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
5 Modified for x86_64 by Max Asbock <masbock@us.ibm.com>
6
7 This file is part of libunwind.
8
9 Permission is hereby granted, free of charge, to any person obtaining
10 a copy of this software and associated documentation files (the
11 "Software"), to deal in the Software without restriction, including
12 without limitation the rights to use, copy, modify, merge, publish,
13 distribute, sublicense, and/or sell copies of the Software, and to
14 permit persons to whom the Software is furnished to do so, subject to
15 the following conditions:
16
17 The above copyright notice and this permission notice shall be
18 included in all copies or substantial portions of the Software.
19
20 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
21 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
22 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
23 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
24 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
25 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
26 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
27
28 #include "unwind_i.h"
29 #include "dwarf_i.h"
30 #include <signal.h>
31
32 /* Recognise PLT entries such as:
33 3bdf0: ff 25 e2 49 13 00 jmpq *0x1349e2(%rip)
34 3bdf6: 68 ae 03 00 00 pushq $0x3ae
35 3bdfb: e9 00 c5 ff ff jmpq 38300 <_init+0x18> */
36 static int
is_plt_entry(struct dwarf_cursor * c)37 is_plt_entry (struct dwarf_cursor *c)
38 {
39 unw_word_t w0, w1;
40 unw_accessors_t *a;
41 int ret;
42
43 a = unw_get_accessors (c->as);
44 if ((ret = (*a->access_mem) (c->as, c->ip, &w0, 0, c->as_arg)) < 0
45 || (ret = (*a->access_mem) (c->as, c->ip + 8, &w1, 0, c->as_arg)) < 0)
46 return 0;
47
48 ret = (((w0 & 0xffff) == 0x25ff)
49 && (((w0 >> 48) & 0xff) == 0x68)
50 && (((w1 >> 24) & 0xff) == 0xe9));
51
52 Debug (14, "ip=0x%lx => 0x%lx 0x%lx, ret = %d\n", c->ip, w0, w1, ret);
53 return ret;
54 }
55
56 PROTECTED int
unw_step(unw_cursor_t * cursor)57 unw_step (unw_cursor_t *cursor)
58 {
59 struct cursor *c = (struct cursor *) cursor;
60 int ret, i;
61
62 #if CONSERVATIVE_CHECKS
63 int val = c->validate;
64 c->validate = 1;
65 #endif
66
67 Debug (1, "(cursor=%p, ip=0x%lx, cfa=0x%lx)\n",
68 c, c->dwarf.ip, c->dwarf.cfa);
69
70 /* Try DWARF-based unwinding... */
71 c->sigcontext_format = X86_64_SCF_NONE;
72 ret = dwarf_step (&c->dwarf);
73
74 #if CONSERVATIVE_CHECKS
75 c->validate = val;
76 #endif
77
78 if (ret < 0 && ret != -UNW_ENOINFO)
79 {
80 Debug (2, "returning %d\n", ret);
81 return ret;
82 }
83
84 if (likely (ret >= 0))
85 {
86 /* x86_64 ABI specifies that end of call-chain is marked with a
87 NULL RBP or undefined return address */
88 if (DWARF_IS_NULL_LOC (c->dwarf.loc[RBP])
89 || DWARF_IS_NULL_LOC(c->dwarf.loc[c->dwarf.ret_addr_column]))
90 {
91 c->dwarf.ip = 0;
92 ret = 0;
93 }
94 }
95 else // ret == -UNW_ENOINFO
96 {
97 /* DWARF failed. There isn't much of a usable frame-chain on x86-64,
98 but we do need to handle two special-cases:
99
100 (i) signal trampoline: Old kernels and older libcs don't
101 export the vDSO needed to get proper unwind info for the
102 trampoline. Recognize that case by looking at the code
103 and filling in things by hand.
104
105 (ii) PLT (shared-library) call-stubs: PLT stubs are invoked
106 via CALLQ. Try this for all non-signal trampoline
107 code. */
108
109 unw_word_t prev_ip = c->dwarf.ip, prev_cfa = c->dwarf.cfa;
110 struct dwarf_loc rbp_loc, rsp_loc, rip_loc;
111
112 /* We could get here because of missing/bad unwind information.
