path: root/libobjc/exception.c

/* The implementation of exception handling primitives for Objective-C.
   Copyright (C) 2004, 2005, 2007, 2008, 2009 Free Software Foundation, Inc.

This file is part of GCC.

GCC 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 3, or (at your option) any
later version.

GCC 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.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */

#include <stdlib.h>
#include "config.h"
#include "objc/objc-api.h"
#include "unwind.h"
#include "unwind-pe.h"


#ifdef __ARM_EABI_UNWINDER__

const _Unwind_Exception_Class __objc_exception_class
  = {'G', 'N', 'U', 'C', 'O', 'B', 'J', 'C'};
  
#else

/* This is the exception class we report -- "GNUCOBJC".  */
static const _Unwind_Exception_Class __objc_exception_class
  = ((((((((_Unwind_Exception_Class) 'G'
            << 8 | (_Unwind_Exception_Class) 'N')
           << 8 | (_Unwind_Exception_Class) 'U')
          << 8 | (_Unwind_Exception_Class) 'C')
         << 8 | (_Unwind_Exception_Class) 'O')
        << 8 | (_Unwind_Exception_Class) 'B')
       << 8 | (_Unwind_Exception_Class) 'J')
      << 8 | (_Unwind_Exception_Class) 'C');

#endif

/* This is the object that is passed around by the Objective C runtime
   to represent the exception in flight.  */

struct ObjcException
{
  /* This bit is needed in order to interact with the unwind runtime.  */
  struct _Unwind_Exception base;

  /* The actual object we want to throw. Note: must come immediately after
     unwind header.  */
  id value;

#ifdef __ARM_EABI_UNWINDER__
  /* Note: we use the barrier cache defined in the unwind control block for
     ARM EABI.  */
#else
  /* Cache some internal unwind data between phase 1 and phase 2.  */
  _Unwind_Ptr landingPad;
  int handlerSwitchValue;
#endif
};



struct lsda_header_info
{
  _Unwind_Ptr Start;
  _Unwind_Ptr LPStart;
  _Unwind_Ptr ttype_base;
  const unsigned char *TType;
  const unsigned char *action_table;
  unsigned char ttype_encoding;
  unsigned char call_site_encoding;
};

/* This hook allows libraries to sepecify special actions when an
   exception is thrown without a handler in place.
 */
void (*_objc_unexpected_exception) (id exception); /* !T:SAFE */

static const unsigned char *
parse_lsda_header (struct _Unwind_Context *context, const unsigned char *p,
		   struct lsda_header_info *info)
{
  _uleb128_t tmp;
  unsigned char lpstart_encoding;

  info->Start = (context ? _Unwind_GetRegionStart (context) : 0);

  /* Find @LPStart, the base to which landing pad offsets are relative.  */
  lpstart_encoding = *p++;
  if (lpstart_encoding != DW_EH_PE_omit)
    p = read_encoded_value (context, lpstart_encoding, p, &info->LPStart);
  else
    info->LPStart = info->Start;

  /* Find @TType, the base of the handler and exception spec type data.  */
  info->ttype_encoding = *p++;
  if (info->ttype_encoding != DW_EH_PE_omit)
    {
      p = read_uleb128 (p, &tmp);
      info->TType = p + tmp;
    }
  else
    info->TType = 0;

  /* The encoding and length of the call-site table; the action table
     immediately follows.  */
  info->call_site_encoding = *p++;
  p = read_uleb128 (p, &tmp);
  info->action_table = p + tmp;

  return p;
}

#ifdef __ARM_EABI_UNWINDER__

static Class
get_ttype_entry (struct lsda_header_info *info, _uleb128_t i)
{
  _Unwind_Ptr ptr;
  
  ptr = (_Unwind_Ptr) (info->TType - (i * 4));
  ptr = _Unwind_decode_target2 (ptr);
  
  if (ptr)
    return objc_get_class ((const char *) ptr);
  else
    return 0;
}

#else

static Class
get_ttype_entry (struct lsda_header_info *info, _Unwind_Word i)
{
  _Unwind_Ptr ptr;

  i *= size_of_encoded_value (info->ttype_encoding);
  read_encoded_value_with_base (info->ttype_encoding, info->ttype_base,
				info->TType - i, &ptr);

  /* NULL ptr means catch-all.  */
  if (ptr)
    return objc_get_class ((const char *) ptr);
  else
    return 0;
}

#endif

/* Like unto the method of the same name on Object, but takes an id.  */
/* ??? Does this bork the meta-type system?  Can/should we look up an
   isKindOf method on the id?  */

static int
isKindOf (id value, Class target)
{
  Class c;

  /* NULL target is catch-all.  */
  if (target == 0)
    return 1;

  for (c = value->class_pointer; c; c = class_get_super_class (c))
    if (c == target)
      return 1;
  return 0;
}

