/BSD PT_NOTE:
    *
    *     In Solaris there are two PT_NOTE segments the first PT_NOTE (if present)
    *     contains /proc structs in the pre-2.6 unstructured /proc format. the last
    *     PT_NOTE has data in new /proc format.
    *
    *     In Solaris, there is only one pstatus (process status). pstatus contains
    *     integer register set among other stuff. For each LWP, we have one lwpstatus
    *     entry that has integer regset for that LWP.
    *
    *     Linux threads are actually 'clone'd processes. To support core analysis
    *     of "multithreaded" process, Linux creates more than one pstatus (called
    *     "prstatus") entry in PT_NOTE. Each prstatus entry has integer regset for one
    *     "thread". Please refer to Linux kernel src file 'fs/binfmt_elf.c', in particular
    *     function "elf_core_dump".
    */

    for (core_php = phbuf, i = 0; i < core_ehdr->e_phnum; i++) {
      switch (core_php->p_type) {
         case PT_NOTE:
            if (core_handle_note(ph, core_php) != true) {
              goto err;
            }
            break;

         case PT_LOAD: {
            if (core_php->p_filesz != 0) {
               if (add_map_info(ph, ph->core->core_fd, core_php->p_offset,
                  core_php->p_vaddr, core_php->p_filesz) == NULL) goto err;
            }
            break;
         }
      }

      core_php++;
   }

   free(phbuf);
   return true;
err:
   free(phbuf);
   return false;
}

// read segments of a shared object
static bool read_lib_segments(struct ps_prochandle* ph, int lib_fd, ELF_EHDR* lib_ehdr, uintptr_t lib_base) {
  int i = 0;
  ELF_PHDR* phbuf;
  ELF_PHDR* lib_php = NULL;

  int page_size=sysconf(_SC_PAGE_SIZE);

  if ((phbuf = read_program_header_table(lib_fd, lib_ehdr)) == NULL) {
    return false;
  }

  // we want to process only PT_LOAD segments that are not writable.
  // i.e., text segments. The read/write/exec (data) segments would
  // have been already added from core file segments.
  for (lib_php = phbuf, i = 0; i < lib_ehdr->e_phnum; i++) {
    if ((lib_php->p_type == PT_LOAD) && !(lib_php->p_flags & PF_W) && (lib_php->p_filesz != 0)) {

      uintptr_t target_vaddr = lib_php->p_vaddr + lib_base;
      map_info *existing_map = core_lookup(ph, target_vaddr);

      if (existing_map == NULL){
        if (add_map_info(ph, lib_fd, lib_php->p_offset,
                          target_vaddr, lib_php->p_filesz) == NULL) {
          goto err;
        }
      } else {
        if ((existing_map->memsz != page_size) &&
            (existing_map->fd != lib_fd) &&
            (existing_map->memsz != lib_php->p_filesz)){

          print_debug("address conflict @ 0x%lx (size = %ld, flags = %d\n)",
                        target_vaddr, lib_php->p_filesz, lib_php->p_flags);
          goto err;
        }

        /* replace PT_LOAD segment with library segment */
        print_debug("overwrote with new address mapping (memsz %ld -> %ld)\n",
                     existing_map->memsz, lib_php->p_filesz);

        existing_map->fd = lib_fd;
        existing_map->offset = lib_php->p_offset;
        existing_map->memsz = lib_php->p_filesz;
      }
    }

    lib_php++;
  }

  free(phbuf);
  return true;
err:
  free(phbuf);
  return false;
}

// process segments from interpreter (ld.so or ld-linux.so or ld-elf.so)
static bool read_interp_segments(struct ps_prochandle* ph) {
   ELF_EHDR interp_ehdr;

   if (read_elf_header(ph->core->interp_fd, &interp_ehdr) != true) {
       print_debug("interpreter is not a valid ELF file\n");
       return false;
   }

   if (read_lib_segments(ph, ph->core->interp_fd, &interp_ehdr, ph->core->ld_base_addr) != true) {
       print_debug("can't read segments of interpreter\n");
       return false;
   }

   return true;
}

// process segments of a a.out
static bool read_exec_segments(struct ps_prochandle* ph, ELF_EHDR* exec_ehdr) {
   int i = 0;
   ELF_PHDR* phbuf = NULL;
   ELF_PHDR* exec_php = NULL;

   if ((phbuf = read_program_header_table(ph->core->exec_fd, exec_ehdr)) == NULL)
      return false;

   for (exec_php = phbuf, i = 0; i < exec_ehdr->e_phnum; i++) {
      switch (exec_php->p_type) {

         // add mappings for PT_LOAD segments
         case PT_LOAD: {
            // add only non-writable segments of non-zero filesz
            if (!(exec_php->p_flags & PF_W) && exec_php->p_filesz != 0) {
               if (add_map_info(ph, ph->core->exec_fd, exec_php->p_offset, exec_php->p_vaddr, exec_php->p_filesz) == NULL) goto err;
            }
            break;
         }

