path: root/gcc/frame-dwarf2.c

/* Subroutines needed for unwinding DWARF 2 format stack frame info
   for exception handling.  */
/* Compile this one with gcc.  */
/* Copyright (C) 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
   Contributed by Jason Merrill <jason@cygnus.com>.

This file is part of GNU CC.

GNU CC 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, or (at your option)
any later version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file into combinations with other programs,
and to distribute those combinations without any restriction coming
from the use of this file.  (The General Public License restrictions
do apply in other respects; for example, they cover modification of
the file, and distribution when not linked into a combine
executable.)

GNU CC 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 GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* It is incorrect to include config.h here, because this file is being
   compiled for the target, and hence definitions concerning only the host
   do not apply.  */

#include "tconfig.h"
#include "tsystem.h"

#ifdef DWARF2_UNWIND_INFO
#include "dwarf2.h"
#include "frame.h"
#include "gthr.h"

#ifdef __GTHREAD_MUTEX_INIT
static __gthread_mutex_t object_mutex = __GTHREAD_MUTEX_INIT;
#else
static __gthread_mutex_t object_mutex;
#endif

/* Don't use `fancy_abort' here even if config.h says to use it.  */
#ifdef abort
#undef abort
#endif

/* Some types used by the DWARF 2 spec.  */

typedef          int  sword __attribute__ ((mode (SI)));
typedef unsigned int  uword __attribute__ ((mode (SI)));
typedef unsigned int  uaddr __attribute__ ((mode (pointer)));
typedef          int  saddr __attribute__ ((mode (pointer)));
typedef unsigned char ubyte;

/* Terminology:
   CIE - Common Information Element
   FDE - Frame Descriptor Element

   There is one per function, and it describes where the function code
   is located, and what the register lifetimes and stack layout are
   within the function.

   The data structures are defined in the DWARF specfication, although
   not in a very readable way (see LITERATURE).

   Every time an exception is thrown, the code needs to locate the FDE
   for the current function, and starts to look for exception regions
   from that FDE. This works in a two-level search:
   a) in a linear search, find the shared image (i.e. DLL) containing
      the PC
   b) using the FDE table for that shared object, locate the FDE using
      binary search (which requires the sorting).  */   

/* The first few fields of a CIE.  The CIE_id field is 0 for a CIE,
   to distinguish it from a valid FDE.  FDEs are aligned to an addressing
   unit boundary, but the fields within are unaligned.  */

struct dwarf_cie {
  uword length;
  sword CIE_id;
  ubyte version;
  char augmentation[0];
} __attribute__ ((packed, aligned (__alignof__ (void *))));

/* The first few fields of an FDE.  */

struct dwarf_fde {
  uword length;
  sword CIE_delta;
  void* pc_begin;
  uaddr pc_range;
} __attribute__ ((packed, aligned (__alignof__ (void *))));

typedef struct dwarf_fde fde;

/* Objects to be searched for frame unwind info.  */

static struct object *objects;

/* The information we care about from a CIE.  */

struct cie_info {
  char *augmentation;
  void *eh_ptr;
  int code_align;
  int data_align;
  unsigned ra_regno;
};

/* The current unwind state, plus a saved copy for DW_CFA_remember_state.  */

struct frame_state_internal
{
  struct frame_state s;
  struct frame_state_internal *saved_state;
};

/* This is undefined below if we need it to be an actual function.  */
#define init_object_mutex_once()

#if __GTHREADS
#ifdef __GTHREAD_MUTEX_INIT_FUNCTION

/* Helper for init_object_mutex_once.  */

static void
init_object_mutex (void)
{
  __GTHREAD_MUTEX_INIT_FUNCTION (&object_mutex);
}

/* Call this to arrange to initialize the object mutex.  */

#undef init_object_mutex_once
static void
init_object_mutex_once (void)
{
  static __gthread_once_t once = __GTHREAD_ONCE_INIT;
  __gthread_once (&once, init_object_mutex);
}

#endif /* __GTHREAD_MUTEX_INIT_FUNCTION */
#endif /* __GTHREADS */
  
/* Decode the unsigned LEB128 constant at BUF into the variable pointed to
   by R, and return the new value of BUF.  */

static void *
decode_uleb128 (unsigned char *buf, unsigned *r)
{
  unsigned shift = 0;
  unsigned result = 0;

  while (1)
    {
      unsigned byte = *buf++;
      result |= (byte & 0x7f) << shift;
      if ((byte & 0x80) == 0)
	break;
      shift += 7;
    }
  *r = result;
  return buf;
}

