dwarf_getcfi_elf.c

/* Get CFI from ELF file's exception-handling info.
   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 <stdlib.h>
#include <string.h>
#include <assert.h>

#include "libdwP.h"
#include "cfi.h"
#include "encoded-value.h"
#include <dwarf.h>


static Dwarf_CFI *
allocate_cfi (Elf *elf, GElf_Addr vaddr)
{
  Dwarf_CFI *cfi = calloc (1, sizeof *cfi);
  if (cfi == NULL)
    {
      __libdw_seterrno (DWARF_E_NOMEM);
      return NULL;
    }

  cfi->e_ident = (unsigned char *) elf_getident (elf, NULL);
  if (cfi->e_ident == NULL)
    {
      free (cfi);
      __libdw_seterrno (DWARF_E_GETEHDR_ERROR);
      return NULL;
    }

  if ((BYTE_ORDER == LITTLE_ENDIAN && cfi->e_ident[EI_DATA] == ELFDATA2MSB)
      || (BYTE_ORDER == BIG_ENDIAN && cfi->e_ident[EI_DATA] == ELFDATA2LSB))
    cfi->other_byte_order = true;

  cfi->frame_vaddr = vaddr;
  cfi->textrel = 0;		/* XXX ? */
  cfi->datarel = 0;		/* XXX ? */

  return cfi;
}

static const uint8_t *
parse_eh_frame_hdr (const uint8_t *hdr, size_t hdr_size, GElf_Addr hdr_vaddr,
		    const GElf_Ehdr *ehdr, GElf_Addr *eh_frame_vaddr,
		    size_t *table_entries, uint8_t *table_encoding)
{
  const uint8_t *h = hdr;

  if (hdr_size < 4 || *h++ != 1)		/* version */
    return (void *) -1l;

  uint8_t eh_frame_ptr_encoding = *h++;
  uint8_t fde_count_encoding = *h++;
  uint8_t fde_table_encoding = *h++;

  if (eh_frame_ptr_encoding == DW_EH_PE_omit)
    return (void *) -1l;

  /* Dummy used by read_encoded_value.  */
  Elf_Data_Scn dummy_cfi_hdr_data =
    {
      .d = { .d_buf = (void *) hdr, .d_size = hdr_size }
    };
  Dwarf_CFI dummy_cfi =
    {
      .e_ident = ehdr->e_ident,
      .datarel = hdr_vaddr,
      .frame_vaddr = hdr_vaddr,
      .data = &dummy_cfi_hdr_data,
    };

  if (unlikely (read_encoded_value (&dummy_cfi, eh_frame_ptr_encoding, &h,
				    eh_frame_vaddr)))
    return (void *) -1l;

  if (fde_count_encoding != DW_EH_PE_omit)
    {
      Dwarf_Word fde_count;
      if (unlikely (read_encoded_value (&dummy_cfi, fde_count_encoding, &h,
					&fde_count)))
	return (void *) -1l;
      if (fde_count != 0 && (size_t) fde_count == fde_count
	  && fde_table_encoding != DW_EH_PE_omit
	  && (fde_table_encoding &~ DW_EH_PE_signed) != DW_EH_PE_uleb128)
	{
	  *table_entries = fde_count;
	  *table_encoding = fde_table_encoding;
	  return h;
	}
    }

  return NULL;
}

static Dwarf_CFI *
getcfi_gnu_eh_frame (Elf *elf, const GElf_Ehdr *ehdr, const GElf_Phdr *phdr)
{
  Elf_Data *data = elf_getdata_rawchunk (elf, phdr->p_offset, phdr->p_filesz,
					 ELF_T_BYTE);
  if (data == NULL || data->d_buf == NULL)
    {
    invalid_hdr:
      /* XXX might be read error or corrupt phdr */
      __libdw_seterrno (DWARF_E_INVALID_CFI);
      return NULL;
    }

  size_t vsize, dmax;
  Dwarf_Addr eh_frame_ptr;
  size_t search_table_entries = 0;
  uint8_t search_table_encoding = 0;
  const uint8_t *search_table = parse_eh_frame_hdr (data->d_buf, phdr->p_filesz,
						    phdr->p_vaddr, ehdr,
						    &eh_frame_ptr,
						    &search_table_entries,
						    &search_table_encoding);

  /* Make sure there is enough room for the entries in the table,
     each entry consists of 2 encoded values.  */
  vsize = encoded_value_size (data, ehdr->e_ident, search_table_encoding,
			      NULL);
  dmax = phdr->p_filesz - (search_table - (const uint8_t *) data->d_buf);
  if (unlikely (search_table == (void *) -1l
		|| vsize == 0
		|| search_table_entries > (dmax / vsize) / 2))
    goto invalid_hdr;

  Dwarf_Off eh_frame_offset = eh_frame_ptr - phdr->p_vaddr + phdr->p_offset;
  Dwarf_Word eh_frame_size = 0;

  /* XXX we have no way without section headers to know the size
     of the .eh_frame data.  Calculate the largest it might possibly be.
     This won't be wasteful if the file is already mmap'd, but if it isn't
     it might be quite excessive.  */
  size_t filesize;
  if (elf_rawfile (elf, &filesize) != NULL)
    eh_frame_size = filesize - eh_frame_offset;

  data = elf_getdata_rawchunk (elf, eh_frame_offset, eh_frame_size, ELF_T_BYTE);
  if (data == NULL)
    {
      __libdw_seterrno (DWARF_E_INVALID_ELF); /* XXX might be read error */
      return NULL;
    }
  Dwarf_CFI *cfi = allocate_cfi (elf, eh_frame_ptr);
  if (cfi != NULL)
    {
      cfi->data = (Elf_Data_Scn *) data;

      if (search_table != NULL)
	{
	  cfi->search_table = search_table;
	  cfi->search_table_len = phdr->p_filesz;
	  cfi->search_table_vaddr = phdr->p_vaddr;
	  cfi->search_table_encoding = search_table_encoding;
	  cfi->search_table_entries = search_table_entries;
	}
    }
  return cfi;
}

