Merge from vendor branch GCC:

[dragonfly.git] / contrib / gdb / gdb / solib.c

/* Handle SunOS and SVR4 shared libraries for GDB, the GNU Debugger.
   Copyright 1990, 91, 92, 93, 94, 95, 96, 98, 1999
   Free Software Foundation, Inc.
   
This file is part of GDB.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* $FreeBSD: src/contrib/gdb/gdb/solib.c,v 1.7 1999/11/22 18:04:53 peter Exp $ */
/* $DragonFly: src/contrib/gdb/gdb/Attic/solib.c,v 1.2 2003/06/17 04:24:02 dillon Exp $ */

#include "defs.h"

/* This file is only compilable if link.h is available. */

#ifdef HAVE_LINK_H

#include <sys/types.h>
#include <signal.h>
#include "gdb_string.h"
#include <sys/param.h>
#include <fcntl.h>
#include <unistd.h>

#ifndef SVR4_SHARED_LIBS
 /* SunOS shared libs need the nlist structure.  */
#include <a.out.h> 
#else
#include "elf/external.h"
#include "elf/common.h"
#endif

#include <link.h>

#include "symtab.h"
#include "bfd.h"
#include "symfile.h"
#include "objfiles.h"
#include "gdbcore.h"
#include "command.h"
#include "target.h"
#include "frame.h"
#include "gnu-regex.h"
#include "inferior.h"
#include "environ.h"
#include "language.h"
#include "gdbcmd.h"

#define MAX_PATH_SIZE 512               /* FIXME: Should be dynamic */

/* On SVR4 systems, a list of symbols in the dynamic linker where
   GDB can try to place a breakpoint to monitor shared library
   events.

   If none of these symbols are found, or other errors occur, then
   SVR4 systems will fall back to using a symbol as the "startup
   mapping complete" breakpoint address.  */

#ifdef SVR4_SHARED_LIBS
static char *solib_break_names[] = {
  "r_debug_state",
  "_r_debug_state",
  "_dl_debug_state",
  "rtld_db_dlactivity",
  NULL
};
#endif

#define BKPT_AT_SYMBOL 1

#if defined (BKPT_AT_SYMBOL) && defined (SVR4_SHARED_LIBS)
static char *bkpt_names[] = {
#ifdef SOLIB_BKPT_NAME
  SOLIB_BKPT_NAME,              /* Prefer configured name if it exists. */
#endif
  "_start",
  "main",
  NULL
};
#endif

/* Symbols which are used to locate the base of the link map structures. */

#ifndef SVR4_SHARED_LIBS
static char *debug_base_symbols[] = {
  "_DYNAMIC",
  "_DYNAMIC__MGC",
  NULL
};
#endif

static char *main_name_list[] = {
  "main_$main",
  NULL
};

/* local data declarations */

#ifndef SVR4_SHARED_LIBS

#define LM_ADDR(so) ((so) -> lm.lm_addr)
#define LM_NEXT(so) ((so) -> lm.lm_next)
#define LM_NAME(so) ((so) -> lm.lm_name)
/* Test for first link map entry; first entry is a shared library. */
#define IGNORE_FIRST_LINK_MAP_ENTRY(x) (0)
static struct link_dynamic dynamic_copy;
static struct link_dynamic_2 ld_2_copy;
static struct ld_debug debug_copy;
static CORE_ADDR debug_addr;
static CORE_ADDR flag_addr;

#else   /* SVR4_SHARED_LIBS */

#define LM_ADDR(so) ((so) -> lm.l_addr)
#define LM_NEXT(so) ((so) -> lm.l_next)
#define LM_NAME(so) ((so) -> lm.l_name)
/* Test for first link map entry; first entry is the exec-file. */
#define IGNORE_FIRST_LINK_MAP_ENTRY(x) ((x).l_prev == NULL)
static struct r_debug debug_copy;
char shadow_contents[BREAKPOINT_MAX];   /* Stash old bkpt addr contents */

#endif  /* !SVR4_SHARED_LIBS */

struct so_list {
  struct so_list *next;                 /* next structure in linked list */
  struct link_map lm;                   /* copy of link map from inferior */
  struct link_map *lmaddr;              /* addr in inferior lm was read from */
  CORE_ADDR lmend;                      /* upper addr bound of mapped object */
  char so_name[MAX_PATH_SIZE];          /* shared object lib name (FIXME) */
  char symbols_loaded;                  /* flag: symbols read in yet? */
  char from_tty;                        /* flag: print msgs? */
  struct objfile *objfile;              /* objfile for loaded lib */
  struct section_table *sections;
  struct section_table *sections_end;
  struct section_table *textsection;
  bfd *abfd;
};

static struct so_list *so_list_head;    /* List of known shared objects */
static CORE_ADDR debug_base;            /* Base of dynamic linker structures */
static CORE_ADDR breakpoint_addr;       /* Address where end bkpt is set */

static int solib_cleanup_queued = 0;    /* make_run_cleanup called */

extern int
fdmatch PARAMS ((int, int));            /* In libiberty */

/* Local function prototypes */

static void
do_clear_solib PARAMS ((PTR));

static int
match_main PARAMS ((char *));

static void
special_symbol_handling PARAMS ((struct so_list *));

static void
sharedlibrary_command PARAMS ((char *, int));

static int
enable_break PARAMS ((void));

static void
info_sharedlibrary_command PARAMS ((char *, int));

static int symbol_add_stub PARAMS ((PTR));

static struct so_list *
alloc_solib PARAMS ((struct link_map *));

static void
free_solib PARAMS ((struct so_list *));

static struct so_list *
find_solib PARAMS ((struct so_list *, int maybe_changed));

static struct link_map *
first_link_map_member PARAMS ((void));

static CORE_ADDR
locate_base PARAMS ((void));

static int solib_map_sections PARAMS ((PTR));

#ifdef SVR4_SHARED_LIBS

static CORE_ADDR
elf_locate_base PARAMS ((void));

#else

static int
disable_break PARAMS ((void));

static void
allocate_rt_common_objfile PARAMS ((void));

static void
solib_add_common_symbols PARAMS ((struct rtc_symb *));

#endif

void _initialize_solib PARAMS ((void));

/* If non-zero, this is a prefix that will be added to the front of the name
   shared libraries with an absolute filename for loading.  */
static char *solib_absolute_prefix = NULL;

/* If non-empty, this is a search path for loading non-absolute shared library
   symbol files.  This takes precedence over the environment variables PATH
   and LD_LIBRARY_PATH.  */
static char *solib_search_path = NULL;

/*

LOCAL FUNCTION

        solib_map_sections -- open bfd and build sections for shared lib

SYNOPSIS

        static int solib_map_sections (struct so_list *so)

DESCRIPTION

        Given a pointer to one of the shared objects in our list
        of mapped objects, use the recorded name to open a bfd
        descriptor for the object, build a section table, and then
        relocate all the section addresses by the base address at
        which the shared object was mapped.

