Re: monit 4.8 segfaults on Redhat EL4

[Mike Jackson]

> Thank you very much for this report Mike. This trace does not make  any 
> sense to me though. It shows 's' with an address and then go on  to say 
> that s is not available. Also not having argc available for  main() is 
> suspicious to say the least. Does this segfault happens all  the time or 
> only sporadic? Do you use any special C libraries that  you are aware of? 
> I cannot reproduce this segfault on any Linux (SMP)  machines I have so I 
> wonder if you can run gdb on monit yourself and  set a breakpoint in 
> 'log_log' and step trough to see if anything  strange is going on or maybe 
> where the problem occurs. Use e.g.

I'm not aware of any special libraries - I mean, I have a lot of stuff 
installed, but libc and whatnot should be stock installs from Redhat. I was 
previously using a CVS copy dated 2006-04-24. This particular segfault 
happens every time monit is started - though when I used the command line 
flags you specified ('-lv'), it did not segfault and started normally. 
Here's the gdb output with -lv specified:

(gdb) break log_log
Breakpoint 1 at 0x408fa0: file log.c, line 360.
(gdb) run -lv
Starting program: /usr/local/src/monit-4.8/monit -lv
[Thread debugging using libthread_db enabled]
[New Thread 182894082848 (LWP 10831)]
[Switching to Thread 182894082848 (LWP 10831)]

Breakpoint 1, log_log (priority=6, s=0x42af60 "Starting %s daemon with http 
interface at [%s:%d]\n", ap=0x7fbffff6b0) at log.c:360
360     static void log_log(int priority, const char *s, va_list ap) {
(gdb) n
362       ASSERT(s);
(gdb) n
360     static void log_log(int priority, const char *s, va_list ap) {
(gdb) n
362       ASSERT(s);
(gdb) n
364       LOCK(log_mutex)
(gdb) n
365         vfprintf(stderr, s, ap);
(gdb) n
Starting monit daemon with http interface at [*:2812]
366         fflush(stderr);
(gdb) n
367       END_LOCK;
(gdb) n
369       if(Run.dolog) {
(gdb) n
385     }
(gdb) n
LogInfo (s=Variable "s" is not available.
) at log.c:248
248       va_end(ap);
(gdb) n
main (argc=Variable "argc" is not available.
) at monitor.c:465
465         if(Run.init != TRUE)
(gdb) n
466           daemonize();
(gdb) n
Detaching after fork from child process 11029.

Program exited normally.

And here's the gdb output without -lv (along with a backtrace):

(gdb) break log_log
Breakpoint 1 at 0x408fa0: file log.c, line 360.
(gdb) run
Starting program: /usr/local/src/monit-4.8/monit
[Thread debugging using libthread_db enabled]
[New Thread 182894082848 (LWP 12359)]
[Switching to Thread 182894082848 (LWP 12359)]

Breakpoint 1, log_log (priority=6, s=0x42af60 "Starting %s daemon with http 
interface at [%s:%d]\n", ap=0x7fbffff6c0) at log.c:360
360     static void log_log(int priority, const char *s, va_list ap) {
(gdb) n
362       ASSERT(s);
(gdb) n
360     static void log_log(int priority, const char *s, va_list ap) {
(gdb) n
362       ASSERT(s);
(gdb) n
364       LOCK(log_mutex)
(gdb) n
365         vfprintf(stderr, s, ap);
(gdb) n
Starting monit daemon with http interface at [*:2812]
366         fflush(stderr);
(gdb) n
367       END_LOCK;
(gdb) n
369       if(Run.dolog) {
(gdb) n
372         if(Run.use_syslog) {
(gdb) n
373           LOCK(log_mutex)
(gdb) n
374             vsyslog(priority, s, ap);
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x0000003106b6fd00 in strlen () from /lib64/tls/libc.so.6
(gdb) bt
#0  0x0000003106b6fd00 in strlen () from /lib64/tls/libc.so.6
#1  0x0000003106b428cc in vfprintf () from /lib64/tls/libc.so.6
#2  0x0000003106bc1e55 in vsyslog () from /lib64/tls/libc.so.6
#3  0x000000000040910c in log_log (priority=6, s=0x42af60 "Starting %s 
daemon with http interface at [%s:%d]\n", ap=0x7fbffff6c0)
   at log.c:374
#4  0x0000000000409358 in LogInfo (s=Variable "s" is not available.
) at log.c:247
#5  0x000000000040b332 in main (argc=Variable "argc" is not available.
) at monitor.c:460

I tried it again from the command line, and it segfaults without the -l 
flag. When it's specified, it starts correctly.