/* Decode the signed LEB128 constant at BUF into the variable pointed to
   by R, and return the new value of BUF.  */

static void *
decode_sleb128 (unsigned char *buf, int *r)
{
  unsigned shift = 0;
  unsigned result = 0;
  unsigned byte;

  while (1)
    {
      byte = *buf++;
      result |= (byte & 0x7f) << shift;
      shift += 7;
      if ((byte & 0x80) == 0)
	break;
    }
  if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
    result |= - (1 << shift);

  *r = result;
  return buf;
}

/* Read unaligned data from the instruction buffer.  */

union unaligned {
  void *p;
  unsigned b2 __attribute__ ((mode (HI)));
  unsigned b4 __attribute__ ((mode (SI)));
  unsigned b8 __attribute__ ((mode (DI)));
} __attribute__ ((packed));
static inline void *
read_pointer (void *p)
{ union unaligned *up = p; return up->p; }
static inline unsigned
read_1byte (void *p)
{ return *(unsigned char *)p; }
static inline unsigned
read_2byte (void *p)
{ union unaligned *up = p; return up->b2; }
static inline unsigned
read_4byte (void *p)
{ union unaligned *up = p; return up->b4; }
static inline unsigned long
read_8byte (void *p)
{ union unaligned *up = p; return up->b8; }

/* Ordering function for FDEs.  Functions can't overlap, so we just compare
   their starting addresses.  */

static inline saddr
fde_compare (fde *x, fde *y)
{
  return (saddr)x->pc_begin - (saddr)y->pc_begin;
}

/* Return the address of the FDE after P.  */

static inline fde *
next_fde (fde *p)
{
  return (fde *)(((char *)p) + p->length + sizeof (p->length));
}

#include "frame.c"

static size_t
count_fdes (fde *this_fde)
{
  size_t count;

  for (count = 0; this_fde->length != 0; this_fde = next_fde (this_fde))
    {
      /* Skip CIEs and linked once FDE entries.  */
      if (this_fde->CIE_delta == 0 || this_fde->pc_begin == 0)
	continue;

      ++count;
    }

  return count;
}

static void
add_fdes (fde *this_fde, fde_accumulator *accu, void **beg_ptr, void **end_ptr)
{
  void *pc_begin = *beg_ptr;
  void *pc_end = *end_ptr;

  for (; this_fde->length != 0; this_fde = next_fde (this_fde))
    {
      /* Skip CIEs and linked once FDE entries.  */
      if (this_fde->CIE_delta == 0 || this_fde->pc_begin == 0)
	continue;

      fde_insert (accu, this_fde);

      if (this_fde->pc_begin < pc_begin)
	pc_begin = this_fde->pc_begin;
      if (this_fde->pc_begin + this_fde->pc_range > pc_end)
	pc_end = this_fde->pc_begin + this_fde->pc_range;
    }

  *beg_ptr = pc_begin;
  *end_ptr = pc_end;
}

/* search this fde table for the one containing the pc */
static fde *
search_fdes (fde *this_fde, void *pc)
{
  for (; this_fde->length != 0; this_fde = next_fde (this_fde))
    {
      /* Skip CIEs and linked once FDE entries.  */
      if (this_fde->CIE_delta == 0 || this_fde->pc_begin == 0)
	continue;

      if ((uaddr)((char *)pc - (char *)this_fde->pc_begin) < this_fde->pc_range)
	return this_fde;
    }
  return NULL;
}

/* Set up a sorted array of pointers to FDEs for a loaded object.  We
   count up the entries before allocating the array because it's likely to
   be faster.  We can be called multiple times, should we have failed to
   allocate a sorted fde array on a previous occasion.  */

static void
frame_init (struct object* ob)
{
  size_t count;
  fde_accumulator accu;
  void *pc_begin, *pc_end;
  fde **array;

  if (ob->pc_begin)
    count = ob->count;
  else if (ob->fde_array)
    {
      fde **p = ob->fde_array;
      for (count = 0; *p; ++p)
	count += count_fdes (*p);
    }
  else
    count = count_fdes (ob->fde_begin);
  ob->count = count;

  if (!start_fde_sort (&accu, count) && ob->pc_begin)
    return;

  pc_begin = (void*)(uaddr)-1;
  pc_end = 0;

  if (ob->fde_array)
    {
      fde **p = ob->fde_array;
      for (; *p; ++p)
	add_fdes (*p, &accu, &pc_begin, &pc_end);
    }
  else
    add_fdes (ob->fde_begin, &accu, &pc_begin, &pc_end);

  array = end_fde_sort (&accu, count);
  if (array)
    ob->fde_array = array;
  ob->pc_begin = pc_begin;
  ob->pc_end = pc_end;
}

