* bout.c (b_out_slurp_reloc_table): Use BFD_ASSERT macro,

[deliverable/binutils-gdb.git] / gdb / solib.c

/* Handle SunOS and SVR4 shared libraries for GDB, the GNU Debugger.
   Copyright 1990, 1991, 1992 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */


#include <sys/types.h>
#include <signal.h>
#include <string.h>
#include <link.h>
#include <sys/param.h>
#include <fcntl.h>
#include <stdio.h>
#include <a.out.h>

#include "defs.h"
#include "symtab.h"
#include "gdbcore.h"
#include "command.h"
#include "target.h"
#include "frame.h"
#include "regex.h"
#include "inferior.h"

extern char *getenv ();
extern char *elf_interpreter ();	/* Interpreter name from exec file */
extern char *re_comp ();

#define MAX_PATH_SIZE 256		/* FIXME: Should be dynamic */

/* On SVR4 systems, for the initial implementation, use main() as the
   "startup mapping complete" breakpoint address.  The models for SunOS
   and SVR4 dynamic linking debugger support are different in that SunOS
   hits one breakpoint when all mapping is complete while using the SVR4
   debugger support takes two breakpoint hits for each file mapped, and
   there is no way to know when the "last" one is hit.  Both these
   mechanisms should be tied to a "breakpoint service routine" that
   gets automatically executed whenever one of the breakpoints indicating
   a change in mapping is hit.  This is a future enhancement.  (FIXME) */

#define BKPT_AT_MAIN 1

/* local data declarations */

#ifndef SVR4_SHARED_LIBS

#define DEBUG_BASE "_DYNAMIC"
#define LM_ADDR(so) ((so) -> lm.lm_addr)
#define LM_NEXT(so) ((so) -> lm.lm_next)
#define LM_NAME(so) ((so) -> lm.lm_name)
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 DEBUG_BASE "_r_debug"
#define LM_ADDR(so) ((so) -> lm.l_addr)
#define LM_NEXT(so) ((so) -> lm.l_next)
#define LM_NAME(so) ((so) -> lm.l_name)
static struct r_debug debug_copy;
char shadow_contents[BREAKPOINT_MAX];	/* Stash old bkpt addr contents */
extern CORE_ADDR proc_base_address ();
extern int proc_address_to_fd ();

#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? */
  bfd *so_bfd;				/* bfd for so_name */
  struct section_table *sections;
  struct section_table *sections_end;
};

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 */


/*

LOCAL FUNCTION

	solib_map_sections -- open bfd and build sections for shared lib

SYNOPSIS

	static void 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 void
solib_map_sections (so)
     struct so_list *so;
{
  char *filename;
  char *scratch_pathname;
  int scratch_chan;
  struct section_table *p;
  
  filename = tilde_expand (so -> so_name);
  make_cleanup (free, filename);
  
  scratch_chan = openp (getenv ("PATH"), 1, filename, O_RDONLY, 0,
			&scratch_pathname);
  if (scratch_chan < 0)
    {
      scratch_chan = openp (getenv ("LD_LIBRARY_PATH"), 1, filename,
			    O_RDONLY, 0, &scratch_pathname);
    }
  if (scratch_chan < 0)
    {
      perror_with_name (filename);
    }  

  so -> so_bfd = bfd_fdopenr (scratch_pathname, NULL, scratch_chan);
  if (!so -> so_bfd)
    {
      error ("Could not open `%s' as an executable file: %s",
	     scratch_pathname, bfd_errmsg (bfd_error));
    }
  if (!bfd_check_format (so -> so_bfd, bfd_object))
    {
      error ("\"%s\": not in executable format: %s.",
	     scratch_pathname, bfd_errmsg (bfd_error));
    }
  if (build_section_table (so -> so_bfd, &so -> sections, &so -> sections_end))
    {
      error ("Can't find the file sections in `%s': %s", 
	     exec_bfd -> filename, bfd_errmsg (bfd_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);
    }
}

/* Read all dynamically loaded common symbol definitions from the inferior
   and add them to the misc_function_vector.  */