FIXMES

        In most (all?) cases the shared object file name recorded in the
        dynamic linkage tables will be a fully qualified pathname.  For
        cases where it isn't, do we really mimic the systems search
        mechanism correctly in the below code (particularly the tilde
        expansion stuff?).
 */

static int
solib_map_sections (arg)
     PTR arg;
{
  struct so_list *so = (struct so_list *) arg;  /* catch_errors bogon */
  char *filename;
  char *scratch_pathname;
  int scratch_chan;
  struct section_table *p;
  struct cleanup *old_chain;
  bfd *abfd;
  
  filename = tilde_expand (so -> so_name);
  
  if (solib_absolute_prefix && ROOTED_P (filename))
    /* Prefix shared libraries with absolute filenames with
       SOLIB_ABSOLUTE_PREFIX.  */
    {
      char *pfxed_fn;
      int pfx_len;

      pfx_len = strlen (solib_absolute_prefix);

      /* Remove trailing slashes.  */
      while (pfx_len > 0 && SLASH_P (solib_absolute_prefix[pfx_len - 1]))
        pfx_len--;

      pfxed_fn = xmalloc (pfx_len + strlen (filename) + 1);
      strcpy (pfxed_fn, solib_absolute_prefix);
      strcat (pfxed_fn, filename);
      free (filename);

      filename = pfxed_fn;
    }

  old_chain = make_cleanup (free, filename);

  scratch_chan = -1;

  if (solib_search_path)
    scratch_chan = openp (solib_search_path,
                          1, filename, O_RDONLY, 0, &scratch_pathname);
  if (scratch_chan < 0)
    scratch_chan = openp (get_in_environ (inferior_environ, "PATH"), 
                          1, filename, O_RDONLY, 0, &scratch_pathname);
  if (scratch_chan < 0)
    {
      scratch_chan = openp (get_in_environ 
                            (inferior_environ, "LD_LIBRARY_PATH"), 
                            1, filename, O_RDONLY, 0, &scratch_pathname);
    }
  if (scratch_chan < 0)
    {
      perror_with_name (filename);
    }
  /* Leave scratch_pathname allocated.  abfd->name will point to it.  */

  abfd = bfd_fdopenr (scratch_pathname, gnutarget, scratch_chan);
  if (!abfd)
    {
      close (scratch_chan);
      error ("Could not open `%s' as an executable file: %s",
             scratch_pathname, bfd_errmsg (bfd_get_error ()));
    }
  /* Leave bfd open, core_xfer_memory and "info files" need it.  */
  so -> abfd = abfd;
  abfd -> cacheable = true;

  /* copy full path name into so_name, so that later symbol_file_add can find
     it */
  if (strlen (scratch_pathname) >= MAX_PATH_SIZE)
    error ("Full path name length of shared library exceeds MAX_PATH_SIZE in so_list structure.");
  strcpy (so->so_name, scratch_pathname);

  if (!bfd_check_format (abfd, bfd_object))
    {
      error ("\"%s\": not in executable format: %s.",
             scratch_pathname, bfd_errmsg (bfd_get_error ()));
    }
  if (build_section_table (abfd, &so -> sections, &so -> sections_end))
    {
      error ("Can't find the file sections in `%s': %s", 
             bfd_get_filename (abfd), bfd_errmsg (bfd_get_error ()));
    }

  for (p = so -> sections; p < so -> sections_end; p++)
    {
      /* Relocate the section binding addresses as recorded in the shared
         object's file by the base address to which the object was actually
         mapped. */
      p -> addr += (CORE_ADDR) LM_ADDR (so);
      p -> endaddr += (CORE_ADDR) LM_ADDR (so);
      so -> lmend = (CORE_ADDR) max (p -> endaddr, so -> lmend);
      if (STREQ (p -> the_bfd_section -> name, ".text"))
        {
          so -> textsection = p;
        }
    }

  /* Free the file names, close the file now.  */
  do_cleanups (old_chain);

  return (1);
}

#ifndef SVR4_SHARED_LIBS

/* Allocate the runtime common object file.  */

static void
allocate_rt_common_objfile ()
{
  struct objfile *objfile;
  struct objfile *last_one;

  objfile = (struct objfile *) xmalloc (sizeof (struct objfile));
  memset (objfile, 0, sizeof (struct objfile));
  objfile -> md = NULL;
  obstack_specify_allocation (&objfile -> psymbol_cache.cache, 0, 0,
                              xmalloc, free);
  obstack_specify_allocation (&objfile -> psymbol_obstack, 0, 0, xmalloc,
                              free);
  obstack_specify_allocation (&objfile -> symbol_obstack, 0, 0, xmalloc,
                              free);
  obstack_specify_allocation (&objfile -> type_obstack, 0, 0, xmalloc,
                              free);
  objfile -> name = mstrsave (objfile -> md, "rt_common");

  /* Add this file onto the tail of the linked list of other such files. */

  objfile -> next = NULL;
  if (object_files == NULL)
    object_files = objfile;
  else
    {
      for (last_one = object_files;
           last_one -> next;
           last_one = last_one -> next);
      last_one -> next = objfile;
    }

  rt_common_objfile = objfile;
}

/* Read all dynamically loaded common symbol definitions from the inferior
   and put them into the minimal symbol table for the runtime common
   objfile.  */

static void
solib_add_common_symbols (rtc_symp)
    struct rtc_symb *rtc_symp;
{
  struct rtc_symb inferior_rtc_symb;
  struct nlist inferior_rtc_nlist;
  int len;
  char *name;

  /* Remove any runtime common symbols from previous runs.  */

  if (rt_common_objfile != NULL && rt_common_objfile -> minimal_symbol_count)
    {
      obstack_free (&rt_common_objfile -> symbol_obstack, 0);
      obstack_specify_allocation (&rt_common_objfile -> symbol_obstack, 0, 0,
                                  xmalloc, free);
      rt_common_objfile -> minimal_symbol_count = 0;
      rt_common_objfile -> msymbols = NULL;
    }

  init_minimal_symbol_collection ();
  make_cleanup ((make_cleanup_func) discard_minimal_symbols, 0);

  while (rtc_symp)
    {
      read_memory ((CORE_ADDR) rtc_symp,
                   (char *) &inferior_rtc_symb,
                   sizeof (inferior_rtc_symb));
      read_memory ((CORE_ADDR) inferior_rtc_symb.rtc_sp,
                   (char *) &inferior_rtc_nlist,
                   sizeof(inferior_rtc_nlist));
      if (inferior_rtc_nlist.n_type == N_COMM)
        {
          /* FIXME: The length of the symbol name is not available, but in the
             current implementation the common symbol is allocated immediately
             behind the name of the symbol. */
          len = inferior_rtc_nlist.n_value - inferior_rtc_nlist.n_un.n_strx;

          name = xmalloc (len);
          read_memory ((CORE_ADDR) inferior_rtc_nlist.n_un.n_name, name, len);

          /* Allocate the runtime common objfile if necessary. */
          if (rt_common_objfile == NULL)
            allocate_rt_common_objfile ();

          prim_record_minimal_symbol (name, inferior_rtc_nlist.n_value,
                                      mst_bss, rt_common_objfile);
          free (name);
        }
      rtc_symp = inferior_rtc_symb.rtc_next;
    }

  /* Install any minimal symbols that have been collected as the current
     minimal symbols for the runtime common objfile.  */

  install_minimal_symbols (rt_common_objfile);
}

#endif  /* SVR4_SHARED_LIBS */


#ifdef SVR4_SHARED_LIBS

static CORE_ADDR
bfd_lookup_symbol PARAMS ((bfd *, char *));

/*

LOCAL FUNCTION

        bfd_lookup_symbol -- lookup the value for a specific symbol

SYNOPSIS

        CORE_ADDR bfd_lookup_symbol (bfd *abfd, char *symname)

DESCRIPTION

        An expensive way to lookup the value of a single symbol for
        bfd's that are only temporary anyway.  This is used by the
        shared library support to find the address of the debugger
        interface structures in the shared library.