/* Return a pointer to the FDE for the function containing PC.  */

static fde *
find_fde (void *pc)
{
  struct object *ob;
  size_t lo, hi;

  init_object_mutex_once ();
  __gthread_mutex_lock (&object_mutex);

  /* Linear search through the objects, to find the one containing the pc. */
  for (ob = objects; ob; ob = ob->next)
    {
      if (ob->pc_begin == 0)
	frame_init (ob);
      if (pc >= ob->pc_begin && pc < ob->pc_end)
	break;
    }

  if (ob == 0)
    {
      __gthread_mutex_unlock (&object_mutex);
      return 0;
    }

  if (!ob->fde_array || (void *)ob->fde_array == (void *)ob->fde_begin)
    frame_init (ob);

  if (ob->fde_array && (void *)ob->fde_array != (void *)ob->fde_begin)
    {
      __gthread_mutex_unlock (&object_mutex);
      
      /* Standard binary search algorithm.  */
      for (lo = 0, hi = ob->count; lo < hi; )
	{
	  size_t i = (lo + hi) / 2;
	  fde *f = ob->fde_array[i];

	  if (pc < f->pc_begin)
	    hi = i;
	  else if (pc >= f->pc_begin + f->pc_range)
	    lo = i + 1;
	  else
	    return f;
	}
    }
  else
    {
      /* Long slow labourious linear search, cos we've no memory. */
      fde *f;
      
      if (ob->fde_array)
	{
	  fde **p = ob->fde_array;
	  
	  do
	    {
	      f = search_fdes (*p, pc);
	      if (f)
		break;
	      p++;
	    }
	  while (*p);
	}
      else
	f = search_fdes (ob->fde_begin, pc);
      __gthread_mutex_unlock (&object_mutex);
      return f;
    }
  return 0;
}

static inline struct dwarf_cie *
get_cie (fde *f)
{
  return ((void *)&f->CIE_delta) - f->CIE_delta;
}

/* Extract any interesting information from the CIE for the translation
   unit F belongs to.  */

static void *
extract_cie_info (fde *f, struct cie_info *c)
{
  void *p;
  int i;

  c->augmentation = get_cie (f)->augmentation;

  if (strcmp (c->augmentation, "") != 0
      && strcmp (c->augmentation, "eh") != 0
      && c->augmentation[0] != 'z')
    return 0;

  p = c->augmentation + strlen (c->augmentation) + 1;

  if (strcmp (c->augmentation, "eh") == 0)
    {
      c->eh_ptr = read_pointer (p);
      p += sizeof (void *);
    }
  else
    c->eh_ptr = 0;

  p = decode_uleb128 (p, &c->code_align);
  p = decode_sleb128 (p, &c->data_align);
  c->ra_regno = *(unsigned char *)p++;

  /* If the augmentation starts with 'z', we now see the length of the
     augmentation fields.  */
  if (c->augmentation[0] == 'z')
    {
      p = decode_uleb128 (p, &i);
      p += i;
    }

  return p;
}

/* Decode a DW_OP stack operation.  */

static void *
decode_stack_op (unsigned char *buf, struct frame_state *state)
{
  enum dwarf_location_atom op;
  int offset;

