kapstok / Post-mortem-debugging (public) (License: MIT) (since 2018-11-16) (hash sha1)
Simple sample on how post mortem debugging in C(++) works.
Clone URLs: https://rocketgit.com/user/kapstok/Post-mortem-debugging ssh://rocketgit@ssh.rocketgit.com/user/kapstok/Post-mortem-debugging git://git.rocketgit.com/user/kapstok/Post-mortem-debugging
master
List of commits:
Subject Hash Author Date (UTC)
Dump to log file. 8aced5b3cbe9fd245b68168de57f55f2b0cd68e9 Jan Allersma 2018-05-30 12:08:53
Add compile info at runtime error. Determine appropiate code for architecture when compiling. 41baa10ac827df8efb3040c2b82197053d6b43c0 Jan Allersma 2018-05-22 12:15:18
Remove redundant variables and header includes. fb31483b36a5f9e249d8fa88f0c3ff66b1fce6cd Jan Allersma 2018-05-22 11:40:35
Initial commit. 86c80da5a6a677f1686e50996b61fd51632259ba Jan Allersma 2018-05-18 13:12:38
Commit 8aced5b3cbe9fd245b68168de57f55f2b0cd68e9 - Dump to log file.
Author: Jan Allersma
Author date (UTC): 2018-05-30 12:08
Committer name: Jan Allersma
Committer date (UTC): 2018-05-30 12:20
Parent(s): 41baa10ac827df8efb3040c2b82197053d6b43c0
Signing key:
Tree: 58b9bcba206dba9d6296fcd1e9f29ba2013e65a5
File Lines added Lines deleted
.gitignore 1 1
README.md 34 10
main.c 29 11
File .gitignore changed (mode: 100644) (index 01db905..cd2133c)
1 1 * *
2 2 !.gitignore !.gitignore
3 !main.cpp
3 !main.c
4 4 !README.md !README.md
File README.md changed (mode: 100644) (index 6cb613d..939a821)
1 1 # Fault handling # Fault handling
2 2
3 When the application crashes, e.g. due to derefencing `NULL`, a dump will be made.
4 The dump will be shown on the Terminal and will saved in a log file called `/var/log/messages`.
5
3 6 ## Compiling ## Compiling
4 7
5 8 > Commands executed from repository's root. > Commands executed from repository's root.
6 9
7 10 ``` ```
8 g++ main.cpp -o exe
9 g++ main.cpp -g -o dbgexe
11 g++ main.c -o exe
12 g++ main.c -g -o dbgexe
10 13 ``` ```
11 14
12 15 ## Post mortem debugging ## Post mortem debugging
 