113 Validate all addresses from now on before dereferencing. */
114 c->validate = 1;
115
116 Debug (13, "dwarf_step() failed (ret=%d), trying frame-chain\n", ret);
117
118 if (unw_is_signal_frame (cursor))
119 {
120 ret = unw_handle_signal_frame(cursor);
121 if (ret < 0)
122 {
123 Debug (2, "returning 0\n");
124 return 0;
125 }
126 }
127 else if (is_plt_entry (&c->dwarf))
128 {
129 /* Like regular frame, CFA = RSP+8, RA = [CFA-8], no regs saved. */
130 Debug (2, "found plt entry\n");
131 c->frame_info.cfa_reg_offset = 8;
132 c->frame_info.cfa_reg_sp = -1;
133 c->frame_info.frame_type = UNW_X86_64_FRAME_STANDARD;
134 c->dwarf.loc[RIP] = DWARF_LOC (c->dwarf.cfa, 0);
135 c->dwarf.cfa += 8;
136 }
137 else if (DWARF_IS_NULL_LOC (c->dwarf.loc[RBP]))
138 {
139 for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
140 c->dwarf.loc[i] = DWARF_NULL_LOC;
141 }
142 else
143 {
144 unw_word_t rbp;
145
146 ret = dwarf_get (&c->dwarf, c->dwarf.loc[RBP], &rbp);
147 if (ret < 0)
148 {
149 Debug (2, "returning %d [RBP=0x%lx]\n", ret,
150 DWARF_GET_LOC (c->dwarf.loc[RBP]));
151 return ret;
152 }
153
154 if (!rbp)
155 {
156 /* Looks like we may have reached the end of the call-chain. */
157 rbp_loc = DWARF_NULL_LOC;
158 rsp_loc = DWARF_NULL_LOC;
159 rip_loc = DWARF_NULL_LOC;
160 }
161 else
162 {
163 unw_word_t rbp1 = 0;
164 rbp_loc = DWARF_LOC(rbp, 0);
165 rsp_loc = DWARF_NULL_LOC;
166 rip_loc = DWARF_LOC (rbp + 8, 0);
167 ret = dwarf_get (&c->dwarf, rbp_loc, &rbp1);
168 Debug (1, "[RBP=0x%lx] = 0x%lx (cfa = 0x%lx) -> 0x%lx\n",
169 (unsigned long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
170 rbp, c->dwarf.cfa, rbp1);
171
172 /* Heuristic to determine incorrect guess. For RBP to be a
173 valid frame it needs to be above current CFA, but don't
174 let it go more than a little. Note that we can't deduce
175 anything about new RBP (rbp1) since it may not be a frame
176 pointer in the frame above. Just check we get the value. */
177 if (ret < 0
178 || rbp < c->dwarf.cfa
179 || (rbp - c->dwarf.cfa) > 0x4000)
180 {
181 rip_loc = DWARF_NULL_LOC;
182 rbp_loc = DWARF_NULL_LOC;
183 }
184
185 c->frame_info.frame_type = UNW_X86_64_FRAME_GUESSED;
186 c->frame_info.cfa_reg_sp = 0;
187 c->frame_info.cfa_reg_offset = 16;
188 c->frame_info.fp_cfa_offset = -16;
189 c->dwarf.cfa += 16;
190 }
191
192 /* Mark all registers unsaved */
193 for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
194 c->dwarf.loc[i] = DWARF_NULL_LOC;
195
196 c->dwarf.loc[RBP] = rbp_loc;
197 c->dwarf.loc[RSP] = rsp_loc;
198 c->dwarf.loc[RIP] = rip_loc;
199 c->dwarf.use_prev_instr = 1;
200 }
201
202 c->dwarf.ret_addr_column = RIP;
203
204 if (DWARF_IS_NULL_LOC (c->dwarf.loc[RBP]))
205 {
206 ret = 0;
207 Debug (2, "NULL %%rbp loc, returning %d\n", ret);
208 return ret;
209 }
210 if (!DWARF_IS_NULL_LOC (c->dwarf.loc[RIP]))
211 {
212 ret = dwarf_get (&c->dwarf, c->dwarf.loc[RIP], &c->dwarf.ip);
213 Debug (1, "Frame Chain [RIP=0x%Lx] = 0x%Lx\n",
214 (unsigned long long) DWARF_GET_LOC (c->dwarf.loc[RIP]),
215 (unsigned long long) c->dwarf.ip);
216 if (ret < 0)
217 {
218 Debug (2, "returning %d\n", ret);
219 return ret;
220 }
221 ret = 1;
222 }
223 else
224 {
225 c->dwarf.ip = 0;
226 ret = 0;
227 }
228
229 if (c->dwarf.ip == prev_ip && c->dwarf.cfa == prev_cfa)
230 {
231 ret = -UNW_EBADFRAME;
232 Debug (2, "returning %d\n", ret);
233 return ret;
234 }
235 }
236
237 Debug (2, "returning %d\n", ret);
238 return ret;
239 }
240