native/libsaproc/ps_core.c

/*
 * Copyright (c) 2003, 2019, 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 <elf.h>
#include <link.h>
#include "libproc_impl.h"
#include "ps_core_common.h"
#include "proc_service.h"
#include "salibelf.h"

// 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)


//---------------------------------------------------------------------------
// 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 = %zu\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 user_regs_struct* regs) {
   // for core we have cached the lwp regs from NOTE section
   thread_info* thr = ph->threads;
   while (thr) {
     if (thr->lwp_id == lwp_id) {
       memcpy(regs, &thr->regs, sizeof(struct user_regs_struct));
       return true;
     }
     thr = thr->next;
   }
   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
};

// read regs and create thread from NT_PRSTATUS entries 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;
   thread_info* newthr;
   print_debug("got integer regset for lwp %d\n", prstat->pr_pid);
   if((newthr = add_thread_info(ph, prstat->pr_pid)) == NULL)
      return false;

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

   if (is_debug()) {
      print_debug("integer regset\n");
#ifdef i386
      // print the regset
      print_debug("\teax = 0x%x\n", newthr->regs.eax);
      print_debug("\tebx = 0x%x\n", newthr->regs.ebx);
      print_debug("\tecx = 0x%x\n", newthr->regs.ecx);
      print_debug("\tedx = 0x%x\n", newthr->regs.edx);
      print_debug("\tesp = 0x%x\n", newthr->regs.esp);
      print_debug("\tebp = 0x%x\n", newthr->regs.ebp);
      print_debug("\tesi = 0x%x\n", newthr->regs.esi);
      print_debug("\tedi = 0x%x\n", newthr->regs.edi);
      print_debug("\teip = 0x%x\n", newthr->regs.eip);
#endif

#if defined(amd64) || defined(x86_64)
      // print the regset
      print_debug("\tr15 = 0x%lx\n", newthr->regs.r15);
      print_debug("\tr14 = 0x%lx\n", newthr->regs.r14);
      print_debug("\tr13 = 0x%lx\n", newthr->regs.r13);
      print_debug("\tr12 = 0x%lx\n", newthr->regs.r12);
      print_debug("\trbp = 0x%lx\n", newthr->regs.rbp);
      print_debug("\trbx = 0x%lx\n", newthr->regs.rbx);
      print_debug("\tr11 = 0x%lx\n", newthr->regs.r11);
      print_debug("\tr10 = 0x%lx\n", newthr->regs.r10);
      print_debug("\tr9 = 0x%lx\n", newthr->regs.r9);
      print_debug("\tr8 = 0x%lx\n", newthr->regs.r8);
      print_debug("\trax = 0x%lx\n", newthr->regs.rax);
      print_debug("\trcx = 0x%lx\n", newthr->regs.rcx);
      print_debug("\trdx = 0x%lx\n", newthr->regs.rdx);
      print_debug("\trsi = 0x%lx\n", newthr->regs.rsi);
      print_debug("\trdi = 0x%lx\n", newthr->regs.rdi);
      print_debug("\torig_rax = 0x%lx\n", newthr->regs.orig_rax);
      print_debug("\trip = 0x%lx\n", newthr->regs.rip);
      print_debug("\tcs = 0x%lx\n", newthr->regs.cs);
      print_debug("\teflags = 0x%lx\n", newthr->regs.eflags);
      print_debug("\trsp = 0x%lx\n", newthr->regs.rsp);
      print_debug("\tss = 0x%lx\n", newthr->regs.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;
        }
      } else if (notep->n_type == NT_AUXV) {
        // Get first segment from entry point
        ELF_AUXV *auxv = (ELF_AUXV *)descdata;
        while (auxv->a_type != AT_NULL) {
          if (auxv->a_type == AT_ENTRY) {
            // Set entry point address to address of dynamic section.
            // We will adjust it in read_exec_segments().
            ph->core->dynamic_addr = auxv->a_un.a_val;
            break;
          }
          auxv++;
        }
      }
      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_memsz) == NULL) {
          goto err;
        }
      } else {
        // Coredump stores value of p_memsz elf field
        // rounded up to page boundary.

        if ((existing_map->memsz != page_size) &&
            (existing_map->fd != lib_fd) &&
            (ROUNDUP(existing_map->memsz, page_size) != ROUNDUP(lib_php->p_memsz, page_size))) {

          print_debug("address conflict @ 0x%lx (existing map size = %ld, size = %ld, flags = %d)\n",
                        target_vaddr, existing_map->memsz, lib_php->p_memsz, 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, ROUNDUP(lib_php->p_memsz, page_size));

        existing_map->fd = lib_fd;
        existing_map->offset = lib_php->p_offset;
        existing_map->memsz = ROUNDUP(lib_php->p_memsz, page_size);
      }
    }

    lib_php++;
  }

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

// process segments from interpreter (ld.so or ld-linux.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 + 1];