#ifndef SVR4_SHARED_LIBS

static void
solib_add_common_symbols (rtc_symp)
    struct rtc_symb *rtc_symp;
{
  struct rtc_symb inferior_rtc_symb;
  struct nlist inferior_rtc_nlist;
  extern void discard_misc_bunches();

  init_misc_bunches ();
  make_cleanup (discard_misc_bunches, 0);

  while (rtc_symp)
    {
    read_memory((CORE_ADDR)rtc_symp,
		&inferior_rtc_symb,
		sizeof(inferior_rtc_symb));
    read_memory((CORE_ADDR)inferior_rtc_symb.rtc_sp,
		&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. */
	int len = inferior_rtc_nlist.n_value - inferior_rtc_nlist.n_un.n_strx;
	char *name, *origname;

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

	/* Don't enter the symbol twice if the target is re-run. */

#ifdef NAMES_HAVE_UNDERSCORE
	if (*name == '_')
	  name++;
#endif
  	if (lookup_misc_func (name) < 0)
  	  prim_record_misc_function (obsavestring (name, strlen (name)),
				     inferior_rtc_nlist.n_value,
				     mf_bss);
	free (origname);
      }
    rtc_symp = inferior_rtc_symb.rtc_next;
    }

  condense_misc_bunches (1);
}

#endif	/* SVR4_SHARED_LIBS */

/*

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).

	FIXME:  See if there is a less "expensive" way of doing this.
	Also see if there is already another bfd or gdb function
	that specifically does this, and if so, use it.
*/

static CORE_ADDR
DEFUN (bfd_lookup_symbol, (abfd, symname),
       bfd *abfd AND
       char *symname)
{
  unsigned int storage_needed;
  asymbol *sym;
  asymbol **symbol_table;
  unsigned int number_of_symbols;
  unsigned int i;
  struct cleanup *back_to;
  CORE_ADDR symaddr = 0;
  enum misc_function_type mf_type;
  
  storage_needed = get_symtab_upper_bound (abfd);

  if (storage_needed > 0)
    {
      symbol_table = (asymbol **) bfd_xmalloc (storage_needed);
      back_to = make_cleanup (free, symbol_table);
      number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table); 
  
      for (i = 0; i < number_of_symbols; i++)
	{
	  sym = *symbol_table++;
	  if (strcmp (sym -> name, symname) == 0)
	    {
	      symaddr = sym -> value;
	      break;
	    }
	}
      do_cleanups (back_to);
    }
  return (symaddr);
}

/*

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 symbol DEBUG_BASE 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
DEFUN (look_for_base, (fd, baseaddr),
       int fd AND
       CORE_ADDR baseaddr)
{
  bfd *interp_bfd;
  CORE_ADDR address;

  /* 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) || 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", NULL, fd)) == NULL)
    {
      return (0);
    }
  if (!bfd_check_format (interp_bfd, bfd_object))
    {
      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. */

  if ((address = bfd_lookup_symbol (interp_bfd, DEBUG_BASE)) == 0)
    {
      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;
  bfd_close (interp_bfd);
  return (1);
}

/*

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 symbol defined by the macro DEBUG_BASE.
	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 misc function vector at the time the symbol
	file's symbols were read, and all we have to do is look it up there.

	The SVR4 version is much more complicated because 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.  We have to go
	to a lot more work to discover the address of DEBUG_BASE.  Because
	of this complexity, we cache the value we find and return that value
	on subsequent invocations.

	Note that we can assume nothing about the process state at the time
	we need to find this address.  We may be stopped on the first instruc-
	tion 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 CORE_ADDR
locate_base ()
{

#ifndef SVR4_SHARED_LIBS

  int i;
  CORE_ADDR address = 0;

  i = lookup_misc_func (DEBUG_BASE);
  if (i >= 0 && misc_function_vector[i].address != 0)
    {
      address = misc_function_vector[i].address;
    }
  return (address);

#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, ask the /proc support interface to iterate
     over the list of mapped address segments, calling look_for_base() for
     each segment.  When we are done, we will have either found the base
     address or not. */

  if (debug_base == 0)
    {
      proc_iterate_over_mappings (look_for_base);
    }
  return (debug_base);

#endif	/* !SVR4_SHARED_LIBS */

}

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

#ifndef SVR4_SHARED_LIBS

  read_memory (debug_base, &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, &ld_2_copy,
		   sizeof (struct link_dynamic_2));
      lm = ld_2_copy.ld_loaded;
    }

#else	/* SVR4_SHARED_LIBS */

  read_memory (debug_base, &debug_copy, sizeof (struct r_debug));
  lm = debug_copy.r_map;

