1/* libunwind - a platform-independent unwind library
2   Copyright (C) 2002-2004 Hewlett-Packard Co
3	Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
4
5This file is part of libunwind.
6
7Permission is hereby granted, free of charge, to any person obtaining
8a copy of this software and associated documentation files (the
9"Software"), to deal in the Software without restriction, including
10without limitation the rights to use, copy, modify, merge, publish,
11distribute, sublicense, and/or sell copies of the Software, and to
12permit persons to whom the Software is furnished to do so, subject to
13the following conditions:
14
15The above copyright notice and this permission notice shall be
16included in all copies or substantial portions of the Software.
17
18THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
19EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
20MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
21NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
22LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
23OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
24WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
25
26#include "unwind_i.h"
27#include "offsets.h"
28
29PROTECTED int
30unw_step (unw_cursor_t *cursor)
31{
32  struct cursor *c = (struct cursor *) cursor;
33  int ret, i;
34
35  Debug (1, "(cursor=%p, ip=0x%08x)\n", c, (unsigned) c->dwarf.ip);
36
37  /* ANDROID support update. */
38  /* Save the current ip/cfa to prevent looping if the decode yields
39     the same ip/cfa as before. */
40  unw_word_t old_ip = c->dwarf.ip;
41  unw_word_t old_cfa = c->dwarf.cfa;
42  /* End of ANDROID update. */
43
44  /* Try DWARF-based unwinding... */
45  ret = dwarf_step (&c->dwarf);
46
47#if !defined(UNW_LOCAL_ONLY)
48  /* Do not use this method on a local unwind. There is a very high
49   * probability this method will try to access unmapped memory, which
50   * will crash the process. Since this almost never actually works,
51   * it should be okay to skip.
52   */
53  if (ret < 0)
54    {
55      /* DWARF failed, let's see if we can follow the frame-chain
56	 or skip over the signal trampoline.  */
57      struct dwarf_loc ebp_loc, eip_loc;
58
59      /* We could get here because of missing/bad unwind information.
60         Validate all addresses before dereferencing. */
61      c->validate = 1;
62
63      Debug (13, "dwarf_step() failed (ret=%d), trying frame-chain\n", ret);
64
65      if (unw_is_signal_frame (cursor))
66        {
67          ret = unw_handle_signal_frame(cursor);
68	  if (ret < 0)
69	    {
70	      Debug (2, "returning 0\n");
71	      return 0;
72	    }
73        }
74      else
75	{
76	  ret = dwarf_get (&c->dwarf, c->dwarf.loc[EBP], &c->dwarf.cfa);
77	  if (ret < 0)
78	    {
79	      Debug (2, "returning %d\n", ret);
80	      return ret;
81	    }
82
83	  Debug (13, "[EBP=0x%x] = 0x%x\n", DWARF_GET_LOC (c->dwarf.loc[EBP]),
84		 c->dwarf.cfa);
85
86	  ebp_loc = DWARF_LOC (c->dwarf.cfa, 0);
87	  eip_loc = DWARF_LOC (c->dwarf.cfa + 4, 0);
88	  c->dwarf.cfa += 8;
89
90	  /* Mark all registers unsaved, since we don't know where
91	     they are saved (if at all), except for the EBP and
92	     EIP.  */
93	  for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
94	    c->dwarf.loc[i] = DWARF_NULL_LOC;
95
96          c->dwarf.loc[EBP] = ebp_loc;
97          c->dwarf.loc[EIP] = eip_loc;
98	}
99      c->dwarf.ret_addr_column = EIP;
100
101      if (!DWARF_IS_NULL_LOC (c->dwarf.loc[EBP]))
102	{
103	  ret = dwarf_get (&c->dwarf, c->dwarf.loc[EIP], &c->dwarf.ip);
104	  if (ret < 0)
105	    {
106	      Debug (13, "dwarf_get([EIP=0x%x]) failed\n", DWARF_GET_LOC (c->dwarf.loc[EIP]));
107	      Debug (2, "returning %d\n", ret);
108	      return ret;
109	    }
110	  else
111	    {
112	      Debug (13, "[EIP=0x%x] = 0x%x\n", DWARF_GET_LOC (c->dwarf.loc[EIP]),
113		c->dwarf.ip);
114	    }
115	}
116      else
117	c->dwarf.ip = 0;
118
119      /* Adjust the return value because the functions above return zero for success. */
120      if (ret == 0)
121        ret = 1;
122    }
123#endif
124
125  /* ANDROID support update. */
126  if (ret >= 0)
127    {
128      if (c->dwarf.ip)
129        {
130          /* Adjust the pc to the instruction before. */
131          c->dwarf.ip--;
132        }
133      /* If the decode yields the exact same ip/cfa as before, then indicate
134         the unwind is complete. */
135      if (old_ip == c->dwarf.ip && old_cfa == c->dwarf.cfa)
136        {
137          Dprintf ("%s: ip and cfa unchanged; stopping here (ip=0x%lx)\n",
138                   __FUNCTION__, (long) c->dwarf.ip);
139          return -UNW_EBADFRAME;
140        }
141      c->dwarf.frame++;
142    }
143  /* End of ANDROID update. */
144  if (unlikely (ret <= 0))
145    return 0;
146
147  return (c->dwarf.ip == 0) ? 0 : 1;
148}
149