/* Search the phdrs for PT_GNU_EH_FRAME.  */
static Dwarf_CFI *
getcfi_phdr (Elf *elf, const GElf_Ehdr *ehdr)
{
  size_t phnum;
  if (unlikely (elf_getphdrnum (elf, &phnum) != 0))
    return NULL;

  for (size_t i = 0; i < phnum; ++i)
    {
      GElf_Phdr phdr_mem;
      GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
      if (unlikely (phdr == NULL))
	return NULL;
      if (phdr->p_type == PT_GNU_EH_FRAME)
	return getcfi_gnu_eh_frame (elf, ehdr, phdr);
    }

  __libdw_seterrno (DWARF_E_NO_DWARF);
  return NULL;
}

static Dwarf_CFI *
getcfi_scn_eh_frame (Elf *elf, const GElf_Ehdr *ehdr,
		     Elf_Scn *scn, GElf_Shdr *shdr,
		     Elf_Scn *hdr_scn, GElf_Addr hdr_vaddr)
{
  Elf_Data *data = elf_rawdata (scn, NULL);
  if (data == NULL || data->d_buf == NULL)
    {
      __libdw_seterrno (DWARF_E_INVALID_ELF);
      return NULL;
    }
  Dwarf_CFI *cfi = allocate_cfi (elf, shdr->sh_addr);
  if (cfi != NULL)
    {
      cfi->data = (Elf_Data_Scn *) data;
      if (hdr_scn != NULL)
	{
	  Elf_Data *hdr_data = elf_rawdata (hdr_scn, NULL);
	  if (hdr_data != NULL && hdr_data->d_buf != NULL)
	    {
	      size_t vsize, dmax;
	      GElf_Addr eh_frame_vaddr;
	      cfi->search_table_vaddr = hdr_vaddr;
	      cfi->search_table
		= parse_eh_frame_hdr (hdr_data->d_buf, hdr_data->d_size,
				      hdr_vaddr, ehdr, &eh_frame_vaddr,
				      &cfi->search_table_entries,
				      &cfi->search_table_encoding);
	      cfi->search_table_len = hdr_data->d_size;

	      /* Make sure there is enough room for the entries in the table,
		 each entry consists of 2 encoded values.  */
	      vsize = encoded_value_size (hdr_data, ehdr->e_ident,
					  cfi->search_table_encoding, NULL);
	      dmax = hdr_data->d_size - (cfi->search_table
					 - (const uint8_t *) hdr_data->d_buf);
	      if (unlikely (cfi->search_table == (void *) -1l
			    || vsize == 0
			    || cfi->search_table_entries > (dmax / vsize) / 2))
		{
		  free (cfi);
		  /* XXX might be read error or corrupt phdr */
		  __libdw_seterrno (DWARF_E_INVALID_CFI);
		  return NULL;
		}

	      /* Sanity check.  */
	      if (unlikely (eh_frame_vaddr != shdr->sh_addr))
		cfi->search_table = NULL;
	    }
	}
    }
  return cfi;
}

/* Search for the sections named ".eh_frame" and ".eh_frame_hdr".  */
static Dwarf_CFI *
getcfi_shdr (Elf *elf, const GElf_Ehdr *ehdr)
{
  size_t shstrndx;
  if (elf_getshdrstrndx (elf, &shstrndx) != 0)
    {
      __libdw_seterrno (DWARF_E_GETEHDR_ERROR);
      return NULL;
    }

  if (shstrndx != 0)
    {
      Elf_Scn *hdr_scn = NULL;
      GElf_Addr hdr_vaddr = 0;
      Elf_Scn *scn = NULL;
      while ((scn = elf_nextscn (elf, scn)) != NULL)
	{
	  GElf_Shdr shdr_mem;
	  GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
	  if (shdr == NULL)
	    continue;
	  const char *name = elf_strptr (elf, shstrndx, shdr->sh_name);
	  if (name == NULL)
	    continue;
	  if (!strcmp (name, ".eh_frame_hdr"))
	    {
	      hdr_scn = scn;
	      hdr_vaddr = shdr->sh_addr;
	    }
	  else if (!strcmp (name, ".eh_frame"))
	    {
	      if (shdr->sh_type != SHT_NOBITS)
		return getcfi_scn_eh_frame (elf, ehdr, scn, shdr,
					    hdr_scn, hdr_vaddr);
	      else
		return NULL;
	    }
	}
    }

  return (void *) -1l;
}

Dwarf_CFI *
dwarf_getcfi_elf (Elf *elf)
{
  if (elf_kind (elf) != ELF_K_ELF)
    {
      __libdw_seterrno (DWARF_E_NOELF);
      return NULL;
    }

  GElf_Ehdr ehdr_mem;
  GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_mem);
  if (unlikely (ehdr == NULL))
    {
      __libdw_seterrno (DWARF_E_INVALID_ELF);
      return NULL;
    }

  Dwarf_CFI *result = getcfi_shdr (elf, ehdr);
  if (result == (void *) -1l)
    result = getcfi_phdr (elf, ehdr);

  return result;
}
INTDEF (dwarf_getcfi_elf)