      // BUF_SIZE is PATH_MAX + NAME_MAX + 1.
      if (exec_php->p_filesz > BUF_SIZE) {
        goto err;
      }
      if (pread(ph->core->exec_fd, interp_name,
                exec_php->p_filesz, exec_php->p_offset) != exec_php->p_filesz) {
        print_debug("Unable to read in the ELF interpreter\n");
        goto err;
      }
      interp_name[exec_php->p_filesz] = '\0';
      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: {
      if (exec_ehdr->e_type == ET_EXEC) {
        ph->core->dynamic_addr = exec_php->p_vaddr;
      } else { // ET_DYN
        // dynamic_addr has entry point of executable.
        // Thus we should substract it.
        ph->core->dynamic_addr += exec_php->p_vaddr - exec_ehdr->e_entry;
      }
      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_LD_OFFSET    offsetof(struct link_map, l_ld)
#define LINK_MAP_NEXT_OFFSET  offsetof(struct link_map, l_next)

#define INVALID_LOAD_ADDRESS -1L
#define ZERO_LOAD_ADDRESS 0x0L

// Calculate the load address of shared library
// on prelink-enabled environment.
//
// In case of GDB, it would be calculated by offset of link_map.l_ld
// and the address of .dynamic section.
// See GDB implementation: lm_addr_check @ solib-svr4.c
static uintptr_t calc_prelinked_load_address(struct ps_prochandle* ph, int lib_fd, ELF_EHDR* elf_ehdr, uintptr_t link_map_addr) {
  ELF_PHDR *phbuf;
  uintptr_t lib_ld;
  uintptr_t lib_dyn_addr = 0L;
  uintptr_t load_addr;
  int i;

  phbuf = read_program_header_table(lib_fd, elf_ehdr);
  if (phbuf == NULL) {
    print_debug("can't read program header of shared object\n");
    return INVALID_LOAD_ADDRESS;
  }

  // Get the address of .dynamic section from shared library.
  for (i = 0; i < elf_ehdr->e_phnum; i++) {
    if (phbuf[i].p_type == PT_DYNAMIC) {
      lib_dyn_addr = phbuf[i].p_vaddr;
      break;
    }
  }

  free(phbuf);

  if (ps_pdread(ph, (psaddr_t)link_map_addr + LINK_MAP_LD_OFFSET,
               &lib_ld, sizeof(uintptr_t)) != PS_OK) {
    print_debug("can't read address of dynamic section in shared object\n");
    return INVALID_LOAD_ADDRESS;
  }

  // Return the load address which is calculated by the address of .dynamic
  // and link_map.l_ld .
  load_addr = lib_ld - lib_dyn_addr;
  print_debug("lib_ld = 0x%lx, lib_dyn_addr = 0x%lx -> lib_base_diff = 0x%lx\n", lib_ld, lib_dyn_addr, load_addr);
  return load_addr;
}

// 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_pdread(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_pdread(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 (ps_pdread(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;

  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_pdread(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_pdread(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
      lib_name[0] = '\0';
      if (lib_name_addr != 0 &&
          read_string(ph, (uintptr_t) lib_name_addr, lib_name, sizeof(lib_name)) != true) {
         print_debug("can't read shared object name\n");
         // don't let failure to read the name stop opening the file.  If something is really wrong
         // it will fail later.
      }

      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)) {
               if (lib_base_diff == ZERO_LOAD_ADDRESS ) {
                 lib_base_diff = calc_prelinked_load_address(ph, lib_fd, &elf_ehdr, link_map_addr);
                 if (lib_base_diff == INVALID_LOAD_ADDRESS) {
                   close(lib_fd);
                   return false;
                 }
               }

               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_pdread(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
JNIEXPORT struct ps_prochandle* JNICALL
Pgrab_core(const char* exec_file, const char* core_file) {
  ELF_EHDR core_ehdr;
  ELF_EHDR exec_ehdr;
  ELF_EHDR lib_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;

  // 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) && (exec_ehdr.e_type != ET_DYN))) {
    print_debug("executable file is not a valid ELF 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;
  }

  return ph;

err:
  Prelease(ph);
  return NULL;
}