         // read the interpreter and it's segments
         case PT_INTERP: {
            char interp_name[BUF_SIZE];

            pread(ph->core->exec_fd, interp_name, MIN(exec_php->p_filesz, BUF_SIZE), exec_php->p_offset);
            print_debug("ELF interpreter %s\n", interp_name);
            // read interpreter segments as well
            if ((ph->core->interp_fd = pathmap_open(interp_name)) < 0) {
               print_debug("can't open runtime loader\n");
               goto err;
            }
            break;
         }

         // from PT_DYNAMIC we want to read address of first link_map addr
         case PT_DYNAMIC: {
            ph->core->dynamic_addr = exec_php->p_vaddr;
            print_debug("address of _DYNAMIC is 0x%lx\n", ph->core->dynamic_addr);
            break;
         }

      } // switch
      exec_php++;
   } // for

   free(phbuf);
   return true;
err:
   free(phbuf);
   return false;
}

#define FIRST_LINK_MAP_OFFSET offsetof(struct r_debug,  r_map)
#define LD_BASE_OFFSET        offsetof(struct r_debug,  r_ldbase)
#define LINK_MAP_ADDR_OFFSET  offsetof(struct link_map, l_addr)
#define LINK_MAP_NAME_OFFSET  offsetof(struct link_map, l_name)
#define LINK_MAP_NEXT_OFFSET  offsetof(struct link_map, l_next)

// read shared library info from runtime linker's data structures.
// This work is done by librtlb_db in Solaris
static bool read_shared_lib_info(struct ps_prochandle* ph) {
  uintptr_t addr = ph->core->dynamic_addr;
  uintptr_t debug_base;
  uintptr_t first_link_map_addr;
  uintptr_t ld_base_addr;
  uintptr_t link_map_addr;
  uintptr_t lib_base_diff;
  uintptr_t lib_base;
  uintptr_t lib_name_addr;
  char lib_name[BUF_SIZE];
  ELF_DYN dyn;
  ELF_EHDR elf_ehdr;
  int lib_fd;

  // _DYNAMIC has information of the form
  //         [tag] [data] [tag] [data] .....
  // Both tag and data are pointer sized.
  // We look for dynamic info with DT_DEBUG. This has shared object info.
  // refer to struct r_debug in link.h

  dyn.d_tag = DT_NULL;
  while (dyn.d_tag != DT_DEBUG) {
    if (ps_pread(ph, (psaddr_t) addr, &dyn, sizeof(ELF_DYN)) != PS_OK) {
      print_debug("can't read debug info from _DYNAMIC\n");
      return false;
    }
    addr += sizeof(ELF_DYN);
  }

  // we have got Dyn entry with DT_DEBUG
  debug_base = dyn.d_un.d_ptr;
  // at debug_base we have struct r_debug. This has first link map in r_map field
  if (ps_pread(ph, (psaddr_t) debug_base + FIRST_LINK_MAP_OFFSET,
                 &first_link_map_addr, sizeof(uintptr_t)) != PS_OK) {
    print_debug("can't read first link map address\n");
    return false;
  }

  // read ld_base address from struct r_debug
#if 0  // There is no r_ldbase member on BSD
  if (ps_pread(ph, (psaddr_t) debug_base + LD_BASE_OFFSET, &ld_base_addr,
                  sizeof(uintptr_t)) != PS_OK) {
    print_debug("can't read ld base address\n");
    return false;
  }
  ph->core->ld_base_addr = ld_base_addr;
#else
  ph->core->ld_base_addr = 0;
#endif

  print_debug("interpreter base address is 0x%lx\n", ld_base_addr);

  // now read segments from interp (i.e ld.so or ld-linux.so or ld-elf.so)
  if (read_interp_segments(ph) != true) {
    return false;
  }

  // after adding interpreter (ld.so) mappings sort again
  if (sort_map_array(ph) != true) {
    return false;
  }

  print_debug("first link map is at 0x%lx\n", first_link_map_addr);

  link_map_addr = first_link_map_addr;
  while (link_map_addr != 0) {
    // read library base address of the .so. Note that even though <sys/link.h> calls
    // link_map->l_addr as "base address",  this is * not * really base virtual
    // address of the shared object. This is actually the difference b/w the virtual
    // address mentioned in shared object and the actual virtual base where runtime
    // linker loaded it. We use "base diff" in read_lib_segments call below.

    if (ps_pread(ph, (psaddr_t) link_map_addr + LINK_MAP_ADDR_OFFSET,
                 &lib_base_diff, sizeof(uintptr_t)) != PS_OK) {
      print_debug("can't read shared object base address diff\n");
      return false;
    }