#endif	/* !SVR4_SHARED_LIBS */

  return (lm);
}

/*

GLOBAL FUNCTION

	find_solib -- step through list of shared objects

SYNOPSIS

	struct so_list *find_solib (struct so_list *so_list_ptr)

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>.
 */

struct so_list *
find_solib (so_list_ptr)
     struct so_list *so_list_ptr;	/* Last lm or NULL for first one */
{
  struct so_list *so_list_next = NULL;
  struct link_map *lm = NULL;
  struct so_list *new;
  
  if (so_list_ptr == NULL)
    {
      /* We are setting up for a new scan through the loaded images. */
      if ((so_list_next = so_list_head) == NULL)
	{
	  /* We have not already read in the dynamic linking structures
	     from the inferior, lookup the address of the base structure. */
	  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
    {
      /* We have been called before, and are in the process of walking
	 the shared library list.  Advance to the next shared object. */
      if ((lm = LM_NEXT (so_list_ptr)) == NULL)
	{
	  /* We have hit the end of the list, so 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;
	    }
	}
      so_list_next = so_list_ptr -> next;
    }
  if ((so_list_next == NULL) && (lm != NULL))
    {
      /* 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));
      (void) memset ((char *) new, 0, sizeof (struct so_list));
      new -> lmaddr = lm;
      /* Add the new node as the next node in the list, or as the root
	 node if this is the first one. */
      if (so_list_ptr != NULL)
	{
	  so_list_ptr -> next = new;
	}
      else
	{
	  so_list_head = new;
	}      
      so_list_next = new;
      read_memory ((CORE_ADDR) lm, &(new -> lm), sizeof (struct link_map));
      /* For the SVR4 version, there is one entry that has no name
	 (for the inferior executable) since it is not a shared object. */
      if (LM_NAME (new) != 0)
	{
	  if (!target_read_string((CORE_ADDR) LM_NAME (new), new -> so_name,
		      MAX_PATH_SIZE - 1))
	      error ("find_solib: Can't read pathname for load map\n");
	  new -> so_name[MAX_PATH_SIZE - 1] = 0;
	  solib_map_sections (new);
	}      
    }
  return (so_list_next);
}

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

static int
symbol_add_stub (arg)
     char *arg;
{
  register struct so_list *so = (struct so_list *) arg;	/* catch_errs bogon */
  
  symbol_file_add (so -> so_name, so -> from_tty,
		   (unsigned int) LM_ADDR (so), 0);
  return (1);
}

/*

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 */
  char *re_err;
  int count;
  int old;
  
  if ((re_err = re_comp (arg_string ? arg_string : ".")) != NULL)
    {
      error ("Invalid regexp: %s", re_err);
    }
  
  /* Getting new symbols may change our opinion about what is
     frameless.  */
  reinit_frame_cache ();
  
  while ((so = find_solib (so)) != NULL)
    {
      if (so -> so_name[0] && re_exec (so -> so_name))
	{
	  if (so -> symbols_loaded)
	    {
	      if (from_tty)
		{
		  printf ("Symbols already loaded for %s\n", so -> so_name);
		}
	    }
	  else
	    {
	      so -> symbols_loaded = 1;
	      so -> from_tty = from_tty;
	      catch_errors (symbol_add_stub, (char *) so,
			    "Error while reading shared library symbols:\n");
	    }
	}
    }
  
  /* Now 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)) != NULL)
	{
	  if (so -> so_name[0])
	    {
	      count += so -> sections_end - so -> sections;
	    }
	}
      
      if (count)
	{
	  /* 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 *)
		realloc ((char *)target -> to_sections,
			 (sizeof (struct section_table)) * (count + old));
	    }
	  else
	    {
	      old = 0;
	      target -> to_sections = (struct section_table *)
		malloc ((sizeof (struct section_table)) * count);
	    }
	  target -> to_sections_end = target -> to_sections + (count + old);
	  
	  /* Add these section table entries to the target's table.  */
	  while ((so = find_solib (so)) != NULL)
	    {
	      if (so -> so_name[0])
		{
		  count = so -> sections_end - so -> sections;
		  bcopy (so -> sections, (char *)(target -> to_sections + old), 
			 (sizeof (struct section_table)) * count);
		  old += count;
		}
	    }
	}
    }
}

