solib.c

早期freebsd实现

	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 ((PTR)so_list_head -> sections);
	}
      if (so_list_head -> so_bfd)
	{
	  bfd_close (so_list_head -> so_bfd);
	}
      next = so_list_head -> next;
      free((PTR)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, (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);
}

/*

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 ()
{

#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));

#else	/* SVR4_SHARED_LIBS */

#ifdef BKPT_AT_MAIN

  struct minimal_symbol *msymbol;

  msymbol = lookup_minimal_symbol ("main", symfile_objfile);
  if ((msymbol != NULL) && (msymbol -> address != 0))
    {
      breakpoint_addr = msymbol -> 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()
{
  
  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);
}

/*

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 Suns, 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 corresponding
	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, so -> objfile);
    }

#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);
}

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.");
}