1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
|
#include <execinfo.h>
#include <unistd.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#define ARRSIZE(a) (sizeof(a) / sizeof(*(a)))
typedef struct frame_info
{
struct frame_info* prev; /* rbp */
void* retaddr; /* rip */
} frame_info;
jmp_buf resume_buf;
static void signal_handler(int signum)
{
/* Should be safe to be called from a signal handler.
* See 21.2.1 "Performing a nonlocal goto from a signal handler" from
* The Linux Programming Interface, Michael Kerrisk */
siglongjmp(resume_buf, 1);
}
static int install_signal_handlers(const int signals[], struct sigaction
handlers[], int count)
{
for (int i = 0; i < count; i++) {
struct sigaction action = { 0 };
action.sa_handler = signal_handler;
sigemptyset(&action.sa_mask);
action.sa_flags = 0;
if (sigaction(signals[i], &action, &handlers[i]) != 0) {
perror("sigaction");
return -1;
}
}
return 0;
}
static int restore_signal_handlers(const int signals[], struct sigaction
handlers[], int count)
{
for (int i = 0; i < count; i++) {
if (sigaction(signals[i], &handlers[i], NULL) != 0) {
perror("sigaction");
return -1;
}
}
return 0;
}
static int safe_read(const struct frame_info* fi, struct frame_info** prev,
void** retaddr)
{
/* Signals to ignore while attempting to read frame_info members */
const int signals[] = { SIGSEGV, SIGBUS };
/* Store original signal handers */
struct sigaction handlers[ARRSIZE(signals)] = { 0 };
int ret = 0;
if (install_signal_handlers(signals, handlers, ARRSIZE(signals)) != 0)
return -1;
if (!sigsetjmp(resume_buf, 1)) {
*prev = fi->prev;
*retaddr = fi->retaddr;
} else {
ret = -1;
}
if (restore_signal_handlers(signals, handlers, ARRSIZE(signals)) != 0)
return -1;
return ret;
}
static void print_location(void* addr)
{
if (!addr)
return;
/* This requires the binary to be linked with '-rdynamic' */
backtrace_symbols_fd(&addr, 1, STDOUT_FILENO);
}
void fp_backtrace(void)
{
struct frame_info *fi;
struct frame_info* next;
void* retaddr;
fi = __builtin_frame_address(0);
retaddr = __builtin_extract_return_addr(__builtin_return_address(0));
for (; fi; fi = next) {
if (safe_read(fi, &next, &retaddr) != 0)
return;
print_location(retaddr);
/* Detect the simplest kind of infinite loop */
if (fi == next) {
printf("fp_backtrace: loop detected\n");
return;
}
}
}
|