/*

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 ()
{
  register struct so_list *so = NULL;  	/* link map state variable */
  int header_done = 0;
  
  if (exec_bfd == NULL)
    {
      printf ("No exec file.\n");
      return;
    }
  while ((so = find_solib (so)) != NULL)
    {
      if (so -> so_name[0])
	{
	  if (!header_done)
	    {
	      printf("%-12s%-12s%-12s%s\n", "From", "To", "Syms Read",
		     "Shared Object Library");
	      header_done++;
	    }
	  printf ("%-12s", local_hex_string_custom (LM_ADDR (so), "08"));
	  printf ("%-12s", local_hex_string_custom (so -> lmend, "08"));
	  printf ("%-12s", so -> symbols_loaded ? "Yes" : "No");
	  printf ("%s\n",  so -> so_name);
	}
    }
  if (so_list_head == NULL)
    {
      printf ("No shared libraries loaded at this time.\n");	
    }
}

/*

GLOBAL FUNCTION

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

SYNOPSIS

	int 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.
 */

int
solib_address (address)
     CORE_ADDR address;
{
  register struct so_list *so = 0;   	/* link map state variable */
  
  while ((so = find_solib (so)) != NULL)
    {
      if (so -> so_name[0])
	{
	  if ((address >= (CORE_ADDR) LM_ADDR (so)) &&
	      (address < (CORE_ADDR) so -> lmend))
	    {
	      return (1);
	    }
	}
    }
  return (0);
}

/* Called by free_all_symtabs */

void 
clear_solib()
{
  struct so_list *next;
  
  while (so_list_head)
    {
      if (so_list_head -> sections)
	{
	  free (so_list_head -> sections);
	}
      if (so_list_head -> so_bfd)
	{
	  bfd_close (so_list_head -> so_bfd);
	}
      next = so_list_head -> next;
      free(so_list_head);
      so_list_head = next;
    }
  debug_base = 0;
}

/*

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.

*/

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, &debug_copy, sizeof (debug_copy));

  /* Get common symbol definitions for the loaded object. */
  if (debug_copy.ldd_cp)
    solib_add_common_symbols (debug_copy.ldd_cp);

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

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

  breakpoint_addr = (CORE_ADDR) debug_copy.ldd_bp_addr;
  write_memory (breakpoint_addr, &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);
}

/*

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 j;

#ifndef SVR4_SHARED_LIBS

  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, &in_debugger, sizeof (in_debugger));

#else	/* SVR4_SHARED_LIBS */

#ifdef BKPT_AT_MAIN

  int i;

  i = lookup_misc_func ("main");
  if (i >= 0 && misc_function_vector[i].address != 0)
    {
      breakpoint_addr = misc_function_vector[i].address;
    }
  else
    {
      return (0);
    }

  if (target_insert_breakpoint (breakpoint_addr, shadow_contents) != 0)
    {
      return (0);
    }

#else	/* !BKPT_AT_MAIN */

  struct symtab_and_line sal;

  /* Read the debugger interface structure directly. */

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

  /* Set breakpoint at the debugger interface stub routine that will
     be called just prior to each mapping change and again after the
     mapping change is complete.  Set up the (nonexistent) handler to
     deal with hitting these breakpoints.  (FIXME). */

  warning ("'%s': line %d: missing SVR4 support code", __FILE__, __LINE__);

#endif	/* BKPT_AT_MAIN */

#endif	/* !SVR4_SHARED_LIBS */

  return (1);
}
  
/*
  
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 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()
{
  CORE_ADDR debug_addr;
  int in_debugger;
  CORE_ADDR in_debugger_addr;
  CORE_ADDR breakpoint_addr;
  int i, j;
  
  if ((debug_base = locate_base ()) == 0)
    {
      /* Can't find the symbol or the executable is statically linked. */
      return;
    }

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

  /* 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 = 0;
  do
    {
      target_resume (0, stop_signal);
      wait_for_inferior ();
    }
  while (stop_signal != SIGTRAP);
  stop_soon_quietly = 0;
  
  /* 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");
    }

  solib_add ((char *) 0, 0, (struct target_ops *) 0);
}

/*

GLOBAL FUNCTION

	sharedlibrary_command -- handle command to explicitly add library

SYNOPSIS

	void sharedlibrary_command (char *args, int from_tty)

DESCRIPTION

*/

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

void
_initialize_solib()
{
  
  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.");
}