... ... g++ main.cpp -g -o dbgexe
14 17 Running `./exe` results in this output: Running `./exe` results in this output:
15 18
16 19 ``` ```
17 Fout 11 at 0:
18 Called from 4197438.
19 Compiled at: May 22 2018 13:58:27
20 Error 11 at (nil):
21 Called from 0x40233f
22 Compiled at: May 30 2018 09:24:41
20 23 Aborted (geheugendump gemaakt) Aborted (geheugendump gemaakt)
21 24 ``` ```
22 25
23 See what caused the error:
26 In order to read the dump from the log file, while filtering all log info from other applications, one should execute the following command in a Terminal:
27
28 ```
29 # cat /var/log/messages | grep "postmortem-debugging" | sed 's/#012/\n\t/g' | less
30 ```
31
32 > Syslog turns newlines ('\n') in '#012'. The sed command reverts that.
33
34 Possible output would be:
35
36 ```
37 May 30 09:38:14 localhost postmortem-debugging[14671]: Error 11 at (nil):
38 May 30 09:38:14 localhost postmortem-debugging[14671]: Called from 0x40233f.
39 May 30 09:38:14 localhost postmortem-debugging[14671]: Compiled at: May 30 2018 09:24:41
40 ```
41
42 Let's see what caused the error by executing this one-liner:
24 43
25 > Use the output from running ./exe ('Called from 4197438').
44 ```
45 $ gdb ./dbgexe
46 ```
47
48 Then you need to use the information from the log file. Execute this code in `gdb`:
26 49
27 50 ``` ```
28 gdb ./dbgexe
29 l *4197438
51 l *0x40233f
30 52 ``` ```
31 53
54 > Use the output from running ./exe ('Called from 0x40233f').
55
32 56 As `gdb` states, the error was caused at line 57: As `gdb` states, the error was caused at line 57:
33 57
34 58 ``` ```
35 0x400c3e is in main() (main.cpp:57).
59 0x40233f is in main() (main.cpp:71).
36 60 ``` ```
File main.c renamed from main.cpp (similarity 53%) (mode: 100644) (index dca9011..833523d)
1 #include <iostream>
1 #ifndef _GNU_SOURCE
2 #define _GNU_SOURCE
3 #endif
2 4
3 5 #include <unistd.h> #include <unistd.h>
4 6 #include <signal.h> #include <signal.h>
7 #include <syslog.h>
8
9 #ifdef __cplusplus
10 #include <iostream>
11 #define ERR(X) std::cerr << X
12 #define ABRT() std::abort()
13 #else
14 #include <ucontext.h>
15 #include <stdio.h>
16 #include <stdlib.h>
17 #define ERR(X) perror(X)
18 #define ABRT() abort()
19 #endif
5 20
6 21 void setHandler(void (*handler)(int,siginfo_t *,void *)) { void setHandler(void (*handler)(int,siginfo_t *,void *)) {
7 22 struct sigaction action; struct sigaction action;
 
... ... void setHandler(void (*handler)(int,siginfo_t *,void *)) {
9 24 action.sa_sigaction = handler; action.sa_sigaction = handler;
10 25
11 26 if (sigaction(SIGFPE, &action, NULL) == -1) { if (sigaction(SIGFPE, &action, NULL) == -1) {
12 std::cerr << "sigfpe: sigaction";
27 ERR("sigfpe: sigaction");
13 28 _exit(1); _exit(1);
14 29 } }
15 30 if (sigaction(SIGSEGV, &action, NULL) == -1) { if (sigaction(SIGSEGV, &action, NULL) == -1) {
16 std::cerr << "sigsegv: sigaction";
31 ERR("sigsegv: sigaction");
17 32 _exit(1); _exit(1);
18 33 } }
19 34 if (sigaction(SIGILL, &action, NULL) == -1) { if (sigaction(SIGILL, &action, NULL) == -1) {
20 std::cerr << "sigill: sigaction";
35 ERR("sigill: sigaction");
21 36 _exit(1); _exit(1);
22 37 } }
23 38 if (sigaction(SIGBUS, &action, NULL) == -1) { if (sigaction(SIGBUS, &action, NULL) == -1) {
24 std::cerr << "sigbus: sigaction";
39 ERR("sigbus: sigaction");
25 40 _exit(1); _exit(1);
26 41 } }
27 42 } }
 
... ... void faultHandler(int signo, siginfo_t* info, void* extra) {
37 52 #error Compiling for invalid architecture. #error Compiling for invalid architecture.
38 53 #endif #endif
39 54
40 std::cout << "Fout " << (int)signo << " at ";
41 std::cout << (int&)info->si_addr << ": " << std::endl;
42 std::cout << "Called from " << (int)i << "." << std::endl;
43 std::cout << "Compiled at: " << __DATE__ << " " << __TIME__ << std::endl;
55 openlog("postmortem-debugging", LOG_PERROR | LOG_PID, LOG_LOCAL0);
56
57 syslog(LOG_ERR, "Error %d at %p:\n", signo, info->si_addr);
58 syslog(LOG_ERR, "Called from %p.\n", i);
59 syslog(LOG_ERR, "Compiled at: %s %s\n", __DATE__, __TIME__);
60
61 closelog();
44 62
45 abort();
63 ABRT();
46 64 } }
47 65
48 66 int main() { int main() {
49 int* badptr = nullptr;
67 int* badptr = NULL;
50 68
51 69 setHandler(faultHandler); setHandler(faultHandler);
52 70
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