        Note that 0 is specifically allowed as an error return (no
        such symbol).
*/

static CORE_ADDR
bfd_lookup_symbol (abfd, symname)
     bfd *abfd;
     char *symname;
{
  long storage_needed;
  asymbol *sym;
  asymbol **symbol_table;
  unsigned int number_of_symbols;
  unsigned int i;
  struct cleanup *back_to;
  CORE_ADDR symaddr = 0;
  
  storage_needed = bfd_get_symtab_upper_bound (abfd);

  if (storage_needed > 0)
    {
      symbol_table = (asymbol **) xmalloc (storage_needed);
      back_to = make_cleanup (free, (PTR)symbol_table);
      number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table); 
  
      for (i = 0; i < number_of_symbols; i++)
        {
          sym = *symbol_table++;
          if (STREQ (sym -> name, symname))
            {
              /* Bfd symbols are section relative. */
              symaddr = sym -> value + sym -> section -> vma;
              break;
            }
        }
      do_cleanups (back_to);
    }

  if (symaddr) return (symaddr);

  storage_needed = bfd_get_dynamic_symtab_upper_bound (abfd);

  if (storage_needed > 0)
    {
      symbol_table = (asymbol **) xmalloc (storage_needed);
      back_to = make_cleanup (free, (PTR)symbol_table);
      number_of_symbols = bfd_canonicalize_dynamic_symtab (abfd, symbol_table); 
  
      for (i = 0; i < number_of_symbols; i++)
        {
          sym = *symbol_table++;
          if (STREQ (sym -> name, symname))
            {
              /* Bfd symbols are section relative. */
              symaddr = sym -> value + sym -> section -> vma;
              break;
            }
        }
      do_cleanups (back_to);
    }
  return (symaddr);
}

#ifdef HANDLE_SVR4_EXEC_EMULATORS

/*
        Solaris BCP (the part of Solaris which allows it to run SunOS4
        a.out files) throws in another wrinkle. Solaris does not fill
        in the usual a.out link map structures when running BCP programs,
        the only way to get at them is via groping around in the dynamic
        linker.
        The dynamic linker and it's structures are located in the shared
        C library, which gets run as the executable's "interpreter" by
        the kernel.

        Note that we can assume nothing about the process state at the time
        we need to find these structures.  We may be stopped on the first
        instruction of the interpreter (C shared library), the first
        instruction of the executable itself, or somewhere else entirely
        (if we attached to the process for example).
*/

static char *debug_base_symbols[] = {
  "r_debug",    /* Solaris 2.3 */
  "_r_debug",   /* Solaris 2.1, 2.2 */
  NULL
};

static int
look_for_base PARAMS ((int, CORE_ADDR));

/*

LOCAL FUNCTION

        look_for_base -- examine file for each mapped address segment

SYNOPSYS

        static int look_for_base (int fd, CORE_ADDR baseaddr)

DESCRIPTION

        This function is passed to proc_iterate_over_mappings, which
        causes it to get called once for each mapped address space, with
        an open file descriptor for the file mapped to that space, and the
        base address of that mapped space.

        Our job is to find the debug base symbol in the file that this
        fd is open on, if it exists, and if so, initialize the dynamic
        linker structure base address debug_base.

        Note that this is a computationally expensive proposition, since
        we basically have to open a bfd on every call, so we specifically
        avoid opening the exec file.
 */

static int
look_for_base (fd, baseaddr)
     int fd;
     CORE_ADDR baseaddr;
{
  bfd *interp_bfd;
  CORE_ADDR address = 0;
  char **symbolp;

  /* If the fd is -1, then there is no file that corresponds to this
     mapped memory segment, so skip it.  Also, if the fd corresponds
     to the exec file, skip it as well. */

  if (fd == -1
      || (exec_bfd != NULL
          && fdmatch (fileno ((FILE *)(exec_bfd -> iostream)), fd)))
    {
      return (0);
    }

  /* Try to open whatever random file this fd corresponds to.  Note that
     we have no way currently to find the filename.  Don't gripe about
     any problems we might have, just fail. */

  if ((interp_bfd = bfd_fdopenr ("unnamed", gnutarget, fd)) == NULL)
    {
      return (0);
    }
  if (!bfd_check_format (interp_bfd, bfd_object))
    {
      /* FIXME-leak: on failure, might not free all memory associated with
         interp_bfd.  */
      bfd_close (interp_bfd);
      return (0);
    }

  /* Now try to find our debug base symbol in this file, which we at
     least know to be a valid ELF executable or shared library. */

  for (symbolp = debug_base_symbols; *symbolp != NULL; symbolp++)
    {
      address = bfd_lookup_symbol (interp_bfd, *symbolp);
      if (address != 0)
        {
          break;
        }
    }
  if (address == 0)
    {
      /* FIXME-leak: on failure, might not free all memory associated with
         interp_bfd.  */
      bfd_close (interp_bfd);
      return (0);
    }

  /* Eureka!  We found the symbol.  But now we may need to relocate it
     by the base address.  If the symbol's value is less than the base
     address of the shared library, then it hasn't yet been relocated
     by the dynamic linker, and we have to do it ourself.  FIXME: Note
     that we make the assumption that the first segment that corresponds
     to the shared library has the base address to which the library
     was relocated. */

  if (address < baseaddr)
    {
      address += baseaddr;
    }
  debug_base = address;
  /* FIXME-leak: on failure, might not free all memory associated with
     interp_bfd.  */
  bfd_close (interp_bfd);
  return (1);
}
#endif /* HANDLE_SVR4_EXEC_EMULATORS */

/*

LOCAL FUNCTION

        elf_locate_base -- locate the base address of dynamic linker structs
        for SVR4 elf targets.

SYNOPSIS

        CORE_ADDR elf_locate_base (void)

DESCRIPTION

        For SVR4 elf targets the address of the dynamic linker's runtime
        structure is contained within the dynamic info section in the
        executable file.  The dynamic section is also mapped into the
        inferior address space.  Because the runtime loader fills in the
        real address before starting the inferior, we have to read in the
        dynamic info section from the inferior address space.
        If there are any errors while trying to find the address, we
        silently return 0, otherwise the found address is returned.

 */

static CORE_ADDR
elf_locate_base ()
{
  sec_ptr dyninfo_sect;
  int dyninfo_sect_size;
  CORE_ADDR dyninfo_addr;
  char *buf;
  char *bufend;

  /* Find the start address of the .dynamic section.  */
  dyninfo_sect = bfd_get_section_by_name (exec_bfd, ".dynamic");
  if (dyninfo_sect == NULL)
    return 0;
  dyninfo_addr = bfd_section_vma (exec_bfd, dyninfo_sect);

  /* Read in .dynamic section, silently ignore errors.  */
  dyninfo_sect_size = bfd_section_size (exec_bfd, dyninfo_sect);
  buf = alloca (dyninfo_sect_size);
  if (target_read_memory (dyninfo_addr, buf, dyninfo_sect_size))
    return 0;

