xref: /third_party/elfutils/libdw/fde.c

/* FDE reading.
   Copyright (C) 2009-2010, 2014, 2015 Red Hat, Inc.
   This file is part of elfutils.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * 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

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include "cfi.h"
#include <search.h>
#include <stdlib.h>

#include "encoded-value.h"

static int
compare_fde (const void *a, const void *b)
{
  const struct dwarf_fde *fde1 = a;
  const struct dwarf_fde *fde2 = b;

  /* Find out which of the two arguments is the search value.
     It has end offset 0.  */
  if (fde1->end == 0)
    {
      if (fde1->start < fde2->start)
	return -1;
      if (fde1->start >= fde2->end)
	return 1;
    }
  else
    {
      if (fde2->start < fde1->start)
	return 1;
      if (fde2->start >= fde1->end)
	return -1;
    }

  return 0;
}

static struct dwarf_fde *
intern_fde (Dwarf_CFI *cache, const Dwarf_FDE *entry)
{
  /* Look up the new entry's CIE.  */
  struct dwarf_cie *cie = __libdw_find_cie (cache, entry->CIE_pointer);
  if (cie == NULL)
    return (void *) -1l;

  struct dwarf_fde *fde = malloc (sizeof (struct dwarf_fde));
  if (fde == NULL)
    {
      __libdw_seterrno (DWARF_E_NOMEM);
      return NULL;
    }

  fde->instructions = entry->start;
  fde->instructions_end = entry->end;
  if (unlikely (read_encoded_value (cache, cie->fde_encoding,
				    &fde->instructions, &fde->start))
      || unlikely (read_encoded_value (cache, cie->fde_encoding & 0x0f,
				       &fde->instructions, &fde->end)))
    {
      free (fde);
      __libdw_seterrno (DWARF_E_INVALID_DWARF);
      return NULL;
    }
  fde->end += fde->start;

  /* Make sure the fde actually covers a real code range.  */
  if (fde->start >= fde->end)
    {
      free (fde);
      return (void *) -1;
    }

  fde->cie = cie;

  if (cie->sized_augmentation_data)
    {
      /* The CIE augmentation says the FDE has a DW_FORM_block
	 before its actual instruction stream.  */
      Dwarf_Word len;
      get_uleb128 (len, fde->instructions, fde->instructions_end);
      if ((Dwarf_Word) (fde->instructions_end - fde->instructions) < len)
	{
	  free (fde);
	  __libdw_seterrno (DWARF_E_INVALID_DWARF);
	  return NULL;
	}
      fde->instructions += len;
    }
  else
    /* We had to understand all of the CIE augmentation string.
       We've recorded the number of data bytes in FDEs.  */
    fde->instructions += cie->fde_augmentation_data_size;

  /* Add the new entry to the search tree.  */
  struct dwarf_fde **tres = tsearch (fde, &cache->fde_tree, &compare_fde);
  if (tres == NULL)
    {
      free (fde);
      __libdw_seterrno (DWARF_E_NOMEM);
      return NULL;
    }
  else if (*tres != fde)
    {
      /* There is already an FDE in the cache that covers the same
	 address range.  That is odd.  Ignore this FDE.  And just use
	 the one in the cache for consistency.  */
      free (fde);
      return *tres;
    }

  return fde;
}

struct dwarf_fde *
internal_function
__libdw_fde_by_offset (Dwarf_CFI *cache, Dwarf_Off offset)
{
  Dwarf_CFI_Entry entry;
  Dwarf_Off next_offset;
  int result = INTUSE(dwarf_next_cfi) (cache->e_ident,
				       &cache->data->d, CFI_IS_EH (cache),
				       offset, &next_offset, &entry);
  if (result != 0)
    {
      if (result > 0)
      invalid:
	__libdw_seterrno (DWARF_E_INVALID_DWARF);
      return NULL;
    }

  if (unlikely (dwarf_cfi_cie_p (&entry)))
    goto invalid;

  /* We have a new FDE to consider.  */
  struct dwarf_fde *fde = intern_fde (cache, &entry.fde);
  if (fde == (void *) -1l || fde == NULL)
    return NULL;

  /* If this happened to be what we would have read next, notice it.  */
  if (cache->next_offset == offset)
    cache->next_offset = next_offset;

  return fde;
}

/* Use a binary search table in .eh_frame_hdr format, yield an FDE offset.  */
static Dwarf_Off
binary_search_fde (Dwarf_CFI *cache, Dwarf_Addr address)
{
  const size_t size = 2 * encoded_value_size (&cache->data->d, cache->e_ident,
					      cache->search_table_encoding,
					      NULL);
  if (unlikely (size == 0))
    return (Dwarf_Off) -1l;