    // read address of the name
    if (ps_pread(ph, (psaddr_t) link_map_addr + LINK_MAP_NAME_OFFSET,
                  &lib_name_addr, sizeof(uintptr_t)) != PS_OK) {
      print_debug("can't read address of shared object name\n");
      return false;
    }

    // read name of the shared object
    if (read_string(ph, (uintptr_t) lib_name_addr, lib_name, sizeof(lib_name)) != true) {
      print_debug("can't read shared object name\n");
      return false;
    }

    if (lib_name[0] != '\0') {
      // ignore empty lib names
      lib_fd = pathmap_open(lib_name);

      if (lib_fd < 0) {
        print_debug("can't open shared object %s\n", lib_name);
        // continue with other libraries...
      } else {
        if (read_elf_header(lib_fd, &elf_ehdr)) {
          lib_base = lib_base_diff + find_base_address(lib_fd, &elf_ehdr);
          print_debug("reading library %s @ 0x%lx [ 0x%lx ]\n",
                       lib_name, lib_base, lib_base_diff);
          // while adding library mappings we need to use "base difference".
          if (! read_lib_segments(ph, lib_fd, &elf_ehdr, lib_base_diff)) {
            print_debug("can't read shared object's segments\n");
            close(lib_fd);
            return false;
          }
          add_lib_info_fd(ph, lib_name, lib_fd, lib_base);
          // Map info is added for the library (lib_name) so
          // we need to re-sort it before calling the p_pdread.
          if (sort_map_array(ph) != true) {
            return false;
          }
        } else {
          print_debug("can't read ELF header for shared object %s\n", lib_name);
          close(lib_fd);
          // continue with other libraries...
        }
      }
    }

    // read next link_map address
    if (ps_pread(ph, (psaddr_t) link_map_addr + LINK_MAP_NEXT_OFFSET,
                  &link_map_addr, sizeof(uintptr_t)) != PS_OK) {
      print_debug("can't read next link in link_map\n");
      return false;
    }
  }

  return true;
}

// the one and only one exposed stuff from this file
struct ps_prochandle* Pgrab_core(const char* exec_file, const char* core_file) {
  ELF_EHDR core_ehdr;
  ELF_EHDR exec_ehdr;

  struct ps_prochandle* ph = (struct ps_prochandle*) calloc(1, sizeof(struct ps_prochandle));
  if (ph == NULL) {
    print_debug("can't allocate ps_prochandle\n");
    return NULL;
  }

  if ((ph->core = (struct core_data*) calloc(1, sizeof(struct core_data))) == NULL) {
    free(ph);
    print_debug("can't allocate ps_prochandle\n");
    return NULL;
  }

  // initialize ph
  ph->ops = &core_ops;
  ph->core->core_fd   = -1;
  ph->core->exec_fd   = -1;
  ph->core->interp_fd = -1;

  print_debug("exec: %s   core: %s", exec_file, core_file);

  // open the core file
  if ((ph->core->core_fd = open(core_file, O_RDONLY)) < 0) {
    print_debug("can't open core file\n");
    goto err;
  }

  // read core file ELF header
  if (read_elf_header(ph->core->core_fd, &core_ehdr) != true || core_ehdr.e_type != ET_CORE) {
    print_debug("core file is not a valid ELF ET_CORE file\n");
    goto err;
  }

  if ((ph->core->exec_fd = open(exec_file, O_RDONLY)) < 0) {
    print_debug("can't open executable file\n");
    goto err;
  }

  if (read_elf_header(ph->core->exec_fd, &exec_ehdr) != true || exec_ehdr.e_type != ET_EXEC) {
    print_debug("executable file is not a valid ELF ET_EXEC file\n");
    goto err;
  }

  // process core file segments
  if (read_core_segments(ph, &core_ehdr) != true) {
    goto err;
  }

  // process exec file segments
  if (read_exec_segments(ph, &exec_ehdr) != true) {
    goto err;
  }

  // exec file is also treated like a shared object for symbol search
  if (add_lib_info_fd(ph, exec_file, ph->core->exec_fd,
                      (uintptr_t)0 + find_base_address(ph->core->exec_fd, &exec_ehdr)) == NULL) {
    goto err;
  }

  // allocate and sort maps into map_array, we need to do this
  // here because read_shared_lib_info needs to read from debuggee
  // address space
  if (sort_map_array(ph) != true) {
    goto err;
  }

  if (read_shared_lib_info(ph) != true) {
    goto err;
  }

  // sort again because we have added more mappings from shared objects
  if (sort_map_array(ph) != true) {
    goto err;
  }

  if (init_classsharing_workaround(ph) != true) {
    goto err;
  }

  print_debug("Leave Pgrab_core\n");
  return ph;

err:
  Prelease(ph);
  return NULL;
}

#endif // __APPLE__

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