  /* Find the DT_DEBUG entry in the the .dynamic section.
     For mips elf we look for DT_MIPS_RLD_MAP, mips elf apparently has
     no DT_DEBUG entries.  */
#ifndef TARGET_ELF64
  for (bufend = buf + dyninfo_sect_size;
       buf < bufend;
       buf += sizeof (Elf32_External_Dyn))
    {
      Elf32_External_Dyn *x_dynp = (Elf32_External_Dyn *)buf;
      long dyn_tag;
      CORE_ADDR dyn_ptr;

      dyn_tag = bfd_h_get_32 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
      if (dyn_tag == DT_NULL)
        break;
      else if (dyn_tag == DT_DEBUG)
        {
          dyn_ptr = bfd_h_get_32 (exec_bfd, (bfd_byte *) x_dynp->d_un.d_ptr);
          return dyn_ptr;
        }
#ifdef DT_MIPS_RLD_MAP
      else if (dyn_tag == DT_MIPS_RLD_MAP)
        {
          char pbuf[TARGET_PTR_BIT / HOST_CHAR_BIT];

          /* DT_MIPS_RLD_MAP contains a pointer to the address
             of the dynamic link structure.  */
          dyn_ptr = bfd_h_get_32 (exec_bfd, (bfd_byte *) x_dynp->d_un.d_ptr);
          if (target_read_memory (dyn_ptr, pbuf, sizeof (pbuf)))
            return 0;
          return extract_unsigned_integer (pbuf, sizeof (pbuf));
        }
#endif
    }
#else /* ELF64 */
  for (bufend = buf + dyninfo_sect_size;
       buf < bufend;
       buf += sizeof (Elf64_External_Dyn))
    {
      Elf64_External_Dyn *x_dynp = (Elf64_External_Dyn *)buf;
      long dyn_tag;
      CORE_ADDR dyn_ptr;

      dyn_tag = bfd_h_get_64 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
      if (dyn_tag == DT_NULL)
        break;
      else if (dyn_tag == DT_DEBUG)
        {
          dyn_ptr = bfd_h_get_64 (exec_bfd, (bfd_byte *) x_dynp->d_un.d_ptr);
          return dyn_ptr;
        }
    }
#endif

  /* DT_DEBUG entry not found.  */
  return 0;
}

#endif  /* SVR4_SHARED_LIBS */

/*

LOCAL FUNCTION

        locate_base -- locate the base address of dynamic linker structs

SYNOPSIS

        CORE_ADDR locate_base (void)

DESCRIPTION

        For both the SunOS and SVR4 shared library implementations, if the
        inferior executable has been linked dynamically, there is a single
        address somewhere in the inferior's data space which is the key to
        locating all of the dynamic linker's runtime structures.  This
        address is the value of the debug base symbol.  The job of this
        function is to find and return that address, or to return 0 if there
        is no such address (the executable is statically linked for example).

        For SunOS, the job is almost trivial, since the dynamic linker and
        all of it's structures are statically linked to the executable at
        link time.  Thus the symbol for the address we are looking for has
        already been added to the minimal symbol table for the executable's
        objfile at the time the symbol file's symbols were read, and all we
        have to do is look it up there.  Note that we explicitly do NOT want
        to find the copies in the shared library.

        The SVR4 version is a bit more complicated because the address
        is contained somewhere in the dynamic info section.  We have to go
        to a lot more work to discover the address of the debug base symbol.
        Because of this complexity, we cache the value we find and return that
        value on subsequent invocations.  Note there is no copy in the
        executable symbol tables.

 */

static CORE_ADDR
locate_base ()
{

#ifndef SVR4_SHARED_LIBS

  struct minimal_symbol *msymbol;
  CORE_ADDR address = 0;
  char **symbolp;

  /* For SunOS, we want to limit the search for the debug base symbol to the
     executable being debugged, since there is a duplicate named symbol in the
     shared library.  We don't want the shared library versions. */

  for (symbolp = debug_base_symbols; *symbolp != NULL; symbolp++)
    {
      msymbol = lookup_minimal_symbol (*symbolp, NULL, symfile_objfile);
      if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
        {
          address = SYMBOL_VALUE_ADDRESS (msymbol);
          return (address);
        }
    }
  return (0);

#else   /* SVR4_SHARED_LIBS */

  /* Check to see if we have a currently valid address, and if so, avoid
     doing all this work again and just return the cached address.  If
     we have no cached address, try to locate it in the dynamic info
     section for ELF executables.  */

  if (debug_base == 0)
    {
      if (exec_bfd != NULL
          && bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
        debug_base = elf_locate_base ();
#ifdef HANDLE_SVR4_EXEC_EMULATORS
      /* Try it the hard way for emulated executables.  */
      else if (inferior_pid != 0 && target_has_execution)
        proc_iterate_over_mappings (look_for_base);
#endif
    }
  return (debug_base);

#endif  /* !SVR4_SHARED_LIBS */

}

/*

LOCAL FUNCTION

        first_link_map_member -- locate first member in dynamic linker's map

SYNOPSIS

        static struct link_map *first_link_map_member (void)

DESCRIPTION

        Read in a copy of the first member in the inferior's dynamic
        link map from the inferior's dynamic linker structures, and return
        a pointer to the copy in our address space.
*/

static struct link_map *
first_link_map_member ()
{
  struct link_map *lm = NULL;

#ifndef SVR4_SHARED_LIBS

  read_memory (debug_base, (char *) &dynamic_copy, sizeof (dynamic_copy));
  if (dynamic_copy.ld_version >= 2)
    {
      /* It is a version that we can deal with, so read in the secondary
         structure and find the address of the link map list from it. */
      read_memory ((CORE_ADDR) dynamic_copy.ld_un.ld_2, (char *) &ld_2_copy,
                   sizeof (struct link_dynamic_2));
      lm = ld_2_copy.ld_loaded;
    }

#else   /* SVR4_SHARED_LIBS */

  read_memory (debug_base, (char *) &debug_copy, sizeof (struct r_debug));
  /* FIXME:  Perhaps we should validate the info somehow, perhaps by
     checking r_version for a known version number, or r_state for
     RT_CONSISTENT. */
  lm = debug_copy.r_map;

#endif  /* !SVR4_SHARED_LIBS */

  return (lm);
}

/*

LOCAL FUNCTION

        free_solib -- free a so_list structure

SYNOPSIS

        void free_solib (struct so_list *so_list_ptr)

DESCRIPTION

        Free the memory used by a struct so_list.

 */

void
free_solib (so)
     struct so_list *so;
{
  char *bfd_filename;
  if (so -> sections)
    {
      free ((PTR)so -> sections);
    }
  if (so -> abfd)
    {
      bfd_filename = bfd_get_filename (so -> abfd);
      if (!bfd_close (so -> abfd))
        warning ("cannot close \"%s\": %s",
                 bfd_filename, bfd_errmsg (bfd_get_error ()));
    }
  else
    /* This happens for the executable on SVR4.  */
    bfd_filename = NULL;
      
  if (bfd_filename)
    free ((PTR)bfd_filename);
  free ((PTR)so);
}

/*

LOCAL FUNCTION

        alloc_solib -- free a so_list structure

SYNOPSIS

        struct so_list *alloc_solib (struct link_map *lm)

DESCRIPTION

        Allocate the struct so_list to cache debugging information
        for a struct link_map entry in the target.