  op = *buf++;
  switch (op)
    {
    case DW_OP_reg0:
    case DW_OP_reg1:
    case DW_OP_reg2:
    case DW_OP_reg3:
    case DW_OP_reg4:
    case DW_OP_reg5:
    case DW_OP_reg6:
    case DW_OP_reg7:
    case DW_OP_reg8:
    case DW_OP_reg9:
    case DW_OP_reg10:
    case DW_OP_reg11:
    case DW_OP_reg12:
    case DW_OP_reg13:
    case DW_OP_reg14:
    case DW_OP_reg15:
    case DW_OP_reg16:
    case DW_OP_reg17:
    case DW_OP_reg18:
    case DW_OP_reg19:
    case DW_OP_reg20:
    case DW_OP_reg21:
    case DW_OP_reg22:
    case DW_OP_reg23:
    case DW_OP_reg24:
    case DW_OP_reg25:
    case DW_OP_reg26:
    case DW_OP_reg27:
    case DW_OP_reg28:
    case DW_OP_reg29:
    case DW_OP_reg30:
    case DW_OP_reg31:
      state->cfa_reg = op - DW_OP_reg0;
      break;
    case DW_OP_regx:
      buf = decode_sleb128 (buf, &offset);
      state->cfa_reg = offset;
      break;
    case DW_OP_breg0:
    case DW_OP_breg1:
    case DW_OP_breg2:
    case DW_OP_breg3:
    case DW_OP_breg4:
    case DW_OP_breg5:
    case DW_OP_breg6:
    case DW_OP_breg7:
    case DW_OP_breg8:
    case DW_OP_breg9:
    case DW_OP_breg10:
    case DW_OP_breg11:
    case DW_OP_breg12:
    case DW_OP_breg13:
    case DW_OP_breg14:
    case DW_OP_breg15:
    case DW_OP_breg16:
    case DW_OP_breg17:
    case DW_OP_breg18:
    case DW_OP_breg19:
    case DW_OP_breg20:
    case DW_OP_breg21:
    case DW_OP_breg22:
    case DW_OP_breg23:
    case DW_OP_breg24:
    case DW_OP_breg25:
    case DW_OP_breg26:
    case DW_OP_breg27:
    case DW_OP_breg28:
    case DW_OP_breg29:
    case DW_OP_breg30:
    case DW_OP_breg31:
      state->cfa_reg = op - DW_OP_breg0;
      buf = decode_sleb128 (buf, &offset);
      state->base_offset = offset;
      break;
    case DW_OP_bregx:
      buf = decode_sleb128 (buf, &offset);
      state->cfa_reg = offset;
      buf = decode_sleb128 (buf, &offset);
      state->base_offset = offset;
      break;
    case DW_OP_deref:
      state->indirect = 1;
      break;
    case DW_OP_plus_uconst:
      buf = decode_uleb128 (buf, &offset);
      state->cfa_offset = offset;
      break;
    default:
      abort ();
    }
  return buf;
}
/* Decode one instruction's worth of DWARF 2 call frame information.
   Used by __frame_state_for.  Takes pointers P to the instruction to
   decode, STATE to the current register unwind information, INFO to the
   current CIE information, and PC to the current PC value.  Returns a
   pointer to the next instruction.  */

static void *
execute_cfa_insn (void *p, struct frame_state_internal *state,
		  struct cie_info *info, void **pc)
{
  unsigned insn = *(unsigned char *)p++;
  unsigned reg;
  int offset;

  if (insn & DW_CFA_advance_loc)
    *pc += ((insn & 0x3f) * info->code_align);
  else if (insn & DW_CFA_offset)
    {
      reg = (insn & 0x3f);
      p = decode_uleb128 (p, &offset);
      if (reg == state->s.cfa_reg)
	/* Don't record anything about this register; it's only used to
	   reload SP in the epilogue.  We don't want to copy in SP
	   values for outer frames; we handle restoring SP specially.  */;
      else
	{
	  offset *= info->data_align;
	  state->s.saved[reg] = REG_SAVED_OFFSET;
	  state->s.reg_or_offset[reg] = offset;
	}
    }
  else if (insn & DW_CFA_restore)
    {
      reg = (insn & 0x3f);
      state->s.saved[reg] = REG_UNSAVED;
    }
  else switch (insn)
    {
    case DW_CFA_set_loc:
      *pc = read_pointer (p);
      p += sizeof (void *);
      break;
    case DW_CFA_advance_loc1:
      *pc += read_1byte (p);
      p += 1;
      break;
    case DW_CFA_advance_loc2:
      *pc += read_2byte (p);
      p += 2;
      break;
    case DW_CFA_advance_loc4:
      *pc += read_4byte (p);
      p += 4;
      break;

    case DW_CFA_offset_extended:
      p = decode_uleb128 (p, &reg);
      p = decode_uleb128 (p, &offset);
      if (reg == state->s.cfa_reg)
	/* Don't record anything; see above.  */;
      else
	{
	  offset *= info->data_align;
	  state->s.saved[reg] = REG_SAVED_OFFSET;
	  state->s.reg_or_offset[reg] = offset;
	}
      break;
    case DW_CFA_restore_extended:
      p = decode_uleb128 (p, &reg);
      state->s.saved[reg] = REG_UNSAVED;
      break;