  /* Dummy used by read_encoded_value.  */
  Elf_Data_Scn dummy_cfi_hdr_data =
    {
      .d = { .d_buf = (void *) cache->search_table,
	     .d_size = cache->search_table_len }
    };

  Dwarf_CFI dummy_cfi =
    {
      .e_ident = cache->e_ident,
      .datarel = cache->search_table_vaddr,
      .frame_vaddr = cache->search_table_vaddr,
      .data = &dummy_cfi_hdr_data
    };

  size_t l = 0, u = cache->search_table_entries;
  while (l < u)
    {
      size_t idx = (l + u) / 2;

      /* Max idx * size is checked against search_table len when
	 loading eh_frame_hdr.  */
      const uint8_t *p = &cache->search_table[idx * size];
      Dwarf_Addr start;
      if (unlikely (read_encoded_value (&dummy_cfi,
					cache->search_table_encoding, &p,
					&start)))
	break;
      if (address < start)
	u = idx;
      else
	{
	  l = idx + 1;

	  Dwarf_Addr fde;
	  if (unlikely (read_encoded_value (&dummy_cfi,
					    cache->search_table_encoding, &p,
					    &fde)))
	    break;

	  /* If this is the last entry, its upper bound is assumed to be
	     the end of the module.
	     XXX really should be end of containing PT_LOAD segment */
	  if (l < cache->search_table_entries)
	    {
	      /* Look at the start address in the following entry.  */
	      Dwarf_Addr end;
	      if (unlikely (read_encoded_value
			    (&dummy_cfi, cache->search_table_encoding, &p,
			     &end)))
		break;
	      if (address >= end)
		continue;
	    }

	  return fde - cache->frame_vaddr;
	}
    }

  return (Dwarf_Off) -1l;
}

struct dwarf_fde *
internal_function
__libdw_find_fde (Dwarf_CFI *cache, Dwarf_Addr address)
{
  /* Look for a cached FDE covering this address.  */

  const struct dwarf_fde fde_key = { .start = address, .end = 0 };
  struct dwarf_fde **found = tfind (&fde_key, &cache->fde_tree, &compare_fde);
  if (found != NULL)
    return *found;

  /* Use .eh_frame_hdr binary search table if possible.  */
  if (cache->search_table != NULL)
    {
      Dwarf_Off offset = binary_search_fde (cache, address);
      if (offset == (Dwarf_Off) -1l)
	goto no_match;
      struct dwarf_fde *fde = __libdw_fde_by_offset (cache, offset);
      if (likely (fde != NULL))
	{
	  /* Sanity check the address range.  */
	  if (unlikely (address < fde->start))
	    {
	      __libdw_seterrno (DWARF_E_INVALID_DWARF);
	      return NULL;
	    }
	  /* .eh_frame_hdr does not indicate length covered by FDE.  */
	  if (unlikely (address >= fde->end))
	    goto no_match;
	}
      return fde;
    }

  /* It's not there.  Read more CFI entries until we find it.  */
  while (1)
    {
      Dwarf_Off last_offset = cache->next_offset;
      Dwarf_CFI_Entry entry;
      int result = INTUSE(dwarf_next_cfi) (cache->e_ident,
					   &cache->data->d, CFI_IS_EH (cache),
					   last_offset, &cache->next_offset,
					   &entry);
      if (result > 0)
	break;
      if (result < 0)
	{
	  if (cache->next_offset == last_offset)
	    /* We couldn't progress past the bogus FDE.  */
	    break;
	  /* Skip the loser and look at the next entry.  */
	  continue;
	}

      if (dwarf_cfi_cie_p (&entry))
	{
	  /* This is a CIE, not an FDE.  We eagerly intern these
	     because the next FDE will usually refer to this CIE.  */
	  __libdw_intern_cie (cache, last_offset, &entry.cie);
	  continue;
	}

      /* We have a new FDE to consider.  */
      struct dwarf_fde *fde = intern_fde (cache, &entry.fde);

      if (fde == (void *) -1l)	/* Bad FDE, but we can keep looking.  */
	continue;

      if (fde == NULL)		/* Bad data.  */
	return NULL;

      /* Is this the one we're looking for?  */
      if (fde->start <= address && fde->end > address)
	return fde;
    }

 no_match:
  /* We found no FDE covering this address.  */
  __libdw_seterrno (DWARF_E_NO_MATCH);
  return NULL;
}