 */

struct so_list *
alloc_solib (lm)
     struct link_map *lm;
{
  struct so_list *new;

  /* Get next link map structure from inferior image and build a local
         abbreviated load_map structure */
  new = (struct so_list *) xmalloc (sizeof (struct so_list));
  memset ((char *) new, 0, sizeof (struct so_list));
  new -> lmaddr = lm;

  read_memory ((CORE_ADDR) lm, (char *) &(new -> lm),
               sizeof (struct link_map));
  /* For SVR4 versions, the first entry in the link map is for the
         inferior executable, so we must ignore it.  For some versions of
         SVR4, it has no name.  For others (Solaris 2.3 for example), it
         does have a name, so we can no longer use a missing name to
         decide when to ignore it. */
  if (!IGNORE_FIRST_LINK_MAP_ENTRY (new -> lm))
    {
      int errcode;
      char *buffer;
      target_read_string ((CORE_ADDR) LM_NAME (new), &buffer,
                          MAX_PATH_SIZE - 1, &errcode);
      if (errcode != 0)
        error ("find_solib: Can't read pathname for load map: %s\n",
               safe_strerror (errcode));
      strncpy (new -> so_name, buffer, MAX_PATH_SIZE - 1);
      new -> so_name[MAX_PATH_SIZE - 1] = '\0';
      free (buffer);
      solib_map_sections (new);
    }      

  return new;
}

/*

LOCAL FUNCTION

        find_solib -- step through list of shared objects

SYNOPSIS

        struct so_list *find_solib (struct so_list *so_list_ptr, int maybe_changed)

DESCRIPTION

        This module contains the routine which finds the names of any
        loaded "images" in the current process. The argument in must be
        NULL on the first call, and then the returned value must be passed
        in on subsequent calls. This provides the capability to "step" down
        the list of loaded objects. On the last object, a NULL value is
        returned.

        The arg and return value are "struct link_map" pointers, as defined
        in <link.h>.

        If it is expected that the contents of the shared library list has changed
        (e.g. when the special shared library breakpoint is hit) then pass non-zero
        for maybe_changed, otherwise zero.
 */

static struct so_list *
find_solib (so_list_ptr, maybe_changed)
     struct so_list *so_list_ptr;       /* Last lm or NULL for first one */
     int maybe_changed;                 /* non-zero if shlib list might have changed */
{
  struct link_map *lm = NULL;
  struct so_list *new;
  struct so_list *so_list_next;
  struct so_list *p, **prev;
  
  if (so_list_ptr == NULL)
    {
      struct so_list **map;

      /* If we have not already read in the dynamic linking structures
         from the inferior, lookup the address of the base structure. */
      if (debug_base == 0)
        debug_base = locate_base ();
      if (debug_base != 0)
        {
          /* Read the base structure in and find the address of the first
             link map list member. */
          lm = first_link_map_member ();
        }
      else
        lm = NULL;

      prev = &so_list_head;
      so_list_ptr = so_list_head;
    }
  else
    {
      /* We have been called before, and are in the process of walking
         the shared library list.  Advance to the next shared object.

         Always read from the target to check to see if any were
         added, but be quiet if we can't read from the target any more. */
      int status = target_read_memory ((CORE_ADDR) so_list_ptr -> lmaddr,
                                       (char *) &(so_list_ptr -> lm),
                                       sizeof (struct link_map));

      if (status == 0)
        {
          lm = LM_NEXT (so_list_ptr);
        }
      else
        {
          lm = NULL;
        }

      prev = &so_list_ptr -> next;
      so_list_ptr = so_list_ptr -> next;
    }

  /* If we don't believe that the list has changed, just return the cached copy. */
  if (!maybe_changed)
      return (so_list_ptr);

  /* At this point, lm is the address of the next list element in the target and
     so_list_ptr is our cached entry for it. */

  if (lm != NULL)
    {
      if (so_list_ptr == NULL || so_list_ptr -> lmaddr != lm)
        {
          /* We have detected a change in the list.  Check for a deletion by searching
             forward in the cached list */
          if (so_list_ptr)
            {
              for (p = so_list_ptr -> next; p; p = p -> next)
                if (p -> lmaddr == lm)
                  break;
            }
          else
            p = NULL;

          if (p)
            {
              /* This lib has been deleted */
              while (so_list_ptr != p)
                {
                  *prev = so_list_ptr -> next;
                  free_solib (so_list_ptr);
                  so_list_ptr = *prev;
                }
            }
          else
            {
              /* A new lib has been inserted into the list */
              new = alloc_solib (lm);
              new -> next = so_list_ptr;
              *prev = new;
              so_list_ptr = new;
            }
        }
    }
  else
    {
      if (so_list_ptr != NULL)
        {
          so_list_head = new;

          if (! solib_cleanup_queued)
            {
              make_run_cleanup (do_clear_solib, NULL);
              solib_cleanup_queued = 1;
            }
          
        }      
      so_list_next = new;
      if (lm)
          target_read_memory ((CORE_ADDR) lm, (char *) &(new -> lm),
                              sizeof (struct link_map));
      /* For SVR4 versions, the first entry in the link map is for the
         inferior executable, so we must ignore it.  For some versions of
         SVR4, it has no name.  For others (Solaris 2.3 for example), it
         does have a name, so we can no longer use a missing name to
         decide when to ignore it. */
      if (lm && new && !IGNORE_FIRST_LINK_MAP_ENTRY (new -> lm))
        {
          int errcode;
          char *buffer;
          target_read_string ((CORE_ADDR) LM_NAME (new), &buffer,
                              MAX_PATH_SIZE - 1, &errcode);
          if (errcode != 0)
            {
              warning ("find_solib: Can't read pathname for load map: %s\n",
                       safe_strerror (errcode));
              return (so_list_next);
            }
          strncpy (new -> so_name, buffer, MAX_PATH_SIZE - 1);
          new -> so_name[MAX_PATH_SIZE - 1] = '\0';
          free (buffer);
          catch_errors (solib_map_sections, new,
                        "Error while mapping shared library sections:\n",
                        RETURN_MASK_ALL);
        }      
    }

  return (so_list_ptr);
}

/* A small stub to get us past the arg-passing pinhole of catch_errors.  */

static int
symbol_add_stub (arg)
     PTR arg;
{
  register struct so_list *so = (struct so_list *) arg; /* catch_errs bogon */
  CORE_ADDR text_addr = 0;

  if (so -> textsection)
    text_addr = so -> textsection -> addr;
  else if (so -> abfd != NULL)
    {
      asection *lowest_sect;

      /* If we didn't find a mapped non zero sized .text section, set up
         text_addr so that the relocation in symbol_file_add does no harm.  */

      lowest_sect = bfd_get_section_by_name (so -> abfd, ".text");
      if (lowest_sect == NULL)
        bfd_map_over_sections (so -> abfd, find_lowest_section,
                               (PTR) &lowest_sect);
      if (lowest_sect)
        text_addr = bfd_section_vma (so -> abfd, lowest_sect)
                    + (CORE_ADDR) LM_ADDR (so);
    }
  
  ALL_OBJFILES (so -> objfile)
    {
      if (strcmp (so -> objfile -> name, so -> so_name) == 0)
        return 1;
    }
  so -> objfile =
    symbol_file_add (so -> so_name, so -> from_tty,
                     text_addr,
                     0, 0, 0, 0, 1);
  return (1);
}

/* This function will check the so name to see if matches the main list.
   In some system the main object is in the list, which we want to exclude */

static int match_main (soname)
    char *soname;
{
  char **mainp;

  for (mainp = main_name_list; *mainp != NULL; mainp++)
    {
      if (strcmp (soname, *mainp) == 0)
        return (1);
    }

  return (0);
}

/*

GLOBAL FUNCTION

        solib_add -- add a shared library file to the symtab and section list

SYNOPSIS

        void solib_add (char *arg_string, int from_tty,
                        struct target_ops *target)

