1/* Return backtrace of current program state.
2 Copyright (C) 1998-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <execinfo.h>
20#include <stdlib.h>
21#include <unwind-link.h>
22
23struct trace_arg
24{
25 void **array;
26 struct unwind_link *unwind_link;
27 int cnt, size;
28 void *lastebp, *lastesp;
29};
30
31static _Unwind_Reason_Code
32backtrace_helper (struct _Unwind_Context *ctx, void *a)
33{
34 struct trace_arg *arg = a;
35
36 /* We are first called with address in the __backtrace function.
37 Skip it. */
38 if (arg->cnt != -1)
39 arg->array[arg->cnt]
40 = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetIP) (ctx);
41 if (++arg->cnt == arg->size)
42 return _URC_END_OF_STACK;
43
44 /* %ebp is DWARF2 register 5 on IA-32. */
45 arg->lastebp
46 = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetGR) (ctx, 5);
47 arg->lastesp
48 = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);
49 return _URC_NO_REASON;
50}
51
52
53/* This is a global variable set at program start time. It marks the
54 highest used stack address. */
55extern void *__libc_stack_end;
56
57
58/* This is the stack layout we see with every stack frame
59 if not compiled without frame pointer.
60
61 +-----------------+ +-----------------+
62 %ebp -> | %ebp last frame--------> | %ebp last frame--->...
63 | | | |
64 | return address | | return address |
65 +-----------------+ +-----------------+
66
67 First try as far to get as far as possible using
68 _Unwind_Backtrace which handles -fomit-frame-pointer
69 as well, but requires .eh_frame info. Then fall back to
70 walking the stack manually. */
71
72struct layout
73{
74 struct layout *ebp;
75 void *ret;
76};
77
78
79int
80__backtrace (void **array, int size)
81{
82 struct trace_arg arg =
83 {
84 .array = array,
85 .unwind_link = __libc_unwind_link_get (),
86 .size = size,
87 .cnt = -1,
88 };
89
90 if (size <= 0 || arg.unwind_link == NULL)
91 return 0;
92
93 UNWIND_LINK_PTR (arg.unwind_link, _Unwind_Backtrace)
94 (backtrace_helper, &arg);
95
96 if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
97 --arg.cnt;
98 else if (arg.cnt < size)
99 {
100 struct layout *ebp = (struct layout *) arg.lastebp;
101
102 while (arg.cnt < size)
103 {
104 /* Check for out of range. */
105 if ((void *) ebp < arg.lastesp || (void *) ebp > __libc_stack_end
106 || ((long) ebp & 3))
107 break;
108
109 array[arg.cnt++] = ebp->ret;
110 ebp = ebp->ebp;
111 }
112 }
113 return arg.cnt != -1 ? arg.cnt : 0;
114}
115weak_alias (__backtrace, backtrace)
116libc_hidden_def (__backtrace)
117

source code of glibc/sysdeps/i386/backtrace.c