[Xymon] rrd logs and graphs

[Vernon Everett]

[tmp]$ make CC=/usr/local/bin/gcc test
/usr/local/bin/gcc    -o test test.c
[tmp]$ ./test
Segmentation Fault (core dumped)

As you predicted.

On 11 March 2015 at 14:50, Jeremy Laidman <jlaidman at rebel-it.com.au> wrote:

> Yes, apparently, "(null)" is what GNU's printf outputs when asked to print
> a string pointer that is null.  The POSIX behaviour is not defined, and so
> in some systems, it dumps core rather than detecting the illegal string.
>
> This bit of code demonstrates:
>
> #include <stdio.h>
> int main() {
>         printf("test: %s\n",NULL);
> }
>
> On Linux and FreeBSD, this prints out "test: (null)" but on Solaris 10
> this dumps core.
>
> Fixing this is beyond my skill level.  But I would start looking at the
> functions errprintf() and dbgprintf() to see if NULL strings can be
> detected and prevented from being passed through to *printf.
>
> But that might be somewhat tricky.  Alternatively, updating
> dump_tcp_services() to do the same, is probably a much simpler task, but
> doesn't safeguard any other code from the same fate.
>
> J
>
>
> On 11 March 2015 at 17:38, Jeremy Laidman <jlaidman at rebel-it.com.au>
> wrote:
>
>> Even simpler:
>>
>> #include <stdio.h>
>> int main() {
>>         printf("test: %s\n",NULL);
>> }
>>
>>
>>
>> On 11 March 2015 at 17:33, Jeremy Laidman <jlaidman at rebel-it.com.au>
>> wrote:
>>
>>> On 11 March 2015 at 15:43, Vernon Everett <everett.vernon at gmail.com>
>>> wrote:
>>>
>>>> We have 4.3.12
>>>> And the command dumps core in the same way.
>>>>
>>>
>>> That's good.
>>>
>>> Can you try this out?  Plop into a text file, eg test.c, then "make
>>> test" and then "./test".
>>>
>>> #include <stdio.h>
>>> #include <stdarg.h>
>>> void dbgprintf(const char *fmt, ...)
>>> {
>>>         va_list args;
>>>         va_start(args, fmt);
>>>         vfprintf(stdout, fmt, args);
>>>         va_end(args);
>>>         fflush(stdout);
>>> }
>>> int main() {
>>>         dbgprintf("test: %s\n",NULL);
>>> }
>>>
>>> This is the essence of the Xymon code that prints the empty send/expect
>>> strings.  But I've pared away all of the Xymon code to leave just the call
>>> to vprintf() and whatever is needed to make it run.
>>>
>>> On my systems I get the following output:
>>>
>>> test: (null)
>>>
>>> I'm guessing on your system you'll get a core dump.  If so, it would
>>> suggest a difference in implementations of the standard library functions.
>>> If that's the case, we simply (!) need to catch the attempts to print NULL
>>> pointers, and substitute our own "(null)" string.
>>>
>>> Indeed, I just tested this on a Solaris system and it dumped core.  On
>>> Linux and FreeBSD systems, it printed "(null)".
>>>
>>> J
>>>
>>>
>>
>


-- 
"Accept the challenges so that you can feel the exhilaration of victory"
- General George Patton
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