DESCRIPTION

*/

void
solib_add (arg_string, from_tty, target)
     char *arg_string;
     int from_tty;
     struct target_ops *target;
{       
  register struct so_list *so = NULL;           /* link map state variable */

  /* Last shared library that we read.  */
  struct so_list *so_last = NULL;

  char *re_err;
  int count;
  int old;
  
  if ((re_err = re_comp (arg_string ? arg_string : ".")) != NULL)
    {
      error ("Invalid regexp: %s", re_err);
    }
  
  /* Add the shared library sections to the section table of the
     specified target, if any.  */
  if (target)
    {
      /* Count how many new section_table entries there are.  */
      so = NULL;
      count = 0;
      while ((so = find_solib (so, 1)) != NULL)
        {
          if (so -> so_name[0] && !match_main (so -> so_name))
            {
              count += so -> sections_end - so -> sections;
            }
        }
      
      if (count)
        {
          int update_coreops;

          /* We must update the to_sections field in the core_ops structure
             here, otherwise we dereference a potential dangling pointer
             for each call to target_read/write_memory within this routine.  */
          update_coreops = core_ops.to_sections == target->to_sections;
                     
          /* Reallocate the target's section table including the new size.  */
          if (target -> to_sections)
            {
              old = target -> to_sections_end - target -> to_sections;
              target -> to_sections = (struct section_table *)
                xrealloc ((char *)target -> to_sections,
                         (sizeof (struct section_table)) * (count + old));
            }
          else
            {
              old = 0;
              target -> to_sections = (struct section_table *)
                xmalloc ((sizeof (struct section_table)) * count);
            }
          target -> to_sections_end = target -> to_sections + (count + old);
          
          /* Update the to_sections field in the core_ops structure
             if needed.  */
          if (update_coreops)
            {
              core_ops.to_sections = target->to_sections;
              core_ops.to_sections_end = target->to_sections_end;
            }

          /* Add these section table entries to the target's table.  */
          while ((so = find_solib (so, 1)) != NULL)
            {
              if (so -> so_name[0])
                {
                  count = so -> sections_end - so -> sections;
                  memcpy ((char *) (target -> to_sections + old),
                          so -> sections, 
                          (sizeof (struct section_table)) * count);
                  old += count;
                }
            }
        }
    }
  
  /* Now add the symbol files.  */
  while ((so = find_solib (so, 1)) != NULL)
    {
      if (so -> so_name[0] && re_exec (so -> so_name) && 
      !match_main (so -> so_name))
        {
          so -> from_tty = from_tty;
          if (so -> symbols_loaded)
            {
              if (from_tty)
                {
                  printf_unfiltered ("Symbols already loaded for %s\n", so -> so_name);
                }
            }
          else if (catch_errors
                   (symbol_add_stub, so,
                    "Error while reading shared library symbols:\n",
                    RETURN_MASK_ALL))
            {
              so_last = so;
              so -> symbols_loaded = 1;
            }
        }
    }

  /* Getting new symbols may change our opinion about what is
     frameless.  */
  if (so_last)
    reinit_frame_cache ();

  if (so_last)
    special_symbol_handling (so_last);
}

/*

LOCAL FUNCTION

        info_sharedlibrary_command -- code for "info sharedlibrary"

SYNOPSIS

        static void info_sharedlibrary_command ()

DESCRIPTION

        Walk through the shared library list and print information
        about each attached library.
*/

static void
info_sharedlibrary_command (ignore, from_tty)
     char *ignore;
     int from_tty;
{
  register struct so_list *so = NULL;   /* link map state variable */
  int header_done = 0;
  int addr_width;
  char *addr_fmt;

  if (exec_bfd == NULL)
    {
      printf_unfiltered ("No exec file.\n");
      return;
    }

#ifndef TARGET_ELF64
  addr_width = 8+4;
  addr_fmt = "08l";
#else
  addr_width = 16+4;
  addr_fmt = "016l";
#endif

  while ((so = find_solib (so, 0)) != NULL)
    {
      if (so -> so_name[0])
        {
          if (!header_done)
            {
              printf_unfiltered("%-*s%-*s%-12s%s\n", addr_width, "From",
                                addr_width, "To", "Syms Read",
                                "Shared Object Library");
              header_done++;
            }

          printf_unfiltered ("%-*s", addr_width,
                  local_hex_string_custom ((unsigned long) LM_ADDR (so),
                                           addr_fmt));
          printf_unfiltered ("%-*s", addr_width,
                  local_hex_string_custom ((unsigned long) so -> lmend,
                                           addr_fmt));
          printf_unfiltered ("%-12s", so -> symbols_loaded ? "Yes" : "No");
          printf_unfiltered ("%s\n",  so -> so_name);
        }
    }
  if (so_list_head == NULL)
    {
      printf_unfiltered ("No shared libraries loaded at this time.\n"); 
    }
}

/*

GLOBAL FUNCTION

        solib_address -- check to see if an address is in a shared lib

SYNOPSIS

        char * solib_address (CORE_ADDR address)

DESCRIPTION

        Provides a hook for other gdb routines to discover whether or
        not a particular address is within the mapped address space of
        a shared library.  Any address between the base mapping address
        and the first address beyond the end of the last mapping, is
        considered to be within the shared library address space, for
        our purposes.

        For example, this routine is called at one point to disable
        breakpoints which are in shared libraries that are not currently
        mapped in.
 */

char *
solib_address (address)
     CORE_ADDR address;
{
  register struct so_list *so = 0;      /* link map state variable */
  
  while ((so = find_solib (so, 0)) != NULL)
    {
      if (so -> so_name[0])
        {
          if ((address >= (CORE_ADDR) LM_ADDR (so)) &&
              (address < (CORE_ADDR) so -> lmend))
            return (so->so_name);
        }
    }
  return (0);
}

/* Called by free_all_symtabs */

void 
clear_solib()
{
  struct so_list *next;
  char *bfd_filename;
  
  while (so_list_head)
    {
      next = so_list_head -> next;
      free_solib (so_list_head);
      so_list_head = next;
    }
  debug_base = 0;
}

static void
do_clear_solib (dummy)
     PTR dummy;
{
  solib_cleanup_queued = 0;
  clear_solib ();
}

#ifdef SVR4_SHARED_LIBS

/* Return 1 if PC lies in the dynamic symbol resolution code of the
   SVR4 run time loader.  */

static CORE_ADDR interp_text_sect_low;
static CORE_ADDR interp_text_sect_high;
static CORE_ADDR interp_plt_sect_low;
static CORE_ADDR interp_plt_sect_high;

int
in_svr4_dynsym_resolve_code (pc)
     CORE_ADDR pc;
{
  return ((pc >= interp_text_sect_low && pc < interp_text_sect_high)
          || (pc >= interp_plt_sect_low && pc < interp_plt_sect_high)
          || in_plt_section (pc, NULL));
}
#endif

/*

LOCAL FUNCTION

        disable_break -- remove the "mapping changed" breakpoint

SYNOPSIS

        static int disable_break ()

DESCRIPTION

        Removes the breakpoint that gets hit when the dynamic linker
        completes a mapping change.

