1/* Advance to next CFI entry.
2   Copyright (C) 2009-2010 Red Hat, Inc.
3   This file is part of Red Hat elfutils.
4
5   Red Hat elfutils is free software; you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by the
7   Free Software Foundation; version 2 of the License.
8
9   Red Hat elfutils is distributed in the hope that it will be useful, but
10   WITHOUT ANY WARRANTY; without even the implied warranty of
11   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12   General Public License for more details.
13
14   You should have received a copy of the GNU General Public License along
15   with Red Hat elfutils; if not, write to the Free Software Foundation,
16   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.
17
18   In addition, as a special exception, Red Hat, Inc. gives You the
19   additional right to link the code of Red Hat elfutils with code licensed
20   under any Open Source Initiative certified open source license
21   (http://www.opensource.org/licenses/index.php) which requires the
22   distribution of source code with any binary distribution and to
23   distribute linked combinations of the two.  Non-GPL Code permitted under
24   this exception must only link to the code of Red Hat elfutils through
25   those well defined interfaces identified in the file named EXCEPTION
26   found in the source code files (the "Approved Interfaces").  The files
27   of Non-GPL Code may instantiate templates or use macros or inline
28   functions from the Approved Interfaces without causing the resulting
29   work to be covered by the GNU General Public License.  Only Red Hat,
30   Inc. may make changes or additions to the list of Approved Interfaces.
31   Red Hat's grant of this exception is conditioned upon your not adding
32   any new exceptions.  If you wish to add a new Approved Interface or
33   exception, please contact Red Hat.  You must obey the GNU General Public
34   License in all respects for all of the Red Hat elfutils code and other
35   code used in conjunction with Red Hat elfutils except the Non-GPL Code
36   covered by this exception.  If you modify this file, you may extend this
37   exception to your version of the file, but you are not obligated to do
38   so.  If you do not wish to provide this exception without modification,
39   you must delete this exception statement from your version and license
40   this file solely under the GPL without exception.
41
42   Red Hat elfutils is an included package of the Open Invention Network.
43   An included package of the Open Invention Network is a package for which
44   Open Invention Network licensees cross-license their patents.  No patent
45   license is granted, either expressly or impliedly, by designation as an
46   included package.  Should you wish to participate in the Open Invention
47   Network licensing program, please visit www.openinventionnetwork.com
48   <http://www.openinventionnetwork.com>.  */
49
50#ifdef HAVE_CONFIG_H
51# include <config.h>
52#endif
53
54#include "cfi.h"
55#include "encoded-value.h"
56
57#include <string.h>
58
59
60int
61dwarf_next_cfi (e_ident, data, eh_frame_p, off, next_off, entry)
62     const unsigned char e_ident[];
63     Elf_Data *data;
64     bool eh_frame_p;
65     Dwarf_Off off;
66     Dwarf_Off *next_off;
67     Dwarf_CFI_Entry *entry;
68{
69  /* Dummy struct for memory-access.h macros.  */
70  BYTE_ORDER_DUMMY (dw, e_ident);
71
72  /* If we reached the end before don't do anything.  */
73  if (off == (Dwarf_Off) -1l
74      /* Make sure there is enough space in the .debug_frame section
75	 for at least the initial word.  We cannot test the rest since
76	 we don't know yet whether this is a 64-bit object or not.  */
77      || unlikely (off + 4 >= data->d_size))
78    {
79      *next_off = (Dwarf_Off) -1l;
80      return 1;
81    }
82
83  /* This points into the .debug_frame section at the start of the entry.  */
84  const uint8_t *bytes = data->d_buf + off;
85  const uint8_t *limit = data->d_buf + data->d_size;
86
87  /* The format of a CFI entry is described in DWARF3 6.4.1:
88   */
89
90  uint64_t length = read_4ubyte_unaligned_inc (&dw, bytes);
91  size_t offset_size = 4;
92  if (length == DWARF3_LENGTH_64_BIT)
93    {
94      /* This is the 64-bit DWARF format.  */
95      offset_size = 8;
96      if (unlikely (limit - bytes < 8))
97	{
98	invalid:
99	  __libdw_seterrno (DWARF_E_INVALID_DWARF);
100	  return -1;
101	}
102      length = read_8ubyte_unaligned_inc (&dw, bytes);
103    }
104  if (unlikely ((uint64_t) (limit - bytes) < length)
105      || unlikely (length < offset_size + 1))
106    goto invalid;
107
108  /* Now we know how large the entry is.  Note the trick in the
109     computation.  If the offset_size is 4 the '- 4' term undoes the
110     '2 *'.  If offset_size is 8 this term computes the size of the
111     escape value plus the 8 byte offset.  */