    case DW_CFA_undefined:
    case DW_CFA_same_value:
    case DW_CFA_nop:
      break;

    case DW_CFA_register:
      {
	unsigned reg2;
	p = decode_uleb128 (p, &reg);
	p = decode_uleb128 (p, &reg2);
	state->s.saved[reg] = REG_SAVED_REG;
	state->s.reg_or_offset[reg] = reg2;
      }
      break;

    case DW_CFA_def_cfa:
      p = decode_uleb128 (p, &reg);
      p = decode_uleb128 (p, &offset);
      state->s.cfa_reg = reg;
      state->s.cfa_offset = offset;
      break;
    case DW_CFA_def_cfa_register:
      p = decode_uleb128 (p, &reg);
      state->s.cfa_reg = reg;
      break;
    case DW_CFA_def_cfa_offset:
      p = decode_uleb128 (p, &offset);
      state->s.cfa_offset = offset;
      break;
    case DW_CFA_def_cfa_expression:
      {
	void *end;
	state->s.cfa_reg = 0;
	state->s.cfa_offset = 0;
	state->s.base_offset = 0;
	state->s.indirect = 0;

	p = decode_uleb128 (p, &offset);
	end = p + offset;
	while (p < end)
	  p = decode_stack_op (p, &(state->s));
	break;
      }
      
    case DW_CFA_remember_state:
      {
	struct frame_state_internal *save =
	  (struct frame_state_internal *)
	  malloc (sizeof (struct frame_state_internal));
	memcpy (save, state, sizeof (struct frame_state_internal));
	state->saved_state = save;
      }
      break;
    case DW_CFA_restore_state:
      {
	struct frame_state_internal *save = state->saved_state;
	memcpy (state, save, sizeof (struct frame_state_internal));
	free (save);
      }
      break;

      /* FIXME: Hardcoded for SPARC register window configuration.  */
    case DW_CFA_GNU_window_save:
      for (reg = 16; reg < 32; ++reg)
	{
	  state->s.saved[reg] = REG_SAVED_OFFSET;
	  state->s.reg_or_offset[reg] = (reg - 16) * sizeof (void *);
	}
      break;

    case DW_CFA_GNU_args_size:
      p = decode_uleb128 (p, &offset);
      state->s.args_size = offset;
      break;

    case DW_CFA_GNU_negative_offset_extended:
      p = decode_uleb128 (p, &reg);
      p = decode_uleb128 (p, &offset);
      offset *= info->data_align;
      state->s.saved[reg] = REG_SAVED_OFFSET;
      state->s.reg_or_offset[reg] = -offset;
      break;

    default:
      abort ();
    }
  return p;
}

/* Called from __throw to find the registers to restore for a given
   PC_TARGET.  The caller should allocate a local variable of `struct
   frame_state' (declared in frame.h) and pass its address to STATE_IN.  */

struct frame_state *
__frame_state_for (void *pc_target, struct frame_state *state_in)
{
  fde *f;
  void *insn, *end, *pc;
  struct cie_info info;
  struct frame_state_internal state;

  f = find_fde (pc_target);
  if (f == 0)
    return 0;

  insn = extract_cie_info (f, &info);
  if (insn == 0)
    return 0;

  memset (&state, 0, sizeof (state));
  state.s.retaddr_column = info.ra_regno;
  state.s.eh_ptr = info.eh_ptr;

  /* First decode all the insns in the CIE.  */
  end = next_fde ((fde*) get_cie (f));
  while (insn < end)
    insn = execute_cfa_insn (insn, &state, &info, 0);

  insn = ((fde *)f) + 1;

  if (info.augmentation[0] == 'z')
    {
      int i;
      insn = decode_uleb128 (insn, &i);
      insn += i;
    }

  /* Then the insns in the FDE up to our target PC.  */
  end = next_fde (f);
  pc = f->pc_begin;
  while (insn < end && pc <= pc_target)
    insn = execute_cfa_insn (insn, &state, &info, &pc);

  memcpy (state_in, &state.s, sizeof (state.s));
  return state_in;
}
#endif /* DWARF2_UNWIND_INFO */