*/

#ifndef SVR4_SHARED_LIBS

static int
disable_break ()
{
  int status = 1;

#ifndef SVR4_SHARED_LIBS

  int in_debugger = 0;
  
  /* Read the debugger structure from the inferior to retrieve the
     address of the breakpoint and the original contents of the
     breakpoint address.  Remove the breakpoint by writing the original
     contents back. */

  read_memory (debug_addr, (char *) &debug_copy, sizeof (debug_copy));

  /* Set `in_debugger' to zero now. */

  write_memory (flag_addr, (char *) &in_debugger, sizeof (in_debugger));

  breakpoint_addr = (CORE_ADDR) debug_copy.ldd_bp_addr;
  write_memory (breakpoint_addr, (char *) &debug_copy.ldd_bp_inst,
                sizeof (debug_copy.ldd_bp_inst));

#else   /* SVR4_SHARED_LIBS */

  /* Note that breakpoint address and original contents are in our address
     space, so we just need to write the original contents back. */

  if (memory_remove_breakpoint (breakpoint_addr, shadow_contents) != 0)
    {
      status = 0;
    }

#endif  /* !SVR4_SHARED_LIBS */

  /* For the SVR4 version, we always know the breakpoint address.  For the
     SunOS version we don't know it until the above code is executed.
     Grumble if we are stopped anywhere besides the breakpoint address. */

  if (stop_pc != breakpoint_addr)
    {
      warning ("stopped at unknown breakpoint while handling shared libraries");
    }

  return (status);
}

#endif  /* #ifdef SVR4_SHARED_LIBS */

/*

LOCAL FUNCTION

        enable_break -- arrange for dynamic linker to hit breakpoint

SYNOPSIS

        int enable_break (void)

DESCRIPTION

        Both the SunOS and the SVR4 dynamic linkers have, as part of their
        debugger interface, support for arranging for the inferior to hit
        a breakpoint after mapping in the shared libraries.  This function
        enables that breakpoint.

        For SunOS, there is a special flag location (in_debugger) which we
        set to 1.  When the dynamic linker sees this flag set, it will set
        a breakpoint at a location known only to itself, after saving the
        original contents of that place and the breakpoint address itself,
        in it's own internal structures.  When we resume the inferior, it
        will eventually take a SIGTRAP when it runs into the breakpoint.
        We handle this (in a different place) by restoring the contents of
        the breakpointed location (which is only known after it stops),
        chasing around to locate the shared libraries that have been
        loaded, then resuming.

        For SVR4, the debugger interface structure contains a member (r_brk)
        which is statically initialized at the time the shared library is
        built, to the offset of a function (_r_debug_state) which is guaran-
        teed to be called once before mapping in a library, and again when
        the mapping is complete.  At the time we are examining this member,
        it contains only the unrelocated offset of the function, so we have
        to do our own relocation.  Later, when the dynamic linker actually
        runs, it relocates r_brk to be the actual address of _r_debug_state().

        The debugger interface structure also contains an enumeration which
        is set to either RT_ADD or RT_DELETE prior to changing the mapping,
        depending upon whether or not the library is being mapped or unmapped,
        and then set to RT_CONSISTENT after the library is mapped/unmapped.
*/

static int
enable_break ()
{
  int success = 0;

#ifndef SVR4_SHARED_LIBS

  int j;
  int in_debugger;

  /* Get link_dynamic structure */

  j = target_read_memory (debug_base, (char *) &dynamic_copy,
                          sizeof (dynamic_copy));
  if (j)
    {
      /* unreadable */
      return (0);
    }

  /* Calc address of debugger interface structure */

  debug_addr = (CORE_ADDR) dynamic_copy.ldd;

  /* Calc address of `in_debugger' member of debugger interface structure */

  flag_addr = debug_addr + (CORE_ADDR) ((char *) &debug_copy.ldd_in_debugger -
                                        (char *) &debug_copy);

  /* Write a value of 1 to this member.  */

  in_debugger = 1;
  write_memory (flag_addr, (char *) &in_debugger, sizeof (in_debugger));
  success = 1;

#else   /* SVR4_SHARED_LIBS */

#ifdef BKPT_AT_SYMBOL

  struct minimal_symbol *msymbol;
  char **bkpt_namep;
  asection *interp_sect;

  /* First, remove all the solib event breakpoints.  Their addresses
     may have changed since the last time we ran the program.  */
  remove_solib_event_breakpoints ();

#ifdef SVR4_SHARED_LIBS
  interp_text_sect_low = interp_text_sect_high = 0;
  interp_plt_sect_low = interp_plt_sect_high = 0;

  /* Find the .interp section; if not found, warn the user and drop
     into the old breakpoint at symbol code.  */
  interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
  if (interp_sect)
    {
      unsigned int interp_sect_size;
      char *buf;
      CORE_ADDR load_addr;
      bfd *tmp_bfd;
      CORE_ADDR sym_addr = 0;

      /* Read the contents of the .interp section into a local buffer;
         the contents specify the dynamic linker this program uses.  */
      interp_sect_size = bfd_section_size (exec_bfd, interp_sect);
      buf = alloca (interp_sect_size);
      bfd_get_section_contents (exec_bfd, interp_sect,
                                buf, 0, interp_sect_size);

      /* Now we need to figure out where the dynamic linker was
         loaded so that we can load its symbols and place a breakpoint
         in the dynamic linker itself.

         This address is stored on the stack.  However, I've been unable
         to find any magic formula to find it for Solaris (appears to
         be trivial on GNU/Linux).  Therefore, we have to try an alternate
         mechanism to find the dynamic linker's base address.  */
      tmp_bfd = bfd_openr (buf, gnutarget);
      if (tmp_bfd == NULL)
        goto bkpt_at_symbol;

      /* Make sure the dynamic linker's really a useful object.  */
      if (!bfd_check_format (tmp_bfd, bfd_object))
        {
          warning ("Unable to grok dynamic linker %s as an object file", buf);
          bfd_close (tmp_bfd);
          goto bkpt_at_symbol;
        }

      /* We find the dynamic linker's base address by examining the
         current pc (which point at the entry point for the dynamic
         linker) and subtracting the offset of the entry point.  */
      load_addr = read_pc () - tmp_bfd->start_address;

      /* Record the relocated start and end address of the dynamic linker
         text and plt section for in_svr4_dynsym_resolve_code.  */
      interp_sect = bfd_get_section_by_name (tmp_bfd, ".text");
      if (interp_sect)
        {
          interp_text_sect_low =
            bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
          interp_text_sect_high =
            interp_text_sect_low + bfd_section_size (tmp_bfd, interp_sect);
        }
      interp_sect = bfd_get_section_by_name (tmp_bfd, ".plt");
      if (interp_sect)
        {
          interp_plt_sect_low =
            bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
          interp_plt_sect_high =
            interp_plt_sect_low + bfd_section_size (tmp_bfd, interp_sect);
        }

      /* Now try to set a breakpoint in the dynamic linker.  */
      for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
        {
          sym_addr = bfd_lookup_symbol (tmp_bfd, *bkpt_namep);
          if (sym_addr != 0)
            break;
        }

      /* We're done with the temporary bfd.  */
      bfd_close (tmp_bfd);

      if (sym_addr != 0)
        {
          create_solib_event_breakpoint (load_addr + sym_addr);
          return 1;
        }

      /* For whatever reason we couldn't set a breakpoint in the dynamic
         linker.  Warn and drop into the old code.  */
bkpt_at_symbol:
      warning ("Unable to find dynamic linker breakpoint function.\nGDB will be unable to debug shared library initializers\nand track explicitly loaded dynamic code.");
    }
#endif

  /* Scan through the list of symbols, trying to look up the symbol and
     set a breakpoint there.  Terminate loop when we/if we succeed. */

  breakpoint_addr = 0;
  for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
    {
      msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
      if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
        {
          create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
          return 1;
        }
    }

  /* Nothing good happened.  */
  success = 0;

#endif  /* BKPT_AT_SYMBOL */

#endif  /* !SVR4_SHARED_LIBS */

  return (success);
}
  
/*
  
GLOBAL FUNCTION
  
        solib_create_inferior_hook -- shared library startup support
  
SYNOPSIS
  
        void solib_create_inferior_hook()
  
DESCRIPTION
  
        When gdb starts up the inferior, it nurses it along (through the
        shell) until it is ready to execute it's first instruction.  At this
        point, this function gets called via expansion of the macro
        SOLIB_CREATE_INFERIOR_HOOK.

