In this example, we'll be debugging our “Hello, world!” program via a TCP/IP link. We go through the following steps:
The buildfile for the image follows these sections.
Let's assume an x86 target using a basic TCP/IP configuration. The following lines (from the sample buildfile below) show what's needed to host the sample session:
io-pkt-v4-hc -d abc100 -ptcpip if=ndi0:10.0.1.172 devc-pty & [+session] pdebug 8000 &
The above specifies that the host IP address is 10.0.1.172. The pdebug program is configured to use port 8000.
We'll be using the x86 compiler. Note the -g option, which makes the compiler include debugging information:
$ qcc -V gcc_ntox86 -g -o hello hello.c
For this simple example, the source can be found in our working directory. First, let's start the session; to reduce document clutter, we'll run the debugger in quiet mode:
ntox86-gdb -quiet
The gdb debugger provides its own shell; by default its prompt is (gdb). Specify the target IP address and the port used by pdebug:
(gdb) target qnx 10.0.1.172:8000 Remote debugging using 10.0.1.172:8000 0x0 in ?? ()
Upload the debug executable to the target. (This can be a slow operation. If the executable is large, you may prefer to build the executable into your target image.) Note that the file has to be in the target system's pathname space, so we can get the executable via a network filesystem, ftp, or, if no filesystem is present, via the upload command:
(gdb) upload hello /tmp/hello
Load the symbolic debug information from the current working directory (in this case, hello must reside on the host system):
(gdb) sym hello Reading symbols from hello...done.
Start the program:
(gdb) run /tmp/hello Starting program: /tmp/hello Trying to find symbol file for ldqnx.so.2 Retrying dynamic interpreter in libc.so.4
Set a breakpoint on main():
(gdb) break main Breakpoint 1 at 0x80483ae: file hello.c, line 8.
Allow the program to continue to the breakpoint found at main():
(gdb) c Continuing. Breakpoint 1, main () at hello.c:8 8 gettimeofday (&when, NULL);
We're now ready to start the debug session:
(gdb)
While you're in a debug session, you can use any of the following commands as the next action for starting the actual debugging of the project:
For more information about these commands and their arguments, see https://www.gnu.org/software/gdb/documentation/, or use the help cmd command in gdb.
Let's see how to use some of these basic commands. First, here's the list command:
(gdb) l
3
4 main () {
5 struct timeval when;
6 int x,y,z;
7
8 gettimeofday (&when, NULL);
9 printf ("Hi ya!\n");
10
11 x=3;
12 y=2;
Press Enter to repeat the last command:
(gdb) <enter> 13 z=3*2; 14 15 exit (0); 16 17 }
Break on line 11:
(gdb) break 11 Breakpoint 2 at 0x80483c7: file hello.c, line 11.
Continue until the first breakpoint:
(gdb) c Continuing. Hi ya! Breakpoint 2, main () at hello.c:11 11 x=3;
Notice that the above command went past the printf() statement at line 9, so the output from the call is displayed on the screen.
Inspect variable y, using the short form of the inspect command:
(gdb) ins y $1 = -1338755812
Get some help on the step and next commands:
(gdb) help s Step program until it reaches a different source line. Argument N means do this N times (or till program stops for another reason). (gdb) help n Step program, proceeding through subroutine calls. Like the "step" command as long as subroutine calls don't happen; when they do, the call is treated as one instruction. Argument N means do this N times (or till program stops for another reason).
Go to the next line of execution:
(gdb) n 12 y=2; (gdb) n 13 z=3*2; (gdb) inspect z $2 = 1 (gdb) n 15 exit (0); (gdb) inspe z $3 = 6
Continue program execution:
(gdb) continue Continuing. Program exited normally.
Quit the debugger session:
(gdb) quit The program is running. Exit anyway? (y or n) y
[virtual=x86,bios +compress] boot = {
startup-x86 -N node428
PATH=/proc/boot:./ procnto
}
[+script] startup-script = {
# explicitly running in edited mode for the console link
devc-ser8250 -e -b115200 &
reopen
display_msg Welcome to QNX Neutrino on a PC-compatible BIOS system
# tcp/ip with the fictitious ABC100 Ethernet adaptor
io-pkt-v4-hc -d abc100 -ptcpip if=ndi0:10.0.1.172
waitfor /dev/socket
pipe
# pdebug needs devc-pty
devc-pty &
# Start pdebug on port 8000
[+session] pdebug 8000 &
}
[type=link] /usr/lib/ldqnx.so.2=/proc/boot/libc.so.4
[type=link] /tmp=/dev/shmem # tmp points to shared memory
[type=link] /dev/console=/dev/ser2 # no local terminal
[perms=+r,+x] # Boot images made under MS-Windows need
# to be reminded of permissions.
devnp-abc100.so
libc.so
fpemu.so
libsocket.so
devc-ser8250
io-pkt-v4-hc
pipe
devc-pty
pdebug
esh
ping
ls