/* Using a different personality function name causes link failures
   when trying to mix code using different exception handling models.  */
#ifdef SJLJ_EXCEPTIONS
#define PERSONALITY_FUNCTION	__gnu_objc_personality_sj0
#define __builtin_eh_return_data_regno(x) x
#else
#define PERSONALITY_FUNCTION	__gnu_objc_personality_v0
#endif

#ifdef __ARM_EABI_UNWINDER__

#define CONTINUE_UNWINDING \
  do								\
    {								\
      if (__gnu_unwind_frame(ue_header, context) != _URC_OK)	\
	return _URC_FAILURE;					\
      return _URC_CONTINUE_UNWIND;				\
    }								\
  while (0)

_Unwind_Reason_Code
PERSONALITY_FUNCTION (_Unwind_State state,
		      struct _Unwind_Exception *ue_header,
		      struct _Unwind_Context *context)
#else

#define CONTINUE_UNWINDING return _URC_CONTINUE_UNWIND

_Unwind_Reason_Code
PERSONALITY_FUNCTION (int version,
		      _Unwind_Action actions,
		      _Unwind_Exception_Class exception_class,
		      struct _Unwind_Exception *ue_header,
		      struct _Unwind_Context *context)
#endif
{
  struct ObjcException *xh = (struct ObjcException *) ue_header;

  struct lsda_header_info info;
  const unsigned char *language_specific_data;
  const unsigned char *action_record;
  const unsigned char *p;
  _Unwind_Ptr landing_pad, ip;
  int handler_switch_value;
  int saw_cleanup = 0, saw_handler, foreign_exception;
  void *return_object;
  int ip_before_insn = 0;

#ifdef __ARM_EABI_UNWINDER__
  _Unwind_Action actions;
  
  switch (state & _US_ACTION_MASK)
    {
    case _US_VIRTUAL_UNWIND_FRAME:
      actions = _UA_SEARCH_PHASE;
      break;

    case _US_UNWIND_FRAME_STARTING:
      actions = _UA_CLEANUP_PHASE;
      if (!(state & _US_FORCE_UNWIND)
	  && ue_header->barrier_cache.sp == _Unwind_GetGR (context, 13))
	actions |= _UA_HANDLER_FRAME;
      break;

    case _US_UNWIND_FRAME_RESUME:
      CONTINUE_UNWINDING;
      break;

    default:
      abort();
    }
  actions |= state & _US_FORCE_UNWIND;

  /* TODO: Foreign exceptions need some attention (e.g. rethrowing doesn't
     work).  */
  foreign_exception = 0;

  /* The dwarf unwinder assumes the context structure holds things like the
     function and LSDA pointers.  The ARM implementation caches these in
     the exception header (UCB).  To avoid rewriting everything we make the
     virtual IP register point at the UCB.  */
  ip = (_Unwind_Ptr) ue_header;
  _Unwind_SetGR (context, 12, ip);

#else  /* !__ARM_EABI_UNWINDER.  */
  /* Interface version check.  */
  if (version != 1)
    return _URC_FATAL_PHASE1_ERROR;
  
  foreign_exception = (exception_class != __objc_exception_class);
#endif

  /* Shortcut for phase 2 found handler for domestic exception.  */
  if (actions == (_UA_CLEANUP_PHASE | _UA_HANDLER_FRAME)
      && !foreign_exception)
    {
#ifdef __ARM_EABI_UNWINDER__
      handler_switch_value = (int) ue_header->barrier_cache.bitpattern[1];
      landing_pad = (_Unwind_Ptr) ue_header->barrier_cache.bitpattern[3];
#else
      handler_switch_value = xh->handlerSwitchValue;
      landing_pad = xh->landingPad;
#endif
      goto install_context;
    }

  language_specific_data = (const unsigned char *)
    _Unwind_GetLanguageSpecificData (context);

  /* If no LSDA, then there are no handlers or cleanups.  */
  if (! language_specific_data)
    CONTINUE_UNWINDING;

  /* Parse the LSDA header.  */
  p = parse_lsda_header (context, language_specific_data, &info);
  info.ttype_base = base_of_encoded_value (info.ttype_encoding, context);
#ifdef HAVE_GETIPINFO
  ip = _Unwind_GetIPInfo (context, &ip_before_insn);
#else
  ip = _Unwind_GetIP (context);
#endif
  if (!ip_before_insn)
    --ip;
  landing_pad = 0;
  action_record = 0;
  handler_switch_value = 0;

#ifdef SJLJ_EXCEPTIONS
  /* The given "IP" is an index into the call-site table, with two
     exceptions -- -1 means no-action, and 0 means terminate.  But
     since we're using uleb128 values, we've not got random access
     to the array.  */
  if ((int) ip < 0)
    return _URC_CONTINUE_UNWIND;
  else
    {
      _uleb128_t cs_lp, cs_action;
      do
	{
	  p = read_uleb128 (p, &cs_lp);
	  p = read_uleb128 (p, &cs_action);
	}
      while (--ip);