112  *next_off = off + (2 * offset_size - 4) + length;
113
114  limit = bytes + length;
115
116  const uint8_t *const cie_pointer_start = bytes;
117  if (offset_size == 8)
118    entry->cie.CIE_id = read_8ubyte_unaligned_inc (&dw, bytes);
119  else
120    {
121      entry->cie.CIE_id = read_4ubyte_unaligned_inc (&dw, bytes);
122      /* Canonicalize the 32-bit CIE_ID value to 64 bits.  */
123      if (!eh_frame_p && entry->cie.CIE_id == DW_CIE_ID_32)
124	entry->cie.CIE_id = DW_CIE_ID_64;
125    }
126  if (eh_frame_p)
127    {
128      /* Canonicalize the .eh_frame CIE pointer to .debug_frame format.  */
129      if (entry->cie.CIE_id == 0)
130	entry->cie.CIE_id = DW_CIE_ID_64;
131      else
132	{
133	  /* In .eh_frame format, a CIE pointer is the distance from where
134	     it appears back to the beginning of the CIE.  */
135	  ptrdiff_t pos = cie_pointer_start - (const uint8_t *) data->d_buf;
136	  if (unlikely (entry->cie.CIE_id > (Dwarf_Off) pos)
137	      || unlikely (pos <= (ptrdiff_t) offset_size))
138	    goto invalid;
139	  entry->cie.CIE_id = pos - entry->cie.CIE_id;
140	}
141    }
142
143  if (entry->cie.CIE_id == DW_CIE_ID_64)
144    {
145      /* Read the version stamp.  Always an 8-bit value.  */
146      uint8_t version = *bytes++;
147
148      if (version != 1 && (unlikely (version < 3) || unlikely (version > 4)))
149	goto invalid;
150
151      entry->cie.augmentation = (const char *) bytes;
152
153      bytes = memchr (bytes, '\0', limit - bytes);
154      if (unlikely (bytes == NULL))
155	goto invalid;
156      ++bytes;
157
158      /* The address size for CFI is implicit in the ELF class.  */
159      uint_fast8_t address_size = e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8;
160      uint_fast8_t segment_size = 0;
161      if (version >= 4)
162	{
163	  if (unlikely (limit - bytes < 5))
164	    goto invalid;
165	  /* XXX We don't actually support address_size not matching the class.
166	     To do so, we'd have to return it here so that intern_new_cie
167	     could use it choose a specific fde_encoding.  */
168	  if (unlikely (*bytes != address_size))
169	    {
170	      __libdw_seterrno (DWARF_E_VERSION);
171	      return -1;
172	    }
173	  address_size = *bytes++;
174	  segment_size = *bytes++;
175	  /* We don't actually support segment selectors.  We'd have to
176	     roll this into the fde_encoding bits or something.  */
177	  if (unlikely (segment_size != 0))
178	    {
179	      __libdw_seterrno (DWARF_E_VERSION);
180	      return -1;
181	    }
182	}
183
184      const char *ap = entry->cie.augmentation;
185
186      /* g++ v2 "eh" has pointer immediately following augmentation string,
187	 so it must be handled first.  */
188      if (unlikely (ap[0] == 'e' && ap[1] == 'h'))
189	{
190	  ap += 2;
191	  bytes += address_size;
192	}
193
194      get_uleb128 (entry->cie.code_alignment_factor, bytes);
195      get_sleb128 (entry->cie.data_alignment_factor, bytes);
196
197      if (version >= 3)		/* DWARF 3+ */
198	get_uleb128 (entry->cie.return_address_register, bytes);
199      else			/* DWARF 2 */
200	entry->cie.return_address_register = *bytes++;
201
202      /* If we have sized augmentation data,
203	 we don't need to grok it all.  */
204      entry->cie.fde_augmentation_data_size = 0;
205      bool sized_augmentation = *ap == 'z';
206      if (sized_augmentation)
207	{
208	  get_uleb128 (entry->cie.augmentation_data_size, bytes);
209	  if ((Dwarf_Word) (limit - bytes) < entry->cie.augmentation_data_size)
210	    goto invalid;
211	  entry->cie.augmentation_data = bytes;
212	  bytes += entry->cie.augmentation_data_size;
213	}
214      else
215	{
216	  entry->cie.augmentation_data = bytes;
217
218	  for (; *ap != '\0'; ++ap)
219	    {
220	      uint8_t encoding;
221	      switch (*ap)
222		{
223		case 'L':		/* Skip LSDA pointer encoding byte.  */
224		case 'R':		/* Skip FDE address encoding byte.  */
225		  encoding = *bytes++;
226		  entry->cie.fde_augmentation_data_size
227		    += encoded_value_size (data, e_ident, encoding, NULL);
228		  continue;
229		case 'P':   /* Skip encoded personality routine pointer. */
230		  encoding = *bytes++;
231		  bytes += encoded_value_size (data, e_ident, encoding, bytes);
232		  continue;
233		case 'S':		/* Skip signal-frame flag.  */
234		  continue;
235		default:
236		  /* Unknown augmentation string.  initial_instructions might
237		     actually start with some augmentation data.  */
238		  break;
239		}
240	      break;
241	    }
242	  entry->cie.augmentation_data_size
243	    = bytes - entry->cie.augmentation_data;
244	}
245
246      entry->cie.initial_instructions = bytes;
247      entry->cie.initial_instructions_end = limit;
248    }
249  else
250    {
251      entry->fde.start = bytes;
252      entry->fde.end = limit;
253    }
254
255  return 0;
256}
257INTDEF (dwarf_next_cfi)
258