One the projects I'm working on is a SyncML server, written from scratch in D, It's currently in testing mode, and we found that the server was mysteriously crashing. Unfortunatly, since it's threaded, and forked as a daemon, we didn't really want to run it under GDB, (and since GDB segfaults on startup anyway). we where at a bit of a quagmire about how to find the bug.
So after a bit of searching through code.google.com I came across the idea of catching the SIGSEGV signal and calling
backtrace and backtrace_symbols
This little trick can product output that looks something like
/path/to/application [0xAAAAAA] << address of code
/path/to/application [0xAAAAAA] << address of code
/path/to/application [0xAAAAAA] << address of code
/path/to/application [0xAAAAAA] << address of code
which initially seemed a bit cryptic, but by putting it together with
addr2line can result in some great debugging information.
This is my little backtrace logger for the deamon logger.
static void print_trace()
{
void *btarray[10];
size_t size;
char **strings;
size_t i;
pid_t pid = getpid();
//writefln("SEG");
size = backtrace(cast(void**)btarray, 10);
strings = backtrace_symbols(cast(void**)btarray, size);
std.process.system("/bin/echo '----BACKTRACE------' " ~
"> /var/log/myproject/backtrace.log");
for(i = 0; i < size; i++) {
char[] line = std.string.toString(strings[i]);
char[][] bits = std.string.split(line, "[");
char[] left = std.string.strip(bits[0]);
if (!left.length) {
continue;
}
// skip lines with ( in them...
if (std.string.find(left,"(") > -1) {
continue;
}
char[] addr = bits[1][2..length-1];
std.process.system("/bin/echo '----" ~ addr
~ "------' >> /var/log/myproject/backtrace.log");
std.process.system("/usr/bin/addr2line -f -e " ~
left ~ " " ~ addr ~ " >> /var/log/myproject/myproject.log");
}
free(strings);
}
of course you need to use a few C externs to make this work:
extern (C) {
int backtrace(void **__array, int __size);
char** backtrace_symbols(void **__array, int __size);
pid_t getpid();
sighandler_t signal(int signum, sighandler_t handler);
void sigsegv(int sig)
{
// reset the handler.
signal(SIGSEGV, cast(sighandler_t) 0);
print_trace();
// really die
exit(SIGSEGV);
}
}
and to add it to you application, stick this in main() somewhere
signal(SIGSEGV, &sigsegv);
testing it is quite simple, just do this in D
void testSegfault()
{
class SegTest {
void test() {}
}
SegTest a;
a.test();
}
Now looking at the debug file, you can work out where it failed...
----BACKTRACE------
----805e971------ (THIS IS MY OUTPUT CODE)
_D9myproject7cmdLine6daemon11print_traceFZv
init.c/src/myproject/cmdLine/daemon.d:306
----805e46b------
sigsegv
init.c/src/myproject/cmdLine/daemon.d:121
----804db18------ (AND NOW FOR THE LOCATION OF THE SEGFAULT)
_D9myprojectfort7manager7manager7runOptsFZAa
init.c/src/myproject/manager.d:50
----805617a------
_D9myproject10webRequest10webRequest5parseFAaAaKAaZAa
init.c/src/myproject/webRequest.d:89
----8050c3e------
_D9pmyproject14myprojectThread14myprojectThread18dealWithWebRequestFAaAaZv
init.c/src/myproject/myprojectThread.d:331
----80503d0------
_D9myproject14myprojectThread14myprojectThread3runFZi
init.c/src/myproject/myprojectThread.d:111
----8076260------
_D3std6thread6Thread11threadstartUPvZPv
??:0
----a7fd10bd------
??
I'm sure with some more work, you could get it to log to syslog...