      /* Can never have null landing pad for sjlj -- that would have
         been indicated by a -1 call site index.  */
      landing_pad = cs_lp + 1;
      if (cs_action)
	action_record = info.action_table + cs_action - 1;
      goto found_something;
    }
#else
  /* Search the call-site table for the action associated with this IP.  */
  while (p < info.action_table)
    {
      _Unwind_Ptr cs_start, cs_len, cs_lp;
      _uleb128_t cs_action;

      /* Note that all call-site encodings are "absolute" displacements.  */
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_start);
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_len);
      p = read_encoded_value (0, info.call_site_encoding, p, &cs_lp);
      p = read_uleb128 (p, &cs_action);

      /* The table is sorted, so if we've passed the ip, stop.  */
      if (ip < info.Start + cs_start)
	p = info.action_table;
      else if (ip < info.Start + cs_start + cs_len)
	{
	  if (cs_lp)
	    landing_pad = info.LPStart + cs_lp;
	  if (cs_action)
	    action_record = info.action_table + cs_action - 1;
	  goto found_something;
	}
    }
#endif /* SJLJ_EXCEPTIONS  */

  /* If ip is not present in the table, C++ would call terminate.  */
  /* ??? As with Java, it's perhaps better to tweek the LSDA to
     that no-action is mapped to no-entry.  */
  CONTINUE_UNWINDING;

 found_something:
  saw_cleanup = 0;
  saw_handler = 0;

  if (landing_pad == 0)
    {
      /* If ip is present, and has a null landing pad, there are
	 no cleanups or handlers to be run.  */
    }
  else if (action_record == 0)
    {
      /* If ip is present, has a non-null landing pad, and a null
         action table offset, then there are only cleanups present.
         Cleanups use a zero switch value, as set above.  */
      saw_cleanup = 1;
    }
  else
    {
      /* Otherwise we have a catch handler.  */
      _sleb128_t ar_filter, ar_disp;

      while (1)
	{
	  p = action_record;
	  p = read_sleb128 (p, &ar_filter);
	  read_sleb128 (p, &ar_disp);

	  if (ar_filter == 0)
	    {
	      /* Zero filter values are cleanups.  */
	      saw_cleanup = 1;
	    }

	  /* During forced unwinding, we only run cleanups.  With a
	     foreign exception class, we have no class info to match.  */
	  else if ((actions & _UA_FORCE_UNWIND) || foreign_exception)
	    ;

	  else if (ar_filter > 0)
	    {
	      /* Positive filter values are handlers.  */

	      Class catch_type = get_ttype_entry (&info, ar_filter);

	      if (isKindOf (xh->value, catch_type))
		{
		  handler_switch_value = ar_filter;
		  saw_handler = 1;
		  break;
		}
	    }
	  else
	    {
	      /* Negative filter values are exception specifications,
	         which Objective-C does not use.  */
	      abort ();
	    }

	  if (ar_disp == 0)
	    break;
	  action_record = p + ar_disp;
	}
    }

  if (! saw_handler && ! saw_cleanup)
    CONTINUE_UNWINDING;

  if (actions & _UA_SEARCH_PHASE)
    {
      if (!saw_handler)
	CONTINUE_UNWINDING;

      /* For domestic exceptions, we cache data from phase 1 for phase 2.  */
      if (!foreign_exception)
        {
#ifdef __ARM_EABI_UNWINDER__
	  ue_header->barrier_cache.sp = _Unwind_GetGR (context, 13);
	  ue_header->barrier_cache.bitpattern[1] = (_uw) handler_switch_value;
	  ue_header->barrier_cache.bitpattern[3] = (_uw) landing_pad;
#else
          xh->handlerSwitchValue = handler_switch_value;
          xh->landingPad = landing_pad;
#endif
	}
      return _URC_HANDLER_FOUND;
    }

 install_context:
  if (saw_cleanup == 0)
    {
      return_object = xh->value;
      if (!(actions & _UA_SEARCH_PHASE))
	_Unwind_DeleteException(&xh->base);
    }
  
  _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),
		 __builtin_extend_pointer (saw_cleanup ? xh : return_object));
  _Unwind_SetGR (context, __builtin_eh_return_data_regno (1),
		 handler_switch_value);
  _Unwind_SetIP (context, landing_pad);
  return _URC_INSTALL_CONTEXT;
}

static void
__objc_exception_cleanup (_Unwind_Reason_Code code __attribute__((unused)),
			  struct _Unwind_Exception *exc)
{
  free (exc);
}

void
objc_exception_throw (id value)
{
  struct ObjcException *header = calloc (1, sizeof (*header));
  
  memcpy (&header->base.exception_class, &__objc_exception_class,
	  sizeof (__objc_exception_class));
  header->base.exception_cleanup = __objc_exception_cleanup;
  header->value = value;

#ifdef SJLJ_EXCEPTIONS
  _Unwind_SjLj_RaiseException (&header->base);
#else
  _Unwind_RaiseException (&header->base);
#endif

  /* Some sort of unwinding error.  */
  if (_objc_unexpected_exception != 0)
    {
      (*_objc_unexpected_exception) (value);
    }
  abort ();
}