HOWTO understand and find cause of exited with code -11 errors
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One of the most common questions we hear on the ns-3 developers list is a variation on the following theme: I wrote my program, but when I run it I get a red line that ends with "exited with code -11". Please tell me what I did wrong.
The complete output from waf will look something like,
./waf --run hs Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-dev/ns-3-dev/build' Waf: Leaving directory `/home/craigdo/repos/ns-3-allinone-dev/ns-3-dev/build' 'build' finished successfully (0.881s) Command ['/home/craigdo/repos/ns-3-allinone-dev/ns-3-dev/build/debug/scratch/hs'] exited with code -11
In this HOWTO, we describe what this means and how you can go about finding your problem.
HOWTO understand and find cause of exited with code -11 errors
The zeroth thing to understand about debugging is that one of the least productive things you can do is post a pile of your code on a developers list and ask why it doesn't work. Developers are very busy people who won't have a lot of spare time to do your work for you. Try and figure it out on your own. You are doing the right thing by reading this page!
The first thing to understand is that debugging anything is an art and skill that you need to learn. Some jokers have observed that programming can be defined as the act of introducing bugs. This is not too far from the truth (which is why it is funny). Since you will be programming in the ns-3 environmnent, you are going to have to develop debugging skills, whether you like it or not, in order to remove the bugs you create. This HOWTO is only going to scratch the surface of the subject of debugging and hopefully provide you with a direction and a few hits regarding how to start. You are going to have to figure most of this out on your own, though. Don't worry, it gets easier.
It will be much easier on you if you learn from the experience of others. There are many books available that will help you learn the details of this huge subject. If you go to Amazon.com and search for "debugging" in their books section, you will find over 2,000 results. A couple of books that have been recommended on 'ns-developers' are
- Agans, "Debugging"
- Matloff and Salzman, "The Art of Debugging with GDB, DDD, and Eclipse"
Reproduce the Problem
If you have read a good book on debugging, you will know that the first step in finding any problem is to figure out how to reproduce it. In this case, we need to produce it, so let's take the simplest ns-3 example and create a reproducible problem.
The hello-simulator.cc example, you may recall, just prints the text "Hello Simulator" on your console using the ns-3 logging system. It is simple enough that we can reproduce it here:
#include "ns3/core-module.h"
NS_LOG_COMPONENT_DEFINE ("HelloSimulator");
using namespace ns3;
int
main (int argc, char *argv[])
{
NS_LOG_UNCOND ("Hello Simulator");
}
Go ahead and copy the example into the scratch directory. The following assumes that you are in the base directory of an ns-3 distribution (the directory where RELEASE, VERSION and src are found).
cp examples/tutorial/hello-simulator.cc scratch/hs.cc
Now pull up the file you just created (scratch/hs.cc) in you favorite programmer's editor and add a line so that the main funtion looks like this:
int
main (int argc, char *argv[])
{
NS_LOG_UNCOND ("Hello Simulator");
return 1;
}
Go ahead and build and run the new program:
./waf ./waf --run hs
You should see something that looks like:
Waf: Entering directory `/your/directory/path/ns-3-allinone-dev/ns-3-dev/build' Waf: Leaving directory `/your/directory/path/ns-3-allinone-dev/ns-3-dev/build' 'build' finished successfully (0.872s) Hello Simulator Command ['/your/directory/path/ns-3-allinone-dev/ns-3-dev/build/debug/scratch/hs'] exited with code 1
You should now have a reproducible bug, since if you repeat the waf run command, your program exits with code 1 every time.
What the Problem Means
The short answer is that the program did not return a zero as its exit or return code. Waf reports this back in red since it usually means that the program has failed in some way. This return code can either come from the return value from your main function, or it can be supplied by the operating system or run-time system if your program does not complete for some reason.
In general, strictly positive return codes indicate a program that completed "normally" (that is, the main function returned some value) but detected some error. In the code above, the hs program completed normally, but returned the value one. In real-world programs, this would indicate an error condition that you as a user could look up in the hs documentation and interpret.
Negative return codes typically indicate that the program has failed in some way such that it cannot complete. In Unix and Linux, these codes are usually the negative of a so-called SIGNAL. You can find a list of signals in /usr/include/asm/signal.h if you are interested. The first few are:
#define SIGHUP 1 #define SIGINT 2 #define SIGQUIT 3 #define SIGILL 4 #define SIGTRAP 5 #define SIGABRT 6 #define SIGIOT 6 #define SIGBUS 7 #define SIGFPE 8 #define SIGKILL 9 #define SIGUSR1 10 #define SIGSEGV 11 #define SIGUSR2 12 #define SIGPIPE 13 #define SIGALRM 14 #define SIGTERM 15
Craigdo 19:32, 22 April 2010 (UTC)