        For SunOS executables, this first instruction is typically the
        one at "_start", or a similar text label, regardless of whether
        the executable is statically or dynamically linked.  The runtime
        startup code takes care of dynamically linking in any shared
        libraries, once gdb allows the inferior to continue.

        For SVR4 executables, this first instruction is either the first
        instruction in the dynamic linker (for dynamically linked
        executables) or the instruction at "start" for statically linked
        executables.  For dynamically linked executables, the system
        first exec's /lib/libc.so.N, which contains the dynamic linker,
        and starts it running.  The dynamic linker maps in any needed
        shared libraries, maps in the actual user executable, and then
        jumps to "start" in the user executable.

        For both SunOS shared libraries, and SVR4 shared libraries, we
        can arrange to cooperate with the dynamic linker to discover the
        names of shared libraries that are dynamically linked, and the
        base addresses to which they are linked.

        This function is responsible for discovering those names and
        addresses, and saving sufficient information about them to allow
        their symbols to be read at a later time.

FIXME

        Between enable_break() and disable_break(), this code does not
        properly handle hitting breakpoints which the user might have
        set in the startup code or in the dynamic linker itself.  Proper
        handling will probably have to wait until the implementation is
        changed to use the "breakpoint handler function" method.

        Also, what if child has exit()ed?  Must exit loop somehow.
  */

void 
solib_create_inferior_hook()
{
  /* If we are using the BKPT_AT_SYMBOL code, then we don't need the base
     yet.  In fact, in the case of a SunOS4 executable being run on
     Solaris, we can't get it yet.  find_solib will get it when it needs
     it.  */
#if !(defined (SVR4_SHARED_LIBS) && defined (BKPT_AT_SYMBOL))
  if ((debug_base = locate_base ()) == 0)
    {
      /* Can't find the symbol or the executable is statically linked. */
      return;
    }
#endif

  if (!enable_break ())
    {
      warning ("shared library handler failed to enable breakpoint");
      return;
    }

#if !defined(SVR4_SHARED_LIBS) || defined(_SCO_DS)
  /* SCO and SunOS need the loop below, other systems should be using the
     special shared library breakpoints and the shared library breakpoint
     service routine.

     Now run the target.  It will eventually hit the breakpoint, at
     which point all of the libraries will have been mapped in and we
     can go groveling around in the dynamic linker structures to find
     out what we need to know about them. */

  clear_proceed_status ();
  stop_soon_quietly = 1;
  stop_signal = TARGET_SIGNAL_0;
  do
    {
      target_resume (-1, 0, stop_signal);
      wait_for_inferior ();
    }
  while (stop_signal != TARGET_SIGNAL_TRAP);
  stop_soon_quietly = 0;

#if !defined(_SCO_DS)
  /* We are now either at the "mapping complete" breakpoint (or somewhere
     else, a condition we aren't prepared to deal with anyway), so adjust
     the PC as necessary after a breakpoint, disable the breakpoint, and
     add any shared libraries that were mapped in. */

  if (DECR_PC_AFTER_BREAK)
    {
      stop_pc -= DECR_PC_AFTER_BREAK;
      write_register (PC_REGNUM, stop_pc);
    }

  if (!disable_break ())
    {
      warning ("shared library handler failed to disable breakpoint");
    }

  if (auto_solib_add)
    solib_add ((char *) 0, 0, (struct target_ops *) 0);
#endif /* ! _SCO_DS */
#endif
}

/*

LOCAL FUNCTION

        special_symbol_handling -- additional shared library symbol handling

SYNOPSIS

        void special_symbol_handling (struct so_list *so)

DESCRIPTION

        Once the symbols from a shared object have been loaded in the usual
        way, we are called to do any system specific symbol handling that 
        is needed.

        For SunOS4, this consists of grunging around in the dynamic
        linkers structures to find symbol definitions for "common" symbols
        and adding them to the minimal symbol table for the runtime common
        objfile.

*/

static void
special_symbol_handling (so)
struct so_list *so;
{
#ifndef SVR4_SHARED_LIBS
  int j;

  if (debug_addr == 0)
    {
      /* Get link_dynamic structure */

      j = target_read_memory (debug_base, (char *) &dynamic_copy,
                              sizeof (dynamic_copy));
      if (j)
        {
          /* unreadable */
          return;
        }

      /* Calc address of debugger interface structure */
      /* FIXME, this needs work for cross-debugging of core files
         (byteorder, size, alignment, etc).  */

      debug_addr = (CORE_ADDR) dynamic_copy.ldd;
    }

  /* Read the debugger structure from the inferior, just to make sure
     we have a current copy. */

  j = target_read_memory (debug_addr, (char *) &debug_copy,
                          sizeof (debug_copy));
  if (j)
    return;             /* unreadable */

  /* Get common symbol definitions for the loaded object. */

  if (debug_copy.ldd_cp)
    {
      solib_add_common_symbols (debug_copy.ldd_cp);
    }

#endif  /* !SVR4_SHARED_LIBS */
}


/*

LOCAL FUNCTION

        sharedlibrary_command -- handle command to explicitly add library

SYNOPSIS

        static void sharedlibrary_command (char *args, int from_tty)

DESCRIPTION

*/

static void
sharedlibrary_command (args, from_tty)
char *args;
int from_tty;
{
  dont_repeat ();
  solib_add (args, from_tty, (struct target_ops *) 0);
}

#endif /* HAVE_LINK_H */

void
_initialize_solib()
{
#ifdef HAVE_LINK_H

  add_com ("sharedlibrary", class_files, sharedlibrary_command,
           "Load shared object library symbols for files matching REGEXP.");
  add_info ("sharedlibrary", info_sharedlibrary_command, 
            "Status of loaded shared object libraries.");

  add_show_from_set
    (add_set_cmd ("auto-solib-add", class_support, var_zinteger,
                  (char *) &auto_solib_add,
                  "Set autoloading of shared library symbols.\n\
If nonzero, symbols from all shared object libraries will be loaded\n\
automatically when the inferior begins execution or when the dynamic linker\n\
informs gdb that a new library has been loaded.  Otherwise, symbols\n\
must be loaded manually, using `sharedlibrary'.",
                  &setlist),
     &showlist);

  add_show_from_set
    (add_set_cmd ("solib-absolute-prefix", class_support, var_filename,
                  (char *) &solib_absolute_prefix,
                  "Set prefix for loading absolute shared library symbol files.\n\
For other (relative) files, you can add values using `set solib-search-path'.",
                  &setlist),
     &showlist);
  add_show_from_set
    (add_set_cmd ("solib-search-path", class_support, var_string,
                  (char *) &solib_search_path,
                  "Set the search path for loading non-absolute shared library symbol files.\n\
This takes precedence over the environment variables PATH and LD_LIBRARY_PATH.",
                  &setlist),
     &showlist);

#endif /* HAVE_LINK_H */
}